Characteristics Of Plant Communities Under Succession Gradient And Their Effects On Soil Erodibility

The relationship between vegetation and soil erosion has attracted much attention because of its important scientific significance,and it has always been a hot scientific issue in the field of surface processes.Plant communitiy is a basic unit of forming vegetation.During the process of community succession,material circulation and energy flow were continuously carried out between the soil and the plant community.To date,many attempts are made to the prevention and control of soil erosion by vegetation,but there are mostly engaged in research on the species level,less attention to the level of community work.Secondly,due to root concealment and complexity of root distribution in the soil,it is relatively difficult to study than the above-ground part,and the research work is relatively slow.In this study,five typical stages of vegetation restoration in Hujiashan Small Watershed were selected,that is,wild land（0 a）,grassland（1² a）,shrub（5 a）,side berlin（20 a）,and arbor mixed forest（25 a）.Taking the method with space instead of time,and on the basis of the theories of botany,soil physics,chemistry,geography and mathematical statistics,indoor analysis and field vegetation survey and dyeing tracer tests were conducted to analyze the dynamic relationship between vegetation parameter changes and soil factors during community succession.The variation rules of soil preferential flow characteristics under different succession degrees were analyzed,and the effects of root parameters and soil properties on preferential flow and water transport were discussed.At the same time,four herbaceous plant roots（Imperata cylindrical,Conyza canadensis,Carex parva and Arthraxon hispidus）in this basin were selected as the research objects.The root tensile test and potassium bromide tablets were conducted to analyze the changes of mechanical properties and Fourier transform infrared spectroscopy（FTIR）properties of four tested herbaceous species,and to provide theoretical support and practical guidance for vegetation restoration and soil erosion prevention and control in this area.Main results were shown as follows:（1）The relationship between plant community characteristics and soil properties under different succession gradientsIn the early stage of succession,the composition of plant community was relatively simple.The richness index,diversity index and evenness index of plant communities increased as the succession progressed,but in the middle and later stage of succession,the evenness index was non-significant.The fine roots with the diameter less tan 0.5 mm taked the majority the plant community,and they were mainly distributed in the 0²0 cm soil layer.With the succession progressed,root weight density increased,while the specific root length decreased.Soil physical-chemical properties displayed significant differences under different succession gradients.With the succession progressed,the contents of soil organic matter and easily extracted glomalin-related soil protein increased significantly,the content of total glomalin-related soil protein increased significantly then decreased,and mean weight diameter of aggregate increased first stabilized later.In the early stage of succession,the order of aggregates stability was MWD_WS>MWD_SW>MWD_FW,in the middle and late stage of succession,there was non-significant difference in the mean weight diameter of aggregate under different succession degrees.Compared with the aboveground parameters of vegetation,the correlation between soil physical-chemical properties and root parameters is greater.With the succession progressed,vegetation parameters and soil physical-chemical properties had improved to a certain extent.In the later stage of succession,vegetation parameters and soil physical-chemical properties improved best.（2）Characteristics of soil preferential flow and its influencing factors under different succession gradientsWith the succession progressed,the number of soil preferential flow increased and the migration path increased.The soil preferential flow zones were different of the five succession gradients.The soil staining area ratio was in the order of Platycladus orientalis forest>Arbor and shrubs mixed forest>Shrubs>Grasslands>Wasteland.With the succession progressed,the number of soil staining pathway width<20 mm dyeing paths in soil increased,while the number of soil staining pathway width>200 mm decreased.The number of soil dyeing paths at different width grades varied was different in different soil layers.With the succession progressed,the correlation between soil physical-chemical properties index and soil staining area ratio gradually weakened,while the correlation between root parameters and soil staining area ratio gradually increased.（3）Study on FTIR and mechanical properties of herbaceous roots in DanjiangkouIn the same plant roots,the position,intensity and shape of the absorption peaks were resembled;there were still some differences in the position,intensity and shape of the absorption peaks of different vegetation roots.The root tensile force increased with diameter,and it indicated positive.However,there was not follow a power law equation between the tensile strength and the root diameter.When the root moisture was lowed,the tensile strength was larged.With the increased of root moisture,the root tensile strength was decreased.The content of cellulose,hemicellulose and lignin in the roots of Imperata cylindrica was the highest of four tested herbaceous species.Carex parva and Imperata cylindrica had significant function in slope protection.