Study On Organic Carbon Decomposition Characteristics And Its Influencing Factors Of Typical Paddy Soils

Soil organic carbon?SOC?pool is the largest carbon pool in terrestrial ecosystems,which is closely related to the global carbon cycle.And the decomposition of soil organic carbon has an important impact on CO2 concentration in the atmosphere.The total area of paddy soils accounts for about 1/5 of the total cultivatable land in China,and produces about 4/5 of all grain in China.The SOC decompositon characteristics of paddy soils are different with arid land soils.Therefore,it is essential to carry out the study on SOC decomposition of paddy soils,which will play an important role in reliving the presure of CO2 emission reduction,and relieving the effect of green-gas effect,and stablizing the grain yield.The object of research is profile soils?0-100 cm?in Taoyuan County,Hunan province and top soils?0-20 cm?in Jurong City,Jiangsu province.We incubated profile soil samples for 50 d at 25?,top soil samples for 50 d at 5?,15?,25?,35?.The study was based on the theory of three-pool-and-first-order dynamic and laboratory incubation experiments.After that,we devided soil organic carbon into active organic carbon?Ca?pool,slow organic carbon?Cs?pool and passive organic carbon?Cp?pool and analyzed SOC decompositon characteristics with soil layer changing and incubation temperature changing.In-deep analyzed the effect of incubation temperature on Q₁₀ and three carbon pools' estimation.Thorough a large number of laboratory experiments,the major resultes were as follows:1.The decomposition rate and cumulative decomposition amount of SOC increased rapidly at the beginning,then decreased slowly,and reached a stable statement at the end of incubation.According to decomposition rate characteristics,soil organic carbon decomposition rate could be divided into fast decomposition stage?an average of about 7.94 d?,slow decomposition stage?an average of about 28 d?and stable decomposition stage.SOC decomposition rate and cumulative decomposition amount decreased with soil depth decreasing,when incubated in 25?.The soil organic carbon decomposition rate and the cumulative amount of decomposition increased significantly with the increase of incubation temperature range from 5 ? to 35 ?.The cumulative amount of organic carbon decomposition at 15 ?,25 ?,35 ? was 1.94 times,3.55 times,6.01 times as large as at 5 ?,respectively.2.Carbon content order in different layers was Ct>Cp>Cs>Ca.The content of Ca?0.841?,Cs?0.833?,Cp?0.773?were highly negative correlated with soil depth?P<0.01?.With soil depth decreasing,Ca/Ct decreased,while Cp/Ct and the stability of soil organic carbon increased.Cumulative decomposition amounts were highly negative correlated with Ct,soil total nitrogen content,C/N ratio and highly positive correlated with pH,clay content.Partial correlation analysis shows that three components of SOC and cumulative decomposition amounts were highly correlated with soil total nitrogen content and pH,and uncorrelated with total phosphorus,total kalium,avtive phosphorus,active kalium,C/N ratio,clay content.3.The fitted results got from organic carbon decomposition curve incubated in different temperature were significant different,when Q₁₀ valued 2.The fitted values of Ca were increasing with the incubation temperature increase,while the fitted values of Cs were decreasing with the incubation temperature increase.Incubation temperature was great influenced on the fitted results of three carbon pools,especially the influence on Ca.The coefficient of variation for fitted active carbon pool size about three paddy soils incubated at different temperature were 64.9%,66.7%and 48.5%,respectively.Q₁₀ decreased with temperature and incubation time increase when calculated inaccordance with the definition,varying in the range of 1,48 to 2,88,Q₁₀ values were correlated with SOC content and SOC decomposition rates,and incorrelated with ccumulatve decomposition amount.Three carbon pools were fitted using a calculated Q₁₀ value got from the definitional equation or a fixed Q₁₀ value assumed to be 2.Ca and Cs were not affected by The value of Q₁₀ assumed 2 or a measured value,while mean residue time of active carbon?MRTa?and mean residue time of slow carbon pool?MRTs?were highly affected.In summary,the belowground SOC paticitated in the global carbon cycle for its slow pace and similar processes to the surface,so appropriate measures could increase their carbon fixation.Fitted C pool values were highly influenced by the incubation temperature,so 25 ? incubation results couldn't describe all the features of carbon decomposition.Q₁₀ values calculated according to the definition were highly influenced on the fitted MRTa and MRTs,and slightly influenced on the fitted carbon pool size,so fixed value 2 could be used for three pool estimation.