Ongoing climate change increases the frequency and intensity of extreme climatic events with unknown consequences for ecosystem functioning. Currently, ecological experiments predominantly focus on drought impact, with less attention paid to predicted scenarios of heavy rainfall events. Moreover, ecosystem functioning is usually measured by focusing on primary production, though results have been mixed as to whether extreme climatic events elicit extreme ecological responses across multiple response parameters. Combining both ends of precipitation extremes with multiple ecosystem responses is necessary to understand grassland systems regulation under future precipitation regimes.
We report on the impacts of extreme drought events relative to heavy rainfall from a six-year (2005 - 2010) precipitation manipulation experiment in a Central European mesic grassland. Grassland communities were planted at multiple diversity levels, and drought and heavy rainfall treatments were imposed by simulating 1000-year events based on the local climate records. We report on 30 measured response parameters representing five categories of ecosystem functioning: Primary production, water regulation, carbon fixation, nutrient cycling, and community response.
Results/Conclusions
Heavy rainfall induced significant responses in 24 of the 30 measured parameters in at least one year. Most striking was an observed increase in primary production under heavy rainfall, while drought had no significant effect. Additionally, decomposition rate, mycorrhization rate, and soil microbial biomass increased due to heavy rain spells with increasing availability of soil nitrogen in the form of nitrate and ammonium. Moreover, we observed changes in plant physiology and community dynamics. Collectively, this indicates that mesic temperate grasslands can be water-limited, and heavy rainfall may cause more ecological changes than drought.
We concluded that our mesic grassland communities are drought resistant in terms of primary production. In this system, response dynamics to heavy rainfall were rapid and promoted increased productivity across multiple trophic levels, while drought effects initiated ecosystem-regulating functions to maintain levels of plant biomass. This suggests that climate change research should focus on both severe drought and heavy rainfall effects to understand the linkages between extreme climatic events and resilience of ecological responses.