Natural restoration after clear-cutting can increase the energy flux of soil nematode food web in temperate forests

Abstract

Forest restoration is expanding globally, which involves dramatic changes in energy fluxes through soil ecosystem food webs. Soil nematodes are the most abundant animals and occupy multiple trophic positions, providing an excellent method to study energy transfer processes in soil micro-food webs. However, the driving mechanisms underlying the evolution of soil nematode energy flux during natural forest restoration remain poorly understood. Here, we selected an undisturbed native forest and four natural secondary forests (20, 32, 47, and 61 years) at different recovery stages as study sites to assess the effects of forest restoration on soil nematode community structure and energy flux. Results showed that forest restoration increased the abundance and diversity of nematode communities, but different trophic groups exhibited varying responses to forest restoration. The improvement of resources and abiotic environment was a key factor in increasing nematode abundance and diversity. The increase in root biomass and microbial biomass promoted the abundance of herbivores and microbivores, further leading to an increase in the number and diversity of omnivores-predators. The total energy flux of nematode community increased with forest restoration. Compared to 20 years, the total energy flux increased by 4.12 %, 132.56 %, and 176.68 % in 32, 47, and 61 years, respectively. However, they were all significantly lower than in the primary forest stage. Multiple regression analysis showed that soil properties, microbial characteristics, and root biomass contributed most to omnivores-predators and total energy flux. The random forest analysis showed that omnivores-predators, herbivores, and root biomass were the most important biotic factors in predicting soil nematode energy flux, together explained 32.8 % of the total energy flux variation. Meanwhile, soil organic carbon (SOC) and mean weight diameter (MWD) were identified as the most important abiotic factors for predicting nematode energy flux, together explained 10.1 % of the total energy flux variation. Microbial resources (microbial biomass) mainly indirectly regulate total energy flux by affecting the microbivores. These results provide direct evidence that, as forest restoration progresses, improved nutrient availability (e.g., SOC) and soil physical conditions (e.g., MWD), along with strengthened trophic interactions within the nematode community (e.g., predator-prey dynamics), collectively drive the overall energy flux within the nematode assemblage.