Future climate change scenarios predict greater frequency of extreme precipitation events. Experiments predominantly focus on drought events, with less attention paid to predicted scenarios of heavy rainfall events. Moreover, ecosystem functioning is usually measured as primary production, though results have been mixed as to whether drought reduces biomass or not. Combining both ends of precipitation extremes with multiple ecosystem responses is necessary to understand grassland systems regulation by future precipitation regimes.
We report on the effects of heavy rainfall relative to drought effects from a six-year rainfall-manipulation experiment in a European grassland. Grassland communities were planted at multiple diversity levels, and drought and heavy rainfall treatments were imposed by simulating 1000-year events. We focused holistically on the ecosystem and report on measured response parameters representing five ecosystem function categories: Primary production, water regulation, gas exchange, nutrient cycling, and community response.
Heavy rainfall induced significant responses in 24 of the 30 measured parameters in at least one year. Most striking were observed increases in primary production parameters, since drought showed no significant effects on any of them. Additionally, decomposition rates, mycorrhization rates and increased soil microbial biomass were observed alongside increases to available plant soil nitrogen in the form of nitrate and ammonium. Moreover, we observed changes in plant physiology and community dynamics.
In our grassland system, response dynamics for heavy rainfall were rapid and promoted increased productivity across multiple trophic levels, while drought effects initiated ecosystem-regulating functions while maintaining levels of plant biomass. Collectively, this indicates that mesic temperate grasslands can be water limited, and heavy rainfall may cause more changes than drought.