Abstract
Abstract Climate change predictions suggest that summer droughts will become more intense and recurrent in Europe. While drought‐induced reductions in grassland primary productivity are well documented, the drivers behind drought resistance (the capacity to withstand change) and recovery (the capacity for recovery of function) of above‐ and below‐ground biomass remain poorly understood. Across eight grasslands differing in plant community productivity (CP), we investigated the effects of summer drought on plant and soil microbial variables, plant nutrient content, and soil nitrogen (N) availability. We examined the linkages between CP, soil N, drought responses of plant and microbial communities, and relative drought responses of plant and microbial biomass. Plant and microbial variables were recorded at the end of a 3‐month rainfall exclusion period. Plant variables were also assessed during a 10‐month drought recovery period. Experimental drought decreased plant biomass and increased plant C:N ratios, but had no effect on total microbial biomass across sites. Instead, drought caused shifts in plant and microbial community structures as well as an increase in arbuscular mycorrhiza fungi biomass. Overall, plant biomass drought resistance was unrelated to CP or microbial community structure but was positively related to drought resistance of forbs. In the month after rewetting, soil N availability increased in droughted plots across sites. Two months post‐rewetting, droughted plots had higher plant N concentration, but lower plant N use efficiency. The short‐term drought recovery of plant biomass was unrelated to CP or soil N availability, but positively related to the response of grass biomass, reflecting incomplete recovery at high CP. Ten months after rewetting, drought effects on plant biomass and plant N content were no longer apparent. Synthesis. Our results suggest that drought resistance and recovery are more sensitive to plant community composition than to community productivity. Short‐term recovery of plant biomass may also benefit from increased soil N availability after drought and from a high abundance of soil fungi in low productivity sites. Our findings underline the importance of plant functional groups for the stability of permanent grasslands in a changing climate with more frequent drought.
Highlights
Climate change predictions suggest that central Europe will experience longer and more intense summer droughts in the future accompanied by an increase in summer temperatures (IPCC, 2013)
Across eight grasslands differing in plant community productivity (CP) we investigated the effects of summer drought on plant and soil microbial variables, plant nutrient content and soil nitrogen (N) availability
Drought caused reductions in the biomass of all plant functional groups, but only grass biomass mirrored the interaction between drought and CP observed for total plant biomass (Fig. 1C)
Summary
Climate change predictions suggest that central Europe will experience longer and more intense summer droughts in the future accompanied by an increase in summer temperatures (IPCC, 2013). Drought-induced decreases in soil moisture have direct and indirect effects on plant productivity (Frank et al, 2015). Variation in the drought resistance of biomass production across grasslands may partly be linked to differences in plant stress tolerance (Grime et al, 2008; Volaire, Barkaoui, & Norton, 2014) and/or plant productivity, since high biomass systems with high water demand are expected to decrease soil moisture and increase ecosystem vulnerability to drought (Wang, Yu, & Wang, 2007). Drought-induced decreases in soil moisture content may modify soil microbial activity and/or community composition with consequences for substrate diffusion, soil nutrient retention and availability which feeds back to plant productivity (Schimel, Balser, & Wallenstein, 2007; Bloor & Bardgett, 2012; Frank et al, 2015). Information on the effects of drought on coupled plant/microbial responses under field conditions is lacking (Mariotte, Robroek, Jassey, & Buttler, 2015; Karlowsky et al, 2017)
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