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Biomass production and species composition change in a tall grass prairie ecosystem after long-term exposure to elevated CO2
Abstract
To determine the long-term impact of elevated CO2 on primary production of native tallgrass prairie, we compared the responses of tallgrass prairie at ambient and twice-ambient atmospheric CO2 levels over an 8-year period. Plots in open-top chambers (4.5 m diameter) were exposed continuously (24 h) to ambient and elevated CO2 from early April to late October each year. Unchambered plots were monitored also. Above-ground peak biomass was determined by clipping each year in early August, and root growth was estimated by harvesting roots from root ingrowth bags. Plant community composition was censused each year in early June. In the last 2 years of the study, subplots were clipped on 1 June or 1 July, and regrowth was harvested on 1 October. Volumetric soil water content of the 0–100 cm soil layer was determined using neutron scattering, and was generally higher in elevated CO2 plots than ambient. Peak above-ground biomass was greater on elevated CO2 plots than ambient CO2 plots with or without chambers during years with significant plant water stress. Above-ground regrowth biomass was greater under elevated CO2 than under ambient CO2 in a year with late-season water stress, but did not differ in a wetter year. Root ingrowth biomass was also greater in elevated CO2 plots than ambient CO2 plots when water stress occurred during the growing season. The basal cover and relative amount of warm-season perennial grasses (C4) in the stand changed little during the 8-year period, but basal cover and relative amount of cool-season perennial grasses (C3) in the stand declined in the elevated CO2 plots and in ambient CO2 plots with chambers. Forbs (C3) and members of the Cyperaceae (C3) increased in basal cover and relative amount in the stand at elevated compared to ambient CO2. Greater biomass production under elevated CO2 in C4-dominated grasslands may lead to a greater carbon sequestration by those ecosystems and reduce peak atmospheric CO2 concentrations in the future.
... aperture since the C demand of photosynthesis is met earlier, which decreases stomatal conductance. This results in reduced transpirational water loss and increased water-use efficiency (WUE), which can translate into slower soil moisture depletion and, thus, reduced water stress for plants 3,7,[19][20][21] . Therefore, in this classic carbon-centric view, the CFE can be assumed to be particularly high under drier and/or hotter weather conditions. ...
... Free-air carbon dioxide enrichment (FACE) experiments represent the most appropriate technology for testing the effects of multiple environmental factors on CFE 5-7 . Few studies have addressed the CFE of grasslands with regard to the changing environmental conditions over timescales of several years 19,21 . Those studies have primarily relied on forced manipulations 10,11,25,26 , which may cause unintended artificial alterations 26 year (for experiment-support variables, for example, average air temperature, see Supplementary Table 1). ...
... Plants that are adapted to a good water supply should be susceptible to improved WUE under [eCO 2 ] in combination with reduced water availability. However, the reduced CFE found under drier conditions (Fig. 3) indicates a limitation of the positive effect of enhanced WUE under [eCO 2 ], which stays in contrast to previous studies 3, 6,[19][20][21] . Similar observations were reported in FACE experiments on drier temperate grasslands in Australia 11 and in the United States 10 . ...
The increase in atmospheric greenhouse gas concentrations from anthropogenic activities is the major driver of recent global climate change.The stimulationofplantphotosynthesis due to rising atmospheric carbon dioxide concentrations ([CO2]) is widely assumed to increase the net primary productivity (NPP) of C3 plants—the CO2 fertilization (CFE). However, the magnitude and persistence of the CFE under future climates, including more frequent weather extremes, are controversial. Here we use data from 16 years of temperate grassland grown under ‘free-air carbon dioxide enrichment’ conditions to show that the CFE on above-ground biomass is strongest under local average environmental conditions. The observed CFE was reduced or disappeared under wetter, drier and/or hotter conditions when the forcing variable exceeded its intermediate regime. This is in contrast to predictions of an increased CO2 fertilization under drier and warmer conditions. Such extreme weather conditions are projected to occur more intensely and frequently under future climate scenarios. Consequently, current biogeochemical models might overestimate the future
NPP sink capacity of temperate C3 grasslands and hence underestimate future atmospheric [CO2] increase.
... At the "UP Dairy" site, the dry season average rainfall was 450 mm, and the wet season rainfall was 716 mm (Supplementary Figure S5). As the rain has a direct relationship with vegetation and pasture growth (Owensby et al., 1999;Fay et al., 2011;Yan et al., 2015), therefore, forage production was predicted based on the amount of rainfall received for these two sites (Supplementary Table S3). The results estimated that the monthly forage production per 100 acres of land in the "OK Dairy" site was 69 tons during the wet season and 43 tons during the dry season when other factors remained constant. ...
... High temperature accelerates early senescence and desiccation of C3 grasses during the middle and late seasons (Cleland et al., 2006), which causes a scarcity of available forage for livestock which might shift current pasture-based husbandry into grain-grass mixed practice. Increased CO 2 concentration can positively bolster photosynthetic activity in C3 plants (Parton et al., 2007;Izaurralde et al., 2011) with a commensurate increment in biomass (Owensby et al., 1999). Therefore, future grazing strategies in Hawai'i and tropical regions might be biased toward selecting and including a higher proportion of C3 species than C4 species for the higher elevation sites where the temperature is relatively cooler. ...
... At the "UP Dairy" site, the dry season average rainfall was 450 mm, and the wet season rainfall was 716 mm (Supplementary Figure S5). As the rain has a direct relationship with vegetation and pasture growth (Owensby et al., 1999;Fay et al., 2011;Yan et al., 2015), therefore, forage production was predicted based on the amount of rainfall received for these two sites (Supplementary Table S3). The results estimated that the monthly forage production per 100 acres of land in the "OK Dairy" site was 69 tons during the wet season and 43 tons during the dry season when other factors remained constant. ...
... High temperature accelerates early senescence and desiccation of C3 grasses during the middle and late seasons (Cleland et al., 2006), which causes a scarcity of available forage for livestock which might shift current pasture-based husbandry into grain-grass mixed practice. Increased CO 2 concentration can positively bolster photosynthetic activity in C3 plants (Parton et al., 2007;Izaurralde et al., 2011) with a commensurate increment in biomass (Owensby et al., 1999). Therefore, future grazing strategies in Hawai'i and tropical regions might be biased toward selecting and including a higher proportion of C3 species than C4 species for the higher elevation sites where the temperature is relatively cooler. ...
Proper knowledge and understanding of climatic variability across different seasons are important in farm management. To learn more about the potential effects of climate change on dairying in Hawaii, we conducted a study on site-specific climate characterization using several variables including rainfall, wind speed, solar radiation, and temperature, at two dairy farms located on Hawai`i Island, Hawai`i, in Ookala named “OK DAIRY,” and in Upolu Point named “UP DAIRY.” Temperature-Humidity Index (THI) and wind speed variations in the hottest four months (JUN-SEP) were analyzed to determine when critical thresholds that affect animal health are exceeded. Rainfall data were used to estimate the capacity of forage production in 6-month wet (NOV-APR) and dry (MAY-OCT) seasons. Future projections of temperature and rainfall were assessed using mid- and end-century gridded data products for low (RCP 4.5) and high emissions (RCP 8.5) scenarios. Our results showed that the “OK DAIRY” site received higher rainfall than the “UP DAIRY” site, favoring grass growth and forage availability. In addition, the “UP DAIRY” site was more stressful for animals during the summer (THI 69 to 73) than the “OK DAIRY” site (THI 67 to 70) as the THI exceeded the critical threshold of 68 which is conducive for high lactating cattle. On the “UP DAIRY” site, the THI did not drop below 68 during the summer nights, which created fewer opportunities for cattle to recover from heat stress. Future projections indicated that air temperature would increase 1.3 to 1.8 °C by mid-century and 1.6 to 3.2 °C by the end of the century at both farms, and rainfall will increase at the “OK DAIRY” site and decrease at the “UP DAIRY” site by the end-of-century. The agriculture and livestock industries, particularly the dairy and beef subsectors in Hawai`i, are vulnerable to climate changes as higher temperatures and less rainfall will have adverse effects on cattle. The findings in this study demonstrated how both observed and projected changes in climates support the development of long-term strategies for breeding and holistic livestock management practices to adapt to changing climate conditions.
... In wetter years, when water is less limiting, the relative eCO 2 enhancement for ANPP and LAI is often minimal 9,30 (Extended Data Fig. 1). This result holds for multiple sites, including semi-arid shortgrass steppe dominated by C 3 species, mixed grass prairie 9,38 and mesic but frequently water-stressed C 4 tallgrass prairie 30 . In these experimental CO 2 enrichment sites, instead of LAI increasing in wetter years, there was evidence of community shifts to greater abundance of invasive grass species that are usually adapted to moister conditions as well as substantial biomass enhancement of subshrub species 20,39 . ...
... The relatively more restricted LAI responses in grasslands would reduce the indirect effect enhancing carbon assimilation through enhanced LAI. Instead, excessive soil water in some grassland sites may increase N leaching losses and N limitation 22,30 and in others may trigger changes in species composition 20,39 . Given that woody ecosystems have a markedly stronger ANPP enhancement than grasslands (24% versus 13% for eCO 2 level at ~550 ppm), occupy ~50% of Earth's land (including forests, shrublands and woody savannas) and generally have a greater ANPP, our results suggest that eCO 2 -enhanced terrestrial ANPP is likely to become increasingly dominated by woody plants under rising atmospheric CO 2 , independent of other disturbance-and climate-related effects. ...
Experiments show that elevated atmospheric CO2 (eCO2) often enhances plant photosynthesis and productivity, yet this effect varies substantially and may be climate sensitive. Understanding if, where and how water supply regulates CO2 enhancement is critical for projecting terrestrial responses to increasing atmospheric CO2 and climate change. Here, using data from 14 long-term ecosystem-scale CO2 experiments, we show that the eCO2 enhancement of annual aboveground net primary productivity is sensitive to annual precipitation and that this sensitivity differs between woody and grassland ecosystems. During wetter years, CO2 enhancement increases in woody ecosystems but declines in grass-dominated systems. Consistent with this difference, woody ecosystems can increase leaf area index in wetter years more effectively under eCO2 than can grassland ecosystems. Overall, and across different precipitation regimes, woody systems had markedly stronger CO2 enhancement (24%) than grasslands (13%). We developed an empirical relationship to quantify aboveground net primary productivity enhancement on the basis of changes in leaf area index, providing a new approach for evaluating eCO2 impacts on the productivity of terrestrial ecosystems.
... The vegetation primary productivity on land is proportional to the available photosynthetically active radiation at the surface (Pinker and Laszlo, 1992), which is the sum of direct and diffuse solar radiation (Alados and Alados-Arboledas, 1999). In our stratospheric aerosol experiments, a reduction in direct solar radiation reaching the surface is simulated due to the increased SW scattering by the aerosols (Fig. S9, Table 2). ...
... In the 2XCO2 experiment, there is an increase of 26.72 Gt C yr −1 (22.5 %) in gross primary productivity (GPP) compared to the 1XCO2 experiment although the amount of radiation available for productivity is approximately the same in both cases. A doubling of CO 2 concentration causes an increase in the plant productivity due to the CO 2 fertilization effect (Farquhar, 1997;Owensby et al., 1999). To exclude the CO 2 fertilization effect and assess the changes due to only the prescribed aerosols in the stratospheric aerosol experiments, changes in radiation and productivity are discussed relative to the 2XCO2 experiment below. ...
Reduction of surface temperatures of the planet by injecting sulfate aerosols
in the stratosphere has been suggested as an option to reduce the amount of
human-induced climate warming. Several previous studies have shown that for a
specified amount of injection, aerosols injected at a higher altitude in the
stratosphere would produce more cooling because aerosol sedimentation would
take longer. In this study, we isolate and assess the sensitivity of
stratospheric aerosol radiative forcing and the resulting climate change to
the altitude of the aerosol layer. We study this by prescribing a specified
amount of sulfate aerosols, of a size typical of what is produced by
volcanoes, distributed uniformly at different levels in the stratosphere. We
find that stratospheric sulfate aerosols are more effective in cooling
climate when they reside higher in the stratosphere. We explain this
sensitivity in terms of effective radiative forcing: volcanic aerosols heat
the stratospheric layers where they reside, altering stratospheric water
vapor content, tropospheric stability, and clouds, and consequently the
effective radiative forcing. We show that the magnitude of the effective
radiative forcing is larger when aerosols are prescribed at higher altitudes
and the differences in radiative forcing due to fast adjustment processes can
account for a substantial part of the dependence of the amount of cooling on
aerosol altitude. These altitude effects would be additional to dependences
on aerosol microphysics, transport, and sedimentation, which are outside the
scope of this study. The cooling effectiveness of stratospheric sulfate
aerosols likely increases with the altitude of the aerosol layer both because
aerosols higher in the stratosphere have larger effective radiative forcing
and because they have higher stratospheric residence time; these two effects
are likely to be of comparable importance.
... We set the average annual NPP at the ARC site to 740 gC m −2 by taking the average NPP in 2010 and 2011 from Xu et al. (2013). The GPP was assumed to be twice the NPP, based on existing measurements in tall grassland ecosystems (Johnson and Matchett, 2001;Owensby et al., 1999;Williams et al., 2004). The NPP and GPP for the WLR site were calibrated against 570 and 1140 gC The TEM-HD 2L includes regional climate and atmospheric chemistry, plant physiology, land-surface water balance, soil biogeochemistry, and soil hydrology. ...
... Our modeling approach did not account for variation in plant community structure or physiology. Species composition may change under long-term drought, which may maintain ecosystem stability (Owensby et al., 1999). Species turnover can be expected following an extreme drought and intraspecific variability can be a more important driver of the short-term functional response of plant communities to drought (Jung et al., 2014). ...
Atmospheric CO2 increased in the 20th century and is expected to continue to do so in the 21st century, with resultant warming. Even so, the effects of these changes on the ecological systems, such as carbon sequestration in grassland ecosystems, are still poorly understood. To improve our understanding of the carbon balance, we developed a two-layer soil hydrology model for Terrestrial Ecosystem Model-Hydro Daily to simulate the carbon fluxes of moist grasslands more accurately. Using the outputs of two Representative Concentration Projection scenarios (RCP4.5 and 8.5) from five Coupled Model Inter-comparison Project Phase 5 climate models, we investigated if projected warming and rising atmospheric CO2 could stimulate net primary production (NPP), net ecosystem productivity (NEP), and ecosystem respiration of two highly productive grassland sites in the central Great Plains (USA) in the 21st century. Our study shows that elevated atmospheric CO2 has a fertilization effect in boosting NPP in grassland ecosystems, with a sensitivity of 0.53 gC m⁻² yr⁻¹ and 1.06 gC m⁻² yr⁻¹ under the RCP4.5 and RCP8.5 climate scenarios, respectively. Warming is more harmful to NPP in the grassland adapted to a warmer climate. Under the RCP4.5 scenario, both grassland sites likely experience a variable net ecosystem carbon exchange. However, the RCP8.5 scenario and accompanying severe warming would turn both grassland sites to net carbon sources by the end of the century, decreasing NEP by 0.97 gC m⁻² yr⁻¹ at the warmer site and by 0.96 gC m⁻² yr⁻¹ at the cooler site, driven by increased respiration and limited plant growth.
... Secondly, taking into account the water-use efficiency. With higher atmospheric CO 2 concentrations, trees under drought stress might benefit from increased water-use efficiency, helping to alleviate drought effects and postpone the decrease in photosynthesis due to stomatal closure [61]. This allows for a prolonged growing season [25]. ...
The increase in global carbon emissions has intensified the effects of CO2 fertilization on the carbon cycle. CO2 fertilization is shaped by several factors, including the physiological differences among trees of varied forest ages and types, as well as the influence of different climatic conditions. It is essential to investigate the differences in CO2 fertilization effects across diverse climate zones and delve into the association between these effects and forest age and type. Such exploration will deepen our knowledge of forest responses to environmental changes. This study used annual ring width data from the International Tree-Ring Data Bank, employing the generalized additive mixed models and the Random Forest model to discern the pattern of the CO2 fertilization effect concerning forest age in the Northern Hemisphere. This study also explored the variations in the effect of CO2 fertilization across unique climate zones and the disparities among various forest types within the same climatic zone. The results indicated a link between forest age and the CO2 fertilization effect: it tends to increase in sapling forests and middle-aged forests and diminish in mature forests. Warmer, drier environments had a more marked effect of increased CO2 on tree fertilization. Additionally, coniferous forests demonstrated a more substantial CO2 fertilization effect than broadleaf forests, and deciduous needle-leaf forests surpassed evergreen needle-leaf forests in this regard. This research is pivotal in understanding the shifting patterns of CO2 fertilization effects and how forests respond to atmospheric changes.
... Soil nutrients also affect biomass to some extent (Paoli et al., 2008). However, few studies have emphasized the effect of these stressful factors, such as UV (Zavala & Ravetta, 2002) and P O2 (Owensby et al., 1999), especially on a large scale. Therefore, we assumed that, under a complex ecological environment such as that of the QTP, the spatial pattern of vegetation biomass should be influenced by its unique climatic factors to some extent, in addition to the common temperature and precipitation mentioned-above. ...
... Though, even at static species richness levels, species in local plant communities react asynchronously to changes in the environment to stabilize productivity (Wilcox et al. 2017). Additionally, species composition and productivity can change concurrently in response to environmental changes (Owensby et al. 1999), creating additional uncertainty whether productivity changes directly with the environment or is mediated by species composition (Hautier et al. 2020). ...
Plant community biomass production is co-dependent on climatic and edaphic factors that are often covarying and non-independent. Disentangling how these factors act in isolation is challenging, especially along large climatic gradients that can mask soil effects. As anthropogenic pressure increasingly alters local climate and soil resource supply unevenly across landscapes, our ability to predict concurrent changes in plant community processes requires clearer understandings of independent and interactive effects of climate and soil. To address this, we developed a multispecies phytometer (i.e., standardized plant community) for separating key drivers underlying plant productivity across gradients. Phytometers were composed of three globally cosmopolitan herbaceous perennials, Dactylis glomerata, Plantago lanceolata, and Trifolium pratense. In 2017, we grew phytometer communities in 18 sites across a pan-European aridity gradient in local site soils and a standardized substrate and compared biomass production. Standard substrate phytometers succeeded in providing a standardized climate biomass response independent of local soil effects. This allowed us to factor out climate effects in local soil phytometers, establishing that nitrogen availability did not predict biomass production, while phosphorus availability exerted a strong, positive effect independent of climate. Additionally, we identified a negative relationship between biomass production and potassium and magnesium availability. Species-specific biomass responses to the environment in the climate-corrected biomass were asynchronous, demonstrating the importance of species interactions in vegetation responses to global change. Biomass production was co-limited by climatic and soil drivers, with each species experiencing its own unique set of co-limitations. Our study demonstrates the potential of phytometers for disentangling effects of climate and soil on plant biomass production and suggests an increasing role of P limitation in the temperate regions of Europe.
... Forage quality also depends on the degree to which it can meet the nutritional requirements of different types of animals (Allen & Segarra, 2001). It has been reported that association between forage quality and nutritional requirements of grazing animals has an impact on the management and utilization of pasture forage (Owensby, Ham, Knapp, & Auen, 1999). It has been suggested that some medicinal-rangeland plants that grow in Torbat-e-Jam Rangelands can easily provide the maintenance requirement of livestock (Kazemi & Valizadeh, 2019a, b). ...
A diverse group of rangeland-medicinal plants are being used by ruminant whilst some of them have not been assessed for their nutritional value. This study was aimed to evaluate the chemical and mineral composition, buffering capacity, and in vitro fermentation of some rangeland-medicinal plants including Thymus kotschyanus, Ziziphora persica, Lallemantia royleana, and Scutellaria litwinowii in the family Lamiaceae, and Hypericum scabrum, in the family Hypericaceae. The results indicated that crude protein (CP) content ranged from 8.66% (S. litwinowii) to 12.17% of DM (H. scabrum). It was found that Z. persica had the highest potential gas production, metabolism energy (ME), relative feed value (RFV), and dry matter digestibility (DMD) values of 53.44 (mL 200-1 mg DM), 5.84 (MJ kg-1 DM), 170.66 and 70.88%, respectively. Mineral content differed among plants; Ca ranged from 5.79 to 41.96 g kg-1 DM. The concentrations of Ca, K, Mg, Fe, Zn, and Co were highest for L. royleana. Total volatile fatty acids (TVFA) and propionate concentrations were highest in the culture medium cultured with Z. persica, however, acetate, and butyrate were highest in H. scabrum. Acid-base buffering capacity was lower in T. kotschyanus and H. scabrum compared to other plants, while it was higher in S. litwinowii. Overall, it can be concluded that among plants evaluated in this study, Z. persica had higher nutritional value for sheep feeding.
... Though, even at static species richness levels, species in local plant communities react asynchronously to changes in the environment to stabilize productivity (Wilcox et al. 2017). Additionally, species composition and productivity can change concurrently in response to environmental changes (Owensby et al. 1999), creating additional uncertainty whether productivity changes directly with the environment or is mediated by species composition (Hautier et al. 2020). ...
Plant community biomass production is co‐dependent on climatic and edaphic factors that are often covarying and non‐independent. Disentangling how these factors act in isolation is challenging, especially along large climatic gradients that can mask soil effects. As anthropogenic pressure increasingly alters local climate and soil resource supply unevenly across landscapes, our ability to predict concurrent changes in plant community processes requires clearer understandings of independent and interactive effects of climate and soil. To address this, we developed a multispecies phytometer (i.e., standardized plant community) for separating key drivers underlying plant productivity across gradients. Phytometers were composed of three globally cosmopolitan herbaceous perennials, Dactylis glomerata, Plantago lanceolata, and Trifolium pratense. In 2017, we grew phytometer communities in 18 sites across a pan‐European aridity gradient in local site soils and a standardized substrate and compared biomass production. Standard substrate phytometers succeeded in providing a standardized climate biomass response independent of local soil effects. This allowed us to factor out climate effects in local soil phytometers, establishing that nitrogen availability did not predict biomass production, while phosphorus availability exerted a strong, positive effect independent of climate. Additionally, we identified a negative relationship between biomass production and potassium and magnesium availability. Species‐specific biomass responses to the environment in the climate‐corrected biomass were asynchronous, demonstrating the importance of species interactions in vegetation responses to global change. Biomass production was co‐limited by climatic and soil drivers, with each species experiencing its own unique set of co‐limitations. Our study demonstrates the potential of phytometers for disentangling effects of climate and soil on plant biomass production and suggests an increasing role of P limitation in the temperate regions of Europe.
... Differences in soil water content are often examined when searching for evidence of an eCO 2 effect on plant water use. In some field-based crop and grassland experiments, soil water content has been observed to be higher in eCO 2 , thereby delaying drought onset (Field et al., 1997;Owensby et al., 1999;Morgan et al., 2004Morgan et al., , 2011Kimball, 2016). However, higher soil water content in eCO 2 is often not consistently observed from year-to-year (Morgan et al., 2011;Gray et al., 2016). ...
Plant responses to elevated atmospheric carbon dioxide (eCO2) have been hypothesized as a key mechanism that may ameliorate the impact of future drought. Yet, despite decades of experiments, the question of whether eCO2 reduces plant water use, yielding ‘water savings’ that can be used to maintain plant function during periods of water stress, remains unresolved. In this Viewpoint, we identify the experimental challenges and limitations to our understanding of plant responses to drought under eCO2. In particular, we argue that future studies need to move beyond exploring whether eCO2 played ‘a role’ or ‘no role’ in responses to drought, but instead more carefully consider the timescales and conditions that would induce an influence. We also argue that considering emergent differences in soil water content may be an insufficient means of assessing the impact of eCO2. We identify eCO2 impact during severe drought (e.g. to the point of mortality), interactions with future changes in vapour pressure deficit and uncertainty about changes in leaf area as key gaps in our current understanding. New insights into CO2 × drought interactions are essential to better constrain model theory that governs future climate model projections of land–atmosphere interactions during periods of water stress.
... Although the effects of enriched CO2 on plants are variable and not universal, plants growing under elevated CO2 conditions often exhibit enhanced photosynthetic activity, increased productivity and leaf area or biomass (Owensby et al., 1999). Elevated CO2 might also alter primary and secondary metabolism of plants. ...
... A wide variety of equipment, including open-top chambers (OTC), controlled-environment (CE) systems, and free-air CO 2 enrichment (FACE) systems, has been used to study the effects of elevated C a . In the OTC system, plants are held in a chamber with an open top that facilitates gas exchange with the atmosphere (Owensby et al., 1999). However, the temperature is generally higher inside the chamber than outside, inevitably increasing plant transpiration, which influences plant growth rates. ...
Photosynthesis of wheat and maize declined when grown with NH4⁺ as a nitrogen (N) source at ambient CO2 concentration compared to those grown with a mixture of NO3– and NH4⁺, or NO3– as the sole N source. Interestingly, these N nutritional physiological responses changed when the atmospheric CO2 concentration increases. We studied the photosynthetic responses of wheat and maize growing with various N forms at three levels of growth CO2 levels. Hydroponic experiments were carried out using a C3 plant (wheat, Triticum aestivum L. cv. Chuanmai 58) and a C4 plant (maize, Zea mays L. cv. Zhongdan 808) given three types of N nutrition: sole NO3– (NN), sole NH4⁺ (AN) and a mixture of both NO3– and NH4⁺ (Mix-N). The test plants were grown using custom-built chambers where a continuous and desired atmospheric CO2 (Ca) concentration could be maintained: 280 μmol mol–1 (representing the pre-Industrial Revolution CO2 concentration of the 18th century), 400 μmol mol–1 (present level) and 550 μmol mol–1 (representing the anticipated futuristic concentration in 2050). Under AN, the decrease in net photosynthetic rate (Pn) was attributed to a reduction in the maximum RuBP-regeneration rate, which then caused reductions in the maximum Rubisco-carboxylation rates for both species. Decreases in electron transport rate, reduction of electron flux to the photosynthetic carbon [Je(PCR)] and electron flux for photorespiratory carbon oxidation [Je(PCO)] were also observed under AN for both species. However, the intercellular (Ci) and chloroplast (Cc) CO2 concentration increased with increasing atmospheric CO2 in C3 wheat but not in C4 maize, leading to a higher Je(PCR)/ Je(PCO) ratio. Interestingly, the reduction of Pn under AN was relieved in wheat through higher CO2 levels, but that was not the case in maize. In conclusion, elevating atmospheric CO2 concentration increased Ci and Cc in wheat, but not in maize, with enhanced electron fluxes towards photosynthesis, rather than photorespiration, thereby relieving the inhibition of photosynthesis under AN. Our results contributed to a better understanding of NH4⁺ involvement in N nutrition of crops growing under different levels of CO2.
... 8 OTC (open-top chamber) [CO 2 ] , , [89] . ...
... The atmospheric CO 2 is going to double from the current level and the global average surface temperature will increase by 1.5-6°C by the end of this century (IPCC 2001). Higher levels of CO 2 increase photosynthetic rate of plants leading to more accumulation of biomass (Owensby et al. 1999), resulting in reduced foliar nitrogen and wider C/N ratio in the plant tissues (Goverde and Erhardt 2003). Insects feeding on such crops alter their growth, development, survival and reproduction (Wu et al. 2006), due to the reduction in the nutritional value of the plant (Asshoff and Hättenschwiler 2005). ...
Pink Stem Borer, Sesamia inferens Walker (Lepidoptera: Noctuidae) incidence has increased on graminaceous crops in the north-western plains of India during recent years. To understand the effect of climate change on the northward spread of the pest, studies on the growth and development of S. inferens on maize (Zea mays L.) were planned with combinations of temperature and CO2. The combinations were 27: 22 °C and 375 ppm of CO2, 32: 26 °C and 375 ppm of CO2, 27: 22 °C and 450 ppm of CO2 and 32: 26 °C and 450 ppm of CO2. Various developmental parameters of S. inferens were analyzed using analysis of variance for the main effects of temperature and CO2 and their interactions. At elevated temperature, the growth of egg, larval and pupal stages were faster and the developmental period decreased by 30.9%. At elevated CO2, the larval and pupal development delayed and there was 5.7% increase in developmental period. Both temperature and CO2 individually and in combination significantly influenced adult longevity. Adult longevity reduced 24.9% and 21.7% in male and female, respectively at elevated temperature. Whereas, at elevated CO2, adult longevity increased 7.6% in male and 6.8% in female, respectively. The fecundity was positively influenced (+10.8%) by elevated temperature and negatively (−14.4%) by elevated CO2. The effects of temperature and CO2 on the development of pink stem borer were opposite, with temperature being positive and predominant in influencing the biology of S. inferens. So, it is probable that the faster development of S. inferens on maize in the warm climate might slightly get mitigated by the adverse effect of elevated CO2. The overall effect of rapid development of pest population and damage on maize on large area basis needs to be further investigated.
... 仅仅足够高的温度与中等程度的干旱(或者 湿润)相结合非常有利于 C 4 植物的生长, 就像全新世 期间中纬度带地区 [18,19] 和末次冰期期间低纬度带地 区的植被 [9,14] 一样. 植物相对量生物量变化影响不大 [67] . ...
... If at all, C 3 grasses should profit more from elevated CO 2 than C 4 grasses, but this has not always been found (e.g. Owensby et al. 1999 ;Reich et al. 2018). It often appears that species belonging to one PFT vary far more in their traits than do PFT's among each other (Körner 1993). ...
In this review, I discuss, and partly challenge, a number of paradigms, assumptions and definitions that apply to many fields of plant ecology. The main points include the need for a distinction between a growth-or yield-oriented versus a fitness-or biodiversity-oriented concept of limitation and stress, and the challenges of a meaningful handling of plant traits and their functional significance. Further, I discuss the central role of biological variation in plant ecology, including the various forms of adaptive adjustments, and the task of scaling plant responses in space and time. I close this review with a critical comment on data stratification in the analysis of large biological datasets (e.g. meta-analysis). ARTICLE HISTORY
... If at all, C 3 grasses should profit more from elevated CO 2 than C 4 grasses, but this has not always been found (e.g. Owensby et al. 1999 ;Reich et al. 2018). It often appears that species belonging to one PFT vary far more in their traits than do PFT's among each other (Körner 1993). ...
In this review, I discuss, and partly challenge, a number of paradigms, assumptions and definitions that apply to many fields of plant ecology. The main points include the need for a distinction between a growth- or yield-oriented versus a fitness- or biodiversity-oriented concept of limitation and stress, and the challenges of a meaningful handling of plant traits and their functional significance. Further, I discuss the central role of biological variation in plant ecology, including the various forms of adaptive adjustments, and the task of scaling plant responses in space and time. I close this review with a critical comment on data stratification in the analysis of large biological datasets (e.g. meta-analysis).
... Water availability varies across gradients in soil physical and related hydrological properties at spatial scales over which precipitation is similar. CO 2 enrichment typically shows greater enhancement of productivity in drier years or at drier localities, the result of increased WUE (Owensby et al., 1999;Morgan et al., 2004;Nowak et al., 2004;Fatichi et al., 2016). A similar mechanism may contribute to soil differences in the productivity response to CO 2 enrichment. ...
Atmospheric CO2 enrichment usually increases the aboveground net primary productivity (ANPP) of grassland vegetation, but the magnitude of the ANPP–CO2 response differs among ecosystems. Soil properties affect ANPP via multiple mechanisms and vary over topographic to geographic gradients, but have received little attention as potential modifiers of the ANPP–CO2 response.
We assessed the effects of three soil types, sandy loam, silty clay and clay, on the ANPP response of perennial C3/C4 grassland communities to a subambient to elevated CO2 gradient over 10 yr in Texas, USA. We predicted an interactive, rather than additive, effect of CO2 and soil type on ANPP.
Contrary to prediction, CO2 and soil additively influenced grassland ANPP. Increasing CO2 by 250 μl l⁻¹ increased ANPP by 170 g m⁻² across soil types. Increased clay content from 10% to 50% among soils reduced ANPP by 50 g m⁻². CO2 enrichment increased ANPP via a predominant direct effect, accompanied by a smaller indirect effect mediated by a successional shift to increased dominance of the C4 tallgrass Sorghastrum nutans.
Our results indicate a large, positive influence of CO2 enrichment on grassland productivity that resulted from the direct physiological benefits of CO2 augmented by species succession, and was expressed similarly across soils of differing physical properties.
... Of this material, 83% of the carbon is respired, so 17% returns to the soil organic carbon pool, while 50% of the nitrogen goes to the soil organic nitrogen pool in the form of manure, and 50% goes to the soil inorganic nitrogen pool in the form of urine. Agricultural lands are calibrated with active management, using maize data from Kellogg Biological Station, MI for crops (Smith & Gross, 2006), C4 tall grass pasture data from Konza Prairie, KN for arid pasture (Johnson & Matchett, 2001;Owensby et al., 1999;Williams et al., 2004), and orchardgrass data from the Rodale Institute Experimental Farm in PA (Jiang et al., 2015) for mesic pastures. No tilling or irrigation is assumed. ...
Many flux-based data and related models indicate that the United States is currently a strong carbon sink, but this flux imbalance does not account for carbon lost from previous disturbance. Here we take a modeling approach that involves a full carbon accounting to include the effect of previous human-induced land use changes and management during a period of abiotic changes to the environment since the 1700s. The goal is to show how land use and land cover change has affected carbon loss in the context of other environmental changes like climate, elevated CO2, and nitrogen deposition that tend to enhance growth. Here we show that land use and land cover change has led to the loss of carbon since 1700 (42 PgC), while growth enhancements since the start of the 20th century have only partially countered this loss (1.8 PgC). Fertilized croplands are the largest carbon sink in the first decade of the 21st century (477 TgC/year), followed by forests (266 TgC/year) and grazing pastures (223 TgC/year), if not accounting for land use conversion fluxes, product decomposition, and livestock respiration (i.e., net ecosystem productivity). When accounting for these disturbance fluxes, only returning forests (40 TgC/year) and grasslands (16 TgC/year) remain a carbon sink. A carbon accounting of human disturbances should be considered when determining the climate and policy implications of forest regrowth on the terrestrial carbon sink.
... Salinity, flooding, water stress, and eutrophication can all potentially influence the effects of CO 2 fertilization on marsh plants (Langley et al., 2009(Langley et al., , 2013Lenssen et al., 1993;Owensby et al., 1999;Rozema et al., 1991;Ward et al., 1999). Overall, the available evidence is coherent in pointing to a significant CO 2 fertilization effect on organic accretion and plant production even in the presence of other simultaneous environmental changes Langley et al., 2009;Langley and Megonigal, 2010;Rasse et al., 2005). ...
... However, a number of studies have shown that the productivity of vascular plants, particularly graminoids, increases in response to elevated CO 2 (Morgan et al., 2011;Norby et al., 2002;Nowak, Ellsworth, & Smith, 2004;Owensby, Ham, Knapp, & Auen, 1999). ...
Widespread changes in arctic and boreal Normalized Difference Vegetation Index (NDVI) values captured by satellite platforms indicate that northern ecosystems are experiencing rapid ecological change in response to climate warming. Increasing temperatures and altered hydrology are driving shifts in ecosystem biophysical properties that, observed by satellites, manifest as long‐term changes in regional NDVI. In an effort to examine the underlying ecological drivers of these changes, we used field‐scale remote sensing of NDVI to track peatland vegetation in experiments that manipulated hydrology, temperature, and carbon dioxide (CO2) levels. In addition to NDVI, we measured percent cover by species and leaf area index (LAI). We monitored two peatland types broadly representative of the boreal region. One site was a rich fen located near Fairbanks, Alaska at the Alaska Peatland Experiment (APEX), and the second site was a nutrient‐poor bog located in Northern Minnesota within the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment. We found that NDVI decreased with long‐term reductions in soil moisture at the APEX site, coincident with a decrease in photosynthetic leaf area and the relative abundance of sedges. We observed increasing NDVI with elevated temperature at the SPRUCE site, associated with an increase in the relative abundance of shrubs and a decrease in forb cover. Warming treatments at the SPRUCE site also led to increases in the LAI of the shrub‐layer. We found no strong effects of elevated CO2 on community composition. Our findings support recent studies suggesting that changes in NDVI observed from satellite platforms may be the result of changes in community composition and ecosystem structure in response to climate warming.
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... Rising CO 2 concentration in the atmosphere and global warming can also impact productivity and water use in grasslands. For example, an examination of the long-term impact (8 years, 1989-1996) of elevated CO 2 on biomass production in a tallgrass prairie site north of Manhattan, Kansas, USA, showed reduced plant transpiration, increased water use efficiency (WUE) and reduced drought stress (higher volumetric soil water content for the 0-100 cm soil layer) in elevated CO 2 compared with ambient CO 2 plots (Owensby et al., 1999). This ultimately resulted in greater above-and below-ground biomass of a C 4 -dominated tallgrass prairie in the years with periodic drought stress but not in the relatively wet years. ...
... The terrestrial carbon cycle is largely governed by the balance between net primary production (the difference between gross primary production, GPP, and plant autotrophic respiration) and soil heterotrophic respiration [20]. Increasing atmospheric CO 2 directly enhances plant productivity through CO 2 -fertilization effect [37,38]. Solar geoengineering in a high-CO 2 world, while maintaining the CO 2 -fertilization effect, would affect the terrestrial biosphere via changes in the amount of direct and diffuse sunlight, climate (temperature, precipitation, etc.), and atmospheric chemistry (e.g., ozone). ...
Purpose of Review
Review existing studies on the carbon cycle impact of different solar geoengineering schemes.
Recent Findings
The effect of solar geoengineering on terrestrial primary productivity is typically much smaller than that of CO2 fertilization. Changes in the partitioning between direct and diffuse radiation in response to stratospheric aerosol injection could substantially alter modeled plant productivity. Inclusion of the nitrogen cycle would further modify the terrestrial response to solar geoengineering. Relative to a high-CO2 world, solar geoengineering, via cooling the surface ocean, would increase CO2 solubility, enhancing oceanic CO2 uptake. However, the effect from geoengineering-induced changes in ocean circulation and marine biology would be more complicated. Solar geoengineering would have a small effect on surface ocean acidification, but could accelerate acidification in the deep ocean. Solar geoengineering would reduce atmospheric CO2, but the relative contribution from the ocean sink and land sink is uncertain.
Summary
To date, there are only a few studies on the carbon cycle response to solar geoengineering. Coordinated geoengineering model intercomparison studies are needed to gain a better understanding of the carbon cycle impact of solar geoengineering and feedback on climate change.
... Global climate change may affect ecosystem functioning by increasing temperature and changing precipitation amounts and patterns (Fiala et al., 2009), and climate is the major factor influencing carbon fluxes in grasslands (Paruelo et al., 2010). Precipitation and temperature are the main factors affecting grassland biomass (Hielkema et al., 1986;Nicholson et all., 1990;Tucker et al., 1991;Clenton et al., 1999;DuPlessis, 1999;Wang et al., 2001). These two factors affect the biologic and physiological activities of plants such as photosynthesis, inhalation and sweating, affecting either positively or negatively amount of biomass production in the grassland ecosystems. ...
Above and belowground biomasses of grasslands are important parameters for characterizing regional and global carbon cycles in grassland ecosystems within terrestrial ecosystems. The objective of this study was to determine above and below ground biomass in the grassland areas of Bicakcilar and Kilickaya province in Artvin within Coruh River Basin located northeastern Turkey. Additionally, the amount of carbon contents were also calculated in the study areas in relation to regional distribution patterns of above and below ground biomass and their relationships with environmental factors were also investigated. To implement the study, 55 sampling sites were selected for different altitudes to determine the amounts of above and below ground biomass. For determination of above ground biomass (AGB), 1x1 meters in size wire cages were placed in the selected sample plots before the beginning of the vegetation period. These protected areas/plots (1x1 m 2) were harvested from soil levels at the end of the vegetation period and then dry weighed in laboratory. Root sampling for the below ground biomass (BGB) was also carried out using steel pipe of 6,4 cm in diameter and 30 cm in length. According to the obtained results, the amounts of AGB and BGB were ranged from 1 ton/ha to 3,8 ton/ha and from 3 ton/ha to 6,3 ton/ha in the Bicakcilar, respectively. As for the study areas of Kilickaya, the amounts of AGB and BGB were ranged from 0,8 ton/ha to 4 ton/ha and from 2,4 ton/ha to 5,2 ton/ha, respectively. The average carbon contents in the grassland of Bicakcilar and Kilickaya were estimated as 3,4 ton/ha and 3 ton/ha, respectively. At the same time, it was found that the amount of AGB increased to a certain altitude and then decreased, while the amount of BGB increased or decreased contrarily. Additionally, statistical analysis indicated that precipitation was the key determining factor for the amount of AGB and BGB in respect to the altitudinal change.
... Studies focusing on the long-term variations in CO 2 exchange (source/ sink behaviour) are of great importance (e.g. Owensby et al. 1999;Bousquet et al. 2000;Acosta et al. 2017), and also play indirectly an important role in decreasing pollution and the emission of greenhouse gases (Andres et al. 2012;Seinfeld, Pandis 2016;Venhari et al. 2017). ...
Croplands have been identified as binding large amounts of carbon. About one third of the total area in
Poland is covered by croplands. In this paper, we analyze data describing the yields and structure of crops available for 13 selected subareas of Poland between 1960 and 2009 to evaluate the greenhouse gas mitigation potential due to carbon (C) uptake of this land cover type. Seven selected subareas located in Western Poland (area A), and six subareas in the southeast of Poland (area B) were chosen for detailed analysis. Cereals were identified as the most dominant crop planted in both areas during 1960-2009. Still, differences in yield could be found, with larger production in area A than in area B. By the year 2009, arable land (cereals, beetroot, potato, rapeseed and maize) covered nearly 10 Mio ha of Poland. The average uptake of C by crops between 1960 and 2009 was 3,24 ± 0,17 Mg C ha-1 a-1 for area A, 2,84 ± 0,12 Mg C ha-1 a-1 for area B and 2,88 ± 0,11 Mg C ha-1 a-1 for the whole country. Given the fact that about 3% of the total assimilated carbon remains in the soil, we calculated that 0,98 Tg C were stored in Polish croplands in 2009. Due to this fact, croplands are short time storage of carbon and thus contribute to greenhouse gas mitigation.
... Global mean CO 2 concentration has increased from 290 to 375 lmol mol -1 during the last 100 years and is conservatively projected to be doubled by the end of 21st century, strongly dependent on future scenarios of anthropogenic emissions (Nagel et al. 2005). The ongoing increase in atmospheric CO 2 may cause changes in species composition of ecosystems, either by altering global climate (Chapin et al. 1995) or, more directly, by favoring certain photosynthetic pathways (Arp et al. 1993) or changing competition dynamics within ecosystems (Owensby et al. 1999). Invasive species, which may exploit the new environmental conditions caused by global change such as CO 2 enrichment, may gain footholds in previously inhospitable ecosystems, changing species composition, and biological invasions have become a serious environmental and socioeconomic problem and hot topic of ecological research worldwide (Dukes and Mooney 1999). ...
Both global change and biological invasions threaten biodiversity worldwide. However, their interactions and related mechanisms are still not well elucidated. To elucidate potential traits contributing to invasiveness and whether ongoing increase in CO2 aggravates invasions, noxious invasive Wedelia trilobata and native Wedelia urticifolia and Wedelia chinensis were compared under ambient and doubled atmospheric CO2 concentrations in terms of growth, biomass allocation, morphology, and physiology. The invader had consistently higher leaf mass fraction (LMF) and specific leaf area than the natives, contributing to a higher leaf area ratio, and therefore to faster growth and invasiveness. The higher LMF of the invader was due to lower root mass fraction and higher fine root percent. On the other hand, the invader allocated a higher fraction of leaf nitrogen (N) to photosynthetic apparatus, which was associated with its higher photosynthetic rate, and resource use efficiency. All these traits collectively contributed to its invasiveness. CO2 enrichment increased growth of all studied species by increasing actual photosynthesis, although it decreased photosynthetic capacities due to decreased leaf and photosynthetic N contents. Responses of the invasive and native plants to elevated CO2 were not significantly different, indicating that the ongoing increase in CO2 may not aggravate biological invasions, inconsistent with the prevailing results in references. Therefore, more comparative studies of related invasive and native plants are needed to elucidate whether CO2 enrichment facilitates invasions. © 2017 Springer Science+Business Media B.V., part of Springer Nature
... Still, the generalization has been used to rationalize why the eCO 2induced enhancement response of deserts will be large (Jordan et al., 1999), why arid and semi-arid zones have shown greening and shrub encroachment over the past 20 years (Ahlstr€ om et al., 2015;Donohue, Roderick, Mcvicar, & Farquhar, 2013) and why the eCO 2induced enhancement of grasslands is larger in dry vs. wet years (Owensby, Ham, Knapp, & Auen, 1999). Hence, this particular phenomenon deserves closer investigation especially in water-limited ecosystems because even small increases in soil water content in dry climate zones can have significant effects on processes such as growing season length (Reyes-Fox et al., 2014), nutrient mineralization and organic matter decomposition (Morgan et al., 2004;Wullschleger, Tschaplinski, & Norby, 2002), and survival of plants during dry periods (Bond & Midgley, 2012). ...
Elevated atmospheric CO2 (eCO2) is expected to reduce the impacts of drought and increase photosynthetic rates via two key mechanisms: first, through decreased stomatal conductance (gs) and increased soil water content (VSWC) and second, through increased leaf internal CO2 (Ci) and decreased stomatal limitations (Slim). It is unclear if such findings from temperate grassland studies similarly pertain to warmer ecosystems with periodic water deficits. We tested these mechanisms in three important C3 herbaceous species in a periodically dry Eucalyptus woodland and investigated how eCO2-induced photosynthetic enhancement varied with seasonal water availability, over a 3 year period. Leaf photosynthesis increased by 10%–50% with a 150 μmol mol−1 increase in atmospheric CO2 across seasons. This eCO2-induced increase in photosynthesis was a function of seasonal water availability, given by recent precipitation and mean daily VSWC. The highest photosynthetic enhancement by eCO2 (>30%) was observed during the most water-limited period, for example, with VSWC <0.07 in this sandy surface soil. Under eCO2 there was neither a significant decrease in gs in the three herbaceous species, nor increases in VSWC, indicating no “water-savings effect” of eCO2. Periods of low VSWC showed lower gs (less than ≈ 0.12 mol m−2 s−1), higher relative Slim (>30%) and decreased Ci under the ambient CO2 concentration (aCO2), with leaf photosynthesis strongly carboxylation-limited. The alleviation of Slim by eCO2 was facilitated by increasing Ci, thus yielding a larger photosynthetic enhancement during dry periods. We demonstrated that water availability, but not eCO2, controls gs and hence the magnitude of photosynthetic enhancement in the understory herbaceous plants. Thus, eCO2 has the potential to alter vegetation functioning in a periodically dry woodland understory through changes in stomatal limitation to photosynthesis, not by the “water-savings effect” usually invoked in grasslands.
... For example, ponderosa pine (Pinus ponderosa) established in grassland-forest ecotones in northern Colorado during years when spring and autumn precipitation were high in association with El Niño events (League and Veblen 2006). By increasing soil water content, higher CO 2 and precipitation also favor recruitment of taprooted invasive forbs like leafy spurge (Euphorbia esula), diffuse knapweed (Centaurea diffusa), and baby's breath (Gypsophila paniculata), as well as some subshrubs (Owensby et al. 1999;Morgan et al. 2007;Blumenthal et al. 2008). ...
Climate change science predicts warming and greater climatic variability for the foreseeable future. These changes in climate, together with direct effects of increased atmospheric CO2 concentration on plant growth and transpiration, will influence factors such as soil water and nitrogen availability that regulate the provisioning of plant and animal products from rangelands. Ecological consequences of the major climate change drivers—warming, precipitation modification, and CO2 enrichment—will vary among rangelands partly because temperature and precipitation shifts will vary regionally, but also because driver effects frequently are nonadditive, contingent on current environment conditions, and interact synergistically with disturbance regimes and human interventions. Consequences of climate change that are of special relevance to rangelands are modification of forage quantity and quality, livestock metabolism, and plant community composition. Warming is anticipated to be accompanied by a decrease in precipitation in already arid to semiarid rangelands in the southwestern USA, Central America, and south and southwestern Australia. Higher temperatures combined with drought will significantly impair livestock production by negatively impacting animal physiological performance, increasing ectoparasite abundances, and reducing forage quality and quantity. Conversely, the warmer, wetter conditions anticipated in the northwestern USA, southern Canada, and northern Asia may increase animal productivity by moderating winter temperatures, lengthening the growing season, and increasing plant productivity. Synergist interactions between climate change drivers and other human impacts, including changes in land-use patterns, intensification of disturbances, and species introductions and movements, may further challenge ecosystem integrity and functionality. Evidence from decades of research in the animal and ecological sciences indicates that continued directional change in climate will substantially modify ecosystem services provisioned by the world’s rangelands.
... Effects of rising atmospheric CO 2 concentrations have since then been studied across different types of grasslands with field scale manipulations such as open-top chambers and Free Air Carbon dioxide Enrichment (FACE) techniques. In these experiments, the response of plant biomass to eCO 2 was mainly positive (Feng et al., 2015;Owensby, Ham, Knapp, & Auen, 1999). Furthermore, crop yields were increased by eCO 2 by about 19% on average (grasses: ...
Future increase of atmospheric CO2 concentrations will potentially enhance grassland biomass production and shift the functional group composition with consequences for ecosystem functioning. In the 'GiFACE' experiment (Giessen Free Air Carbon dioxide Enrichment), fertilized grassland plots were fumigated with elevated CO2 (eCO2 ) year-round during daylight hours since 1998, at a level of +20% relative to ambient concentrations (in 1998 aCO2 was 364 ppm and eCO2 399 ppm; in 2014 aCO2 was 397 ppm and eCO2 518 ppm). Harvests were conducted twice annually through 23 years including 17 years with eCO2 (1998 to 2014). Biomass consisted of C3 grasses and forbs, with a small proportion of legumes. The total aboveground biomass (TAB) was significantly increased under eCO2 (p = 0.045 and 0.025, at first and second harvest). The dominant plant functional group grasses responded positively at the start, but for forbs the effect of eCO2 started out as a negative response. The increase in TAB in response to eCO2 was approximately 15% during the period from 2006 to 2014, suggesting that there was no attenuation of eCO2 effects over time, tentatively a consequence of the fertilization management. Biomass and soil moisture responses were closely linked. The soil moisture surplus (c. 3%) in eCO2 manifested in the latter years was associated with a positive biomass response of both functional groups. The direction of the biomass response of the functional group forbs changed over the experimental duration, intensified by extreme weather conditions, pointing to the need of long-term field studies for obtaining reliable responses of perennial ecosystems to eCO2 and as a basis for model development. This article is protected by copyright. All rights reserved.
Diversification of insects has occurred through 450 million years of earth’s fluctuating climate, yet swiftly deviating patterns of temperature and rainfall present unexpected obstacles along with the anthropogenic stresses. Climate variance and extreme weather events have a considerable impact on insect population dynamics. Insects are very sensitive to the ongoing climate warming. The temperature has a direct impact on the maintenance of essential life functions in insects such as survival, growth, development, metabolism, voltinism, and even availability of the host. A decrease in precipitation leads to drought-like conditions, which affect the abundance and diversity of soil insects. Global warming supports the manifestation of insect-transmitted plant diseases, and the population of the insect vectors gets increased. Research findings suggest that with a rise of temperature by 2 °C, insects experience more than the expected life cycles in a season. Elevation of carbon dioxide levels affects the behavior and production of insects as the host plant grown in such conditions is less nutritious for the insects. Alteration in the pattern of precipitation influences the insect pest predators, parasites, and diseases emanating in complex dynamics. Climate change incites the change in insect dynamics across the globe, and every day about 45–275 species of insects are becoming extinct. Beetle incidence in a protected forest in New Hampshire, USA, has decreased by 83% in a resampling project spanning 45 years, apparently as a function of warmer temperatures and reduced snowpack. In a subarctic forest in Finland, negative associations with a warming climate were detected for subsets of the moth fauna to name a few. Climate change is itself not one phenomenon but includes a shift in limits (both maxima and minima), average condition, and variance. Hence, multidisciplinary actions are required to be taken for solving the menace of climate change that has a direct or indirect effect on insect diversity.KeywordsClimate varianceExtinctGlobal warmingInsect dynamicsMetabolism
Temporal stability of primary productivity is the key to stable provisioning of ecosystem services to human beings. Yet, the effects of various global changes on grassland stability remain ambiguous.
Here, we conducted a comprehensive meta‐analysis based on 1070 multi‐year paired observations from 173 studies, to examine the impacts of various global changes on productivity, community stability and plant diversity of grasslands on a global scale. The global change drivers include nitrogen (N) addition, phosphorus (P) addition, N and P addition, precipitation increase, precipitation decrease, elevated CO2 and warming.
Global change drivers generally had stronger impacts on grassland productivity than on temporal stability, except for precipitation changes. Community temporal stability was reduced by N addition, N and P addition and precipitation decrease, but was increased by precipitation increase and remained unchanged under P addition, elevated CO2 and warming. In addition, species richness decreased under N addition, N and P addition and precipitation decrease. At the plant functional group level, N and P addition reduced grasses' stability and precipitation increase enhanced forbs' stability.
Nutrient additions decreased community stability via increasing the inter‐annual variation more than the mean of primary productivity, while precipitation changes mainly affected community temporal stability via changing mean productivity. The negative impacts of global change drivers (i.e. N and P addition, warming) on community temporal stability increased with the degree of species loss but decreased with increasing stability of grasses. Moreover, the negative impacts of nutrient addition and precipitation decrease on community stability was lessened while the positive effect of precipitation increase on community stability was enhanced in grasslands with higher historical precipitation variability, greater soil fertility and longer experimental duration.
Synthesis. Our findings demonstrate that N‐based nutrient additions and drought destabilise grassland productivity, while precipitation increase enhances community stability. Impacts of global changes on community productivity and stability are mediated by species richness, plant functional group, site‐specific environmental conditions (i.e. climate, soil) and experimental duration, which deserve more attention in grassland management practices under future global change scenarios.
Anthropogenic global change threatens the Earth’s biodiversity, with the future of plants utilizing carbon-concentrating mechanisms (CCM) being of particular concern. Here, we discuss global change effects on plants utilizing CCMs, relative to plants using the C3 photosynthesis pathway. Terrestrial CCMs include the C4, CAM and C2 photosynthetic pathways, which are collectively utilized by 10% of the world’s plant flora. They are considered at risk because CCMs are adaptations to low CO2 atmospheres which become superfluous at elevated CO2. Rising atmospheric CO2 represents one form of anthropogenic global change, along with climate change, land transformation, over-exploitation of natural species, terrestrial eutrophication, and exotic species invasions. While rising CO2 favors the physiology of C3 over C4 photosynthesis in warmer temperatures, in natural stands where multiple global change drivers are active, outcomes often do not follow what would be predicted from physiological responses. Based on present trends, which already include CO2 enrichment effects, the natural diversity of the C4, CAM and the C2 functional types is declining. A leading cause is aggressive infilling of grassland habitats by woody C3 competitors or invasive species. Woody infilling is the result of a combination of drivers including rising CO2, overgrazing, overhunting of browsers, and land use change.
The lack of forage production during the seedling year is a barrier to wide‐scale adoption of native warm‐season grasses (NWSG). To address this, two NWSG establishment experiments were conducted in Knoxville, TN, 2016–2018, to determine the efficacy of big bluestem (BB; Andropogon gerardii Vitman) and switchgrass (SG; Panicum virgatum L.) establishment with browntop millet [BTM; Urochloa ramosa (L.) Nguyen] as a companion crop. Each experiment was a randomized complete block arranged as a 2 × 3 factorial. Two defoliation strategies [(1) harvests based on BTM maturity (boot to heading stage) for hay (HAY) or (2) clipping to control BTM competition by maintaining >50% sunlight reaching BB and SG seedlings (CLIP)] were coupled with three BTM seeding rates [0 (control), 11.2 (half‐recommended rate), and 22.4 (full‐recommended rate) kg pure live seed (PLS) ha⁻¹]. Only BTM seeding rate affected BB and SG plant density at dormancy. In all cases, the control had greater BB and SG plant density than the full‐recommended rate, indicating that BTM impeded BB and SG establishment. All BTM seeding rates resulted in acceptable stands (≥5.4 plants m⁻²) of BB (both years) and SG (2017 only). Only the control allowed for acceptable stands of SG in 2016 (8.5 plants m⁻²). Managing BTM for HAY produced a mean cumulative dry matter (DM) yield of 3.15 and 2.68 Mg ha⁻¹ in 2016 and 2017, respectively. These findings show that BTM can be a companion crop that helps offset production losses during BB and SG establishment.
Introduction The Northern Great Plains Inventory and Monitoring Network (NGPN) includes thirteen park units located in five northern Great Plains states across six ecoregions. Plant community composition and structure monitoring comprises the core of the vegetation monitoring effort for the NGPN, covering the “Riparian Lowland Plant Communities” and “Upland Plant Communities” vital signs (Gitzen et al. 2010). The narrative portion of the plant community protocol can be found in Symstad et al. 2012. The narrative includes the rationale for vegetation monitoring, an overview of sample design, field methods, data management, and program requirements. This document contains the standard operating procedures needed to implement plant community monitoring.
Peatlands store a significant amount of terrestrial organic carbon in plant biomass and soils. The Spruce and Peatland Responses Under Changing Environments (SPRUCE) project is a warming and elevated carbon dioxide (eCO2) experiment designed to test how the carbon sequestration and storage capacity of peatland ecosystems will respond to climate change. Here, we report changes in the vascular plant community that have occurred during the first five years of SPRUCE. We tracked species composition, diversity, and aboveground net primary production (ANPP) in chambers warmed at a wide range of temperatures (+0, +2.25, +4.5, +6.75, +9 °C), and two CO2 levels (~400 [ambient] and 900 parts per million). We observed an increase in aboveground vascular plant biomass accumulation, due primarily to an increase in shrub abundance. Overall species diversity decreased substantially, likely due in part to shading by increases in shrub density. The main driver of change in the vascular plant community was temperature, with minimal effects of CO2 evident. These results indicate an overall increase in ANPP with warming, but highlight the importance of interactions between direct (warming) and indirect (competition) effects in determining how boreal peatlands will respond to climate change.
Uncontrolled emission of greenhouse gases (GHGs) leads to global warming and climate change. It is progressively changing at an alarming rate in the coming future. Increasing global warming is responsible for the difference in temperature, frequency of precipitation, drought events, and heat waves. By the end of the twenty-first century, the CO2 crosses the concentration more than 600–1000 ppm, and it increases the temperature by 1–2 °C in tropical and subtropical countries. It is anticipated that food grain production would decline up to 30% depending on the plant group (C3 and C4 plant). This chapter deals with how C3 and C4 crop plant responds to elevated CO2 and higher temperature. Increasing concentration of atmospheric CO2 and higher temperature will promote or decrease crop growth period, development, quality, and yield. The various physiological processes like photosynthesis, respiration, and stomatal conductance are the sole mechanisms for endorsing crop growth. C3 crops grown from ambient (360 ppm) to high (720 ppm) CO2 concentrations initially enhances the net CO2 fixation and growth by nearly 30% but later on it reduced in photorespiration processes. Hence, CO2 acclimation lowers down the overall shoot nitrogen concentrations. Later on, this led to a reduction in protein content and ultimately affected the plant growth rate and biomass, whereas even under the ambient CO2, the C4 plant assimilation capability becomes saturated. The higher temperature will be responsible for heat shock injury as well as biochemical and physiological changes. Subsequently, it reduced grain production and yield depending on the geographical place. The higher temperature influences and maintains the equilibrium between C3 photosynthetic carbon assimilation and photorespiration process. It is predicted that after the interaction of atmospheric CO2 and temperature under experimental conditions, C3 plants more favored under elevated CO2 whereas, C4 plant more favored under higher temperature. There is a need for mitigation and adaptation strategies to improve agricultural crop production and minimizes the production risk for sustainable development.
Random species loss has been shown experimentally to reduce ecosystem function, sometimes more than other anthropogenic environmental changes. Yet, controversy surrounds the importance of this finding for natural systems where species loss is non‐random.
We compiled data from 16 multi‐year experiments located at a single native tallgrass prairie site. These experiments included responses to 11 anthropogenic environmental changes, as well as non‐random biodiversity loss either the removal of uncommon/rare plant species or the most common (dominant) species.
As predicted by the mass ratio hypothesis, loss of a dominant species had large impacts on productivity that were comparable to other anthropogenic drivers. In contrast, the loss of uncommon/rare species had small effects on productivity despite having the largest effects on species richness.
The anthropogenic drivers that had the largest effects on productivity nitrogen, irrigation, and fire experienced not only loss of species but also significant changes in the abundance and identity of dominant species.
Synthesis. These results suggest that mass ratio effects, rather than species loss per se, are an important determinant of ecosystem function with environmental change.
Reduction of surface temperatures of the planet by injecting sulfate aerosols in the stratosphere has been suggested as an option to reduce the amount of human-induced climate warming. Several previous studies have shown that for a specified amount of injection, aerosols injected at a higher altitude in the stratosphere would produce more cooling because aerosol sedimentation would take longer time. In this study, we isolate and assess the sensitivity to the altitude of the aerosol layer of stratospheric aerosol radiative forcing and the resulting climate change. We study this by prescribing a specified amount of sulfate aerosols, of a size typical of what is produced by volcanoes, distributed uniformly at different levels in the stratosphere. We find that stratospheric sulfate aerosols are more effective in cooling climate when they reside higher in the stratosphere. We explain this sensitivity in terms of effective radiative forcing: volcanic aerosols heat the stratospheric layers where they reside, altering stratospheric water vapor content, tropospheric stability and clouds, and consequently the effective radiative forcing. We show that the magnitude of the effective radiative forcing is larger when aerosols are prescribed at higher altitudes and the differences in radiative forcing due to fast adjustment processes can account for a substantial part of the dependence of amount of cooling on aerosol altitude. These altitude effects would be additional to dependences on aerosol microphysics, transport, and sedimentation, which are outside the scope of this study. The cooling effectiveness of stratospheric sulfate aerosols likely increases with altitude of the aerosol layer both because aerosols higher in the stratosphere have larger effective radiative forcing and because they have a longer stratospheric residence time; these two effects are likely to be of comparable importance.
The appearance of the C⁴photosynthetic pathway in the Earth’s flora represents one of the most impressive and curious examples of evolutionary diversification and biogeographic expansion in the history of life (Ehleringer and Monson, 1983). This complex pathway, involving novel patterns of biochemical compartmentation and anatomical design, has evolved with independent but convergent patterns approximately fifty times during the relatively short geological span of 12–15 million years (Kellogg, 1999; Monson, 1999; Sage, 2004; Christin et al., 2007). The appearance of C4photosynthesis has changed the nature of photosynthetic productivity and ecosystem structure on Earth, both regionally and globally. Grassland ecosystems emerged in southwestern Asia, Africa and North America during the mid- to late-Miocene (5–10 Ma) and continued through the Pliocene, (~3Ma), with many of these systems dominated by C4species (Cerling, 1999; Beerling and Osborne, 2006). During the appearance of C⁴ grasslands, the trophic structures of grazed ecosystems were completely revised, resulting in the emergence of novel mammalian lineages (Cerling et al., 1993; Wang et al., 1994; MacFadden and Cerling, 1996; Ehleringer et al., 1997). Arguably, there is not a better example in the history of life to illustrate the tightly integrated nature of evolutionary novelty and ecological impact, as that shown in C⁴ photosynthesis. Clearly, C⁴ photosynthesis, though present in only 8,000 of the estimated 250,000 higher plant species, deserves a significant role in the discussion of plant biology.
Various modeling studies (e.g., Hunt et al., 1991; Cole et al., 1993; Ojima et al., 1990) indicate that grasslands could function aseither sinks or sources of C, depending on landmanagement regimes. Two major rangeland management practices are fire and grazing. This chapter assesses their impacts on soil C.
Solar geoengineering has been proposed as a potential mechanism to counteract global warming. Here we use the University of Victoria Earth System Model (UVic) to simulate the effect of idealized sunshade geoengineering on the global carbon cycle. We conduct two simulations. The first is the A2 simulation, where the model is driven by prescribed emission scenario based on the SRES A2 CO2 emission pathway. The second is the solar geoengineering simulation in which the model is driven by the A2 CO2 emission scenario combined with sunshade solar geoengineering. In the model, solar geoengineering is represented by a spatially uniform reduction in solar insolation that is implemented at year 2020 to offset CO2-induced global mean surface temperature change. Our results show that solar geoengineering increases global carbon uptake relative to A2, in particular CO2 uptake by the terrestrial biosphere. The increase in land carbon uptake is mainly associated with increased net primary production (NPP) in the tropics in the geoengineering simulation, which prevents excess warming in tropics. By year 2100, solar geoengineering decreases A2-simulated atmospheric CO2 by 110 ppm (12%) and causes a 60% (251 Pg C) increase in land carbon accumulation compared to A2. Solar geoengineering also prevents the reduction in ocean oxygen concentration caused by increased ocean temperatures and decreased ocean ventilation, but reduces global ocean NPP. Our results suggest that to fully access the climate effect of solar geoengineering, the response of the global carbon cycle should be taken into account.
Prédire la réponse des prairies pâturées à une élévation de la concentration en CO2 revêt une importance majeure dans la mesure où cet écosystème représente environ 20% de la surface terrestre non immergée mais aussi, parce que les sols prairiaux représentent un puit majeur de carbone (C). La réponse des prairies à un enrichissement en CO2 est fortement contrôlée par la disponibilité des autres nutriments et en particulier l'azote (N). De nombreuses expériences ont par le passé étudié le cycle de l'azote en prairie sous CO2 enrichi mais aucunes de ces études n'a inclus le pâturage. Dans le cadre de cette thèse, je présente des données concernant les effets du CO2 sur le cycle de l'N provenant d'un système expérimental (FACE: enrichissement en dioxyde de carbone à l'air libre) permettant d'inclure des ruminants. Cette thèse est dédiée à l'étude des effets de l'élévation en CO2 sur les différents processus impliqués dans les retours de matière organique (MO) de la plante vers le sol et leurs conséquences pour la disponibilité en N. Dans le Chapitre 1, il a été montré que le CO2 pouvait modifier les retours d'N par les ruminants en affectant la partition d'N entre l'urine et les faeces, ce qui induisait des pertes d'N potentiellement accrues. La décomposition de la litière végétale, considérée à l'échelle de l'écosystème, n'a pas été affectée par le CO2 (Chapitre 3) mais une forte augmentation du volume de MO retournant au sol depuis les racines a induit une accumulation de MO grossière dans le sol (Chapitre 4). Au cours du Chapitre 5, à l'aide d'un double marquage isotopique 14C et 15N, nous avons comparé les effets court terme (transmis par la plante) et long terme (transmis par le sol) du CO2 sur la dynamique de la MO du sol et il a été conclu que l'accumulation de MO n'était pas causée par une limitation en C ou en N mais probablement par la disponibilité en autres nutriments. Cette thèse démontre que l'inclusion des ruminants peut fortement modifier la réponse des prairies au CO2. Dans la mesure où ce mode d'utilisation des pâtures est largement majoritaire, prédire les réponses des pâtures à un enrichissement en CO2 doit provenir de systèmes où les ruminants sont partie intégrante.
The net primary production (NPP) of a maize (Zea mays L.) field in Poland was estimated, in weather conditions close to those predicted for the middle of the century, given the ongoing changes in the global climate. The average temperature during the maize cropping period (May-September) was 16.9 degrees C and the total rainfall was 392.5 mm. In such conditions maize NPP reached exceptionally high levels - 3.29 kgm(-2), on average. Such an unprecedented level of NPP was achieved as a result of climatic conditions favourable to C4 photosynthesis. The above-ground biomass of maize made up 78% of the total NPP, while the below-ground production was only 7.7% of NPP; weed production was very low, only slightly exceeding 8 gm(-2) 14.5% of the total NPP consisted of dying and decomposing biomass. Conducted under conditions close to those foreseen for the mid-21st century, this field study enabled NPP levels as well as future relations between plants in different photosynthetic pathways to be predicted. The expected changes in climatic conditions offer good prospects for maize cropping. The beneficial relationship between the above-and below-ground parts of maize and the low percentage of dying and decomposing biomass mean that this plant can be used for silage or biofuel production.
Compared to tree responses to elevated (e) CO 2 , little attention has been paid to understorey plant community responses in forest ecosystem studies, despite their critical role in nutrient cycling and the regeneration of overstorey species. Here, we present data on understorey responses from a 3‐year Free‐Air CO 2 Enrichment experiment in a native, phosphorus‐limited Eucalyptus woodland in Australia (Euc FACE ).
We conducted repeat surveys of the understorey plant community from 2012 to 2016, recording cover at the species level.
Three years of eCO 2 significantly decreased the diversity (Shannon‐Weaver; −30%) and species richness (−15%; c . −1 species per 4 m ² plot) of graminoid species, and the cover of C 4 graminoids in both dominant (−38%) and subordinate (−48%) groups, relative to ambient conditions, leading to a significantly lower graminoid C 4 :C 3 ratio (−59%) in the understorey plant community. The ratio of C 4 :C 3 graminoids was negatively associated with soil nitrogen (N) availability suggesting that previously reported eCO 2 ‐associated increases in N availability may contribute to (or be a consequence of) shifts in the composition of the graminoid community at the study site. There was, however, no effect of eCO 2 on the diversity of forb species, which represented the most species‐rich functional group but only c . 1% of the understorey biomass.
Synthesis . Our results suggest that eCO 2 influences competition between C 4 and C 3 graminoid species both directly and indirectly via increasing N availability. The shift towards lower C 4 :C 3 ratios and enhanced dominance by C 3 species with their generally higher tissue N concentrations could further change soil nutrient availability and potentially accelerate community succession. Thus, eCO 2 has altered the diversity and composition of the understorey plant community in this woodland, with the potential for cascading consequences for trophic interactions and ecosystem function.
Climate-ecosystem interactions and the inherent uncertainty associated with a variable and changing climate pose a formidable threat to the region’s biological diversity and the function of aquatic and terrestrial ecosystems. Recent alterations of seasonal trends and extreme events (i.e., droughts, heat waves, floods, etc.) have affected ecosystem functions and triggered thresholds of physiological and life-cycle patterns of various species. These changes have led to changes in habitat conditions and species composition shifts. These threshold changes also have impacts on species mortality and the persistence of plant and animal populations (Allen 2010). The invasion of exotic species into terrestrial systems is likely to accelerate in response to longer growing seasons, because they will have more time to establish themselves.
Climate–vegetation feedback has the potential to significantly contribute to climate change, but little is known about its range of uncertainties. Here, using an Earth system model of intermediate complexity we address possible uncertainties in the strength of the biogeophysical climate–vegetation feedback using a single-model multi-physics ensemble. Equilibrium experiments with halving (140 ppm) and doubling (560 ppm) of CO2 give a contribution of the vegetation–climate feedback to global temperature change in the range −0.4 to −0.1 °C and −0.1–0.2 °C, respectively. There is an asymmetry between warming and cooling, with a larger, positive vegetation–climate feedback in the lower CO2 climate. Hotspots of climate–vegetation feedback are the boreal zone, the Amazon rainforest and the Sahara. Albedo parameterisation is the dominant source of uncertainty in the subtropics and at high northern latitudes, while uncertainties in evapotranspiration are more relevant in the tropics. Additionally we find that, even considering the upper range of uncertainties, globally the climate–vegetation feedback is rather small compared to the sum of the fast Charney feedbacks. However, it is comparable to the amplitude of the fast feedbacks at high northern latitudes where it can contribute considerably to polar amplification. Furthermore we analyse the separate impact of changes in stomatal conductance, leaf area index and vegetation dynamics on climate and we find that different processes are dominant in lower and higher CO2 worlds. The reduction in stomatal conductance gives the main contribution to temperature increase for a doubling of CO2, while dynamic vegetation is the dominant process in the CO2 halving experiments.
The effect of time of spring burning on herbage yields in pastures grazed throughout the growing season was investigated. Early and mid-spring burning reduced forage yields but late-spring burning caused no reduction. Weed yield was significantly reduced by late-spring burning. Differences in grazing distribution apparently affected treatment responses in ordinary upland and limestone breaks range sites.
The effect of time of burning on weight gains of steers, botanical composition, herbage yield, and soil moisture relations were investigated over seventeen years. Time of burning in relation to period of growth was important in the reaction of individual species. Cool-season species were reduced by spring burning and the desirable warm-season species were favored. Fire also favored some weedy species which had phenology similar to the desirable warm-season grasses. Herbage yields were reduced by early and mid spring burning but remained the same as unburned when late spring burning was applied. Gains on steers were greatest under mid and late spring burning and least under no burning and early spring burning. Higher gains on steers mid and late spring burned pastures came early in the growing season.
Responses to elevated CO2 have not been measured for natural grassland ecosystems. Global carbon budgets will likely be affected by changes in biomass production and allocation in the major terrestrial ecosystems. Whether ecosystems sequester or release excess carbon to the atmosphere will partly determine the extent and rate that atmospheric CO, concentration rises. Elevated CO, also may change plant community species com-position and water status. We determined above-and belowground biomass production, plant community species composition. and measured and modeled water status ofa tallgrass prairie ecosystem in Kansas exposed to ambient and twice-ambient CO2 concentrations in open-top chambers during the entire growing season from 1989 through 199 1. Dominant species were Andropogon gerardii, .4. scoparius, and Sorghastrurn ntltans (C, metabolism) and Pou pratensis (C,). Aboveground biomass and leaf area were estimated by periodic sampling throughout the growing season in 1989 and 1990. In 199 I, peak biomass and leaf area were estimated by an early August harvest. Relative root production among treatments was estimated using root ingrowth bags which remained in place throughout the growing season. Latent heat tlux was simulated with and without water stress. Botanical composition was estimated annually. Compared to ambient COY levels, elevated CO, increased production ofC, grass species. but not of C, grass species. Species composition of C, grasses did not change. but Poa pratrnsis (C,) declined. and C, forbs increased in the stand with elevated CO, compared to ambient. Open-top chambers appeared to reduce latent heat flux and increase water-use efficiency similar to the elevated CO, treatment when water stress was not severe, but under severe water stress. the chamber effect on water-use efficiency was limited. In natural ecosystems with periodic moisture stress. increased water-use efficiency under elevated CO, apparently would have a greater impact on productivity irrespective of photosynthetic pathway.
Undisturbed tallgrass prairie, dominated by the C{sub 4} grass Andropogon gerardii, was exposed to ambient and elevated (double ambient) levels of atmospheric CO{sub 2} in large open-top chambers throughout the 1991 and 1992 growing seasons. Responses in leaf xylem pressure potential ({psi}), net photosynthesis (A), and stomatal conductance (g) were measured for A. gerardii grown within chambers and from adjacent field plots. In 1992, maximum photosynthetic capacity (A{sub max}), apparent quantum requirement (Q{sub r}), the photosynthetic light compensation point (LCP), and dark respiration (R{sub d}) were also measured. Midday {psi} was significantly higher in plants grown at elevated CO{sub 2} in both years; seasonally averaged {psi} was 0.48-0.70 MPa lower in 1991 (a dry year) than 1992 (a wet year). In 1991, A and g were significantly higher in plants grown at elevated vs. ambient CO{sub 2}. Increased A at elevated CO{sub 2} occurred (as much as 7.1 {mu}mol m{sup {minus}2} s{sup {minus}1}) over a broad range of temperatures (17-35 C), but the temperature optimum for A was similar at both 350 and 700 {mu}L L{sup {minus}1} CO{sub 2}. In 1992, no differences in A, A{sub max}, Q{sub r}, LCP, or R{sub d} were detected when ambient and elevated CO{sub 2} plants were compared. In plants collected from field plots, R{sub d}, LCP, and leaf N were significantly higher than in plants within the chambers indicating that a chamber effect exists for these parameters. In both years, g was significantly reduced (21%-51%) when measured at 700 vs. 350 {mu}L L{sup {minus}1} CO{sub 2}. Peak aboveground biomass was increased at elevated CO{sub 2} in 1991 but not in 1992. These data indicate that for C{sub 4} grasses, effects of elevated CO{sub 2} may only be detectable in years with significant water stress, a common occurrence in the central North American tallgrass prairies. 27 refs., 5 figs., 1 tab.
Increasing concentrations of atmospheric carbon dioxide (COâ) may influence plant-water relations in natural and agricultural ecosystems. A tallgrass prairie near Manhattan, KS, was exposed to elevated atmospheric COâ using open-top chambers (OTCs). Heat balance sap flow gauges were used to measure transpiration in ironweed [Vernonia baldwini var. interior (Small) Schub.], aCâforb, and on individual grass culms of big bluestem (Andropogan geradii Vitman) and indiangrass [Sorghastrum nutans (L>) Nash], both Câ grasses, in each of three treatments: (1) CE (chamber enriched, 2x ambient COâ); (2) CA (chamber ambient, no COâ enrichment); and (3) NC (no chamber, no COâ enrichment). Sap flow data were coupled with measurements of stomatal conductance, plant/canopy resistance, and whole-chamber evapotranspiration (ET) to determine the effect of elevated COâ on water use at different scales. Because of frequent rainfall during the study, all data were collected under well-watered conditions. Comparisons of CE and CA showed that sap flow was reduced by 33% in ironweed, 18% in big bluestem, and 22% in indiangrass under COâ enrichment. Whole-chamber ET was reduced by 23 to 27% under COâ enrichment. Comparisons of CA and NC showed that the environmental effect of the OTCs caused a 21 to 24% reduction in transpiration. Stomatal conductance decreased from 7.9 to 3.6 mm sâ»Â¹ in big bluestem and from 5.3 to 3.2 mm sâ»Â¹ in indiangrass under COâ enrichment. Soil water was consistently highest under elevated COâ, reflecting the large reductions in transpiration. During sap flow measurements, whole-plant stomatal resistance to water vapor flux in big bluestem increased from 103 to 194 s mâ»Â¹ under elevated COâ. 23 refs., 7 figs., 4 tabs.
Undisturbed tallgrass prairie was exposed to ambient and elevated (twice-ambient) levels of atmospheric CO, and experimental dry periods. Seasonal and diurnal midday leaf water potential (Psi(leaf)), net photosynthesis (A(net)), and stomatal conductance (g(s)) responses of three tallgrass prairie growth forms-a C-4 grass, Andropogon gerardii; a broad-leaved woody C, shrub, Symphiocarpos orbiculatus; and a C-3 perennial forb, Salvia pitcheri-were assessed. Psi(leaf) in A. gerardii and S, orbiculatus was higher under elevated CO2, regardless of soil moisture, while Psi(leaf) in S. pitcheri responded only to drought. Elevated CO2 always stimulated A(net) in the C-3 species, while A. gerardii A(net) increased only under dry conditions. However, A(net) under elevated CO2 in the C-3 species declined with drought but not in the C,grass, Under wet conditions, g(s) reduced in elevated CO2 for all species. During dry periods, g, at elevated CO, was sometimes higher than in ambient CO2. Our results support claims that elevated CO2 will stimulate tallgrass prairie productivity during dry periods and possibly reduce temporal and spatial variability in productivity in these grasslands.
The objectives of this study were (i) to test the hypothesis that changes in phenology with CO2 are a function of the effect of CO2 upon growth and (ii) to determine if CO2-induced changes in phenology can influence competitive outcome. We examined the effect of 350, 525, and 700 μL∙L−1 CO2 on Guara brachycarpa, Gailardia pulchella, Oenothera laciniata, and Lupinus texensis. Plants were grown as individuals in 150-, 500-, or 1000-mL pots and in competition in 1000-mL pots. Growth and development were monitored at twice-weekly intervals by recording the number of leaves and noting the presence or absence of stem elongation, branching, flower buds, and open flowers. Elevated CO2 affected both growth and phenology, but the direction and magnitude of effects varied with species and soil volume. Elevated CO2 did not appear to affect development through its effect on growth. Those treatments in which there were significant effects of CO2 on growth were generally different from those treatments in which CO2 affected phenology. Rather than affecting phenology by changing plant size, CO2 appeared to affect phenology by modifying the size at which plants switched from one stage to the next. The level of CO2 changed competitive outcome; the importance of Lupinus increased whereas that of Oenothera decreased with increased CO2. These changes were more closely related to the effect of CO2 on growth than its effect on phenology. Key words: time of flowering, size at flowering, competition, photoperiod, rate of development.
At the plant level, physiological responses to CO<sub>2</sub> include enhanced net photosynthesis and reduced stomatal conductance; morphological changes include greater leaf areas, shoot production, and root:shoot ratios. Little is known about community responses or about plant-herbivore dynamics at elevated CO<sub>2</sub>. Changes in herbage quality, tissue turnover, and botanical composition may be expected but confirmation of these responses will only be possible when data are available from long-term studies of grazed pasture at elevated CO<sub>2</sub>. -from Author
Increased biomass production in terrestrial ecosystems with elevated atmospheric CO2 may be constrained by nutrient limitations as a result of increased requirement or reduced availability caused by reduced
turnover rates of nutrients. To determine the short-term impact of nitrogen (N) fertilization on plant biomass production
under elevated CO2, we compared the response of N-fertilized tallgrass prairie at ambient and twice-ambient CO2 levels over a 2-year period. Native tallgrass prairie plots (4.5 m diameter) were exposed continuously (24 h) to ambient
and twice-ambient CO2 from 1 April to 26 October. We compared our results to an unfertilized companion experiment on the same research site. Above-
and belowground biomass production and leaf area of fertilized plots were greater with elevated than ambient CO2 in both years. The increase in biomass at high CO2 occurred mainly aboveground in 1991, a dry year, and belowground in 1990, a wet year. Nitrogen concentration was lower in
plants exposed to elevated CO2, but total standing crop N was greater at high CO2. Increased root biomass under elevated CO2 apparently increased N uptake. The biomass production response to elevated CO2 was much greater on N-fertilized than unfertilized prairie, particularly in the dry year. We conclude that biomass production
response to elevated CO2 was suppressed by N limitation in years with below-normal precipitation. Reduced N concentration in above- and belowground
biomass could slow microbial degradation of soil organic matter and surface litter, thereby exacerbating N limitation in the
long term.
Responses in stomatal conductance (g
st
) and leaf xylem pressure potential (
leaf
) to elevated CO2 (2x ambient) were compared among 12 tallgrass prairie species that differed in growth form and growth rate. Open-top chambers (OTCs, 4.5 m diameter, 4.0 m in height) were used to expose plants to ambient and elevated CO2 concentrations from April through November in undisturbed tallgrass prairie in NE Kansas (USA). In June and August,
leaf
was usually higher in all species at elevated CO2 and was lowest in adjacent field plots (without OTCs). During June, when water availability was high, elevated CO2 resulted in decreased g
st
in 10 of the 12 species measured. Greatest decreases in g
st
(ca. 50%) occurred in growth forms with the highest potential growth rates (C3 and C4 grasses, and C3 ruderals). In contrast, no significant decrease in g
st
was measured in the two C3 shrubs. During a dry period in September, reductions in g
st
at elevated CO2 were measured in only two species (a C3 ruderal and a C4 grass) whereas increased g
st
at elevated CO2 was measured in the shrubs and a C3 forb. These increases in g
st
were attributed to enhanced
leaf
in the elevated CO2 plants resulting from increased soil water availability and/or greater root biomass. During a wet period in September, only reductions in g
st
were measured in response to elevated CO2. Thus, there was significant interspecific variability in stomatal responses to CO2 that may be related to growth form or growth rate and plant water relations. The effect of growth in the OTCs, relative to field plants, was usually positive for g
st
and was greatest (>30%) when water availability was low, but only 6–12% when
leaf
was high.The results of this study confirm the importance of considering interactions between indirect effects of high CO2 of plant water relations and direct effects of elevated CO2 on g
st
, particularly in ecosystems such as grasslands where water availability often limits productivity. A product of this interaction is that the potential exists for either positive or negative responses in g
st
to be measured at elevated levels of CO2.
Though field data for naturally senesced leaf litter are rare, it is commonly assumed that rising atmospheric CO2 concentrations will reduce leaf litter quality and decomposition rates in terrestrial ecosystems and that this will lead
to decreased rates of nutrient cycling and increased carbon sequestration in native ecosystems. We generally found that the
quality of␣naturally senesced leaf litter (i.e. concentrations of C, N and lignin; C:N, lignin:N) of a variety of native plant
species produced in alpine, temperate and tropical communities maintained at elevated CO2 (600–680 μl l−1) was not significantly different from that produced in similar communities maintained at current ambient CO2 concentrations (340–355 μl l−1). When this litter was allowed to decompose in situ in a humid tropical forest in Panama (Cecropia peltata, Elettaria cardamomum, and Ficus benjamina, 130 days exposure) and in a lowland temperate calcareous grassland in Switzerland (Carex flacca and a graminoid species mixture; 261 days exposure), decomposition rates of litter produced under ambient and elevated CO2 did not differ significantly. The one exception to this pattern occurred in the high alpine sedge, Carex curvula, growing in the Swiss Alps. Decomposition of litter produced in situ under elevated CO2 was significantly slower than that of litter produced under ambient CO2 (14% vs. 21% of the initial litter mass had decomposed over a 61-day exposure period, respectively). Overall, our results
indicate that relatively little or no change in leaf litter quality can be expected in plant communities growing under soil
fertilities common in many native ecosystems as atmospheric CO2 concentrations continue to rise. Even in situations where small reductions in litter quality do occur, these may not necessarily
lead to significantly slower rates of decomposition. Hence in many native species in situ litter decomposition rates, and the time course of decomposition, may remain relatively unaffected by rising CO2.
Wheat (C3) and Japanese millet (C4) were grown in pots in monoculture and mixed culture (2 C3:1 C4 and 1 C3:2 C4) at two ambient partial pressures of CO2(320 and 640 μbar), two photosynthetic photon flux densities (PPFDs) (daily maximum 2000 and 500 μmol m-2s-1) and two levels of N nutrition (12 mM and 2 mM NO-3). Elevated atmospheric CO2 stimulated wheat shoot growth in 15 of 16 treatment combinations; stimulation was greatest in plants provided with low NO-3. Root growth of the C3 plants was generally stimulated by elevated CO2, but was only occasionally sensitive to the presence of C4 plants in mixed culture. Growth of the C4 plants was often sensitive to the presence of C3 plants in mixed culture. In mixed cultures, elevated CO2 plants stimulated growth of C4 plants at high PPFD, high-N and in all low-N treatments but this was insufficient to offset a marked decline in shoot growth with increasing proportion of C3 plants in mixed cultures. -from Authors
Burning bluestem range reduces soil moisture. Study of long-continued annual burning in the winter and at various spring dates shows that earliest burnings cause greatest reductions. Foot-by-foot moisture levels in the upper 5 feet of soil during a 4-year period are considered.
Four members of an annual community were used to investigate the effects of changing neighborhood complexity and increased CO"2 concentration on competitive outcome. Plants were grown in monoculture and in all possible combinations of two, three, and four species in CO"2-controlled growth chambers at CO"2 concentrations of 350, 500, and 700 @mL/L with ample moisture and high light. Species responded differently to enhanced CO"2 level. Some species (e.g., Abutilon theophrasti) had increased biomass with increasing CO"2, while others (e.g., Amaranthus retroflexus) had decreased biomass with increasing CO"2 concentration. In mixtures, species tended to interact strongly, and, in some cases, the interaction canceled out the effects of CO"2. Furthermore, there were cleared differences in species behavior in different competitive mixtures as assessed by total biomass and seed biomass, and by an index of response to neighbors. In general, competitive arrays that had C"3 species depressed the response of C"4 species, especially Amaranthus. Ambrosia artemisiifolia was the strongest competitor in this assemblage. Strong statistical interactions between CO"2 and the identity of the competing species in mixtures were found to be primarily due to the as yet unexplained response of plants with CO"2 at 500 @mL/L. The potential effects of CO"2 on community structure could be profound, particularly at the intermediate levels of CO"2 that are predicted to be reached during the first half of the next century.
Two common tallgrass prairie species, Andropogon gerardii, the dominant C4 grass in this North American grassland, and Salvia pitcheri, a C3 forb, were exposed to ambient and elevated (twice ambient) CO2 within open-top chambers throughout the 1993 growing season. After full canopy development, stomatal density on abaxial and adaxial surfaces, guard cell length and specific leaf mass (SLM; mg cm-2) were determined for plants in the chambers as well as in adjacent unchambered plots. Record high rainfall amounts during the 1993 growing season minimized water stress in these plants (leaf xylem pressure potential was usually > -1·5 MPa in A. gerardii) and also minimized differences in water status among treatments. In A. gerardii, stomatal density was significantly higher (190 ± 7 mm-2; mean ± s.e.) in plants grown outside of the chambers compared to plants that developed inside the ambient CO2 chambers (161 ± 5 mm-2). Thus, there was a significant 'chamber effect' on stomatal density. At elevated levels of CO2, stomatal density was even lower (P < 0·05; 121 ± 5 mm-2). Most stomata were on abaxial leaf surfaces in this grass, but the ratio of adaxial to abaxial stomatal density was greater at elevated levels of CO2. In S. pitcheri, stomatal density was also significantly lower when plants were grown in the open-top chambers (235 ± 10 mm-2 outside vs. 140 ± 6 mm-2 in the ambient CO2 chamber). However, stomatal density was greater at elevated CO2 (218 ± 12 mm-2) compared to plants from the ambient CO2 chamber. The ratio of stomata on adaxial vs. abaxial surfaces did not vary significantly in this herb. Guard cell lengths were not significantly affected by growth in the chambers or by elevated CO2 for either species. Growth within the chambers resulted in lower SLM in S. pitcheri, but CO2 concentration had no effect. In A. gerardii, SLM was lower at elevated CO2. These results indicate that stomatal and leaf responses to elevated CO2 are species specific, and reinforce the need to assess chamber effects along with treatment effects (CO2) when using open-top chambers.
Increasing concentrations of atmospheric CO2 may alter the carbon and water relations of prairie ecosystems. A C4-dominated tallgrass prairie near Manhattan, KS, was exposed to 2 × ambient CO2 concentrations using 4.5 m-diameter open-top chambers. Whole-chamber net CO2 exchange (NCE) and evapotranspiration (ET) were continuously monitored in CO2-enriched and ambient (no enrichment) plots over a 34-d period encompassing the time of peak biomass in July and August, 1993. Soil-surface CO2 fluxes were measured with a portable surface chamber, and sap flow (water transport in xylem) in individual grass culms was monitored with heat balance techniques. Environmental measurements were used to determine the effect of CO2 on the surface energy balance and canopy resistances to vapor flux. In 1993, frequent rainfall kept soil water near field capacity and minimized plant water stress. Over the 34-d measurement period, average daily NCE (canopy photosynthesis — soil and canopy respiration) was 9.3 g CO2 m−2 in the ambient treatment adn 11.4 g CO2 m−2 under CO2 enrichment. However, differences in NCE were caused mainly by delayed senescence in the CO2-enriched plots at the end of the growing season. At earlier stages of growth, elevated CO2 had no effect on NCE. Soil-surface CO2 fluxes typically ranged from 0.4 to 0.66 mg CO2 m−2 s−1, but were slightly greater in the CO2_enriched chambers. CO2 enrichment reduced daily ET by 22%, reduced sap flow by 18%, and increased canopy resistance to vapor flux by 24 s m−1. Greater NCE and lower ET resulted in higher daytime water use efficiency (WUE) under CO2 enrichment vs. ambient (9.84 vs. 7.26 g CO2 kg−1 H2O). However, record high precipitation during the 1993 season moderated the effect of WUE on plant growth, and elevated CO2 had no effect on peak aboveground biomass. CO2-induced stomatal closure also affected the energy balance of the surface by reducing latent heat flux (LE), thereby causing a consequent change in sensible heat flux (H). The daytime Bowen ratio (H/LE) for the study period was near zero for the ambient treatment and 0.21 under CO2 enrichment.
In order to investigate the effects, without competition, of COâ on germination, growth, physiological response, and reproduction, the authors focussed on co-occurring species that are prominent members of an annual community in Illinois. Five species of old field annual plants - Abutilon theophrasti (Câ), Amaranthus retroflexus (Câ), Ambrosia artemisiifolia (Câ), Chenopodium album (Câ), and Setaria faberii (Câ) - were grown for their entire life cycle as individuals at COâ concentration of 350 μL/O, 500 μL/L, and 700 μL/L. Emergence time, growth rate, shoot water status, photosynthesis, conductance, flowering time, nitrogen content, and biomass and reproductive biomass were measured. There was no detectable effect of enhanced COâ on timing of emergency in any of the species. The three levels of carbon dioxide concentration were shown to produce varying effects on remaining quantities measured in the five different plants. Some of these differences were not statistically significant. The response of most characters had a significant species à COâ interaction. However, this was not simply caused by the Câ/Câ dichotomy. Reproductive biomass (seed, fruits, and flowers) increased with increasing COâ in Amaranthus (Câ) and in Chenopodium and Ambrosia (both Câ), but there was no change in Setaria (Câ), and Abutilon (Câ) showed a peak at 500 μL/L. Species of the same community differed in their response to COâ, and these differences may help explain the outcome of competitive interactions among these species above ambient COâ levels.
One of the many changes occurring in the biosphere due to human activities is the increase in the carbon dioxide concentration in the atmosphere. This change is due both to the burning of fossil fuels and to deforestation. We do not know how these changes are affecting terrestrial ecosystems. This ignorance is partly because we have relatively poor records of the functional and structural response of any ecosystem through time. More studies are required to be able to accurately assess the effects of carbon dioxide.
Festuca elatior L., C3, and Sorghum halepense (L.) Persoon, C4, were grown in mixed and unmixed cultures under 350 and 600 ppm CO2 for 112 days. High CO2 levels stimulated increases of total dry weight and leaf surface area in Festuca despite unfavorably high temperatures. In Sorghum, delay of leaf senescence and of floral initiation was attributed to high CO2 concentrations. Growth of unmixed cultures of Sorghum under 600 ppm CO2 was relatively poor because of an apparent interaction of high CO2 with self-shading. All instances of culturexCO2 interactions are offered in supported of the hypothesis that elevated CO2 levels will effect the competitive interaction of C3 and C4 species. Peak net assimilation rates of C3 and C4 plants were seasonally separated at 350 ppm CO2 but coincided at 600 ppm. Based on our observations of Festuca and Sorghum, we project that global CO2 enrichment may alter competitive balance between C3 and C4 plants and subsequently affect seasonal niche separation, species distribution patterns, and net primary production within mixed communities.
Reviews the state-of-the art of models of forests and grasslands that could be used to predict the impact of a future climate change arising from increased atmospheric CO2 concentration. Four levels of resolution are recognized: physiologically based models, population models, ecosystem models, and regional or global models. At the physiological level a number of important processes can be described in greater detail, but these models often treat inadequately interactions with nutrient cycles, which operate on longer time scales. Population and ecosystem models can, on the other hand, encapsulate relationshipos between the plants and the soil system, but at the expense of requiring more ad hoc formulations of processes. At the regional and global scale we have so far only steady-state models, which cannot be used to predict transients caused by climate change. Despite the gaps in knowledge, there are several models based on dominant processes that are well enough understood for the predictions of those models to be taken seriously. -Authors
Six species of herbs from the serpentine grassland of Jasper Ridge Nature Preserve (Stanford, California)—Microseris sp., Plantago erecta, Micropus Californicus, Agoseris heterophylla, Layia platyglossa and Lasthenia glabrata—were grown individually and in competitive arrays, under three levels of CO2: 350, 500 and 700 μl/l. CO2 affected the biomass of some species in the individually-grown plants but none in the competitive arrays. Here, in contrast to some previous studies, total community biomass was not significantly affected by CO2 in either condition. In every species where CO2 had a statistically significant effect on nitrogen content, higher CO2 resulted in lower nitrogen content. Competition appeared to decrease the effects of CO2. Our results suggest that in this community, competitive networks and adaptations to a low-resource habitat may strongly damp the effects of CO2. These results contrast with our previous work on annuals of a higher stature system and agree with recent results on Arctic tundra species.
The relationships of photosynthetic characteristics to the competitive interactions of a C3 plant, Chenopodium album, and a C4 plant, Amaranthis retroflexus, were investigated in different temperature and water supply regimes. Both species had similar photosynthetic rates at 25°C, but at higher temperatures, Amaranthus had substantially greater rates than Chenopodium. Conversely, at lower temperatures, Chenopodium had an advantage. The competitive abilities in mixtures exhibited a close parallel to the photosynthetic performances with Amaranthus having an advantage at high temperatures and Chenopodium an advantage at low temperatures. These competitive outcomes were determined primarily by differences in relative growth rates prior to canopy closure. In the respective, temperature regimes, the species having the highest photosynthetic rate, which resulted an more rapid growth, overtopped and shaded the other species at the time of canopy closure. These results demonstrate that differences in photosynthetic temperature response between C4 and C3 plants can be an important determinant in competitive interactions, but at least in this case, the influence is primarily through, events prior to the actual initiation of competition.
In contrast to temperature, growth of the plants under limited water supply had no influence on the competitive interactions. Thus, the presence of the C4 pathway alone was not sufficient to yield a competitive advantage over the C3 species under water limited conditions.
We grew a C4 grass from the Serengeti ecosystem under ambient (370 ppm) and elevated (700 ppm) CO2, and under clipped and unclipped conditions to test whether regrowth following grazing would be affected by elevated CO2. Above-ground productivity was slightly decreased under elevated CO2, and was similar between clipped and unclipped plants. Regrowth (clipping offtake) following clipping was similar in the two CO2 treatments, and there was no CO2 by clipping interaction on biomass, productivity, or leaf nutrient concentrations. Based on this evidence, we suggest that C4 grasses from the Serengeti will show little direct response to future increases in atmospheric CO2.
A general model of ecosystem biogeochemistry was used to examine the responses of arctic tundra and temperate hardwood forests to a doubling of CO2 concentration and to a 5C increase in average growing season temperature. The amount of C stored in both ecosystems increased with both increased CO2 and temperature. Under increased CO2, the increase in C storage was due to increases in the CN ratio of both vegetation and soils. Under increased temperature, the increased C storage in the forest was due to a shift in N from soils (with low CN ratios) to vegetation (with high CN ratios). In the tundra, both a shift in N from soils to vegetation and an increase in CN ratios contributed to increased C storage under higher temperatures. Neither ecosystem sequestered N from external sources because the supply rate was low.
The eastern Colorado shortgrass steppe is dominated by the C4 grass, Bouteloua gracilis, but contains a mixture of C3 grasses as well, including Pascopyrum smithii. Although the ecology of this region has been extensively studied, there is little information on how increasing atmospheric CO2 will affect it. This growth chamber study investigated gas exchange, water relations, growth, and biomass and carbohydrate partitioning in B. gracilis and P. smithii grown under present ambient and elevated CO2 concentrations of 350 μl l−1and 700 μl l−1, respectively, and two deficit irrigation regimes. The experiment was conducted in soil-packed columns planted to either species over a 2-month period under summer-like conditions and with no fertilizer additions. Our objective was to better understand how these species and the functional groups they represent will respond in future CO2-enriched environments. Leaf CO2 assimilation (A
n), transpiration use efficiency (TUE, or A
n/transpiration), plant growth, and whole-plant water use efficiency (WUE, or plant biomass production/water evapotranspired) of both species were greater at elevated CO2, although responses were more pronounced for P. smithii. Elevated CO2 enhanced photosynthesis, TUE, and growth in both species through higher soil water content (SWC) and leaf water potentials (Ψ) and stimulation of photosynthesis. Consumptive water use was greater and TUE less for P. smithii than B. gracilis during early growth when soil water was more available. Declining SWC with time was associated with a steadily increased sequestering of total non-structural carbohydrates (TNCs), storage carbohydrates (primarily fructans for P. smithii) and biomass in belowground organs of P. smithii, but not B. gracilis. The root:shoot ratio of P. smithii also increased at elevated CO2, while the root:shoot ratio of B. gracilis was unresponsive to CO2. These partitioning responses may be the consequence of different ontogenetic strategies of a cool-season and warm-season grass entering a warm, dry summer period; the cool-season P. smithii responds by sequestering TNCs belowground in preparation for summer dormancy, while resource partitioning of the warm-season B. gracilis remains unaltered. One consequence of greater partitioning of resources into P. smithii belowground organs in the present study was maintenance of higher Ψ and A
n rates. This, along with differences in photosynthetic pathway, may have accounted for the greater responsiveness of P. smithii to CO2 enrichment compared to B. gracilis.
Standing dead and green foliage litter was collected in early November 1990 from Andropogon gerardii (C4), Sorghastrum nutans (C4), and Poa pratensis (C3) plants that were grown in large open-top chambers under ambient or twice ambient CO2 and with or without nitrogen fertilization (45 kg N ha−1). The litter was placed in mesh bags on the soil surface of pristine prairie adjacent to the growth treatment plots and allowed
to decay under natural conditions. Litter bags were retrieved at fixed intervals and litter was analyzed for mass loss, carbon
chemistry, and total Kjeldahl nitrogen and phosphorus. The results indicate that growth treatments had a relatively minor
effect on the initial chemical composition of the litter and its subsequent rate of decay or chemical composition. This suggests
that a large indirect effect of CO2 on surface litter decomposition in the tallgrass prairie would not occur by way of changes in chemistry of leaf litter. However,
there was a large difference in characteristics of leaf litter decomposition among the species. Poa leaf litter had a different initial chemistry and decayed more rapidly than C4 grasses. We conclude that an indirect effect of CO2 on decomposition and nutrient cycling could occur if CO2 induces changes in the relative aboveground biomass of the prairie species.
Communities, consisting of six co-occurring, disturbed site annuals, were subjected to CO2 unenriched (300 ppm) and to CO2 enriched (450 and 600 ppm) atmospheres at different levels of light and nutrient availability. In general, total community production increased with CO2 enrichment to 450 ppm, but a further increase in CO2 to 600 ppm had little or no effect. The response of community production to CO2 level was not affected by nutrient availability but was affected by light level.
Of the six species, four display C3 metabolism. The proportion of total community production contributed by these species increased as a result of CO2 enrichment, and was dependent upon both light and nutrient availability. The relative success of some species, particularly in terms of reproduction (total seed biomass), was significantly altered by CO2 concentration depending on the level of nutrients. There were not only changes in reproductive success (seed biomass) and shoot biomass but also changes in the proportion of biomass allocated to seed.
These experiments demonstrate that CO2 enrichment does affect annual plant communities both in terms of productivity and species composition and that the affect of CO2 on such system may depend upon other resources such as light and nutrients.
The response of plants to elevated CO 2 II. Competitive interactions among annual plants under varying light and nutrients
- Zangerl Ar
- Bazzaz
- Fa
Zangerl AR, Bazzaz FA (1984) The response of plants to elevated CO 2 II. Competitive interactions among annual plants under varying light and nutrients. Oecologia, 62, 412–417.
Effects of a CO 2 -enriched atmosphere on the growth and competitive interaction of a C 3 and C 4 grass
- Carter Dr Peterson
Carter DR, Peterson KM (1983) Effects of a CO 2 -enriched atmosphere on the growth and competitive interaction of a C 3 and C 4 grass. Oecologia, 58, 188–193.
Transpiration from a tallgrass prairie exposed to ambient and elevated atmospheric CO*
- Dj Bremer
Bremer DJ (1994) Transpiration from a tallgrass prairie exposed to
ambient and elevated atmospheric CO*. MSc thesis, Department
of Agronomy, Kansas State University, Manhattan, KS.