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Zusammenfassung:
In the literature, contrasting effects of plant species richness on the soil water balance are reported. Our objective was to
assess the effects of plant species and functional richness and functional identity on soil water contents and water fluxes in
the experimental grassland of the Jena Experiment. The Jena Experiment comprises 86 plots on which plant species
richness (0, 1, 2, 4, 8, 16, and 60) and functional group composition (zero to four functional groups: legumes, grasses, tall
herbs, and small herbs) were manipulated in a factorial design. We recorded meteorological data and soil water contents of
the 0·0–0·3 and 0·3–0·7msoil layers and calculated actual evapotranspiration (ETa), downward flux (DF), and capillary rise with a soil
water balance model for the period 2003–2007. Missing water contents were estimated with a Bayesian hierarchical model. Species
richness decreased water contents in subsoil during wet soil conditions. Presence of tall herbs increased soil water contents in topsoil
during dry conditions and decreased soilwater contents in subsoil duringwet conditions. Presence of grasses generally decreasedwater
contents in topsoil, particularly during dry phases; increased ETa and decreased DF from topsoil; and decreased ETa from subsoil.
Presence of legumes, in contrast, decreased ETa and increased DF from topsoil and increased ETa from subsoil. Species richness
probably resulted in complementary water use. Specific functional groups likely affected the water balance via specific root traits
(e.g. shallow dense roots of grasses and deep taproots of tall herbs) or specific shading intensity caused by functional group
effects on vegetation cover.
