Effects of patch-burn grazing on above- and belowground communities in invaded grasslands

Grasslands are threatened by invasive plants, but targeted management strategies can help mitigate invaders and restore biodiversity and ecosystem functions. Patch-burn grazing, which combines prescribed fire with livestock grazing, has been proposed as a strategy to promote heterogeneity and restore invaded grasslands. Nonetheless, the immediate and legacy effects of fire and grazing on plant composition and belowground dynamics in patch-burn systems remain underexplored. In a 64-ha pasture, we found that soil fungi and protists, but not bacteria showed significant shifts in response to patch-burn grazing over a 4-year fire return interval. Invasive grasses, such as Kentucky bluegrass, exhibited faster recovery than native grasses, and this recovery was associated with specific microbial taxa. For example, members of specific bacterial orders such as Geobacterales, Cantharellales, and Corticiales were associated with different recovery stages. We found an increase in fungal and protist saprotrophs and a decrease in mycorrhizal fungi. Our stochasticity and determinism analysis revealed that patch-burn grazing had a deterministic impact on fungal communities. Microbial network connectivity and betweenness centrality changed in response to fire legacies with members of the Cercozoa protists emerging as keystone taxa. These findings highlight how patch-burn grazing influences plant and microbial succession in invaded grasslands. Overall, our study reports that while native plant species may benefit from patch-burn in the short term, invasive grasses recover rapidly after two years. Therefore, despite the potential of patch-burn management, further research is necessary before this strategy can be widely adopted.