Transition from N to P limited soil nutrients over time since restoration in degraded subtropical broadleaved mixed forests

Soil stoichiometry (C:N:P ratio) is an important indicator of soil fertility and plant nutrient status. To understand the impacts of the long-term restoration of degraded subtropical broadleaved mixed forests on soil stoichiometry, we employed a chronosequence to examine the responses of soil nutrient and C-N-P stoichiometry at three soil depths (0-10, 10-20, and 20-30 cm) over time (0 to 35 years) since the cessation of anthropogenic disturbances and used primary forests as a reference in subtropical Southeast China. The soil organic carbon and total nitrogen concentrations increased significantly with longer duration restoration, whereas the soil phosphorus concentration decreased. In the 33-35-year age class, the P concentration in the subtropical degraded broadleaved mixed forest was akin to the primary forest. The soil organic carbon and total nitrogen concentrations decreased with soil depth, while the soil phosphorus concentrations did not differ significantly with soil depth. The soil carbon: phosphorus and nitrogen: phosphorus ratios increased over time, whereas the carbon: nitrogen ratio decreased weakly. Soil stoichiometry ratio in the 33-35-year age class was closer to soil stoichiometry ratio in primary forests. Our results suggest that N-limitation weakens with time since restoration, but P-limitation strengthens with stand development following restoration.

Automated summary

Long-term restoration of degraded subtropical broadleaved mixed forests leads to increased soil organic carbon and total nitrogen concentrations, while soil phosphorus concentration decreases. The C:N:P ratios in the soil show changes over time, with soil stoichiometry in the 33-35-year age class approaching that of primary forests, indicating a shift in nutrient limitations during the restoration process.