Agricultural land use regulates the fate of soil phosphorus fractions following the reclamation of wetlands

Over half of the Earth's wetlands have been reclaimed for agriculture, leading to significant soil P destabilization and leaching risks. To evaluate the effects of agricultural land use on soil P stability, we used sequential P extraction to investigate the long-term effects of wetland cultivation for rice and soybean on soil P fractions, including labile and moderately labile inorganic/organic P (LPi, LPo, MPi, and MPo), and stable P in Northeast China. The results showed that soybean cultivation decreased the total P by 35.9 %, whereas rice cultivation did not influence the total P content (p < 0.05). Both the soybean and rice cultivations significantly increased LPi (p < 0.05). Soybean cultivation significantly decreased the LPo and MPo compared to rice cultivation, and the latter increased MPi by 309.28 % compared with the reference wetlands (p < 0.05). Redundancy analysis indicated that pH, poorly crystalline Fe (Feca), crystalline Fe (Fec), and total organic carbon (TOC) explained similar variations in P fractions during soybean and rice cultivation (54.9 % and 49.7 %, respectively). Similarly, during soybean or rice cultivation, pH negatively influenced LPo and MPo, while Feca positively influenced MPi and LPi. Furthermore, TOC showed a positive role in LPo, and MPo, but a negative effect on LPi and MPi during rice cultivation. Hence, we concluded that the cultivation of soybean or rice create contrasting modifications to wetland soil P fractionation by altering TOC, Feca, Fec, and pH. Our study indicates that agricultural land use can regulate the fate of wetland soil P fractionation, with potential benefits to both i) P risk management in cultivated wetlands and ii) potential approaches for future wetland restoration.