不同类型森林石灰土的团聚体组成及其有机碳分布特征

选取中国西南喀斯特石灰土人工林、次生林、原生林3个主要森林类型的6个代表性群落,建立18个20m×20m的样方,按梅花型5点法采集各样方的原状土壤,基于团聚体的干湿筛2种分组方法,研究不同类型森林石灰土机械性、水稳性团聚体组成及全土、各粒级团聚体的有机碳分布特征。结果显示:(1)3类森林石灰土干湿筛团聚体均以>2mm粒径为主,分别为67.93%～81.24%和30.49%～76.81%,1～10mm粒径的干湿筛优势团聚体分别高达78.18%～88.67%和43.41%～84.00%。(2)团聚体的整体稳定性很好,干湿筛平均重量直径(MWD)为4.82～5.77和0.75～2.13,平均几何直径(GMD)为2.87～4.17和1.45～2.85;>0.25mm和>2mm粒径的团聚体破坏率(PAD)分别仅为6.15～20.91和2.04～52.79。(3)石灰土的有机碳含量很高,全土和干、湿筛团聚体的有机碳含量分别为17.28～58.85、19.12～91.47、17.16～78.86g/kg,其中干筛以<2mm粒径团聚体的有机碳含量较高,湿筛反之,但干湿筛均以>2mm粒径团聚体的有机碳贮量最高。研究表明,中国西南喀斯特石灰土林区土壤沿人工林、次生林、原生林土壤扰动递减梯度,石灰土的团聚化作用越来越强,稳定性越来越好,有机碳含量也越来越丰富。

Distribution of Organic Carbon and Aggregation of Calcareous Soil in Different Forest Types

Three main forest types,manmade forest,secondary forest,and primary forest,were chosen to study sites in karst calcareous soil of southwest of China.Eighteen sample plots of 20 m×20 m were established based on six representative communities.Soil aggregation samples were collected as different particle sizes and separated by dry sieving and wet sieving.Then,composition of machinery-stable aggregation and water-stable aggregation,distribution of total organic carbon,and organic carbon in aggregation were analyzed.The results showed that:(1)Soil machinery-stable aggregations and water-stable aggregations of three type forests were dominated by >2 mm particle size,and the proportion were 67.93%~81.24% and 30.49%~76.81%,respectively.The proportion of 1~10 mm size in machinery-stable aggregation and water-stable aggregation were 78.18%~88.67% and 43.41%~84.00% respectively.(2)The stability of all particle size aggregates were perfectly.The mean weight diameter (MWD) and the mean geometric diameter (GMD) of machinery-stable aggregations were 4.82~5.77 and 2.87~4.17,respectively;the MWD and GMD of water-stable aggregations were 0.75~2.13and 1.45~2.85.Percentage of aggregation destruction (PAD) of >0.25 mm and >2 mm particle size aggregations were 6.15~20.91 and 2.04~52.79,respectively.(3)There is high organic carbon content in the calcareous soil.The content of total organic carbon,organic carbon contents of machinery-stable aggregation and water-stable aggregation were 17.28~58.85 g/kg,19.12~91.47 g/kg and 17.16~78.86 g/kg,respectively.The content of organic carbon in machinery-stable aggregation were dominated by <2 mm particle size,while these of water-stable aggregates reverse.Organic carbon storage in >2 mm aggregations were the highest in all size fractions of machinery-stable and water-stable aggregation.Therefore,with soil disturbance decreasing along the manmade forest,secondary forest and primary forest,soil aggregation and stability and organic carbon content in calcareous soil showed an upward trend.