Spatial And Temporal Distribution Of Soil Microorganisms In Reed Wetland Of Songnen Plain And Their Response Strategies To Exogenous Carbon Addition

As an important carbon sink of the terrestrial ecosystem,the wetland ecosystem is very sensitive to climate change.Wetland soil microorganisms are the main participant in the wetland carbon cycle,which has obvious spatiotemporal heterogeneity due to various factors.The carbon metabolic activity and functional diversity of wetland soil microorganisms will significantly affect the carbon sink function of the wetland ecosystem.In addition,the priming effect may also significantly change the carbon metabolism activity and respiratory temperature sensitivity(Q10)of soil microorganisms.This study collected soil samples from five reed wetlands in the Songnen Plain,including Halahai,Zhalong,Momoge,Niuxintaobao,and Xianghai to reveal the spatiotemporal variation characteristics of soil microorganisms in the Songnen Plain reed wetlands through the Biolog-ECO microplate method,and explored the Q10 and response strategies of soil microorganisms to the addition of exogenous carbon through the variable-temperature culture experiment.Based on statistical methods such as correlation analysis,redundancy analysis,principal component analysis,and structural equation model,the spatiotemporal distribution of soil microorganisms in the Songnen Plain reed wetlands and the driving factors of response strategies to exogenous carbon addition were revealed.The main findings are as follows:(1)The carbon metabolic activity,Shannon index,and substrate richness of soil microorganisms in Niuxintaobao and Xianghai wetlands which are in the south of Songnen Plain were relatively high.While the Halahai and Zhalong wetlands which are in the north were relatively low.The soil microorganisms in Niuxintaobao and Xianghai wetlands which are in the south preferred to use simple carbon sources,while the soil microorganisms in Halahai and Zhalong wetlands which are in the north prefer to use complex carbon sources.The structural equation model indicated that soil microbial carbon metabolic activity was mainly affected by soil total nitrogen(TN)and dissolved organic carbon(DOC),while the functional diversity of soil microorganisms was mainly controlled by soil salinity,soil microbial carbon metabolic activity,and DOC.Geographic location directly affected soil TN,moisture content(MC),and DOC content,and indirectly affected soil microbial carbon metabolism activity and functional diversity.Soil TN had the greatest impact on soil microbial carbon metabolism activity,while soil salinity had the greatest impact on soil microbial functional diversity.(2)The soil microorganisms in the Songnen Plain reed wetlands had significant profile distribution characteristics.The carbon metabolic activity and Shannon index of soil microorganisms decreased with the increase in soil depth,while the soil microbial Evenness index increased with the increase in soil depth.The carbon metabolism activity of soil microorganisms in 60-75 cm layer of Songnen Plain reed wetlands was about 57.41%-74.60% of that in 0-15 cm layer,which is higher than other ecosystems.Soil carbon and nitrogen nutrition contents decreased with the increase in soil depth,which affected the community structure of soil microorganisms.Soil microorganisms in different depths had different preferences for the use of carbon sources.Deep soil microorganisms preferred to use complex carbon sources,while surface soil microorganisms preferred to use simple carbon sources.The content of soil DOC was the most important factor affecting the soil microbial carbon sources utilization preference.(3)The soil microbial carbon metabolic activity and Shannon index of Songnen Plain reed wetlands showed significant seasonal changes.The carbon metabolic activity and Shannon index of soil microorganisms were high in summer and low in winter,while the soil microbial Evenness index was high in spring and winter and low in summer and autumn.The abundance of soil bacteria and fungi was the highest in summer and the lowest in winter.Soil microbial carbon metabolic activity,Shannon index,Evenness index,and substrate richness were affected by soil microbial biomass carbon(MBC),DOC,ammonium nitrogen(NH4+-N),nitrate nitrogen(NO3--N),and total phosphorus(TP)content.As an inland saline-alkali wetland,soil microbial diversity index,Evenness index,and substrate richness were significantly affected by soil p H and electrical conductivity(EC).(4)Exogenous carbon addition led to a significant increase in soil microbial carbon metabolism activity and microbial respiration Q10 of Songnen Plain reed wetlands.The Q10 in the 0-15 cm soil layer was significantly higher than that in the deep soil after exogenous carbon addition,while the Q10 of the control group had no significant difference.The activity of soil β-1,4-glucosidase(BG),cellobiose hydrolase(CBH),and N-Acetyl-β-glucosaminidase(NAG)and the content of NH4+-N and NO3--N increased significantly after the addition of exogenous carbon.The addition of exogenous carbon significantly changed the soil microbial community structure,and the bacterial abundance and bacteria/fungi increased significantly.The addition of exogenous carbon led to the transformation of microorganisms into r-strategies and tends to use simple carbon sources instead of complex carbon sources.The structural equation model showed that exogenous carbon addition could directly affect soil microbial respiration Q10 and soil microbial response strategy.This study clarified the spatiotemporal distribution characteristics of soil microorganisms in the reed wetland in Songnen Plain and their response strategies to exogenous carbon addition,providing basic data and theoretical support for exploring the microbial driving mechanism of the carbon cycle and the maintenance mechanism of carbon sink function in the wetland ecosystem.