纳帕海高原湿地土壤铁结合态有机碳随水位下降的分布特征OA

[Objective]This study aims to investigate the stability of soil organic carbon(SOC)in plateau wetlands under water table decline(WTD),and to clarify the distribution characteristics and key influencing factors of iron-bound organic carbon(OC-Fe).[Methods]At the end of the dry season(early June)in 2024,soil samples were collected from Napahai wetland on the southeastern edge of the Qinghai-Xizang Plateau,spanning hydrological gradients and successional types of plateau wetlands.The relative magnitudes of WTD-small,medium,and large-were represented spatially by three wetland types:swamp(S),swamp meadow(SM),and meadow(M).The forms of soil iron oxides,crystalline mineral composition,iron-bound organic carbon(OC-Fe),mineral-associated organic carbon(MAOC),and particulate organic carbon(POC)were analyzed.Redundancy analysis was employed to examine the changes in iron oxide-mediated SOC and influencing factors following WTD.[Results]Along the S-SM-M succession of wetlands with WTD,the SOC and MAOC contents in the 0-30 cm soil layer exhibited an initial decrease followed by an increase,while OC-Fe content gradually decreased.Additionally,the contributions of MAOC and OC-Fe to SOC decreased,while the concentration of POC and its contribution to SOC increased.In terms of iron oxide forms,SOC in wetlands was primarily associated with oxalate-extractable iron oxides(Feo).Along the WTD,the contents of DCB-extractable iron oxides(Fed)and pyrophosphate-extractable iron(Fep)first increased and then decreased,while Feo continued to decline,leading to reduced activity of soil iron oxides.Furthermore,the content and stability of clay minerals in wetland soil were relatively high and showed insensitivity to water table changes,thereby resulting in minimal impact on MAOC.[Conclusion]Along the WTD,the stability of the organic carbon pool in the surface soil of wetlands diminishes,as evidenced by an increased proportion of POC and a decreased proportion of OC-Fe.The binding mechanism between organic carbon and iron shifts from co-precipitation to adsorption.The main influencing factors include root exudation of organic acids,microbially driven redox reactions,and the aging of Feo.The findings provide a scientific basis for the conservation and carbon sequestration of plateau wetlands.