Soil microbes regulate forest succession in a subtropical ecosystem in China: evidence from a mesocosm experiment

Abstract

Ecological forest succession can be influenced by plant-plant interactions that exert contrasting effects on early- and late-successional species. In this study, we explored the role of indirect plant-plant interactions and the underlying microbial mechanisms in forest succession. In a mesocosm experiment, we used Schima superba, a widespread mid-successional species in subtropical China, as a model species to explore how inoculating the rhizosphere soil of Schima affected the performances of two early-successional species (Pinus massoniana and Rhodomyrtus tomentosa) and two late-successional species (Cryptocarya chinensis and Machilus chinensis). All direct and indirect correlations between plant performance and soil microbial composition were examined using partial least square path models. Schima inoculum inhibited the growth of the early-successional species but had little effect on the growth of the late-successional species. Inoculation reduced non-arbuscular mycorrhizal fungi (non-AMF) colonization in both species groups but increased arbuscular mycorrhizal fungi (AMF) colonization in the late-successional species. The percentage of root lesions in the early-successional species increased with inoculation, while that in the late-successional species decreased. Plant nutrient acquisition was not responsive to inoculation. According to the path models, soil microbes explained 51% of the growth variances in the early-successional species but barely explained any growth variances in the late species. Schima may increase the competitive advantage of the late-successional species over early-successional species by inhibiting the mutualistic association between non-AMF and the latter, which in turn may facilitate forest succession.