Effect of forest conversion to tea plantations on soil aggregate stability and its stoichiometry of carbon, nitrogen and phosphorus

Background and Aims Land-use conversion from natural forest to agricultural land can profoundly alter soil structure and nutrient dynamics. However, the interactive effects of land management (LM) and plantation age (PA) on soil aggregate stability and C:N:P balance following forest-to-tea conversion remain poorly understood. Methods We investigated aggregate-associated nutrients in sloping (ST) and terraced (TT) tea plantations across a chronosequence (<20, 20-40, >40 years), with adjacent natural forest (NF) as a reference. Results Forest-to-tea conversion significantly reduced the proportion of >2 mm aggregate, with terraced plantations at both TT _<20 and TT _>40 showing reductions of 16.7% and 17.5%, respectively, compared to NF. Aggregate stability (MWD and GMD) was strongly governed by the interaction between LM and PA. Among all treatments, ST _>40 exhibited the highest aggregate stability, coinciding with its high root biomass and proportion of 2-1 mm macroaggregates. Aggregate-associated SOC and TN gradually recovered with PA, reaching levels comparable to NF in ST _>40 and TT _20–40 . However, TP declined continuously with PA under both management practice, leading to increases in soil C:P and N:P ratios exceeding 140%, identifying P as the primary limiting nutrient. Path analysis revealed that aggregate stability was directly determined by aggregate-size distribution, with positive effects from 2-1 mm macroaggregates and negative effects from <0.25 mm microaggregates, while nutrient stoichiometry mediated indirect effects of management and age through microbial biomass and root inputs. Conclusion These findings highlight trade-offs between erosion control and nutrient management in tea plantations, emphasizing the need for age- and practice-specific strategies and P-mobilizing practices to address stoichiometric imbalances in intensively managed subtropical soils.