桂林毛村岩溶区不同土地利用方式土壤有机碳矿化及土壤碳结构比较

应用土壤培养法,比较分析了桂林毛村岩溶区不同土地利用方式(农田、灌丛和林地)土壤在25℃、黑暗条件下培养90d有机碳矿化速率的差异(以90d累计释放的CO2-C计)。农田土壤矿化释放的CO2-C含量分别比灌丛和林地少62.9%和56.6%。利用6mol/L的HCl酸解法得到惰性碳含量,并利用三库一级动力学方程在SAS8.2软件中通过非线性拟合得到三种土地利用方式的活性碳库、缓效性碳库的大小及其分解速率,计算得出各库驻留时间。结果表明各土地利用方式均为活性碳库含量最少,占总有机碳的比例在1.82%~2.71%之间,平均驻留时间在8.4~16.3d之间;缓效性碳库次之,占总有机碳的比例在33.91%~45.47%之间,平均驻留时间为4.8~7.7a之间;惰性碳库所占比例最大,在51.82%~64.01%之间,平均驻留时间为假定的1000a。通过固态13C交叉极化魔角自旋核磁共振(13CCPMASNMR)方法对土壤碳结构进行分析,结果表明:与灌丛和林地相比,受人类活动干扰较多的农田烷基C和芳香C的比例增加,烷氧C和羰基C的比例降低;烷基C/烷氧C和疏水C/亲水C的大小顺序均为农田>林地>灌丛,而脂族C/芳香C的大小顺序则相反,即灌丛>林地>农田。这说明农田土壤有机碳分解程度较高,难分解程度增加,难分解有机碳比例增加。 

Comparison of mineralization and chemical structure of the soil organic carbon under different land uses in Maocun karst area, Guilin

Testing the CO2-C content released from the soil is the way to study the mineralization rate of the soil organic carbon（SOC）.Thus,we collected soil samples from farmland,shrub land and forest in Maocun karst area in Guilin,and incubated in the laboratory in the dark at 25 ℃ with a constant moisture of 75 % during 90 days,then analyzed the amount of cumulative CO2-C released over 90 days to study the difference of SOC mineralization rate under different land use types.It was found that the mean concentration of CO2-C（gCO2-C·kg-1soil·90d-1） from SOC mineralization in farmland was 62.9% and 56.6 % lower than those in the shrub land and forestland respectively.Meanwhile,the chemical structure of soil organic carbon pool in above-mention land use types is studied.The SOC pool are divided into three pools,that is passive-,slow-,and ative-organic carbon pool.Firstly,using acid hydrolysis（6M HCl） to fractionate passive organic carbon,then separate active and slow carbon pools and calculates their decomposition rate and residence time with the ＂three-pool first-order model＂.The results showed that active carbon pool（Ca） comprised 1.82 % to 2.71 % of the SOC,with an average mean residence time（MRT） of 8.4 to 16.3 days,while slow carbon pool comprised 33.91 % to 45.47 % of the SOC,with an MRT of 4.8 to 7.7 years,and passive carbon pool comprised 51.82 % to 64.01 %,with an assumed MRT of 1 000 years.Finally,the chemical structure of the organic carbon was analyzed by solid state 13C via polarization magic angle spinning nuclear magnetic resonance（13C CPMAS NMR）.The results showed that,in comparison to the shrub and forest lands,the proportion of alkyl C and aromatic C in farmland which suffered more human disturbance increased,while the proportion of O-alkyl C and O-alkyl C decreased.Both the order of alkyl C/ O-alkyl C and hydrophobic C / hydrophilic C are farmland 〉 forestland 〉 shrub land,while the order of aliphatic C/aromatic C was the opposite.This shows that SOC in farmland has higher degree decomposition and is more difficult to decompose than the above other land types.