Effect of exogenous phosphorus input on the availability and turnover characteristics of soil carbon pool in agro-riparian wetlands

Exogenous nutrients significantly influence wetland ecosystems.In particular, the invasion of exogenous nitrogen (N) and phosphorus (P) significantly influences carbon cycle in wetland soils which further changes global carbon cycle in soil-atmosphere continuum.While there are currently several studies on exogenous N, the study of exogenous P is still lacking.To explore the effect of the input of exogenous P on the availability and turnover characteristics of soil carbon pool in wetlands, an experiment was designed for the simulation of the dynamics of exogenous P accumulation.The study simulated additive P gradient rates of 0(P-0), 5% (P-5), 10%(P-10), 20%(P-20), 30%(P-30) and 60%(P-60) relative to initial total phosphorus (TP) content of sampled soils.Superphosphate was the mode of addition of P to the soil coupled with the simulation of laboratory data.The changes in characteristics of soil carbon composition and biochemical indicators of P with the input of different levels of exogenous P were analyzed using conventional biochemical testing methods.The study also integrated several other factors for Pearson correlation analysis.The results showed that soil TP and Olsen-P contents strictly followed the loading rates of superphosphate, with a notable increase in microbial biomass phosphorus (MBP).The activity of acid phosphatase (AcP) was significantly suppressed by P addition.Dissolved organic carbon (DOC) and microbial biomass carbon (MBC) increased with increasing inputs of exogenous P, while total organic carbon (TOC) decreased at a maximum rate of 23%.For active organic carbon components of the soil, highly labile organic carbon (HLOC) was 54% higher under P-60 treatment than under the control group (P-0).Then recalcitrant organic carbon (ROC) content remarkably decreased with increasing input of exogenous P, with a maximum rate of decline of 22%.To certain extent, the results indicated that soil carbon pool was activated and the efficiency of availability increased.However, mid-labile organic carbon (MLOC) and labile organic carbon (LOC) almost had no change with increasing input of exogenous P.The MLOC and LOC ingredients were stable in the soil.The activities of β-1, 4-glucosidase (βG) and cellobiohydrolase (CBH) significantly increased with increasing levels of exogenous P, but the activity of dehydrogenase (DH) remained largely unchanged.For the analysis of mineralization characteristics of soil organic carbon (SOC), exogenous P addition significantly accelerated SOC mineralization rate.The cumulative mineralization increased with increasing addition of exogenous P.Potential mineralization potential of SOC was positively correlated with the addition of exogenous P.From the above, exogenous P input increased the consumption of soil carbon pool and transformed soil carbon pool from steady state to unstable state.It also increased the activity and content of biological enzyme by stimulating microbial activity.In summary, the availability and turnover rates of wetland soil carbon pool and the risk of wetland soil carbon output significantly increased under exogenous P input.