Research On Soil CO₂Release Mechanism Under Different Vegetation Types Of The Yellow River Delta Wetland

The paper, taking Yellow River Delta wetland as the research target, applying themethods of statistics and quantitative ecology, adopting the monitoring system ofLI-8100A soil carbon flux and combining the history materials and timely monitoring data,quantificationally analyzes the chief hydrothermal factor pattern influencing soil CO2emission of three typical phytocoenosiums (Tamarix community, Suaeda community,Phragmites community). It as well reveals dynamic features of soil CO2emission underdifferent communities and further discusses the influence that soil salinity and nutrienthave had on soil CO2emission. Results are as follows:(1) Variable features of hydrothermal factor. In terms of seasons, the atmospherictemperature and soil temperature of three phytocoenosiums are in the shape of unimodalcurve, what’s more, the peak occurrs at noon in the fall and spring. In summer (monitoringcycle24h), the temperature factor within6:00~18:00period is almost the same as that infall and spring, but it levels off after20:00. In three seasons, the atmospheric humiditychanging trend of each commnity is in contrast to the atmospheric temperature, yet soilmoisture has no obvious changing rules. In terms of communities, the hydrothermal factorin summer of tamarix community and alkaline community both are higher than that inautumn and spring. However, the atmospheric humidity in fall of Phragmites communityas well as soil moisture in spring is relatively higher.(2) The release characteristics of CO2in the soil.In seasonal scales, the CO2releaserate of Phragmite saustralis is higher than other two communities,while tamarixramosissima and Suaedasalsa have little difference between each other. In spring, thechange of three communities CO2emission shows a unimodal curve，and the maximumand the minimum appears at noon and in the morning.In summer (monitoring cycle24h),the Dynamic model of respiration rate of three communities CO2emission have a bigdifference with Spring. The respiration rate of Phragmites community is observably higherthan other two communities,while the minimum and maximum of respiration rate appears at8o’clock and14o’clock.Under the influence of high temperature and high humiditysurroundings, the valley of respiration rate of tamarix ramosissima community appears at10o’clock,and the peak appears at22o’clock. The respiration rate of suaeda salsa is thelowest,and the minimum and maximum of respiration rate appears at8o’clock and4o’clock. The Soil carbon flux of tamarix ramosissima and suaeda salsa is similar tospring,but Phragmites have not higher peak.In community scales,the CO2release rate oftamarix ramosissima and Suaedasalsa of summer is bigger than spring,and spring is biggerthan autumn.while the lowest release rate of Phragmites community appears in spring.(3) The relationship between the CO2release rate and hydrothermal factor.Inspring,the CO2release rate and atmospheric and soil temperature of three communitieshave positive correlation;the respiration rate of tamarix ramosissima and suaeda salsa andatmospheric humidity have negative correlation.In summer,the CO2release rate andatmospheric and soil temperature of Phragmites community have positive correlation;theCO2release rate of tamarix ramosissima and atmospheric humidity have positivecorrelation,and Phragmites have negative correlation with atmospheric humidity.Inautumn,the CO2release rate and atmospheric and soil temperature of tamarix ramosissimaand suaeda salsa community have positive correlation,and have negative correlation withatmospheric humidity.The releasing rate of soil CO2of the three communities is underlower correlation with soil moisture in the seasons of spring, summer and autumn.Multivariate linear polynomial model shows that synthetic action of hydrothermal factor inspring and summer respectively explains the change of soil CO2releasing rate(89.7%~98.3%and82.2%~92.3%) in different communities. Hydrothermal factor inautumn explains the change of soil CO2releasing rate (95.7%and94.7%) in tamarixcommunity and suaeda community.(4) The influence of soil nutrient content and salinity to soil carbon flux. Soil totalphosphorus, available nitrogen, organic carbon in nutrition index were significantlycorrelated with soil CO2release rate of soil. Saline habitats of this organic carbon isdivided into0~10g/kg,10~15g/kg,15~20g/kg three environmental gradients. Themean soil CO2release rate reached a high value to3.667μmol·m-2·s-1in the10~15g/kg carbon environment. K-、Na+、CL-、Mg2+、Ca2+、SO42-total salt, all salt in the soil weresignificantly correlated with soil CO2release rate. Take the full salt indication as the basis,if this environment is divided into0~10g/kg,10~40g/kg,40~70g/kg three full saltgradient, then the mean soil CO2release rate was2.616μmol·m-2·s-1、1.206μmol·m-2·s-1、0.81μmol·m-2·s-1.Regression analysis showed that a cubic polynomial model can better fitthe relationship between total soil salt content of soil respiration rate, and the fitcoefficients R2=0.4162(P＜0.01) showing that the content of the total soil salts have someeffect on the respiration rates.