基于LB法的缙云山典型林分土壤团聚体的稳定性

Soil aggregate stability of typical forest stands in the Jinyun Mountain based on Le Bissonnais method

黄壤坡面是长江中上游地区水土流失主要策源地之一,而针对黄壤地区典型林分下土壤团聚体稳定性的变化特征仍不明晰。选取长江中上游地区重庆缙云山4种典型林分(针阔混交林、常绿阔叶林、毛竹林、灌木林)为研究对象,采用Le Bissonnais(LB)法中快速湿润(FW)、慢速湿润(SW)和机械振荡(ST)3种处理方式区分黄壤团聚体破碎机制,定量分析不同林分类型下土壤团聚体稳定性变化特征及其影响因素。结果表明:1)不同林分土壤团聚体稳定性整体呈现MWDFW1~20 cm)MWD,通常林地内采用的0~20 cm土层土壤团聚体MWD,若不考虑表层(0~1 cm)和下层(>1~20 cm)土壤团聚体间的差异,将会低估表层土壤团聚体的稳定性。4)冗余分析表明,不同团聚体破碎机制下土壤团聚体稳定性的主要影响因素存在差异,FW和SW处理下土壤团聚体稳定性主要受SOM、CEC、交换性Mg2+、Ca2+影响,ST处理下土壤团聚体稳定性则主要受交换性K+、Ca2+、Mg2+和黏粒含量的影响。整体而言,不同林分土壤团聚体稳定性特征存在显著差异,且不同团聚体破碎机制下影响因素不同。

[Background]The slope land of yellow soil is one of the main source of soil erosion for the middle and upper reaches of the Yangtze River,while there is still a research gap in soil aggregate stability under typical forests in the yellow soil area. When using aggregate stability to assess soil erodibility,samples are usually collected from 0-20 cm soil layer. However,the surface of soil( 0-1 cm) is still the active layer where various activities act although there is no obvious crust in forest land.Compared with the study on 0-20 cm soil layer,it is important to clarify the aggregate stability of the very surface layer for forest soil. [Methods]Mixed coniferous and broad-leaved forest,evergreen broadleaved forest,Phyllostachys pubescens forest and shrub forest in the Jinyun Mountain were selected as research sites. In each site,5 m x 20 m plots were selected. Samples were collected from the surface soil( 0-1 cm) and subsoil( > 1-20 cm),and 3 repeats along diagonal of each plot and mixed for each plot. The aggregate breakdown mechanism was distinguished by fast wetting test(FW),slow wetting test( SW) and stirring test( ST) in the Le Bissonnais( LB) method,and their stability was expressed by MWD( mean weight diameter)FW,MWDSW,and MWDST,respectively. Soil properties such as soil particle distributions( PSD),soil organic matter(SOM),total nitrogen(TN),total phosphorus( TP),cation exchange capacity( CEC),and exchangeable cations( K+,Na+,Ca2+,and Mg2+) were measured as potential explanatory factors of soil aggregate stability. [Results] 1) The stability of soil aggregates in different forest stands showed a trend of MWDFW< MWDST< MWDSWin general. 2) The soil aggregates stability of 4 forest stands showed a significant difference under different aggregate breakdown mechanisms. The soil aggregates of evergreen broad-leaved forest were the most stable while that of P. pubescens forest were very weak. 3) MWD of the surface soil was greater than that of the corresponding subsoil under the same stand,and the difference varied with different aggregate breakdown mechanism. 4) Redundancy analysis( RDA) showed that the cumulative explanations of standard soil properties tested on soil aggregate stability were as high as 99. 0%. The main factors influencing soil aggregate stability were different under different aggregate breakdown mechanisms. For FW and SW,soil aggregate stability was mainly affected by SOM,CEC,and exchangeable Mg2+,Ca2+. For ST it was mainly affected by exchangeable K+,Ca2+,Mg2+and clay content. There was a significantly positive correlation between SOM and soil aggregate stability( P = 0. 004),and a negative correlation between exchangeable Na+and the stability under three breakdown mechanism. [Conculsions] There are significant differences in soil aggregate stability in different stands,and the influencing factors are different under different aggregate breakdown mechanisms. Compared with the other three stands,evergreen broad-leaved forest demonstrate the most obvious effect on soil aggregates stability in this area.The mostly used average MWD of the 0-20 cm would,if the difference between surface soil aggregate( 0-1 cm) and subsoil aggregate( > 1-20 cm) is ignored,probably underestimate the aggregate stability of surface soil.