Marcus Guderle, Dörte Bachmann, Alexandru Milcu, Annette Gockele, Marcel Bechmann, Christine Fischer, Christiane Roscher, Damien Landais, Olivier Ravel, Sébastien Devidal, Jacques Roy, Arthur Gessler, Nina Buchmann, Alexandra Weigelt and Anke Hildebrandt
Colourful meadows not only look more beautiful than grasslands cultivated with monocultures, but their biodiversity also makes them more resistant to various environmental changes and extreme events. But why is this resistance so important? Grasslands provide a wide range of functions that are also important for humans. For example, they contribute to carbon fixation, protect soils, and are habitats for innumerable animal and plant species. Furthermore, grasslands couple the water cycle between atmosphere and soil through the movement of water from the soil into roots and out of their leaves into the atmosphere. With increasing drought, these ecosystems are increasingly confronted with water stress, which also affects their stability and functioning.
In this study, we investigated whether grassland ecosystems with more plant species are able to take up water from deeper soil and in higher quantities than grassland ecosystems with fewer plant species. Besides water uptake, we also considered the distribution of the roots in the soil as well as the cover of different plant types and related these to the evaporation processes in the leaves.
In order to get insight into the soil and water uptake of the respective ecosystems, we measured soil moisture to a depth of 60 cm over two months. We were able to derive the specific water uptake at each depth by interpretation of the daytime drop in water content from these measurements.
We showed that ecosystems with a higher number of species were better able to take up water from deeper, wetter soil layers when conditions were dry. In comparison, species-poor ecosystems were not able to do this. Interestingly, in species-poor grasslands, root water uptake followed the spatial distribution of roots in the soil, whereas the root water uptake profiles of species-rich plant communities were able to deviate from the root spatial distribution. The investigation of other plant traits showed that mainly tall herbs contributed to this redistribution of the water uptake.
Our results show that species-rich ecosystems can react more flexibly and effectively to environmental changes and thus stabilize their functions. This is an important reason why biodiversity is so fundamental and needs to be protected.
Image caption: One of twelve macrocosms of the Montpellier European Ecotron (CNRS) with lysimeter extracted from the experimental field site of the Jena Experiment. All environmental measurements were performed in these macrocosms. Photo provided by Christiane Roscher