Exogenous nitrogen enhances aboveground plant phosphorus accumulation through soil moisture and organic carbon in semi-arid grazed wetlands

Abstract

Agricultural utilization of wetlands has witnessed a continuous upward trend, with the semi-arid regions being especially prominent in this regard. These wetlands under human management have consequently emerged as crucial constituents within the agricultural ecosystem. Grazing is considered a predominant land use practice profoundly impacting nutrient cycling and redistribution in semi-arid wetlands, and exogenous nitrogen (N) from atmospheric deposition and agricultural water discharge simultaneously participated these processes. Nevertheless, the impacts of exogenous N input and grazing on phosphorus (P) distribution patterns remain nebulous, especially in the semi-arid Songnen Plain of China, where P limitation prevails. In order to address this knowledge gap, the study conducted a field experiment with four grazing intensities (natural, light, medium, and heavy) and two N addition levels (with and without) in semi-arid wetlands. The results show that grazing and N addition together affect P content in soil and plant organs. Grazing intensity generally reduces soil P, regardless of N addition, while N addition promotes soil P accumulation in natural wetlands. P content in plant organs increases with grazing intensity. Soil organic carbon (SOC), soil water content (SWC), electrical conductivity, and soil N are positively correlated with soil P but negatively correlated with P in stems and leaves. RDA shows that SWC and SOC are key factors influencing P distribution in soil and plant organs. Plant growth strategies create a positive correlation between root and soil P contents, and a negative correlation between P in stems, leaves, and soil. SEM further shows that grazing significantly affects P levels in soil and plant organs, while N addition boosts P uptake in roots and its transfer to aboveground organs, mediated by SWC and SOC. These findings show that exogenous N input alters P acquisition strategies and distribution in plant organs and soil in grazed wetlands of semi-arid regions. This study enhances understanding of P cycling and offers practical guidelines for sustainable wetland management.