Near-natural conversion of plantations primarily enhances the abundance and functionality of nematodes within medium-sized soil aggregates

Adopting "close-to-nature" forestry practices to rejuvenate struggling tree plantations has shown promise in restoring soil fauna. However, the micro-scale mechanisms behind these restoration efforts and their impact on soil fauna functions remain poorly understood. We replanted coniferous (Pinus massoniana) plantations with native broadleaf trees (Cinnamomum longipaniculatum) and studied the effects on soil nematodes within soil aggregates after eight years. We found the replantation influenced nematode communities differently across soil aggregates, regardless of the bulk or rhizosphere soil. Specifically, nematode abundance and carbon metabolism function ramped up mostly in medium-sized soil aggregates (0.25∼1 and 1∼2 mm). This improvement was linked to higher soil moisture levels resulting from the replantation. Meanwhile, the link between microbial biomass and nematodes flipped from negative to positive as aggregate size increased. These changes in nematode communities ultimately contributed to higher soil organic carbon content. In conclusion, the replantation exerted the strongest effects on nematode communities in medium-sized soil aggregates, ultimately regulating soil carbon cycling. This study provides valuable insights into the micro-scale restoration mechanisms of soil nematode communities. The results suggest that increasing the proportion of medium-sized soil aggregates could be more effective in promoting functional soil communities during plantation management.