Effects of migratory birds activities on the stoichiometry of soil carbon, nitrogen and phosphorus in a Carex-dominated wetland of Poyang Lake

Studying the stoichiometric characteristics of soil nutrients aids in evaluating soil quality and deciphering the coupling of soil nutrients. The influence of migratory bird activities on the dynamics of wetland soil nutrients and their stoichiometric remains unclear. We classified the central, peripheral and adjacent natural grassy areas as severe, mild, and no bird activity (control), respectively, in Donghu Carex meadow, a representative migratory bird habitat in Poyang Lake, based on flock characteristics and initial surveys. We analyzed the contents and stoichio-metry of soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) across soil depths of 0-100 cm under different intensities of migratory bird activities. The results showed that the activities of migratory birds significantly impacted nutrient levels exclusively within 0-30 cm soil. Mild activities markedly enhanced SOC and TN across 0-30 cm soil, while both mild and severe activities significantly raised TP within the same depth. For the 0-100 cm soil profiles, soil C/N ratios were 10.0, 10.8, and 9.9, C/P ratios were 23.5, 30.0, and 22.7, and N/P ratios were 2.3, 2.7, and 2.3 under no, mild, and severe bird activities, respectively. Further, mild activities of migratory birds significantly increased soil C/N, C/P and N/P ratios only within the 0-30 cm depth, while the stoichiometric ratios of all soil layer had no significant difference under severe bird activity. Soil stoichiometric ratios strongly correlated with physicochemical properties. SOC, TN, and TP primarily mediated the effects of migratory bird activity on soil carbon, nitrogen, and phosphorus stoichiometric ratios in Poyang Lake wetland. In conclusion, the influence of migratory bird activity on the stoichiometric ratios of soil carbon, nitrogen, and phosphorus in Poyang Lake wetland exhibited depth threshold (approximately 30 cm), aligning with the "Intermediate Distur-bance Hypothesis". These findings could provide a new perspective for the protection of wetlands and migratory birds.