Divergent response of surface and deep soil nitrogen mineralization to nitrogen and phosphorus additions in a subtropical forest
摘要
N input has a strong impact on soil net N mineralization. P input mitigates the impact of N input in subtropical forests. Soil net N mineralization is driven more by abiotic than biotic factors. Soil protists are more sensitive to N input than bacteria and fungi.
Soil net nitrogen (N) mineralization rate (Nmin) is closely linked to N availability in forests, while the combined impact of N and phosphorus (P) deposition on Nmin remains unclear in subtropical forests. In this study, the impact of N and P input on the dynamics of Nmin via laboratory incubation approach as well as the controlling factors along the soil depths (i.e., 0–20, 20–40, 40–60, 60–80 cm), were investigated based on a long-term N and P simulated field experiment in a subtropical forest. The addition of N significantly increased soil Nmin by 44%–400%, while P addition mitigates the impact of N deposition. Vertical stratification of soil properties and microbial traits was detected with surface soils exhibiting higher nutrient availability and microbial diversity than deep soils; while fungal diversity showed notable increase with depth. Linear mixed-effects models and structural equation modeling analyses suggested that soil abiotic factors including NH4+-N, NO3−-N, and dissolved organic carbon, play primary roles in driving Nmin than biotic factors, indicating the role of soil substrate in controlling Nmin in subtropical forest soils. These findings demonstrate the depth-dependent effect of N and P on soil Nmin in P-limited subtropical forests, shedding new light on the availability of N in the context of global change.