Changes in fungal community composition are driven by rapid anthropogenic alterations of environmental conditions, a hallmark of the Anthropocence. We examined the responses of fungal composition (particularly arbuscular mycorrhizal fungi AMF) to human-caused atmospheric nitrogen deposition and plant species invasion.We sampled roots and bulk soils (n=6) from the dominant native chaparral shrub, Adenostoma fasciculatum, and from one invasive grass species (either Bromus diandrus or Avena fatua) at two sites. We hypothesize that (1) native shrubs will associate with both rhizophilic (‘root-loving’ e.g. Glomeraceae) and edaphophilic (‘soil-loving’ e.g. Gigasporaceae) AMF taxa, while invasive grasses will primarily form associations with rhizophilic taxa; (2) invasive grasses will harbor relatively fewer pathogens than native shrubs; and, (3) invasion and elevated soil N concentrations will reduce the abundance of edaphophilic AMF families in invaded sites. We test these hypotheses within a guild framework, using next-generation sequencing coupled with statistical modeling.
Results/Conclusions
Fungal composition responded to N deposition and plant invasion differently between roots and soils. Invasive plant species hosted a lower richness of non-AMF symbionts, and all three functional groups of AMF. We expected that AMF functional groups would be negatively associated with NO3, however edaphophilic and rhizophilic AMF richness in roots was positively associated with soil NO3. Additionally, higher soil NH4 concentrations in native soils were associated with increased edaphophilic, rhizophilic and ancestral AMF (e.g. Acaulosporaceae) richness in roots. Non-AMF symbionts abundance and richness negatively responded to higher NH4. We detected more pathogenic taxa in invasive plant roots than native plants, which matched a greater pathogen richness and abundance in soils under invasive grasses. Invasion decreased the abundance and diversity of both AMF and non-AMF symbionts, suggesting that natives host a higher diversity and abundance of some symbiotic fungal taxa.