Forb species benefit more than grasses from a diverse arbuscular mycorrhizal fungal community in semi-arid grasslands
Abstract. In exchange for the carbon assimilated by plants, mycorrhizal fungi increase plant nutrient supply, protect them against pathogens and drought, and influence soil formation and aggregation, among other benefits. These processes, in turn, affect the diversity of vegetation and various ecosystem functions, including biomass production. While plant functional diversity is known to mediate mycorrhizal effects on dryland diversity and functioning, experimental tests of such effects are scarce. We conducted an experiment using simplified grassland communities with forbs and grasses to evaluate the effect of arbuscular mycorrhizal fungi (AMF) and their diversity on plant biomass production. At the community level, the impact of AMF richness on plant biomass production was negative, with shoot and root production consistently decreasing with higher AMF richness. However, the biomass response was somewhat mediated by plant functional group identity, revealing that forb species benefit more than grasses from a diverse AMF community. Specifically, leaf production was controlled by grass dominance, leading to grass-dominant communities with low-diversity AMF inoculum producing the most shoot biomass. This research suggests that a full understanding of AMF–plant interactions requires accounting for the complexities of nutrient economy mechanisms, and joint assessment of AMF community diversity and plant functional traits or groups enables us to disentangle these mechanisms in semi-arid grasslands.