Dynamic niche partitioning in root water uptake facilitates efficient water use in more diverse grassland plant communities

Abstract

Abstract1. Efficient extraction of soil water is essential for the productivity of plant communities. However, research on the complementary use of resources in mixed plant communities, and especially the impact of plant species richness on root water uptake, is limited. So far, these investigations have been hindered by a lack of methods allowing for the estimation of root water uptake profiles.2. The overarching aim of our study was to determine whether diverse grassland plant communities in general exploit soil water more deeply and whether this shift occurs all the time or only during times of enhanced water demand.3. Root water uptake was derived by analysing the diurnal decrease in soil water content separately at each measurement depth, thus yielding root water uptake profiles for 12 experimental grasslands communities with two different levels of species richness (4 and 16 sown species). Additional measurements of leaf water potential, stomatal conductance, and root traits were used to identify differences in water relations between plant functional groups.4. Although the vertical root distribution did not differ between diversity levels, root water uptake shifted towards deeper layers (30 and 60 cm) in more diverse plots during periods of high vapour pressure deficit. Our results indicate that the more diverse communities were able to adjust their root water uptake, resulting in increased water uptake per root area compared to less diverse communities (52% at 20 cm, 118% at 30 cm, and 570% at 60 cm depth) and a more even distribution of water uptake over depth. Tall herbs, which had lower leaf water potential and

Plant species richness and functional groups have different effects on soil water content in a decade‐long grassland experiment

“…The effects of legumes and grasses in topsoil can be related partly to their different rooting strategies, with higher root biomass in the presence of grasses compared to legumes (Ravenek et al, ). For example, grasses, although showing a lower stomatal conductance compared to other functional groups (Guderle et al, ; Siebenkäs, Schumacher, & Roscher, ), typically have a shallower root system (Archer, Quinton, & Hess, ; Ravenek et al, ) and concentrate water uptake near the surface, leading to dry topsoils (February & Higgins, ; Leimer et al, ). In contrast, many legumes and tall herbs have a taproot systems taking up water from deeper soil (Dawson & Pate, ; Guderle et al, ; Leimer et al, ).…”

“…However, the effect of specific plant functional groups could only partly be explained by root biomass. This may be due to the fact that root water uptake potentially is increased independently of root biomass, which may be attributable to specific root system structures not accounted for by root biomass, like tap roots in tall herbs (Bechmann et al, ; Guderle et al, ; Schneider, Attinger, Delfs, & Hildebrandt, ). Additionally, the presence of legumes may positively affect soil water content by increasing water‐use efficiency (Hernandez & Picon‐Cochard, ) or their more horizontally positioned leaves enhance shading.…”

“…This suggests a general potential for below‐ground resource partitioning (Leimer et al, ). However, the actual location of root water uptake depends on several factors including competition and environmental conditions (Barkaoui et al, ; Guderle et al, ) and may converge towards poor resource partitioning over time (Barkaoui et al, ; Fort et al, ).…”

“…Because of its importance as a resource, water has repeatedly been studied in experiments investigating the relationships between biodiversity and ecosystem functioning. This water-related research has generally focused on the efficiency of resource use (Leimer et al, 2014(Leimer et al, , 2018Milcu et al, 2016), drought stress (Dimitrakopoulos & Schmid, 2004;Vogel, Scherer-Lorenzen, & Weigelt, 2012), and complementarity (Cardinale et al, 2007;Guderle et al, 2018;Hernandez & Picon-Cochard, 2016;Van Peer, Nijs, Reheul, & Cauwer, 2004), while only a few have considered diversity effects on soil characteristics (Fischer et al, 2015;Gould, Quinton, Weigelt, Deyn, & Bardgett, 2016;Pérès et al, 2013).…”

“…For example, increased leaf area in species-rich grassland communities (Lange et al, 2014;Spehn, Joshi, Schmid, Diemer, & Korner, 2000) may decrease evaporation because of shading (Kreutziger, 2006;Milcu et al, 2016;Rosenkranz, Wilcke, Eisenhauer, & Oelmann, 2012) and improve water-use efficiency (Caldeira, Ryel, Lawton, & Pereira, 2001;Milcu et al, 2014;Verheyen et al, 2008), which increases soil water content, particularly in the topsoil. At the same time, greater leaf area also increases the transpiring surface and hence transpiration (De Boeck et al, 2006;Guderle et al, 2018), which may decrease soil water content in species-rich plant communities. For instance, Caldeira et al (2001) observed both positive and negative effects of plant species richness on soil water content depending on soil depth.…”