Differences in the effects of broadleaf and coniferous trees on soil nematode communities and soil fertility across successional stages

Purpose Soil nematodes are among the most important fauna in soils and participate actively in soil ecological processes. However, whether and how soil nematodes are involved in the effects of tree species type on soil fertility remain unclear, especially during subalpine forest secondary succession. Methods A monoculture pot experiment of two broadleaf ( Betula platyphylla and Betula albosinensis ) and two coniferous ( Picea asperata and Abies faxoniana ) trees, using sterilized soils inoculated with unsterilized soils beneath dominant plants from different successional stages, was conducted in a greenhouse. After a period of plant growth, soil nematode communities and soil fertility in each pot were investigated. Results Significant differences were noted in nematode community composition under the broadleaf and coniferous trees. Coniferous trees accumulated more abundant microbivores and omnivore-predators than broadleaf trees. Moreover, the contrasting effects of tree species type on soil nematode communities were associated with successional stages, with the greatest differences noted in the early successional stages. In addition, soil nematodes might play a significant mediating role in the effects of broadleaf and coniferous trees on soil fertility. However, the indirect regulatory effects induced by soil nematodes weakened with the successional stages. Conclusion Overall, our study suggested that tree species type might affect soil fertility by regulating soil nematode communities across successional stages. Compared with broadleaf trees, more abundant microbivores under coniferous trees might contribute to the improvement of soil nitrogen mineralization but not to the increase in soil carbon storage, which might be limited by new carbon input into soils.