Effects Of Soil Microbial Community On Carbon Cycle And Its Response To Warming In Coastal Wetlands Of The Yellow-Bohai Sea

Coastal wetland is the most active zone of land-sea interaction,which has its own unique hydrological,soil and vegetation environment.Its carbon accumulation flux per unite area is dozens of times higher than that of terrestrial ecosystems.It is an important resource of blue carbon sink.However,it is usually located in the most sensitive zone to climate change and the area with the strongest human activities.In a warmer world,the evolution direction and degree of carbon sink in this ecosystem is the frontier of international science and technology and key research topic of carbon cycle research.In coastal wetlands,soil microorganisms are the main drivers of soil carbon cycle.Understanding the responses of wetland microbial communities and their impact on carbon cycle in a warmer world will help reveal the feedback mechanism and direction of coastal wetlands to future climate warming.In this study,four coastal wetlands(Yancheng wetlands(CROWN I,CROWN II),Yellow River delta(CROWNIII)and Liaohe delta(CROWN IV))in different latitudes were selected.Using open-top chamber(OTC),high-throughput sequencing(16S,ITS,and metagenomics)and fluorescent quantitative PCR technology to explore the composition and function of wetland soil microbial communities and their response to warming.Then combined with the carbon decomposition test and Bradford protein assay to explore the influence of microbial community on the decomposition and accumulation of organic carbon.The highlights of this study are as follows:(1)In the coastal wetlands around the Yellow-Bohai Sea,the soil microbial community was dominated by prokaryotes,and the proportion of fungi was extremely low.Prokaryotes were mainly composed of Proteobacteria followed by Chloroflexi,Actinobacteria,Acidobacteria and Planctomycetes in all wetland samples.For soil fungi,they were mainly Ascomycota and Basidiomycota.Due to differences in environmental condition and spatial location,the microbial community structure differed significantly among sites.Mantel analysis showed that soil microbial community structure was highly correlated with edaphic factors(K,salinity,water content,organic carbon,and Fe).In the time series,except for CROWN IV,the composition of soil microbial communities did not show a regular seasonal succession.(2)The community structures of prokaryotes and fungi were found to be significantly altered by warming,and the higher latitude the more significant,and the fungi were more significant than the prokaryotes.By determining the relationship between community differences and time,warming significantly accelerated the succession rate of soil microorganisms,resulting in an increasing difference in soil microbial communities between the warming treatment and the control treatment,that is,there was a significant cumulative effect of warming on microorganisms.(3)The soil carbon metabolism process of coastal wetlands may have its own fixed and relatively stable model,with the Proteobacteria and Actinomycetes as the main contributors.However,the decomposition strategies of soil microorganism to each component of organic carbon were different among different sites.In general,the decomposition rate of each site was CROWN III > CROWN IV ≈ CROWN II ≥CROWN I.In warming conditions,the functional genes of wetland soil carbon metabolism changed significantly,with the higher latitude the more significant.Moreover,the carbon decomposition test showed that the decomposition rate of organic matter in the warming treatment at high-latitude stations(CROWN III and CROWN IV)was slightly higher than that in control treatment,but not significant.(4)GRSP,derivative of arbuscular mycorrhizal fungi(AMF),was widely distributed in coastal wetland.It contributed about 11% of soil organic carbon and was an important component of wetland soil organic carbon.Its content was controlled by the types of surface vegetation and the physicochemical properties of the soil.In the coastal wetland soil,its content was highly correlated with the chemical weathering index and various nutrient elements,implying the contribution of arbuscular mycorrhizal fungi to weathering.Under warming conditions,the GRSP content and its contribution to soil organic carbon showed an increasing trend.Combined with the response of AMF to warming,it was inferred that AMF colonization could cause a negative feedback of warming to organic matter decomposition.This conclusion could well explain the reason of the decomposition rate of soil organic matter in above(3)is not significant in response to warming.(5)According to the comparison of the water and salt environment and the soil organic carbon content among CROWN sites,appropriate salinity is beneficial to inhibit soil microbial activities,and will also inhibit methane generation,which is beneficial to carbon sink.The high and stable water level in wetlands not only inhibited the decomposition activities of soil microorganisms,but also facilitated the increase of fine roots biomass of plant and the preservation of organic matter in situ.Based on this,it is proposed that “salt adjustment” and “water control” will be very effective measures to increase carbon sink in future coastal wetland management.