Effects of extreme rainfall events are independent of plant species richness in an experimental grassland community
2019
Global climate models predict more frequent periods of drought stress alternated by heavier, but fewer rainfall events in the future. Biodiversity studies have shown that such changed drought stress may be mitigated by plant
species richness. Here, we investigate if grassland communities, differing in
species richness, respond differently to climatic extremes within the growing season. In a 3-year outdoor
mesocosmexperiment, four grassland species in both
monocultureand mixture were subjected to a rainfall distribution regime with two levels: periods of severe drought in the summer intermitted by extreme rainfall events versus regular rainfall over time. Both treatments received the same amount of water over the season. Extreme rainfall combined with drought periods resulted in a 15% decrease in aboveground biomass in the second and third year, compared to the regular rainfall regime. Root biomass was also reduced in the extreme rainfall treatment, particularly in the top soil layer (− 40%). All species developed higher water use efficiencies (less negative leaf
δ13C) in extreme rainfall than in regular rainfall. These responses to the rainfall/drought treatment were independent of
species richness, although the mixtures were on an average more productive in terms of biomass than the
monocultures. Our experimental results suggest that mixtures are similarly able to buffer these within-season rainfall extremes than
monocultures, which contrasts with findings in the studies on natural droughts. Our work demonstrates the importance of investigating the interactions between rainfall distribution and drought periods for understanding effects of climate change on plant community performance.
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