Tropical forest restoration promotes soil phosphorus bioavailability in SW China: Processes and predictors

Abstract

The conversion of primary forests into monoculture plantations is a widespread phenomenon in the tropics, while the restoration of abandoned agricultural lands has gained considerable attention in recent years. Phosphorus (P) is an essential nutrient with very low availability from the soil, constraining the productivity and functioning of tropical ecosystems. However, the impacts of forest restoration on soil P cycling and the underlying mechanisms remain unclear. In Southwestern China, we investigated the plant community characteristics, soil P cycling dynamics, and soil physicochemical properties under different land uses (including monoculture plantations, farmland-regenerated secondary forests, rubber plantation-regenerated secondary forests, and primary rainforests), and identified the predictors of soil available P. We found that the conversion of primary rainforests into monoculture plantations not only substantially decreased tree diversity but also modified soil P cycling (such as total, available, microbial P and phosphatase activity). In contrast, the regeneration of secondary forests (from both farmlands and rubber plantations) significantly enhanced tree diversity and improved soil physicochemical conditions compared to monoculture plantations, thereby promoting soil P bioavailability through increased soil organic carbon, microbial P and phosphatase activity. Soil organic carbon, microbial biomass P and fine root were the main predictors of soil available P, for both annual and seasonal timeframes. Notably, the soil C:P ratio exhibited a more pronounced impact on soil available P during the dry season, while acid phosphatase exerted greater influence during the rainy season. Furthermore, the presence of fine roots and leguminous trees significantly and positively influenced soil P cycling, particularly in the surface soil layers. Thus, these results suggest that establishing legumes-rich, diverse communities and ensuring organic inputs is beneficial for sustaining soil P resources in tropical areas. This work offers important guidance for policy-makers to navigate the trade-offs between conservation and production goals in land development.