Nutrient cycles in transition: C:N:P stoichiometry by forest conversion to plantations

According to stoichiometric homeostasis, organisms can maintain the content of elements and their ratios stable to ensure optimal growth; principles of terrestrial ecology related to ecosystem feedback postulate that mechanisms exist to help resist pool change. However, few tests of these hypotheses have been done to reveal responses of soil pool C:N:P stoichiometry related to land use change. We conducted a meta-analysis of 126 studies to uncover the effects of forest-to-plantation conversion on the C:N:P stoichiometric balance of soil pools and processes. Soil C and N contents, microbial biomass, enzyme activities, and soil C:P decreased under the conversion. Microbial C:P increased, and microbial biomass showed a weak homeostasis relative to resource change. These results suggested the presence of amplifying feedback in soil and microbial biomass pools to the shifts in litter quality. Stabilizing feedbacks were revealed for C:N and N:P for soil and microbial pools and activities of enzymes. The soil C:N, N:P, and C:P ratios were regulated by pH and climatic variables; leaf, root, and litter C:N, N:P, and N:P ratios were the main factors driving microbial and enzyme activity stoichiometric responses. These results indicate decoupled responses of soil C:N:P pools to land use conversion, regulated by multidirectional ecosystem feedback.