Distribution,Influencing Factors And Stability Of Soil Organic Carbon In Different Mangrove Wetlands In China

Mangrove wetland is the main wetland type in subtropical and tropical coastal zone.Its high deposition rate and low organic carbon decomposition rate make mangrove wetland one of the most important carbon sinks.The distribution characteristics of soil carbon pool in different tide levels are also different due to the differences of water and salt factors,but there are still obvious deficiencies in the study of the distribution characteristics and influencing factors of soil carbon pool in intertidal zone of mangrove distribution area from the perspective of geographical regional pattern scale.Based on this,the typical subtropical and tropical mangrove distribution areas in China are selected as the research object to explore the distribution,influencing factors and stability characteristics of mangrove soil organic carbon in landward zone（LW）,middle zone（MZ）and seaward zone（SW）,which is of great significance to clarify the evolution of mangrove blue carbon functional pattern in China.The main results are as follows:（1）Mangrove vegetation biomass showed an increasing trend from SW to LW.Soil pH was inconsistent in different regions in different study areas.The water content and electrical conductivity generally increased gradually from the LW to the SW,and the bulk density generally decreased gradually from the LW to the SW.The soil particle size distribution in different study areas was inconsistent.The soil TN content decreased gradually from the LW to the SW,and the regional difference of TP and AP content in different study areas was not obvious.（2）The average content of SOC in the study area was between 15.85-37.08 g kg^-1.In general,the soil SOC content in the mangrove distribution area decreased sequentially from the LW to the SW,and the distribution characteristics of SOCS in each area were consistent with the performance of SOC.The soil EOC content in the mangrove distribution area decreased sequentially from the LW to the SW（except Zhangjiang River and Zhenzhu Bay）.The distribution characteristics of DOC content generally showed that the LW was higher than the MZ and the SW,but the results were different in the Jiulong River Estuary and Dongzhai Port.The MBC content showed inconsistent laws in different study areas.The distance from the sea significantly affected the distribution characteristics of soil organic carbon components in different soil layers（p<0.01）.（3）The distribution characteristics of soil organic carbon were affected by many factors.Correlation analysis showed that vegetation biomass had significant effects on SOC content in different soil layers（p<0.01）.On the other hand,the age of overlying vegetation in mangrove wetlands was one of the important factors affecting soil SOC content.Mangrove soil carbon pool was more affected by local environmental factors and vegetation factors,and less affected by large-scale factors such as climate and latitude.The effect of the distance from the sea on the distribution of soil organic carbon was mainly reflected in the difference of vegetation biomass and soil TN content.With the increase of the distance from the sea surface,the aboveground and underground biomass of vegetation and soil TN showed an increasing trend,and the increase of vegetation biomass and soil TN content led to the increase of soil SOC content（p<0.01）.（4）Overall,the soil water-stable aggregates in the mangrove distribution areas were dominated by the particle size<53μm,and the different tidal levels did not significantly change the distribution characteristics of each soil particle size.The SOC content of aggregates in each particle size was the lowest in<53μm particle size.There was a significant linear correlation between soil bound organic carbon and SOC and SOCS at LW（p<0.05）,while the law was opposite at SW and MZ.（5）Among the fungi in intertidal soil,Metarhizoum and Mortierella were significantly positively correlated with the contents of soil doc and SOC（p<0.05）.There was a significant positive correlation between Kluyveromyces and soil DOC content（p<0.05）.Paraphaeosphaeria was significantly negatively correlated with soil DOC content（p<0.05）.Aspergillus,Teichospora,Thalaromyces and Penicillium showed significant negative correlation with soil DOC content（p<0.05）.Among the bacteria in intertidal soil,Mycobacterium was positively correlated with soil SOC（p<0.05）.Paenibacillus,Thiohalophilus and Halothiobacillus were significantly negatively correlated with soil doc and SOC（p<0.05）.There was a significant positive correlation between Flavobacterium and soil DOC（p<0.05）.（6）There was no significant difference in the protection of aggregates in the intertidal regions.At LW,there was a significant positive correlation between soil bound organic carbon and SOC retention.The soil microbial community was diversified for the retention of soil organic carbon components.