Ecosystem functions are threatened by both recurrent droughts and declines in biodiversity at a global scale, but the drought dependency of diversity-productivity relationships remains poorly understood. Here, we use a two-phase mesocosm experiment with simulated drought and model oldfield communities (360 experimental mesocosms/plant communities) to examine drought-induced changes in soil microbial communities along a plant species richness gradient and to assess interactions between past drought (soil legacies) and subsequent drought on plant diversity-productivity relationships. We show that (i) drought decreases bacterial and fungal richness and modifies relationships between plant species richness and microbial groups; (ii) drought soil legacy increases net biodiversity effects, but responses of net biodiversity effects to plant species richness are unaffected; and (iii) linkages between plant species richness and complementarity/selection effects vary depending on past and subsequent drought. These results provide mechanistic insight into biodiversity-productivity relationships in a changing environment, with implications for the stability of ecosystem function under climate change.
Biodiversity loss and drought are substantially altering both above‐ and below‐ground terrestrial ecosystem functioning, but mechanistic understanding of plant diversity effects on the drought resistance of soil microbial biomass remains limited. We designed a mesocosm experiment to examine drought resistance of soil microbial biomass along a plant species richness gradient (five plant species richness levels based on old‐field communities). We calculated resistance of microbial biomass to drought and recorded key below‐ground properties which may influence microbial resistance to drought (i.e. microbial diversity, microbial community structure, soil carbon stocks and root biomass). Plant species richness had a positive effect on microbial resistance to drought. Variation in microbial resistance to drought was linked to properties of the fungal community in ambient soil (Shannon diversity, arbuscular mycorrhizal fungal richness and abundance) but not soil bacterial diversity. Moreover, microbial resistance to drought increased with increasing root biomass and dissolved organic carbon recorded under ambient conditions. These results highlight the importance of plant diversity for microbial biomass stability in our old‐field study system with implications for biogeochemical cycling, and suggest that indirect effects of plant species richness on labile soil carbon and soil fungi may drive resistance of soil microbial biomass to drought. Read the free Plain Language Summary for this article on the Journal blog.
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