Abstract:

Objective: This study aims to investigate the mutual feedback between decomposition dynamics of Pinus massoniana roots and soil nematode trophic groups, as well as the response to forest window transformation, providing a basis for the close-to-nature management of plantations based on biodiversity maintenance and soil nutrient improvement. Method: Forest gaps with different sizes (100, 200, 400 m²) and control plots were set up in P. massoniana plantations. Through root grading and litter decomposition experiments, the decomposition rate and nutrient release of different grades of P. massoniana roots were analyzed. Morphological methods were used to identify soil nematodes in root decomposition bags, and structural equation modeling was used to systematically explore the regulatory effects of forest gap size on root decomposition, nematode communities and soil chemistry properties. Result: 1) Forest gap size significantly affected the residual rate of root mass. The 1–3 order roots decomposed faster in 200 m² forest gaps than in 100 m² and 400 m² forest gaps, while 4–5 order roots decomposed fastest in 200 m² forest gaps during 0–360 days and 400 m² forest gaps during 360–720 days. The decomposition rate of lower-order roots (1–3 order) was higher than that of higher-order roots (4–5 order). During the decomposition process, root N and P contents generally exhibited a trend of first increasing and then decreasing. 2) Forest gap increased soil nematode abundance. The Shannon-Wiener diversity index, Maturity (c-p 2–5) and biomass of soil nematodes were the highest in forest gap of 200 m², and significantly higher than those in forest gap of 400 m² (P<0.05). With the increase of root decomposition time, the abundance and biomass of soil nematodes showed a trend of first increasing and then decreasing, reaching the highest value on the 210th day. Among them, herbivorous nematodes accounted for the highest proportion in each treatment (50.13%), followed by bacterivores nematodes (21.76%). The proportion of herbivorous nematodes remained the highest across all treatments and showed an overall upward trend with the increase of root decomposition time. 3) Root decomposition and nematode trophic groups formed a two-way feedback. Structural equation modeling revealed that root decomposition time and root mass remaining rate had a significant negative impact on the proportion of omnivorous nematodes, while omnivorous nematodes had a significant positive impact on bacterivorous nematodes, and bacterivorous nematodes had a significant positive impact on root nitrogen content. This constructed a“root-nematode-nutrient”synergistic decomposition pathway. Conclusion: Forest gap significantly affects the decomposition dynamics of P. massoniana roots and changes soil nematode diversity and community structure. P. massoniana roots regulate the composition of soil nematode trophic groups through decomposition rate and nutrient release under forest gap management. Meanwhile, the trophic groups of soil nematodes with high trophic levels control the community structure through predation, thereby affecting root decomposition and soil nutrient cycling. The forest gap of 200 m² shows the best performance in the synergistic improvement of root decomposition and soil nematode diversity. The research results provide a scientific basis for the ecological restoration of degraded P. massoniana and the sustainable management of plantations in subtropical.

Key words: Pinus massoniana plantations, close-to-nature management, root decomposition, soil nematodes, soil nutrients