More than a decade of slight grazing enhances soil phosphorus availability rather than storage in slight salinization wetlands

Grazing is the dominant and most pervasive land use across wetlands worldwide. Soil salinization poses an increasing threat to inland wetlands. Although the importance of soil phosphorus (P) availability in supporting net primary productivity and ecological functions in wetland ecosystems is well established, studies on the effects of grazing and salinization on soil P storage and availability remain limited. To address this gap, this study investigated the effects of four grazing intensities (none, slight, moderate, and heavy) and four salinization levels (none, slight, moderate, and severe) on the soil P content and availability over 13 years. Our results revealed that grazing and salinization significantly influenced soil P storage and availability. Total P (TP), organic P (Po), inorganic P (Pi), and available P (AP) decreased with increasing salinity. TP, Po, and Pi did not differ significantly between the non-salinized and slightly salinized wetlands. However, slight grazing in slightly salinized wetlands significantly increased the AP content. The TP and AP was predominantly governed by a combination of soil organic matter, nitrate nitrogen, and bacterial abundance. Partial least squares structural equation modeling revealed that grazing and salinization affected AP by altering soil abiotic properties, which in turn regulated soil biotic properties related to AP. Grazing also indirectly affected AP by directly affecting soil biotic properties. It is concluded that combined grazing and salinization reduce soil P stocks. However, slight grazing in slightly salinized wetlands enhanced P availability. These findings elucidate the ecological implications of grazing within wetland ecosystems, offering a robust theoretical framework for the adaptive management of salinized wetlands.