Effects of mycorrhizal fungi and the functional diversity of plants on ecosystem functioning: an experimental approach

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. AMF treatment increased plant biomass production, but no effect of plant functional diversity on biomass was observed. Additionally, no interactive effects of functional diversity and mycorrhizal treatment on biomass were found. The impact of AMF diversity on plant growth was context-dependent and differed between above- and belowground biomass. Root production consistently decreased with higher AMF richness, while leaf production was mainly controlled by grass dominance, leading to grass-dominant communities benefiting more from low-diversity AMF inocula. This research suggests that a full understanding of AMF-plant interactions requires accounting for the complexities of nutrient economy mechanisms. It also underscores the importance of integrating soil microorganisms and mycorrhizal-plant relationships into studies of ecosystem functioning, highlighting the need for a comprehensive view of belowground processes.To assess inoculation success, percentage colonization by AM fungi of the roots of the plant individuals in experimental plant communities was estimated from a subset of samples for every treatment combination (n = 5 x 3 x 2 = 30 individual samples).DNA was extracted from 0.5 g of frozen soil with the DNeasy PowerSoil Pro Kit (Qiagen) following the companys instructions. AM fungal sequences were amplified from soil DNA extracts using the fungal-specific primers for the second internal transcribed spacer (ITS2) ribosomal RNA gene region: forward primer - fITS7 (5'-GTGARTCATCGAATCTTTG-3') (Ihrmark et al., 2012); reverse primer - ITS4 (5'-TCCTCCGCTTATTGATATGC-3') (White et al., 1990). These primers also included the Illumina sequencing primer sequences attached to their 5 ends.