Plant–soil feedback (PSF) is a key mechanism that can facilitate tree species coexistence and diversity. Substantial evidence suggests that species-specific soil-borne pathogens around adult trees limit the performance of home (conspecific) seedlings relative to foreign (heterospecific) seedlings. However, the underlying mechanism remains largely elusive.

Here, we conducted a reciprocal transplant pot experiment using seedlings and from two tree species, Pinus massoniana and Lithocarpus glaber that are dominant and coexist in a subtropical, evergreen, broad-leaf forest in Gutianshan, Zhejiang Province of eastern China. We examined how seedlings from the two tree species responded to soils originating from underneath their own versus the other tree species, using a full-factorial design. Additionally, we added a fungicide (benomyl) to half of the pots to evaluate the role of soil-borne fungi on seedling growth.

We found that the seedlings from L. glaber grew better in soils that were collected from beneath the canopy of P. massoniana, while seedling growth of P. massioniana was not affected by soil origin. The addition of fungicide benomyl resulted in a shift towards more positive PSF effects for L. glaber, indicating that L. glaber seedlings performed better in their own soils than in soils from P. massoniana in the absence of fungi. Our findings highlight the importance of soil-borne pathogenic and ectomycorrhizal fungi in driving PSF, and indicate that PSF may promote the coexistence of two subtropical tree species by reducing the performance of L. glaber in own soils.