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The magnitude of hydraulic redistribution of soil water by roots and its impact on soil water balance were estimated by monitoring time courses of soil water status at multiple depths and root sap flow under drought conditions in a dry ponderosa pine (Pinus ponderosa Dougl. ex Laws) ecosystem and in a moist Douglas-fir (Pseudotsuga menziesii (Mirb....
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Plant transpiration depends on environmental conditions, and soil water availability is its primary control under water deficit conditions. In this study, we improve a simplified process‐based model proposed by Buckley, Turnbull & Adams (2012) (hereafter "BTA") by including soil water potential (ψsoil) to explicitly represent the dependence of plan...
Summary The magnitude and direction of water transport by the roots of eight dominant Brazilian savanna (Cerrado) woody species were determined with a heat pulse system that allowed bidirectional measurements of sap flow. The patterns of sap flow observed during the dry season in species with dimorphic root systems were consistent with the occurren...
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A dynamic model for simulating water flow in a Scots pine (Pinus sylvestris L.) tree was developed. The model is based on the cohesion theory and the assumption that fluctuating water tension driven by transpiration, together with the elasticity of wood tissue, causes variations in the diameter of a tree stem and branches. The change in xylem diame...
A simple non-invasive field based method for directly parameterizing
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Citations
... The addition of the remaining basal area increased total stand-level transpiration to 581.2 mm and HR to 226.7 mm. Contributions of understory species to stand-level transpiration are often overlooked in ecosystem water budgets (Brooks et al., 2002;Domec et al., 2010;Emerman & Dawson, 1996). The best estimates of groundcover transpiration within the P. palustris ecosystem range from 70-325 mm year À1 (Powell et al., 2005(Powell et al., , 2008. ...
Hydraulic redistribution (HR) is a common phenomenon in water‐limited ecosystems; however, it remains unclear how the volume of water transported via HR compares to other components of the hydrologic budget and how HR influences water availability for understory plant communities. In this study, we investigate the absolute and relative magnitude of HR on a forest water budget and identify potential impacts of this water subsidy to understory plant communities. We scaled tree‐level estimates of transpiration and HR of three common tree species naturally occurring in a longleaf pine woodland with plot‐level measurements of basal area to determine their magnitude at the stand scale. We trenched plots containing understory vegetation but devoid of mature trees and their connected roots to exclude HR subsidies to understory plant species. We analysed soil water isotopes and assessed leaf water potential (Ψ L ) in trenched and control plots to determine if HR results in mixing of water among soil strata and improves understory plant moisture status. Water inputs from HR were equivalent to >30% of total rainfall for the site during the observation period and ~40% of total tree water uptake, depending on species. A stable isotope mixing model confirmed that soil water within HR‐exposed plots was more similar to groundwater, whereas soil water within trenched plots was more similar to precipitation. Exclusion of HR via trenching decreased soil moisture and pre‐dawn Ψ L for all understory species. These three lines of evidence suggest that HR from overstory trees redistributes a sizable portion of water from deeper to shallower soil profiles and that this water subsidy enhances understory plant water status.
... The trees selected for this study were located on steep, north-facing slopes and growing in relatively deep (>2 m) soils (Jarecke et al., 2021). Previous research by Brooks et al. (2002) demonstrated that hydraulic redistribution of water from depths below 60 cm supplied approximately 40 % of the daily transpiration in a Douglas-fir stand during the summer dry season. Consequently, higher amounts of rainfall during the summer would contribute to shallow soil moisture and benefit tree growth. ...
Both elevated temperature and reduced precipitation have been related to growth declines in Douglas-fir (Pseudotsuga menziesii) in the northwest U.S. However, the impact of high vapor pressure deficit (VPD) on Douglas-fir growth and physiological stress is not fully understood. We investigated how inter-and intra-annual rainfall and VPD correlated to the radial growth and carbon isotope signature (δ 13 C) of latewood for ~ 50-year-old Douglas-fir trees in the western Cascade Mountains in Oregon. Latewood δ 13 C reflects variation in stomatal restriction of photosynthetic gas exchange and, therefore, was used as a proxy for the relative degree of physiological water stress. We cored three trees at each of nine sampling sites (n = 27 trees) and used a moving window analysis to test the period of the year in which VPD and rainfall best predicted mean latewood radial growth and δ 13 C. Latewood growth, measured as the basal area increment, was more sensitive to daytime VPD than the timing and amounts of rainfall, especially in early summer. In contrast, δ 13 C was equally sensitive to the average daytime VPD and total rainfall during spring and summer. We used the results of the moving window analysis in a linear mixed effects model to test how the effect of VPD and rainfall on yearly latewood growth and δ 13 C differed among our nine sites. We found no evidence for statistical differences in the effects of VPD and rainfall on growth (p = 0.93 and p = 0.91) or δ 13 C (p = 0.31 and p = 0.81) among our nine sites. However, the marginal effects of VPD on latewood growth at each site were weakly related to soil moisture deficits at 100 cm suggesting that site-to-site differences in soil moisture availability may be important in buffering the negative effects of seasonal aridity on growth. In contrast, there was no evidence that soil moisture differences among sites influenced the marginal effects of VPD on latewood δ 13 C. We conclude that increases in VPD during summer are likely to reduce latewood growth and increase water stress in Douglas-fir in the Pacific Northwest region. However, more research is needed to better understand the magnitude of this effect across sites with variable subsurface water storage and microclimate.
... Ong et al. (1998) showed forGrevillea robusta that deep tap roots sustain most of the stem sapflow when the soil is dry, and that after precipitation events lateral roots increase the sapflow substantially. In a similar experimental setup Brooks et al. (2002) showed how reverse sapflow in roots of ponderosa pine and douglas fir occurred particularly after rewetting of the soil and only on roots close to the irrigation site. ...
The effect of environmental conditions, species-specific plant hydraulic traits and root water uptake dynamics on stomatal conductance are still uncertain. We monitored water potentials and water fluxes in soils, roots, stems, and leaves of beech and spruce to further our understanding of the water status in these segments along the soil-plant hydraulic system. We applied a soil-plant hydraulic model to test our current understanding on the effect of soil-plant hydraulics on stomatal conductance. Our results highlight the different strategies of beech and spruce when regulating stomatal conductance, as spruce typically closed stomata earlier (at less negative water potentials). While root water uptake depths were similar between beech and spruce, spruce showed lower co-variability of water potentials in plant tissues and soil, but higher ability to store water in its tissues. Root water uptake from deep soil layers increased during dry periods, particularly for beech. These observations were reflected in the results from a simple soil-plant hydraulic model relating transpiration to leaf and soil water potentials. Our results confirm that iso- and anisohydric strategies relate to species-specific root hydraulic traits and water uptake dynamics and stress the importance of including such interactions in ecohydrological models.
... The shallow root distribution makes herbaceous plants vulnerable to soil moisture, which has little correlation with SOC but a weak correlation with HWOC. Upward hydraulic redistribution of deep roots of the trees (Brooks et al. 2002) and agricultural irrigation weakens the correlation with water in woodland and arable land, also leading to more accumulation of HWOC in the surface soil ( Figure 2b). This also explains why the depth difference in HWOC in this study was more significant in the natural system. ...
Hot water extractable organic carbon (HWOC), the labile carbon component, is often used to indicate soil organic carbon (SOC) dynamics. Nevertheless, few studies have been carried out in arid climate areas which affects our full understanding of HWOC. Here, we investigated the change in HWOC in the topsoil of different ecosystems in the southern part of the Loess Plateau in the semiarid region of China and compared it with that in other regions. The HWOC concentrations of the study area (0-10 cm) were 0.27 ± 0.12 g C kg⁻¹ and 0.19 ± 0.04 g C kg⁻¹ in the natural and agricultural systems respectively, and the HWOC proportions were 1.38 ± 0.38% and 2.18 ± 0.22%. The HWOC concentration and proportion in the study area were much lower than the reported data in other areas, which may be affected by drought conditions. Irrigation could weaken the difference in HWOC between agricultural systems in different regions. Since HWOC is easily lost due to the impact of the arid climate, the soil carbon balance and carbon sequestration in arid and semiarid areas are relatively unstable, indicating that soil management should be improved in combination with water management.
... These plants can thus share water among their root systems (Caldwell and Richards, 1989) as water hydraulically lifted in roots from deep soil is relayed through mycorrhizal hyphae of the CMN Querejeta et al., 2003;. In the understorey, hydraulic redistribution mediated by CMNs can be crucial for the establishment and recruitment of tree seedlings through connection to potentially allospecific (Richard et al., 2009), similar-aged (Egerton-Warburton et al., 2007 or older individuals (Brooks et al., 2002;Schoonmaker et al., 2007;Warren et al., 2008;Booth and Hoeksema, 2010;Bingham and Simard, 2012). Hydraulic redistribution can also help the survival of herbaceous species under drought stress (Brooks et al., 2002(Brooks et al., , 2006 thanks to AM CMNs, which are even more efficient than EcM CMNs . ...
... In the understorey, hydraulic redistribution mediated by CMNs can be crucial for the establishment and recruitment of tree seedlings through connection to potentially allospecific (Richard et al., 2009), similar-aged (Egerton-Warburton et al., 2007 or older individuals (Brooks et al., 2002;Schoonmaker et al., 2007;Warren et al., 2008;Booth and Hoeksema, 2010;Bingham and Simard, 2012). Hydraulic redistribution can also help the survival of herbaceous species under drought stress (Brooks et al., 2002(Brooks et al., , 2006 thanks to AM CMNs, which are even more efficient than EcM CMNs . ...
Plant interactions play a key role in forest ecosystem dynamics. The tallest plants, namely the overstorey trees, are obvious major drivers, particularly in competition for light. This process has already been amply described. However, the role played by lower strata has often been underestimated. In this review, we first briefly recall the role of over- and understoreys in structuring forest microclimate, mostly through light sharing. We then focus on belowground interactions between over- and understorey, where knowledge is more piecemeal, partly because of measurement difficulties. Even so, some studies show that competition for water and nutrients by the overstorey controls the development of understorey vegetation much more than competition for light. The reverse (overstorey limitation by the understorey) has also been encountered, but has been much less well researched. We also address the involvement of mycorrhizae, specifically their role in alleviating overstorey drought stress and contributing to nutrient cycling. We go on to show how another example of key ecosystem engineers, large mammalian herbivores, shape above- and belowground resources and intervene in over- and understorey interactions. In conclusion, for a better understanding of forest dynamics and adapted management, particularly in the context of global climate change, we advocate taking account not only of trees but of all forest components. Belowground processes need more research. The roles of mycorrhizal networks, root exudates, microbiota, and chemical cues need to be further explored to gain a finer understanding of the interactions between over- and understorey.
... Hydraulic lift by deep-rooted trees may also contribute to the survival of seedlings of surrounding shallow-rooted shrubs, although the influence of facilitation might not offset competition from neighbours and might change during the year (Muler et al., 2018;Prieto et al., 2011). Previous findings suggest that nocturnal hydraulic lift can recharge up to 35%-80% of the water taken up from shallow layers during the dry season (Brooks et al., 2002;Meinzer et al., 2004). The substantial contribution of water hydraulically redistributed by the dominant tree community to shallow soil layers leads to our second hypothesis that the spatiotemporal variation of deep soil water utilization by the dominant deep-rooted tree community should tightly regulate water utilization of the subordinate relatively shallow-rooted understorey community, eventually driving the understorey vegetation community structure. ...
Deep soil water utilization allows plants to cope with drought stress. However, little is known about the roles of the understorey layers in driving spatio‐temporal variations of deep soil water in forests and how the patterns of deep soil water use among life‐forms contribute to community assembly processes.
We assessed the spatio‐temporal patterns and determinants of deep water utilization of tree, shrub and herb layers in subtropical coniferous plantations and investigated associations between deep water use parameters and dominance and richness of understorey vegetation.
We found that the understorey layer had a higher reliance on deep soil water in the dry season, a larger seasonal plasticity of deep soil water uptake, but lower spatial variability in deep soil water utilization than the tree layer. We showed that greater reliance of the tree layer on deep soil water was associated with decreased shrub layer diversity, whereas greater reliance of the shrub layer on deep water was associated with increased herb layer diversity.
Synthesis. Our results highlight the roles of understorey layers in driving the temporal dynamics of deep soil water in forests and improve our understanding of how deep soil water use patterns among life‐forms shape community assembly in forests.
... The first is the amplitude of a daily cycle (Δθ β ) and the other is a more-or-less decreasing linear trend. Δθ β can be estimated from Rose (1968), R. D. Jackson (1973), T. J. Jackson et al. (1997), Brooks et al. (2002), Novak (2016), and the MEF data used in this study and presented later. This yields Δθ β = 0.02 m 3 m −3 (varying between 0 and 0.025 m 3 m −3 ), which suggests that ωΔθ β ≈ 1.4 × 10 −6 s −1 . ...
Changes in atmospheric pressure continuously ventilate soils and snowpacks. This physical process, known as pressure pumping, is a major factor in the exchange fluxes of H2O, CO2, and other trace gases between the soil and atmosphere. Thus models of pressure pumping are relevant to many areas of critical importance. This study compares the three principal models used to describe pressure pumping. Beginning with the fundamental physical principles and whether the flow field is compressible or incompressible, these models are categorized as linear parabolic (one model—compressible) or nonlinear hyperbolic (two models—incompressible). Using observed soil surface pressure data, measured vertical profiles of soil permeability and standard linear analysis and numerical methods, this study shows that nonlinear models produce advective velocities that are one to two orders of magnitude greater than those associated with the linear model. Incorporating soil temperature and moisture dynamics made very little difference to the linear model, but a significant difference in the nonlinear models suggesting that advective velocities induced by pressure changes associated with soil heating and moisture dynamics may not always be small enough to ignore. All numerical results are sensitive to the frequency of the pressure forcing, which was band‐pass filtered into low, mid and high frequencies with the greatest model differences at low frequencies. Partitioning the pressure forcing and model responses helped to establish that mid‐frequency weather‐related phenomena (empirically identified as inertia gravity waves and solitons) are important drivers of gas exchange between the soil and the atmosphere.
... Under the hydraulic lifting effect, deep-rooted species transport and release groundwater to the shallow soil through xylem after nocturnal transpiration decreases and stem refills (Richards and Caldwell 1987;Yu et al. 2018), making shallow-rooted species take use of groundwater indirectly (Emerman and Dawson 1996;Nadezhdina et al. 2010;Hafner et al. 2020). Under drought, hydraulic lifting may facilitate plant growing conditions by easing rhizosphere soil re-wetting or even prolonging the growing season (Brooks et al. 2002;Howard et al. 2009). Moreover, in a mixed forest, species with root access to groundwater may provide one-quarter water demand for shallow-rooted neighbors by hydraulic lifting (Hafner et al. 2017(Hafner et al. , 2020(Hafner et al. , 2021, increasing drought resistance and potentially improving survival (Pang et al. 2013). ...
... Moreover, in a mixed forest, species with root access to groundwater may provide one-quarter water demand for shallow-rooted neighbors by hydraulic lifting (Hafner et al. 2017(Hafner et al. , 2020(Hafner et al. , 2021, increasing drought resistance and potentially improving survival (Pang et al. 2013). However, many studies focused on hydraulic lifting within the growing season (Brooks et al. 2002;Hafner et al. 2021), ignoring the seasonal change in hydraulic lifting. ...
AimsForests with various mixed patterns often show large differences in water use strategies. However, mixed planting may enhance the drought resistance of the whole forest community. We evaluated whether mixed planting could enhance the drought resistance of Robinia pseudoacacia and Quercus acutissima under different seasons in the warm temperate zone of North China.Methods
Shallow-rooted R. pseudoacacia and deep-rooted Q. acutissima were studied to determine plant water use strategies under different seasons and planting methods. We measured hydrogen and oxygen isotope ratios of two species grown under pure and mixed planting methods, as well as those of the environment, including rainwater, soil water, and groundwater in spring, summer, and autumn.ResultsHydrogen and oxygen isotopic contents of soil water were significantly less than groundwater and significantly more than rainwater irrespective of the season. However, season was the key factor influencing the plant water use strategies. In spring and autumn, Q. acutissima used more groundwater while R. pseudoacacia used more soil water; in summer, both of the two species took more use of rainwater and soil water. Mixed planting significantly increased the proportion of groundwater use and the diversity of plant water use strategies of two species.Conclusion
Diversity of plant water use strategies facilitate the coexistence of two species with the same ecosystem irrespective of the changes in water availability in their respective root zones. Besides, mixed planting can enhance the drought resistance of the whole forest community via reducing competition for the seasonal changes in water resources.
... The maximum soil water content due to HR occurred at 06:00-07:00 h. The increased soil water due to HR can be used by jujube trees for transpiration, thereby delaying shallow soil water use (Renée et al., 2002). This can also maintain or induce recovery of root conductivity during the night, resulting in reduced plant water stress, enhanced overall plant carbon assimilation, and increased plant resistance to drought (Prieto and Ryel, 2014). ...
Soil desiccation occurs widely across China’s Loess Plateau due to long-term water demand in excess of water supply. Hydraulic redistribution (HR) - the movement of water from wet to dry soil via roots - and canopy dew (CD) are crucial to water replenishment in dryland ecosystems. However, much is still not known about the response of CD and HR to soil water deficits (including no deficit, slight deficit, moderate deficit, and severe deficit water conditions) in dryland jujube (Ziziphus jujuba Mill.) plantations in China’s Hilly Loess Region. To this end, the duration and intensity of dew were monitored using dielectric leaf wetness sensors to better understand the effects of soil water status on dew. Also, soil water content, sap flow, and meteorological variables were measured during the jujube growing seasons in 2017–2019. The results showed that the time of occurrence of CD under the no deficit condition came earlier than the time of occurrence of CD under slight, moderate, and severe soil water deficit conditions. Peak CD appeared at 5:00–6:30 am and ended at 6:30–9:00 am local time under the four soil water conditions. The amount, duration, and frequency of CD decreased with increasing soil water deficit. The amount and duration of CD under the no deficit condition were significantly higher than under the slight, moderate, and severe soil water deficit conditions (p < 0.05). The amount and frequency of HR (in the 20–60 cm soil layer) increased with increasing soil water deficit. Under the no deficit condition, HR was significantly lower than under the slight, moderate, and severe soil water deficit conditions (p < 0.05). While HR was influenced by CD, CD enhanced HR under the no deficit condition, but inhibited HR under slight, moderate, and severe soil water deficit conditions. For the growing season, the contribution of CD to total actual evapotranspiration (ETc act, CD/ ETc act ratio) was highest under the no deficit condition (maximum CD/ ETc act ratio of 0.21). The contribution of HR to ETc act (HR/ ETc act ratio) was higher under slight, moderate, and severe soil water deficit conditions (maximum of 0.11). The mutual effects of CD and HR lessened soil water deficit, making them important ecohydrological processes affecting the response of dryland jujube plantations to soil desiccation.
... This mechanism requires that plant canopies do not compete for water with the rhizosphere of dry soil layers, limiting hydraulic redistribution to periods when canopy conductance is at or near zero, for example, at night. Hydraulic redistribution has first been described in drylands 43,44 , but has since been reported across a broad range of plant taxa (from old-growth conifers to C 3 grasses) and ecosystems (for example, tropical and temperate forests) 41,42,45 , which are mostly characterized by low soil water holding capacities (for example, well-drained sandy soils) or the presence of a dry season [46][47][48][49] . Hydraulic redistribution outside drylands has also been artificially induced by experimental rainfall exclusion 50 . ...
Responses of terrestrial ecosystems to climate change have been explored in many regions worldwide. While continued drying and warming may alter process rates and deteriorate the state and performance of ecosystems, it could also lead to more fundamental changes in the mechanisms governing ecosystem functioning. Here we argue that climate change will induce unprecedented shifts in these mechanisms in historically wetter climatic zones, towards mechanisms currently prevalent in dry regions, which we refer to as ‘dryland mechanisms’. We discuss 12 dryland mechanisms affecting multiple processes of ecosystem functioning, including vegetation development, water flow, energy budget, carbon and nutrient cycling, plant production and organic matter decomposition. We then examine mostly rare examples of the operation of these mechanisms in non-dryland regions where they have been considered irrelevant at present. Current and future climate trends could force microclimatic conditions across thresholds and lead to the emergence of dryland mechanisms and their increasing control over ecosystem functioning in many biomes on Earth. In drylands, there are unique mechanisms that influence multiple ecosystem processes. In this Perspective, the authors identify these dryland mechanisms and show that they could become more important in non-dryland regions or areas that will become drier in the future. *** FOR ONLINE VIEWING: https://rdcu.be/cSmAD
