Source Characteristics Of GRSP In Mangrove Wetlands And Its Indicative Effect On Metal Transport In Aquaculture Wastewater

The glomalin-related soil protein(GRSP)is derived from the globally widespread arbuscular mycorrhizal fungi.However,studies on GRSP mostly focused on terrestrial ecosystems.In coastal wetlands,contents on GRSP’s distribution,isotope information,contribution to soil organic matter(SOM),and its feedback to human activities should be further studied.This study investigated and analyzed the content of total glomalinrelated soil protein(T-GRSP)in the surface soil of typical mangrove wetlands and its contribution to SOM.The stable isotope characteristics of GRSP and its key influencing factors were firstly clarified.We further studied the influence of long-term aquaculture effluent discharge on metal pollution in adjacent mangrove wetland,and revealed the ecological role of GRSP in it.The main findings are as follows.Through investigation and analysis of GRSP content and its contribution to SOM in 0～20 cm surface mangrove soil samples from Zhangjiang Estuary,Jiulong River Estuary,and Quanzhou Bay,it is found that GRSP can be widely deposited in mangrove topsoil.The content of T-GRSP ranged from 1.00 mg g-1 to 4.69 mg g-1;There were significant positive correlations between T-GRSP and soil organic carbon(OC),and between T-GRSP and soil total nitrogen(TN),indicating that T-GRSP was closely related to the status of surface SOM;The contribution of C in GRSP to soil OC and N in GRSP to soil TN both exceeded 3%,suggesting that GRSP,as a component of recalcitrant organic matter,is important for long-term storage of OC and TN in surface soil of coastal wetlands.Further,this study determined the isotopic information of 0-50 cm columnar mangrove soil,T-GRSP,plant tissues and tidal water,and took the lead in comparing the C,N stable isotope and C/N data of GRSP with other sources of organic matter in the wetland.The δ13C and δ15N information of T-GRSP was-25.04‰ to-22.83‰ and 3.22‰ to 7.24‰,respectively,and average C/N value of T-GRSP in the mangrove vegetation cover area was 12.95,which revealed that T-GRSP is a significant C source from land.The results of redundancy analysis(RDA)indicated that soil pH and water content were significant parameters affecting the isotope values of T-GRSP in mangrove wetlands.In addition,the simultaneous feedback of T-GRSP,isotopes and C/N values in mangrove vegetation area,mudflat and tidewater revealed that GRSP is a novel indicator.This study helps to enhance people’s understanding of the role of GRSP as a recalcitrant organic matter component in carbon sequestration in coastal wetlands,and is of great significance for accurately identifying C sources and estimating global wetland C budget.Since aquaculture effluents containing multiple metals frequently disturb mangrove wetlands around the world,this study investigated the effects of aquaculture activity on transfer and deposition of nine metals(As,Cd,Cr,Cu,Fe,Mn,Ni,Pb and Zn)in the mangrove wetland suffering from different effluent discharge histories(0,8 and 14 years).This included the whole process from feed input to effluent discharge,and then to the combination of GRSP and metals in the wetland.The results showed that the 0-50 cm columnar mangrove soils affected by effluent discharge generally had higher or similar metal loadings than the control sites,and long-term discharge would increase the potential toxicity of metals.The results of RDA showed that the 14-year effluent discharge increased the pH value and bulk density of mangrove soil,and reduced the metal-binding potential of GRSP.The characterization results of scanning electron microscopy and infrared spectroscopy further indicated that the aquaculture disturbance influenced the morphology and sturcture of GRSP.In conclusion,this study explored the binding potential of GRSP on metal pollution of aquaculture activities in mangrove wetlands,clarified the transportation path of various metals,and revealed the ecological effect and fixation mechanism of GRSP on the metals,so as to provide new insights into the future adoption of GRSP as a biological indicator and chelator for aquaculture pollution.