Effects Of Karst Vegetation Restoration On Soil Aggregate Stability And Organic Matter Composition

Vegetation restoration is an important link in the control of karst rocky desertification.In this research,we choosed the soil of different vegetation restoration stage(abandoned land,grassland,bringing land,shrub and secondary forest)as the research object,analyzing the distribution of organic matter in soil aggregates at different vegetation restoration stages,studied the stability characteristics and differences of aggregates with different particle sizes,in order to provide a more in-depth theoretical basis for vegetation restoration and reconstruction in karst areas.The main results are as follows:(1)With the restoration of vegetation,soil physical and chemical properties were significantly improved,which were as follows:soil bulk density decreased,porosity increased,p H decreased and organic matter content increased.Free iron and aluminum oxides are the main forms of iron and aluminum oxides in different vegetation restoration stages.Free iron and aluminum is the main form of Fe-Al oxides,and the content of Fe-Al oxides from large to small is:Fe_d>Al_d>Fe_o>Al_o>Mn_d>Mn_o.Vegetation restoration can reduce the content of free iron oxide.Vermiculite kaolinite and illite are the main clay minerals in the study area.(2)Soil aggregates increased with vegetation restoration,and the AD of microaggregates were all above 40.9%.Soil water-stable aggregates and mechanically stable aggregates were mainly larger than 2 mm in each vegetation restoration stage.Both MWD and GMD increased significantly with vegetation restoration.The changes of MWD and GMD in soil treated by the LB method were consistent,showing SW>WS>FW,and the values of MWD and GMD tended to decrease with the deepening of soil layer.(3)Vegetation restoration increased the input of organic matter and promoted the accumulation of soil organic carbon.At different soil levels,the content of organic carbon in the whole soil and each grain size was higher in the surface layer than in the bottom layer.With the restoration of vegetation,the contents of humic acid and fulvic acid increased gradually,and the topsoil was more conducive to the accumulation of humic acid.With the decrease of aggregate particle size,the grassland and shrub showed a trend of increasing first and then decreasing,while shrub and secondary forest showed a trend of decreasing at the early stage of vegetation restoration.The content of FA is higher than that of HA,indicating that the soil in the study area belongs to fulminic acid soil.With the restoration of vegetation,the humification degree PQ of the whole soil and aggregates with different grain sizes showed an increasing trend.The content of HMi was generally lower than that of HMc,and the content of HMr was the highest,followed by HMc and HMi.The proportions and sizes of organic matter components showed as HMi<HMc<HA<FA<HMr.(4)The influence of organic matter components on the stability of aggregates is not isolated,but a complex process that affects and restricts each other.Stepwise regression analysis showed that HA content in>2 mm aggregates,SOC,FA and HMc content in 2-1 mm aggregates,and HMr content in<0.25 mm aggregates were significantly positively correlated with water-stable aggregates GMD(P<0.05).The above factors are the main factors affecting the stability of soil aggregates.These results indicate that SOC,HA,FA and HMc in large aggregates and HMr in micro aggregates play an important role in improving the stability of aggregates and soil structure in karst areas.It is suggested that the anthropogenic disturbance such as tillage and grazing should be reduced to protect the soil macroaggregates,improve the stability of soil structure and prevent the loss of organic matter components from the macroaggregates.