Implications of Litterfall Dynamics and Stoichiometry for Nutrient Cycling in Subtropical Acid Rain Regions

Selecting appropriate tree species is crucial for mitigating soil acidification and restoring biogeochemical cycles in subtropical acid rain regions. The objective of this study was to elucidate the influence of species selection on litter nutrient dynamics and its implications for soil carbon (C) and nitrogen (N) cycling. To achieve this, three forest types were examined at the Tieshanping Forest Farm (Chongqing, China). Twelve plots were established, including pure stands of Pinus massoniana Lamb. or Cinnamomum camphora (Linn) Presl, and mixed stands of these species. Litterfall was collected monthly (December 2020–November 2021) to determine pH, C, N, phosphorus, potassium, lignin, and cellulose contents, alongside potential nutrient returns and stoichiometric ratios. Results indicated that while total annual litterfall production did not differ significantly among the forest types, their seasonal dynamics varied distinctly, with C. camphora and P. massoniana peaking in spring and summer, respectively. Furthermore, C. camphora stands exhibited significantly higher annual P and K returns. Conversely, P. massoniana litter was characterized by the highest C:P ratio and mean annual lignin content (344.78 mg g−1), indicating lower decomposability that may restrict organic C turnover and N release. Consequently, the nutrient-rich and readily decomposable litter of C. camphora is more effective than P. massoniana at alleviating soil acidification and facilitating healthier C and N cycling. These findings highlight the critical role of aboveground litter quality in driving belowground soil C and N dynamics, providing a vital scientific basis for species selection during ecological restoration in acid rain-affected areas.