Impacts of Soil Fungal Community Shifts on Cottonwoods

Abstract

In southwestern US riparian cottonwood forests, anthropogenic changes have replaced the structuring force of seasonal flooding with novel multifactor disturbance regimes, driving these ecosystems to new states. While the impetus for restoration is high, little attention has been paid to understanding belowground feedbacks from these new drivers. Using high-throughput sequencing of environmental DNA, we compared the impacts of fires, exotic plants, restoration practices and lower levels of disturbance on soil fungal community composition and diversity across a riparian cottonwood landscape in New Mexico. We focused on mycorrhizal fungi for the benefits they may confer upon cottonwoods. We found that along a scale of increasing disturbance, relative abundances of pathotrophs and saprotrophs increased while those of ectomycorrhizal fungi decreased. Surprisingly, the impact from exotic clearing was similar to that of fire. Mature and young cottonwood stands were also similar, suggesting that across an historic landscape of diverse cottonwood age classes, soil fungal community structure may have varied little. Our methods will help resource managers identify supportive soils for cottonwood reforestation and monitor the responses of vital belowground communities to restoration or new disturbances.