The Characteristics Of Soil Organic Carbon Mineralization Under Different Land Uses

The Soil Organic Carbon(SOC)mineralization is an important link of the global carbon cycle,and land uses is an important factor that affects the dynamic of SOC mineralization.Hence,it is necessary to study the dynamic law of SOC mineralization under different land uses.The study of SOC mineralization respond to temperature changes is the fundament of accurate evaluate the relationship between the climate change in the future and the CO2 concentration in the atmosphere.Because we can't directly utilizing already existed SOC components data to stimulate the dynamic of SOC mineralization,exploring their relationship is beneficial to simplify the study of SOC mineralization.The soil samples were taken from six different land uses(paddy field,vegetable garden,orchard,dry land,tea plantation,forest)in Jurong area under the same micro-climate conditions,and it were taken form top soils(0-20cm)in all above land-uses.We incubated the soil samples for 61days at 5,15,25,35 ? in the constant temperature incubator.We measured the rate of every soil samples' SOC mineralization at the fixed time and studied the characteristic of SOC mineralization under different land uses.The rate of SOC mineralization respond to temperature changes was discussed.At the same time,we measured the content of SOC components in each soil samples and discussed the relationship between the parameters of soil organic carbon pools and the compositions of soil organic carbon.According to the contents we mentioned above,the main results are as follows:(1)A series of SOC mineralization data that we measured under the condition of room temperature(25 ?)and controlled humidity are as basic data.Regarding the incubation time as the X-axis and the total accumulation of SOC mineralization as the Y-axis,we draw the dynamic curve of cumulative CO2-C release and it can be fitted with exponentiation model,exponential model and polynomial model respectively.In exponentiation model,we get three kinds of function expression(y=atb?y=a(t-b)c?y=abt1-c/(1+bt1-c))which have wonderful fitting effect;In exponential model,Y-a1-a2e-kt and y=a1(1-e-t/b1)+a2(1-e-t/b2)and y=ea+b/(t+c)have very good fitting effect;In multinomial model,cubic polynomial's fitting correlation coefficient has reached above 0.88,and the more the number of polynomial function,the better the fitting effect.In the function expression of the above model,the double exponential function of exponentiation model has the best fitting effect,which correlation coefficient has over 0.99.(2)With the increasing of temperature,the rate of SOC mineralization are speeding up and the amount of cumulative CO2-C release are adding in different land-use types.The ways of land-use type on the amount of cumulative CO2-C release are more significant under the condition of high temperature(35?)than under the condition of low temperature(5,15?).No matter whether in high temperature or room temperature or low temperature,the cumulative CO2-C release of different land-use types are follows as:forest>orchard>paddy field>tea plantation>dry land,and the change trend is consistent with the peak value size of SOC mineralization rate.(3)Double exponential function model can be used for fitting the curve of cumulative CO2-C release under different land-use types and different incubation temperature.In this way,we got the size and decomposition rate of easily decompositon carbon pool and difficultly decomposition carbon pool.Through analysis of the fitting parameters,we found that the content of easily decompositon carbon pool were added when the temperature were increased,but the change of decomposition rate were irregular.Reciprocal relationship exists between easily decompositon carbon pool and difficultly decomposition carbon pool,hence,with the increase of temperature,the content of difficultly decomposition carbon pool are decreases.The correlation between the decomposition rate and temperature exactly field the exponential function and we get a good modeling effect.(4)The relation between SOC mineralization rate and temperature can be described by exponential function fitting,and the fitting graphics of all the land-use types are show that:the scatter of SOC mineralization rate gathered near the fitted curve when the temperature is lower.With the increase of temperature,the scatter of SOC mineralization rate gradually dispersed.Based on index function,the value of temperature sensitivity coefficient(Q10)was obtained in all land-use types,which their size order are:paddy field>tea plantation>orchard>dry land>forest.(5)The characteristic parameter values of SOC mineralization are acquired based on three-pool-and-first-order dynamic theory.The active carbon pool(Ca)accounted for the smallest percent of total organic carbon(TOC).Ca has a significantly positive correlation with readily oxidized carbon(ROC)and particulate organic carbon(POC)and light fraction organic carbon(LFOC),and the Cs has the same situation.However,the turnover rate of active carbon(Ka)and the turnover rate of slow carbon(Ks)only have significant correlation with LFOC accounts for the percentage of the TOC,hence,we can use LFOC/TOC to indicate the dynamic changes of Ca and Cs.