Effect of ecosystem structure on spatial distribution of root water uptake in a grassland and forest ecosystem

The spatial distribution of root water uptake at the ecosystem scale is difficult to assess, and therefore our knowledge of how ecosystem-related and abiotic factors affect root water uptake and its patterns is still limited. This presentation summarizes the results of observations of root water uptake in two contrasting vegetation types: grassland and forest along community diversity gradients.

Based on field studies in both a grassland and a forest system, we investigated how root water uptake changes with ecosystem assembly. We used a water balance method to estimate (a) vertical profiles of root water uptake in grassland systems and (b) horizontal distribution of water uptake in forests, in both cases along species diversity gradients. In both cases, we find that species diversity strongly affects the location and increases the magnitude of root water uptake. In grasslands, the relationship can be directly linked to deeper uptake by species with deep root systems and higher water requirements, suggesting complementarity in resource use. In forests, uptake is enhanced in the main root zone where both the number of tree species and basal area are high, although the underlying mechanisms remain elusive. 

Overall, our observations show an enhanced capacity for water uptake in diverse ecosystems.

In the future, further insights will be gained by combining techniques for assessing root water uptake at the individual and ecosystem scale together with plant and soil hydraulic assessments.