The influence of soil nutrient status on mycorrhizal symbioses: Consequences for plant community diversity

Arbuscular mycorrhizal fungi (AMF)-plant symbioses are important in tallgrass prairie communities. However, not all plant species benefit equally from AMF.  Previous research has shown that co-occurring warm-season (C4) and cool-season (C3) plants in Kansas prairies vary in their dependence on AMF.  Consequently, community diversity—specifically the relative abundance of C3 vs C4 plants—depends on whether AMF are present.  Previous work has also shown that soil nutrient levels can shift the costs and benefits of the AMF-plant symbiosis along a continuum of mutualism to parasitism.  In a field experiment in northeast Kansas we investigated the interaction between AMF, plant diversity, and soil N:P.  We predicted that if plant functional groups vary in their dependence on AMF, and if the benefits of AMF to plants vary depending on soil nutrient levels, then the influence of AMF on community diversity will shift along a nutrient gradient.  Preliminary results show a nutrient x fungi effect on plant diversity.  At high nitrogen levels, AMF increased plant community richness and evenness; in low-nitrogen soils, plant diversity declined in the presence of AMF.  Our work suggests that soil nutrient levels can impact plant diversity via plant-fungal mutualisms. Consequently, successful restoration of plant diversity in grasslands impacted by anthropogenic nutrient enrichment may depend on the presence of AMF.