Effects of multispecies management on the soil protist community in Pinus massoniana plantations in subtropical China

The decline in ecosystem services provided by monocultures has raised significant concerns, leading to the emergence of multispecies plantations as a promising management approach to forest management. Protists are the primary consumers of bacteria and fungi, and they respond sensitively to changes in vegetation composition and human disturbance. However, the ecological consequences of multispecies plantations on the protist communities remain poorly understood. This study aimed to compare protist community composition between Pinus massoniana monocultures and multispecies plantation forests by examining their differences in both topsoil (0-10 cm) and subsoil (30-50 cm). We compared the diversity, molecular ecological networks, and assembly processes of protist communities in the typical mature Pinus massoniana monocultures and overmature P. massoniana monocultures with those of P. massoniana-broad-leaved mixed plantations, broadleaf mixture plantations, and secondary forests in subtropical China. We further assessed the important drivers for shaping the protist communities. We found that (1) both forest type and soil depth significantly influenced the alpha diversity of protist communities; (2) mixing broadleaf trees with P. massoniana stands could enhance the network complexity and stability of protist communities, and could change the composition of protist communities to a level similar to that of natural forest to an extent; and (3) protist community composition was predominantly influenced by nutrient availability in the topsoil, whereas it was primarily shaped by pH and soil texture in the subsoil. These findings provided scientific guidance for mixed forest plantation in subtropical afforestation and improving P. massoniana monocultures.