Reassembly of soil fungal communities under reforestation and herbivore exclusion

Soil fungi can help improve ecosystem restoration, yet our understanding of how fungi reassemble in degraded land is limited. Here, we studied fungal community structure using DNA metabarcoding in reforested sites following agricultural abandonment and overgrazing. We used a natural experiment in which reforestation with different numbers of tree species and deer exclusion have been applied for multiple decades. We found that local fungal richness (alpha diversity) was 1.9 to 2.9 times greater in reforested stands than in natural forests and total fungal richness (gamma diversity) was 1.3 to 1.9 times greater. These results were regardless of the number of tree species planted in the reforested stands. Conversely, reforested stands had a homogenized community structure with relatively lower degrees of compositional dissimilarity among sites within each stand (beta diversity). These findings were attributable to lower environmental heterogeneity, stronger dispersal limitation, and a comparatively shorter time since the onset of community assembly in reforested stands. Deer exclosures had no detectable effect on fungal community structure. Overall, the agricultural legacy in fungal community structure appears to have persisted for decades, even under proactive restoration of aboveground vegetation. Direct human intervention belowground may therefore be necessary for the recovery of soil biota once homogenized, which may facilitate ecosystem restoration.