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Photographs of leaf transverse sections depicting (a) Triodia schinzii whole leaf section stained with toluidine blue viewed under a light microscope; note the photosynthetic mesophyll tissues (mes) are associated with the adaxial (inner) surface or main groove, (b) Triodia basedowii whole leaf section unstained and viewed with a Nomarski differential interference contrast microscope; note the spine-like papillae (pap) in the main groove and photosynthetic tissues present on both adaxial and abaxial sides, (c) Triodia. schinzii leaf section stained with toluidine blue showing stomata (st) inside the main groove (gr) and bundle sheath extension (bse) cells very distant from vascular tissue, (d) Triodia basedowii leaf section stained with rhodamine B and aniline blue; note the stomatal groves sunken inwards from the abaxial (outer) and adaxial surfaces and (e) and ( f ) iodine staining of Triodia schinzii and Triodia basedowii, respectively, showing presence of starch mainly in bundle sheath and mesophyll cells, with some starch grains in parenchyma cells. Scale bars in all images equate to 0.2 mm. vb = vascular bundles, gr = stomatal groove, mes = mesophyll, bs = bundle sheath, bse = bundle sheath extension cells, pap = papillae, scl = sclerenchyma, par = parenchyma, mr = mid-rib, sn = subsidiary nerve, st = stomata, ep = epidermis.
Source publication
Desert dunes and interdunes provide habitat heterogeneity and profoundly in fluence the spatial and temporal distribution of water and nutrients throughout the landscape. These underlying physical processes shape the plant species composition and their ecophysiology. Spinifex grasses dominate the vegetation throughout much of Australia and are cate...
Contexts in source publication
Context 1
... a needle-like form with the adaxial surface forming the major groove. Papillae, or trichomes, project from the epidermal cells lining this grove which interdigitate and occlude much of the groove volume ( Craig and Goodchild 1977). Triodia schinzii displayed sunken stomatal groves and mesophyll tissue only on the adaxial (inner) side of the leaf (Fig. 2a, c, e), whereas T. basedowii displayed such structures on both the adaxial and abaxial (outer) sides (Fig. 2b, d, f ). Both species demonstrated a modified Kranz leaf anatomy, as the thick-walled bundle sheath cells were accompanied by bundle sheath extension cells, which wrap around the mesophyll (Fig. 2c, d). Iodine staining identified very ...
Context 2
... epidermal cells lining this grove which interdigitate and occlude much of the groove volume ( Craig and Goodchild 1977). Triodia schinzii displayed sunken stomatal groves and mesophyll tissue only on the adaxial (inner) side of the leaf (Fig. 2a, c, e), whereas T. basedowii displayed such structures on both the adaxial and abaxial (outer) sides (Fig. 2b, d, f ). Both species demonstrated a modified Kranz leaf anatomy, as the thick-walled bundle sheath cells were accompanied by bundle sheath extension cells, which wrap around the mesophyll (Fig. 2c, d). Iodine staining identified very high concentrations of starch granules in bundle-sheath cells, mesophyll cells and low concentrations in ...
Context 3
... on the adaxial (inner) side of the leaf (Fig. 2a, c, e), whereas T. basedowii displayed such structures on both the adaxial and abaxial (outer) sides (Fig. 2b, d, f ). Both species demonstrated a modified Kranz leaf anatomy, as the thick-walled bundle sheath cells were accompanied by bundle sheath extension cells, which wrap around the mesophyll (Fig. 2c, d). Iodine staining identified very high concentrations of starch granules in bundle-sheath cells, mesophyll cells and low concentrations in parenchyma cells of both species (Fig. 2e, f ...
Context 4
... a modified Kranz leaf anatomy, as the thick-walled bundle sheath cells were accompanied by bundle sheath extension cells, which wrap around the mesophyll (Fig. 2c, d). Iodine staining identified very high concentrations of starch granules in bundle-sheath cells, mesophyll cells and low concentrations in parenchyma cells of both species (Fig. 2e, f ...
Context 5
... of sunken stomata only on the inner (adaxial) surface of T. schinzii leaves but on both sides of T. basedowii leaves seems counterintuitive considering the latter is distributed across the drier regions of the Australian continent. However, the tightly interlaced folds at the entrance of the abaxial, deeply sunken stomatal crypts of T. basedowii (Fig. 2d) potentially offer better protection than the trichomes in the main groove. The lack of external stomata on leaves of the dune species, T. schinzii, may also confer an advantage to coping with higher wind speeds and sand-blasting typical on dune crests (Seely 1991;Bowers 1996;Fet et al. ...
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Citations
... obs.). Grigg et al. (2008) and Grigg (2009) ...
... Analogous alterations in the proportional representation of bacterial phyla have been observed in precipitation manipulation experiments carried out within forest and polar ecosystems (Fierer et al., 2003;Buelow et al., 2016). This can be explained by the increased water availability, which might stimulate the mineralization of soil organic matter in increased precipitation (Austin et al., 2004;Grigg et al., 2008), and promote the growth of copiotrophic taxa. Conversely, in the early growing season treatments where the water availability was like the control plots, the taxa remain stable, suggesting that soil moisture has played a role in shaping bacterial community structure. ...
Introduction
Global climate change may lead to changes in precipitation patterns. This may have a significant impact on the microbial communities present in the soil. However, the way these communities respond to seasonal variations in precipitation, particularly in the context of increased precipitation amounts, is not yet well understood.
Methods
To explore this issue, a five-year (2012–2016) field study was conducted at the northeast boundary of the Ulan Buh Desert, examining the effects of increased precipitation during different periods of the growing season on both bacterial and fungal communities. The study included five precipitation pattern treatments: a control group (C), as well as groups receiving 50 and 100% of the local mean annual precipitation amount (145 mm) during either the early growing season (E50 and E100) or the late growing season (L50 and L100). The taxonomic composition of the soil bacterial and fungal communities was analyzed using Illumina sequencing.
Results
After 5 years, the bacterial community composition had significantly changed in all treatment groups, with soil bacteria proving to be more sensitive to changes in precipitation timing than to increased precipitation amounts within the desert ecosystem. Specifically, the alpha diversity of bacterial communities in the late growing season plots (L50 and L100) decreased significantly, while no significant changes were observed in the early growing season plots (E50 and E100). In contrast, fungal community composition remained relatively stable in response to changes in precipitation patterns. Predictions of bacterial community function suggested that the potential functional taxa in the bacterial community associated with the cycling of carbon and nitrogen were significantly altered in the late growing season (L50 and L100).
Discussion
These findings emphasize the importance of precipitation timing in regulating microbial communities and ecosystem functions in arid regions experiencing increased precipitation amounts.
... Our results are similar to those of previous studies of desert microbial communities [20,57,58], suggesting that water addition facilitates the growth of oligotrophic taxa and suppresses copiotrophic taxa in desert ecosystems. However, previous studies have suggested that increased water availability could stimulate the mineralization of soil organic matter [49,59] and promote the growth of copiotrophic microbes by providing more nutrients. This discrepancy could be attributed to two possible reasons. ...
The response of microbial communities to continual and prolonged water exposure provides useful insight when facing global climate changes that cause increased and uneven precipitation and extreme rainfall events. In this study, we investigated an in situ manipulative experiment with four levels of water exposure (ambient precipitation +0%, +25%, +50%, and +100% of local annual mean precipitation) in a desert ecosystem of China. After 9 years of water addition, Illumina sequencing was used to analyze taxonomic compositions of the soil bacterial, archaeal, and fungal communities. The results showed significant increases in microbial biomass carbon (MBC) at higher amended precipitation levels, with the highest values reported at 100% precipitation. Furthermore, an increase in the bacterial species richness was observed along the water addition gradient. In addition, the relative abundance of several bacterial phyla, such as Proteobacteria, significantly increased, whereas that of some drought-tolerant taxa, including Actinobacteria, Firmicutes, and Bacteroidetes, decreased. In addition, the phyla Planctomycetes and Nitrospirae, associated with nitrification, positively responded to increased precipitation. Archaeal diversity significantly reduced under 100% treatment, with changes in the relative abundance of Thaumarchaeota and Euryarchaeota being the main contributors to shifts in the archaeal community. The fungal community composition was stable in response to water addition. Results from the Mantel test and structural equation models suggested that bacterial and archaeal communities reacted contrastingly to water addition. Bacterial community composition was directly affected by changing soil moisture and temperature, while archaeal community composition was indirectly affected by changing nitrogen availability. These findings highlight the importance of soil moisture and nitrogen in driving microbial responses to long-term precipitation changes in the desert ecosystem.
... Ring formation occurs in several Triodia species (Burbidge 1945;Lazarides 1997). Of the known ring formers, Triodia basedowii is widespread across the interior of Australia, growing among sand dunes from 19 to 30 S (Lazarides 1997;Grigg et al. 2008). T. basedowii is killed by fire and is therefore an obligate seeder, relying on an accumulated soil seed bank for regeneration (Casson and Fox 1987;Westoby et al. 1988;Rice and Westoby 1999). ...
Ring-forming species of spinifex grasses (Triodia spp.) are a dominant feature across much of Australia's arid and semi-arid zone. Researchers have long been curious about the mechanisms underpinning their striking growth form. However, none of the factors investigated to date provide a convincing explanation for ring formation. Here, we asked whether an accumulation of pathogenic soil microbes might impede seedling emergence and subsequent growth in the centre of Triodia basedowii rings. We collected soil from inside and outside naturally occurring spinifex rings and compared plants grown in soil with live microbes to plants grown in sterilised soil. Consistent with our hypothesis, we found that emergence of T. basedowii seedlings was lower in live soil from inside the rings than in live soil from outside the rings. Further, seedling emergence in soil from inside the rings increased significantly in response to soil sterilisation. We found no significant difference in growth between sterile and live soils. However, this might be due to a lack of power caused by high rates of seedling mortality in all treatments. Overall, our study provides evidence for the role of soil pathogens in shaping this iconic Australian grass.
... Recurrent natural fire events, which may be spatially patchy, burn these Triodia grasslands approximately every 15-30 years, thereby destroying the entire grass vegetation (Levin, Levental, & Morag, 2012;Muñoz-Rojas, Erickson, Martini, Dixon, & Merritt, 2016). Triodia basedowii regenerates entirely from seeds after fire (Grigg, Veneklaas, & Lambers, 2008). ...
... The perennial grass species T. basedowii grows permanently until neighbourhood competition, resource depletion or the central collapse of a hummock leads to plant death or ring formation. Hence, if fire is absent for a long time, considerable amounts of dead leaf material within hummocks accumulate (Grigg et al., 2008) and this increase of combustible material increases the probability of fire (Haydon, Friar, & Pianka, 2000). The research plots FC-L1, FC-L2 and FC-C5 that had not burnt for >15 years, were likely in a terminal phase of this successional stage because their entire grass layers burnt in April 2018 due to a wildfire. ...
So‐called fairy circles (FCs) comprise a spatially periodic gap pattern in arid grasslands of Namibia and north‐west Western Australia. This pattern has been explained with scale‐dependent ecohydrological feedbacks and the reaction‐diffusion, or Turing mechanism, used in process‐based models that are rooted in physics and pattern‐formation theory. However, a detailed ecological test of the validity of the modelled processes is still lacking.
Here, we test in a spinifex‐grassland ecosystem of Western Australia the presence of spatial feedbacks at multiple scales. Drone‐based multispectral analysis and spatially explicit statistics were used to test if grass vitality within five 1‐ha plots depends on the pattern of FCs that are thought to be a critical extra source of water for the surrounding matrix vegetation. We then examined if high‐ and low‐vitality grasses show scale‐dependent feedbacks being indicative of facilitation or competition. Additionally, we assessed facilitation of grass plants for different successional stages after fire at fine scales in 1‐m² quadrats. Finally, we placed soil moisture sensors under bare soil inside the FC gap and under plants at increasing distances from the FC to test if there is evidence for the ‘infiltration feedback’ as used in theoretical modelling.
We found that high‐vitality grasses were systematically more strongly associated with FCs than low‐vitality grasses. High‐vitality grasses also had highly aggregated patterns at short scales being evidence of positive feedbacks while negative feedbacks occurred at larger scales. Within 1‐m² quadrats, grass cover and mutual facilitation of plants was greater near the FC edge than further away in the matrix. Soil moisture after rainfall was lowest inside the FC with its weathered surface crust but highest under grass at the gap edge, and then declined towards the matrix, which confirms the infiltration feedback.
Synthesis. The study shows that FCs are a critical extra source of water for the dryland vegetation, as predicted by theoretical modelling. The grasses act as ‘ecosystem engineers’ that modify their hostile, abiotic environment, leading to vegetation self‐organization. Overall, our ecological findings highlight the validity of the scale‐dependent feedbacks that are central to explain this emergent grassland pattern via the reaction‐diffusion or Turing‐instability mechanism.
... Studies of plants from mostly arid environments include those of Wood (1934) who looked at stomatal distribution on leaves of what he called xerophytes. Voznesenskaya et al. (2008) provided a very detailed examination of the anatomy of the succulent Tecticornia and there have been several studies on the leaf anatomy of the very xerophytic Triodia (McWilliam and Mison 1974;Craig and Goodchild 1977;Grigg et al. 2008). Macklin (1927) examined Casuarinaceae phyllichnia anatomy (some species from relatively dry climates) mainly from a taxonomic perspective and built on that foundation with further examination of Allocasuarina species that ranged from mesic to semiarid environments. ...
... The C 4 grass genus, Triodia is the quintessential desert xeromorph in Australia. The C 4 metabolism ensures a much higher water use efficiency than in C 3 plants (Cowan 1981) and is associated with the distinctive Krantz anatomy of chloroplasts in the palisade of the leaf mesophyll and also chloroplasts in the bundle sheath cells surrounding the vascular bundles, ( fig. 15 in Evans and Loreto 2000; fig. 2 in Grigg et al. 2008). As with the resurrection plants, Triodia still has stomata in grooves in the leaf and has special bulliform cells at the base of the furrows that lose water during dry conditions (McWilliam and Mison 1974) and consequently close the furrows increasing the humidity above the stomata. ...
Plants from arid environments have some of the most diverse morphological and anatomical modifications of any terrestrial plants. Most perennials are classified as xerophytes, and have structures that limit water loss during dry weather, provide structural support to help prevent cell collapse during dry periods or store water in photosynthetic tissues. Some of these traits are also found in sclerophyllous plants and traits that may have developed due to evolution of taxa on nutrient poor soils may also benefit the plants under arid conditions. We examined the morpho-anatomical features of photosynthetic organs of three tree and four shrub species with reduced leaves or photosynthetic stems that occur in arid or semiarid sites in Australia to see if there were patterns of tissue formation particularly associated with xeromorphy. In addition, we reviewed information on succulent and resurrection species. In the tree species (Callitris spp.) with decurrent leaves clothing the stems, the close association between the water transport system and stomata, along with anisotropic physiology would allow the species to fix carbon under increasingly dry conditions in contrast to more broad-leaved species. The shrub species (Tetratheca species and Glischrocaryon flavescens) with photosynthetic stems had extensive sclerenchyma and very dense chlorenchyma. The lack of major anatomical differences between leafless species of Tetratheca from arid areas compared with more mesic sites indicates that quite extreme morphological modifications may not exclude species from growing successfully in competition with species from less arid areas. The sclerophyll flora now characteristic of Australian vegetation from seasonally arid climates may have evolved during mesic times in the past but with relatively minor modifications was able to adjust to the gradually drying climate of much of Australia up to the present time.
... higher in CR in comparison to ID), the higher plant density at ID may compensate for the greater biomass of individual plants at CR, resulting in similar plant biomass per unit area at both habitats. Despite the higher FC and SOC in ID (which are expected to increase AWC; Booth, 1941;Brotherson and Rushforth, 1983;George et al., 2003;Xiao et al., 2010), and the presence of the crust (expected to increase the surface AWC; Grigg et al., 2008aGrigg et al., , 2008bFischer et al., 2010), AWC was lower at ID. This could not have been attributed to differences in the rain amount. ...
... While some previous research studies undertaken at different arid dune fields also reported higher vegetation cover and/or biomass at the dunes, the phenomenon was attributed to other factors, such as different parent materials (Grigg et al., 2008a;Pavlik, 1980;Seely and Louw, 1980;Barnes and Harrison, 1982), or shallow soils with low water storage capacity at the interdunes (Chadwick and Dalke, 1965;Boyer, 1989;Grigg et al., 2008aGrigg et al., , 2008b. However, most studies regard the interdune as a preferential habitat for plants (Moreno-Casasola, 1986;Link et al., 1994;Hamerlynck and McAuliffe, 2008;McAuliffe and Hamerlynck, 2010), attributing the preferential growth at the interdune to a shallow water table that benefits plant growth (Gries et al., 2003;Ohte et al., 2003;Mason et al., 2004;Niu et al., 2005). ...
It is generally accepted that biological soil crusts promote the growth of vascular plants. Nevertheless, contradictory results were recently found for annual plants in the extreme desert dunefield of the Negev (average precipitation of 95 mm) during extreme drought years, explained by the lower available water content (AWC) under the low-albedo biocrusted surfaces at the interdune (ID). Trying to assess whether the biomass and fecundity of the annual plants is higher at the non-crusted dune crest (CR) in comparison to ID also during years with near-average precipitation, surface stability, rain, AWC, fine (silt and clay) content (FC), and soil organic carbon (SOC) were measured in a pair of plots established in CR and ID in two dunes and interdunes. The research was conducted for three years (2009/2010, 2013/14 and 2014/15), having a mean precipitation of 109.4 mm. At the end of each winter, sampling of the annual plants (cover, density, species composition, biomass) took place at CR and ID at 30 cm-diameter miniplots (miniplot-scale), while the biomass and fecundity of 50 randomly-chosen individuals that abundantly inhabited both habitats during the same year were measured at parallel transects (individual plant-scale). Significantly higher cover and generally higher diversity characterized the plants at ID at the miniplot-scale, explained by the higher surface stability. Although characterized by lower FC and SOC, significantly higher biomass and fecundity characterized the individual plants at CR, explained by the higher AWC. Biocrusts were found to have a dual effect on the annual plants: positive due to increased surface stability (cover and for most years also diversity) at the miniplot-scale, and negative due to reduced AWC (low biomass and fecundity) at the individual plant-scale. The higher biomass and fecundity of the individual plants at CR point to the cardinal role played by water (rather than SOC) in this low-nutrient extreme desert. As far the annual plants are concerned, these findings also point at the fact that moderate crust destruction (such as by light trampling) may not necessarily be hazardous to the ecosystem, as it may increase fecundity and subsequently germination success.
... If these two factors operated in tandem (i.e., a severe post-fire drought was succeeded by a fire interval of < 5 years), assemblages dominated by Triodia grasses would presumably be favored. This is because Triodia are strongly xerophytic, having several leaf adaptations that reduce transpiration and enable them to tolerate long dry periods (Grigg et al. 2008;Jacobs 1973;Wells 1999), and they also have a shorter primary juvenile period comparative to Aluta (Jacobs 1973, Wright 2018. ...
Alternative vegetation types that switch from one to another under contrasting fire regimes are termed fire-mediated alternative stable states (FMASS). Typically, pyrophylic communities (i.e., vegetation assemblages favored by burning) dominate under high frequencies or intensities of fire. Conversely, fire-sensitive (pyrophobic) vegetation types persist under long fire-free conditions. As the persistence traits of plants of FMASS systems are generally poorly researched, threshold levels of pyric disturbance that trigger ‘state-switching’ are often unknown. Dense thickets of the obligate-seeder shrub waputi (Aluta maisonneuvei ssp. maisonneuvei [Myrtaceae]) form fire-retarding woody islands within highly flammable spinifex (Triodia spp.) grasslands in arid Australia. To examine the tolerance of Aluta thickets to burning, we investigated: (1) the influence of post-fire rainfall and fire severity on recruitment (a field study); (2) soil seedbank densities (a field study); and (3) fire-related dormancy cues in seeds (a germination trial). We found a positive relationship between recruitment and post-fire rainfall volume, and much higher mean recruitment at sites with high- (5.9 seedlings/m2) than low-severity-burnt (2.2 seedlings/m2) and unburnt shrubs (0.03 seedlings/m2). Post-fire regeneration was mediated by dense soil-borne seedbanks, and the germination trial indicated that smoke promoted germination. Although Aluta shrubs are invariably fire-killed, high-severity fires are unlikely to lead to state shifts from shrubland to grassland because of the ability of mature stands to regenerate from dense, fire-cued seedbanks. Nevertheless, given that Aluta seedlings are exceptionally slow-growing, post-fire droughts combined with fire-return intervals less than the Aluta primary juvenile period of c. 5 years could drive conversion from Aluta- to Triodia-dominated vegetation.
... Rather than having a substantial root system that accesses soil moisture at depth (as is the case with many woody plants in these environments), when under moisture stress, spinifex gradually slows down growth and gas exchange, maintains cell structure and integrity (i.e. does not wilt) and 'suspends' metabolism (Grigg et al. 2008). Under water stress the plant is straw-coloured and has the 'cured' appearance of an annual grass. ...
Although fire is a widespread phenomenon and major ecosystem disturbance at the global scale, fire is a relatively rare event in much of the arid lands as rainfall and productivity are generally too low to support the dense vegetation and continuous fuel needed to sustain fires (Pausas and Bradstock 2007; Pausas and Ribeiro 2013). There are exceptions to this, such as landscapes dominated by xerophytic perennial grasses, where infrequent periods with above-average rainfall can result in exceptional grass and herb growth or where invasive species, particularly alien grasses, enhance fuel loads (Greenville et al. 2009; Keeley et al. 2012; Balch et al. 2013). Changes in land management (e.g. reduction in grazing, land abandonment), climate change and increased atmospheric CO2 concentrations have also been linked to increased fire activity in arid zones across the globe (Bond and Midgley 2012; Pausas and Fernández-Muñoz 2012; Bachelet et al. 2016).
... Dinitrogen-fixing acacias (Fabaceae) are major components of most vegetation types in Australia's arid zone (Orians and Milewski 2007;Gonzalez-Orozco et al. 2011). Other major plant species include Grevillea and Hakea (Proteaceae), Eucalyptus and Corymbia (Myrtaceae) and Triodia (Poaceae) (Grigg et al. 2008b;Goldie et al. 2010). In this chapter, we focus on the mineral nutrition of some major plant families in Australia's arid zone, including the mineral nutrition of Acacia species and non-mycotrophic plants (mainly Proteaceae). ...
Australia’s arid-zone soils are highly leached and resorted (Winkworth 1967; Pillans 2018) and characterised by low levels of available water and nutrients (Orians and Milewski 2007). These soils are particularly low in total phosphorus (P) and nitrogen (N) (Islam et al. 2000; Bennett and Adams 2001; Grigg et al. 2008a). The distribution of these and other nutrients is typically heterogeneous, due to the development of ‘islands of fertility’ and tight nutrient cycling beneath the canopies of long-lived perennial plants (Tongway and Ludwig 1994; He et al. 2011). Nutrient cycling and decomposition of leaf litter are largely restricted to periods after rain, when bacteria (Skopp et al. 1990; Ford et al. 2007) and cyanobacteria, either free-living or as components of biological soil crusts (biocrusts), are active (Austin et al. 2004). Termites also play an important role in litter decomposition and nutrient cycling and contribute to the patchy distribution of nutrients (Tongway et al. 1989; Park et al. 1994).
