| Pinus massoniana is widely distributed in subtropical regions of China, it is a typical native coniferous species, and its distribution area is the first in the country. Because of Pinus massoniana are usually distributed in the low mountains and hills, and the villagers living area, frequently by human disturbance and destruction, which leads to the consequences of its plantation species diversity of plummeted, ecological function degradation. Therefore, the optimization of structure and function, the recovery and transformation of low-efficiency Pinus massoniana forest must be used in. Soil organic carbon stability is an important indicator of soil quality. Soil aggregate plays the role of close storage and barrier to the soil organic carbon, so that the soil organic carbon is not easy to be broken down. Thus, Soil aggregate stability determines the soil organic carbon physical stability. This study made two models of transformation of the experimental area of the low efficiency Pinus massoniana forest:one is that clear cutting of an area about 8 hm2 of the low efficiency Pinus massoniana forest, and adopted the block mosaic mixed mode to constituted a subtropical evergreen broad-leaved forest artificial ecosystem; another is that interference of different size area of forest gap(after clear cutting), and adopted block mosaic to transformed the low-efficiency and low-yield artificial forest, then formed a artificial ecosystem of coniferous and broad leaved mixed forest. Through analyzing, measuring and comparing the indexes of soil total porosity, field capacity, soil bulk density and soil aggregate of each sample plots in experimental area, then the most suitable method to transform the local situation was selected. This thesis explores the effects of different transformation measures on soil physical properties and Soil organic carbon stability, and expect it can contribute to the construction of stable and efficient eco economic type of artificial forest system. The study found that:(1) Soil basic physical properties:the soil total porosity of each transformation sample plots are the following:control plot> 10×10m> 20×20m> 30×30m> 40×40m> clear cutting sample plots (P<0.05),and the relation of field capacity are the same.The result showed that at the initial stage of low-efficiency forest transformation, all of the transformation measures caused some impacts to the original soil structure on different levels. Comparing to the control plot, the soil aeration and soil water-holding capacity all reduced, and the soil compaction increased.(2) The distributions of soil water stable aggregate:in temporal scale:the content of> 0.25mm water-stable aggregates was significant downtrend over time at 0-20cm soil layer(P<0.05). In 10×10m,20×20m and 30×30m sample plots, the content of>5mm water-stable aggregates was uptrend at 0-20cm soil layer(P< 0.05), and the particle size>0.25mm was most(>50%). In 40 X 40m and clear cutting sample plots, the content of>5mm water-stable aggregates at 0-20cm soil layer was low and it has changed a little over time, and the distribution characteristics of each particle size is that the>0.25mm was most. The change regulation was similar between 20-40cm soil layer and 0-20cm soil layer of each sample plots. In spatial scale:the size relations of>0.25mm water-stable aggregate contents was same between 0-20cm soil layer and 20-40cm soil layer:control plot> 10 X 10m>20×20m>30×30m>40×40m>clear(p<0.05).(3) Soil organic carbon physical stability:the transformation measure of 10×10m and 20×20m could effectively improve the stability of the surface soil aggregate at the initial stage of sample plots transformation. But the result of 30 X 30m was not obviously, and the stability of the surface soil of the transformation measure of 40 X 40m and clear cutting sample plots was decrease by degrees. Soil anti-erodibility:in temporal scale, the transformation measure of 10×10m and 20×20m could effectively improve the soil anti-erodibility at the initial stage of transformation, thus improved the soil organic carbon physical stability. In spatial scale, the change regulation of soil anti-erodibility was same between 0-20cm soil layer and 20-40cm soil layer of each sample plots, i.e. control plot> 10×10m> 20×20m> 30×30m> 40×40m> clear. Structural damage rate of soil aggregate:the transformation measure of 10 X 10m could effectively reduce the structural damage rate of the surface soil aggregate at the initial stage of transformation, and improved the stability and structured of soil aggregate, thus improved the soil organic carbon physical stability. But the other transformation measures couldn't effectively reduce the structural damage rate of soil aggregate, hence the soil was vulnerable to erosion under the erode condition. The organic matter in soil aggregate of each particle size was accumulation and recovery with the passage of time, and the rate of increase of organic matter in soil aggregate of particle size>5mm?5-2mm and 2-1mm was greater of 10×10m and 20 X 20m, but the rate of increase of organic matter in soil aggregate of particle size <0.25mm was greater of 40 X 40m and clear cutting sample plots than other sample plots. Because the soil structure and soil nutrient content were caused a great impact by the soil preparation and transformation at the initial stage, the organic matter in soil aggregate of each particle size was reduced obviously. As for the recovery, the transformation measure of 10×10m and 20×20m was better, because they could effectively improve the organic carbon physical stability of the surface soil aggregate at the initial stage of sample plots transformation. The effect of the transformation measure of 30 X 30m was not so obviously. And the transformation measure of 40 X 40m and clear cutting sample plots was even worse, for the organic carbon physical stability of the surface soil decreased by degrees. Soil aggregate stability:in temporal scale, the transformation measure of 10×10m and 20 ×20m could effectively improve the soil aggregate stability at the initial stage of transformation. In spatial scale, the regulation of soil aggregate stability was same between 0-20cm soil layer and 20-40cm soil layer of each sample plots, i.e. control plot> 10× 10m> 20×20m> 30×30m> 40×40m> clear. The transformation measure of 10×10m and 20×20m could effectively reduce the surface soil erodibility at the initial stage of sample plots transformation, and also improve the soil organic matter physical stability. The transformation measure of 30×30m,40×40m and clear cutting couldn't effectively improve the soil organic matter physical stability, and the soil organic carbon was easy to be broken down.(4) Correlation analysis:In 0-20cm and 20-40cm soil layer, the relation between>0.25mm water-stable aggregates percentage contents and MWD was significant positive correlation, the relation between>0.25mm water-stable aggregates percentage contents?K and SD was significant negative correlation.In conclusion, the transformation measure of 10 X 10m and 20 X 20m could effectively improve the soil organic carbon physical stability, thus they could effectively control the strengthening status of the soil erosion at the initial stage of transformation. It proves that at the initial stage of low-efficiency Pinus massoniana forest transformation, appropriate control of the clump and clear cutting area can effectively improve the soil organic carbon physical stability. |
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