Response of soil organic carbon stability and sequestration to long-term phosphorus application: insight from a 9-year field experiment in saline alkaline paddy soil.

Background and aims: Phosphorus (P) addition is considered key factor in soil organic carbon (SOC) cycle. The potential impact mechanisms of P addition on SOC stability and sequestration were explored in saline-alkali soil. Methods: A 9-year field experiment was arranged in the Yellow River Delta, which included (i) CK, no fertilization; (ii) NK, N and K fertilizer application; (iii) NP1K and (iv) NP2K, NK plus 28 and 56 kg P ha−1 year−1 application, respectively. Results: Compared with NK, the content of particulate OC (POC) was significantly increased by 29.9% and 26.8% in NP1K and NP2K treatments, respectively. The variation trend of aromatic-C and microbial biomass C (MBC) was similar to that of POC, which were positively corelated with SOC sequestration. Meanwhile, C and specific C mineralization rate (CMR, SCMR) were increased with P addition, which might be due to the decrease of carboxyl or amidogen-C. Moreover, owing to the increase in root biomass, SOC sequestration was significantly increased by more than 9.3% with P addition. Redundancy analysis further indicated that root biomass was the main factor in regulating SOC. While the CMR and SCMR were higher of NP2K treatment than those of NP1K treatment, this might result in SOC sequestration was no significant change between the two treatments. Conclusion: Long-term low-level P fertilization is a preferable practice to increase POC, stable chemical composition and MBC, and then SOC sequestration. These findings provide important insights into how long-term different levels of P application regulate soil C cycling in saline-alkali paddy soil. [ABSTRACT FROM AUTHOR]