Effects Of Habitat Change On Soil Organic Carbon Mineralization In Coastal Wetlands Of Southeast China

As an indispensable part of global wetland ecosystems,coastal wetlands played a certain role in global carbon cycle and climate change.Soil organic carbon mineralization is an important process of CO₂ and CH₄ production and release,and its small fluctuation will affect the change of atmospheric greenhouse gas concentration,and then have an impact on global climate change.Spartina alterniflora invasion and reclamation are two major threats to the China’s coastal wetlands,which have a profound impact on soil organic carbon mineralization.Without large-scale research data,the response characteristics of soil organic carbon mineralization to plant invasion and aquaculture reclamation in coastal wetlands of China remain largely uncertainty,which limit our understanding ability in soil carbon cycle in coastal wetlands under the background of global change.To fill these knowledge gaps,we systematically studied 24 coastal wetland areas in mainland China.Field sampling campaigns were conducted in five coastal provinces of China,including Shanghai,Zhejiang,Fujian,Guangdong,and Guangxi.By using lab incubation experiment and molecular biology techniques,we determined the SOC mineralization rate,soil properties and bacterial community structure across the native mudflats,S.alterniflora wetland and aquaculture ponds.The main results showed as follows:（1）Compared with mud flat（MFs）,S.alterniflora marshes（SAs）significantly increased soil conductivity EC,Cl^-and SOC contents（P<0.05 or<0.01）.At the same time,soil texture composition was changed,resulting in a significant increase in sand content by13.80%（P<0.05）,and a significant decrease in silt content by 7.90%.Compared with SAs,aquaculture ponds（AQs）significantly decreased soil EC,Cl^-and SOC（P<0.05 or<0.01）.（2）The mean soil MBC contents was significantly higher in AQs habitat,followed by SAs habitat and MFs habitat（P<0.01）.The mean soil MBN contents was significantly higher in SAs habitat,followed by AQs habitat and MFs habitat（P<0.01）.The diversity of soil bacterial communities across the three habitat types were evaluated in terms of OTU richness,Chao1,phylogenetic diversity and Shannon indices.The alpha diversity was significantly lower in the MFs and AQs habitats as compared to the SAs habitat（P<0.05）.The soil bacterial community was dominated by Psychrobacter,Sulfurovum,Sulfurimonas,Desulfobulbus and Planomicrobium.Habitat change did not change the horizontal community composition of dominant bacteria genus in wetland soil,but affected its relative abundance to some extent.The invasion of Spartina alterniflora into mud flat increased the relative abundance of the most dominant bacteria genus Psychrobacter.After reclamation of spartina alterniflora wetland for aquaculture pond,the relative abundance of Psychrobacter decreased,while the relative abundance of Sulfurovum increased to become the most dominant bacterium.（3）Across all the sampling sites,the SOC mineralization rates in habitats MFs,SAs,and AQs during the incubation peroid varied in the ranges of 3.92–20.51,7.20–38.20,and6.62–29.95μg g^-1 d^-1,respectively.With the extended incubation time,the SOCM rates presented an peak at the 3th day,and then obviously decreased at the later stage.Overall,the mean SOC mineralization rates and SOC mineralization cumulative amounts across all sites over the incubation peroid were significantly higher in SAs habitat(20.37±2.13μg g^-1 and 159.50±69.01μg g^-1),followed by AQs habitat(16.88±2.36μg g^-1and 133.68±80.61μg g^-1)and MFs habitat(11.88±1.67μg g^-1 and 99.28±59.37μg g^-1)（ANOVA,p<0.05 or<0.01）.Based on the result of RFA,SOC content,MBC content and soil bacterial community diversity were the variables that best explained the variations in SOC mineralization rates across the three habitat types.