Impacts of ungulate grazers on plant root associated fungi in tallgrass prairie

Background/Question/Methods

Once the dominant and most influential grazer on the great plains, the plains bison (Bison bison) is now a minority in their homelands. Cattle currently outnumber bison 200:1. The near eradication of the keystone species bison, and introduction of cattle into the plains has caused many changes within ecosystem relationships. This project focuses on the impacts of Native and non-native ungulate grazers on symbiotic root mycorrhizal fungi-vegetation relationships, in an area of native tallgrass prairie, at the Konza Prairie, KS, USA. The research focuses on six plants: Andropogon gerardi, Bouteloua curtipendula, Schizachyrium scoparium , Amorpha canescens, Salvia azurea, Ambrosia psilostachya, which were chosen based on their cultural tie to the Indigenous people of the plains, as well as their relative abundance in the study areas. Plant roots and soil core composites were gathered along replicate transects in bison grazed, cattle grazed and ungrazed watersheds. DNA extraction, PCR amplification, and chloroform fumigation were performed to assess the fungal species presence, diversity, and abundance. We predicted that fungal biomass and diversity in soil and root-associated samples would be higher in grazed areas due to animal dispersal of spores, and that bison and cattle would have different effects on fungal communities.

Results/Conclusions

The relative distribution of focal plants was affected by grazing, in that A. gerardi had a lower percent cover in bison grazed than cattle grazed areas, and highest cover in ungrazed areas, and S. scoparium showed a similar pattern (all P≤0.01). A. canescens showed the inverse pattern (P< 0.05), but the other plants did not vary significantly in cover between grazing treatments. Total microbial biomass was marginally higher in ungrazed soils (P=0.04, post-hoc tests P< 0.1), and the carbon:nitrogen ratio of microbial biomass was higher under cattle grazing than bison grazing or no grazing (P< 0.001, post-hoc tests P< 0.002). Previous work has shown that plant root growth is lower in bison grazed areas as a result of grazing-promoted fertility, and that fungi have a higher average carbon:nitrogen ratio than bacteria. So, the data in hand suggest that lower plant root growth could reduce total microbial biomass in both bison and cattle grazed areas, but that cattle may change the relative abundance of soil fungi as compared to native prairie with native ungulate grazers. DNA extraction and PCR for the fungal sequence library preparation is complete, and diversity data will inform our final predictions.