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

Abstract

The temporal and spatial dynamics of soil water are closely interlinked with terrestrial ecosystems functioning. The interaction between plant community properties such as species composition and richness and soil water mirrors fundamental ecological processes determining above‐ground–below‐ground feedbacks. Plant–water relations and water stress have attracted considerable attention in biodiversity experiments. Yet, although soil scientific research suggests an influence of ecosystem productivity on soil hydraulic properties, temporal changes of the soil water content and soil hydraulic properties remain largely understudied in biodiversity experiments. Thus, insights on how plant diversity—productivity relationships affect soil water are lacking. Here, we determine which factors related to plant community composition (species and functional group richness, presence of plant functional groups) and soil (organic carbon concentration) affect soil water in a long‐term grassland biodiversity experiment (The Jena Experiment). Both plant species richness and the presence of particular functional groups affected soil water content, while functional group richness played no role. The effect of species richness changed from positive to negative and expanded to deeper soil with time. Shortly after establishment, increased topsoil water content was related to higher leaf area index in species‐rich plots, which enhanced shading. In later years, higher species richness increased topsoil organic carbon, likely improving soil aggregation. Improved aggregation, in turn, dried topsoils in species‐rich plots due to faster drainage of rainwater. Functional groups affected soil water distribution, likely due to plant traits affecting root water uptake depths, shading, or water‐use efficiency. For instance, topsoils in plots containing grasses were generally drier, while plots with legumes were moister. Synthesis. Our decade‐long experiment reveals that the maturation of grasslands changes the effects of plant richness from influencing soil water content through shading effects to altering soil physical characteristics in addition to modification of water uptake depth. Functional groups affected the soil water distribution by characteristic shifts of root water uptake depth, but did not enhance exploitation of the overall soil water storage. Our results reconcile previous seemingly contradictory results on the relation between grassland species diversity and soil moisture and highlight the role of vegetation composition for soil processes.

Limited evidence for spatial resource partitioning across temperate grassland biodiversity experiments

“…Further, microbial biomass and activity are higher in upper soils relative to lower soil layers (Bardgett et al 1997, Fierer et al 2003, 2009, Griffiths et al 2003. Additionally, plant diversity likely provides a feedback on these factors with plants actively altering topsoil resource dynamics for themselves and other species (Oelmann et al 2011, Reich et al 2012for nitrogen, Eisenhauer et al 2010, for microbes, Milcu et al 2016and Fischer et al 2019. For example, Lange et al (2015) found that the positive relationship between plant diversity and the soil microbial community was mainly related to the increased leaf area index at high plant diversity.…”

Plant traits are poor predictors of long-term ecosystem functioning

“…Volumetric soil water contents were measured with frequency domain reflectometry (FDR) using a mobile manual FDR probe (PR1/6 and PR2/6, Delta-T-Devices, Cambridge, UK) on all plots in 1–2 weekly resolution in the 0.1, 0.2, 0.3, 0.4, and 0.6 m soil depths 68, 69 .…”

Higher species diversity improves soil water infiltration capacity by increasing soil organic matter content in semiarid grasslands

“…PSD also influences soil hydraulic properties. A decade‐long experiment revealed that PSD increased soil infiltration capacity (SIC) and soil water content by altering soil properties (Fischer et al, ; ). SIC is increased by water flow via macropores that are formed by soil fauna or root systems, as well as cracks and fissures in grassland (Wu, Liu, Yang, et al, ).…”

“…Maximizing precipitation infiltration and reducing run-off are critical factors for vegetation restoration and soil and water conservation in semiarid areas. Vegetation type and community composition also impact soil water dynamics (Fischer et al, 2018;Liu et al, 2018), soil properties (Don et al, 2015;Sibylle et al, 2008), and soil hydraulic characteristics (Huang, Tian, Wu, Liu, & Dang, 2017;Wu, Liu, Yang, et al, 2017). PSD also influences soil hydraulic properties.…”