Forest-to-plantation conversion reshapes C:N:P coupling across soil–microbe–enzyme systems

Forest conversion to plantations represents a major global land-use change with profound consequences for soil nutrient cycling and strongly impacts coupled carbon (C), nitrogen (N), and phosphorus (P) stoichiometry across ecosystem compartments. Building on stoichiometric homeostasis theory and ecosystem feedback concepts, we conducted a global meta-analysis of 126 studies to quantify how forest-to-plantation conversion alters C:N:P ratios in plant litter, soil pools, microbial biomass, and extracellular enzyme activities, and to identify the key drivers of these responses.

Overall, forest conversion to plantations was associated with declines in soil C and N contents, microbial biomass, enzyme activities, and soil C:P ratios, whereas microbial biomass C:P ratios increased. These contrasting responses indicate a decoupling of P from C and N cycling following conversion, reflecting enhanced P recycling and intensified P limitation for soil microorganisms. Soil and microbial C:N and N:P ratios had stabilizing feedbacks, showing limited directional change despite large shifts in pool sizes, whereas C:P ratios displayed intensifying feedbacks, particularly within microbial biomass and enzyme activities. These patterns suggested weak microbial stoichiometric homeostasis in response to changes in resource quality and availability within plantation systems. Plant functional traits strongly modulated stoichiometric outcomes. Narrow C:P and N:P ranges in coniferous species pointed to tighter nutrient regulation compared with broadleaf systems, and conversion effects differed markedly depending on plantation type. Litter quantity and quality emerged as key regulators of soil C and N pools, whereas soil P pools responded weakly to conversion, highlighting efficient internal P recycling. Microbial and enzymatic stoichiometric imbalances increased after conversion, indicating growing nutrient divergences between microbial demand and resource supply, except in coniferous-to-coniferous conversions, where some imbalances decreased. Random Forest analyses identified soil pH and climatic variables as dominant abiotic controls of soil stoichiometric responses, while leaf, root, and litter C:N:P ratios were the primary biotic drivers of microbial biomass and enzyme stoichiometry.

This meta-analysis provided the first global, cross-compartment synthesis of C:N:P stoichiometry responses to forest-to-plantation conversion. By linking biogeochemical shifts to microbial homeostasis and ecosystem feedback mechanisms, our findings revealed multidirectional and decoupled nutrient responses that challenge simplified assumptions of uniform nutrient limitation. These insights underscore the importance of species selection, residue management, and long-term monitoring to mitigate stoichiometric imbalances and sustain nutrient cycling in plantation ecosystems.