Effects Of Aquaculture Ponds Returning To Mangrove On The Active Components And Stability Of Soil Organic Carbon Pool

Mangroves are one of the most productive ecosystems in tropical and subtropical coastal zones,and play an extremely important role in purifying water bodies,maintaining biodiversity and carbon sink functions.In recent years,the implementation of the action to return aquaculture ponds to mangroves has gradually restored the area of mangroves in my country.Therefore,the study on the impact of returning aquaculture ponds to mangroves on the composition and stability of soil carbon pool is of great significance to reveal the law of carbon cycle of mangrove restoration wetland,improve the relevant policies of mangrove restoration and conservation,and help China achieve the goal of"double carbon".Based on this,this paper selects the soil in a typical ecological restoration area of returning aquaculture ponds to mangrove as the research object,and explores the effects of returning aquaculture ponds to mangroves on soil carbon composition and stability.The main findings are as follows:（1）Returning the aquaculture ponds to mangroves increased the soil water content,salinity,and total nitrogen content of 0-30 cm for mangroves to a certain extent,and significantly decreased soil p H and bulk density,while the total soil phosphorus content did not change significantly.The content of soil available phosphorus increased significantly under natural restoration treatment（P<0.05）.The soil organic carbon,soil liable organic carbon（LOC）and dissolved organic carbon（DOC）content increased after the pond was returned to mangroves.Although soil microbial biomass carbon（MBC）content increased overall（P<0.05）,there was no significant difference in Zhanjiang and Beilun Estuary（P>0.05）.Correlation analysis showed that the changes of soil organic carbon and its components were significantly correlated with soil water content,total nitrogen and total phosphorus content.In addition,returning the pond to the wetland improved the activity of the wetland soil carbon pool and the carbon pool management index for the mangroves.（2）After returning the ponds to mangroves,the 0-30 cm soil layer of the restored mangrove wetlands was still dominated by 20-2000μm grain size sand,but the proportion of large aggregates in the soil decreased,and the soil aggregate stability parameter MWD（mean weight diameter）,GMD（geometric mean diameter）and DR_0.25 decreased.In general,the return of the pond to the wet reduced soil aggregate stability for mangroves.Although soil aggregate stability decreased,macroaggregate carbon content increased in the two restored mangrove wetlands.The main environmental factors affecting the distribution and stability of aggregates were soil water content,salinity and p H（P<0.05）.（3）After returning the ponds to mangroves,the chemically bonded organic carbon（Ca-SOC,Fe（Al）-SOC）in the soil layer of 0-30 cm in the artificially restored mangrove wetlands increased as a whole,while the chemically bonded organic carbons in the naturally restored wetland soils increased.The difference in organic carbon content was not significant,but the residual SOC content increased in the restored mangrove wetlands.Correlation analysis showed that there was a significant positive correlation between soil chemically bonded organic carbon and total nitrogen content（P<0.01）.（4）The diversity and relative abundance of soil bacterial communities increased after the pond was returned to mangroves,but the diversity and relative abundance of soil fungal communities decreased.Among them,Firmicutes,Proteobacteria,and Chloroflexi soil bacteria are the main bacterial phyla for restoring mangrove wetlands,Ascomycota and Basidiomycota respectively.Soil fungi were the main fungal phyla for restoring mangrove wetlands,and the relative abundances of major bacterial and fungal genera were significantly affected by soil physical and chemical conditions（mainly water content,salinity）and the content of organic carbon and its active components（P<0.05）.