Grassland experiments under climatic extremes: Reproductive fitness versus biomass

Too little is known about changes in plant reproduction caused by modified regimes of extreme weather events. While it is important to understand how climatic extremes affect physiological processes in leaves or roots, on a long scale, it is successful reproduction, which ultimately matters. In an experimental grassland, we investigated the vegetative response and reproductive fitness of the grasses Holcus lanatus and Arrhenathentm elatius to drought and heavy rainfall. We perform a quantitative analysis of biomass, number of flowers per inflorescences, seed weight, germination rate and establishment. Target species were sampled from three grassland assemblages (two species-communities, four-species communities with and without a legume). H. lanatus reacted with a reduced number of flowers per inflorescences and a reduced germinability to climatic extremes. Nevertheless, H. lanatus reacted with an increased seedling establishment in face of extreme weather events. However, the two investigated grass species responded differently in the same experimental communities. A. elatius reached a higher number of flowers per inflorescences, higher germination rate, and higher establishment when exposed to drought compared to control. Yet, heavy rainfall and respective water-saturated soil conditions influenced both grasses more negatively, i.e., leading to a lower number of flowers per inflorescences, germination rate and reproductive biomass, than extreme drought. This study illustrates that the impact on reproduction during short periods needs consideration when long-term responses of grassland ecosystems to climate change are assessed.