Global change effects on plant communities are magnified by time and the number of global change factors imposed

Global change drivers (GCDs) are expected to alter community structure and consequently, the services that ecosystems provide. Yet, few experimental investigations have examined effects of GCDs on plant community structure across multiple ecosystem types, and those that do exist present conflicting patterns. In an unprecedented global synthesis of over 100 experiments that manipulated factors linked to GCDs, we show that herbaceous plant community responses depend on experimental manipulation length and number of factors manipulated. We found that plant communities are fairly resistant to experimentally manipulated GCDs in the short term (<10 y). In contrast, long-term (≥10 y) experiments show increasing community divergence of treatments from control conditions. Surprisingly, these community responses occurred with similar frequency across the GCD types manipulated in our database. However, community responses were more common when 3 or more GCDs were simultaneously manipulated, suggesting the emergence of additive or synergistic effects of multiple drivers, particularly over long time periods. In half of the cases, GCD manipulations caused a difference in community composition without a corresponding species richness difference, indicating that species reordering or replacement is an important mechanism of community responses to GCDs and should be given greater consideration when examining consequences of GCDs for the biodiversity–ecosystem function relationship. Human activities are currently driving unparalleled global changes worldwide. Our analyses provide the most comprehensive evidence to date that these human activities may have widespread impacts on plant community composition globally, which will increase in frequency over time and be greater in areas where communities face multiple GCDs simultaneously

Plant functional groups mediate drought resistance and recovery in a multi-site grassland experiment

1.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 belowground biomass remain poorly understood. 2.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 community productivity, 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 three‐month rainfall exclusion period. Plant variables were also assessed during a 10‐month drought recovery period. 3.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 community productivity or microbial community structure but was positively related to drought resistance of forbs. 4.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 community productivity or soil N availability, but positively related to the response of grass biomass, reflecting incomplete recovery at high community productivity. Ten months after rewetting, drought effects on plant biomass and plant N content were no longer apparent. 5.Synthesis. Our results suggest that drought resistance and recovery are more sensitive to plant community composition than to community productivity (CP). 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

Data from: Plant functional groups mediate drought resistance and recovery in a multi-site grassland experiment

1. 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 belowground biomass remain poorly understood. 2. 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 community productivity, 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 three-month rainfall exclusion period. Plant variables were also assessed during a 10-month drought recovery period. 3. 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 community productivity or microbial community structure but was positively related to drought resistance of forbs. 4. 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 community productivity or soil N availability, but positively related to the response of grass biomass, reflecting incomplete recovery at high community productivity. Ten months after rewetting, drought effects on plant biomass and plant N content were no longer apparent. 5. Synthesis. Our results suggest that drought resistance and recovery are more sensitive to plant community composition than to community productivity (CP). 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

Data from: Species richness effects on grassland recovery from drought depend on community productivity in a multisite experiment

Biodiversity can buffer ecosystem functioning against extreme climatic events, but few experiments have explicitly tested this. Here, we present the first multisite biodiversity × drought manipulation experiment to examine drought resistance and recovery at five temperate and Mediterranean grassland sites. Aboveground biomass production declined by 30% due to experimental drought (standardised local extremity by rainfall exclusion for 72–98 consecutive days). Species richness did not affect resistance but promoted recovery. Recovery was only positively affected by species richness in low-productive communities, with most diverse communities even showing overcompensation. This positive diversity effect could be linked to asynchrony of species responses. Our results suggest that a more context-dependent view considering the nature of the climatic disturbance as well as the productivity of the studied system will help identify under which circumstances biodiversity promotes drought resistance or recovery. Stability of biomass production can generally be expected to decrease with biodiversity loss and climate change

Understanding ecosystems of the future will require more than realistic climate change experiments – a response to Korell et al.

Response to the editor. In response to Korell, L., et al. (2020). We need more realistic climate change experiments for understanding ecosystems of the future. Global Change Biology 26(2): 325-327

Understanding ecosystems of the future will require more than realistic climate change experiments - a response to Korell et al.

Response to the editor. In response to Korell, L., et al. (2020). We need more realistic climate change experiments for understanding ecosystems of the future. Global Change Biology 26(2): 325-327