Global Change Induced Threats Across Scales: Assessing the Impact of Extreme Drought and Nitrogen Loading on a Temperate Grassland
Two major threats to the stable functioning of grasslands are 1) nitrogen loading due to pollution, 2) and increasing droughts related to climate change. They are important drivers which can strongly alter species competition, cause substantial species shifts and affect the whole soil-plant-atmosphere continuum. We experimentally studied the response of a temperate grassland to these drivers (singularly and added) across scales. For that, we combined classical grassland methods to describe biodiversity and vegetation structures with high resolution ecosystem flux and stable isotope techniques. Field measurements were complemented by laboratory experiments to deepen our knowledge of underlying mechanisms. Two years after the experiment's start in 2015, we found large treatment effects on the ecosystem carbon cycling related to diversity loss. Nitrogen addition caused a significant loss in forb species (-25 %), which resulted in a strong decline in the ecosystem carbon sequestration (-60 %, combined with drought: -73 %), while drought alone reduced carbon sequestration by 43 % (Kübert et al. 2019). During the summer drought, the grass dominated and species-poor community on fertilized plots suffered from a strong aboveground dieback, likely caused by weaker drought adaptations of the species community. On the leaf/plant level, however, we only found small adaptations on physiological controls, i.e. on leaf gas exchange and water use/uptake. The two grassland functional groups, though, showed fundamentally different strategies related to drought. While grasses seemed to avoid strong seasonal drought stress by phenological adaptation, forbs abundance was generally decreased by experimental drought. Moreover, combining isotopic techniques with statistical models we could show a contrasting root water uptake response of grassland species to drought and rain events. However, plant functional traits other than at leaf control level seemed to be decisive for the drought response; below-ground processes and related plant traits such as root biomass and rooting depths have a huge impact on drought responses. Overall, our results emphasize the importance of preserving high functional diversity of grasslands to strengthen their resistance against extreme events, in particular in face of climate change.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- 1041 Stable isotope geochemistry;
- 1813 Eco-hydrology;