Forest restoration increases energy flow through the fungal channel and decreases energy flow through the herbivorous channel in soil micro-food webs

Chinese fir (Cunninghamia lanceolata) is one of the most important economic tree species in Central South China. Several decades of successive rotation of C. lanceolata monocultures have resulted in serious ecosystem degradation. Substantial efforts are underway to convert C. lanceolata monocultures to mixed forests to restore ecosystem functions and services. However, it is unclear whether forest restoration will improve soil quality. Soil nematodes were employed as an ecological indicator of soil quality to assess soil food web structure and energy flow along a forest restoration chronosequence. The chronosequence of transformation stages include: (i) early stage C. lanceolata monocultures aged 5, 10, and 20 years old; (ii) mid-stage conifer-broadleaf mixed forest aged over 20 years old; and (iii) late-stage broadleaf forest aged over 40 years old. Our results suggest that forest restoration changed soil nematode abundance, diversity, and community composition in both dry and wet seasons. Abundance of soil nematodes increased progressively along the restoration chronosequence, peaking in the conifer-broadleaf mixed forest. The relative abundance and energy flow of herbivorous nematodes decreased progressively by 25% and 82% with forest restoration stage, respectively. Forest restoration from C. lanceolata to mixed forests increased energy flow from basal resources to fungivorous nematodes and from fungivorous to omnivorous-carnivorous nematodes by 58% and 52%, respectively. Our findings suggest that forest restoration from C. lanceolata monocultures to mixed forests increases soil biodiversity and food web energy flows to trophic groups higher in the food chain. Therefore, converting C. lanceolata plantations to mixed forests has potential to boost forest ecosystem services and promote sustainable forest management.