Increased arbuscular mycorrhizal fungal biomass and diversity in soil under long-term climate drying and warming.

Arbuscular mycorrhizal fungi (AMF) support critical ecosystem services including plant resource acquisition and productivity. AMF functional traits such as relative biomass investment in root vs soil colonization or drought tolerance are thought to be evolutionarily conserved within AMF lineages and might influence AMF community responses to climate change. In a long-term field experiment, six coexisting native shrub species were exposed to 9 yr of simulated climate warming (2°C), rainfall reduction (30%) or their combination in a semiarid shrubland. Photosynthesis and aboveground plant biomass growth were reduced by warming combined with rainfall reduction, while both AMF biomass and diversity in soil increased markedly. In particular, the richness of virtual taxa of the Glomeraceae lineage increased steeply with topsoil desiccation, resulting in overwhelming dominance over other AMF lineages under warming combined with rainfall reduction. Higher AMF biomass and diversity in soil under warming combined with rainfall reduction suggests increased carbon investment in mycorrhizal fungi by climatically stressed host plants. High tolerance to soil drying appears to be widespread across the Glomeraceae, which may enable AMF in this lineage to buffer the impacts of a drier climate on host plants through effective phosphorus acquisition from dry soil and enhanced plant water use efficiency.