| To study the sustainability of the effects of the Three Gorges Reservoir Area Vegetation Protection, In15non-standard runoff plot, we select4kinds of herb for the target species,which is Medicago sativa、Paspalum notatum、Cynodon dactylon、 Vetiver, and plant in plot, including comparison. According to plot experiment and analyzing the physical and chemical properties of soil samples, we studied the change of soil physical and chemical properties, the relationship between soil and different different herbal plant root, and the effects of different time on herbal plant root indexes. Further provides a theoretical basis for the control of soil erosion and reservoir drawdown area of the Three Gorges Reservoir vegetation recovery. the results indicated that:(1)Four Herbaceous root parameters:root weight density, root length density, root surface area density and time life regression equation fitting, Results:with the growth of the planting fixed number of year, total root length density, root surface area, density, respectively show exponential growth, the rule of logarithmic function growth, and root weight density without rules. and root surface density value of4kinds of plant decrease with the increase of soil depth, except the root length density value of Medicago sativa as it increase first and then decrease with the increase of soil depth. With years change, the root weight density, root length density, root surface area density of all samples increased in the same soil layer, but increasing range decreased. According to the vertical distribution characteristics of the different herb root parameters, it indicated that the amount of root system value of Medicago sativa and vetiver accounts for91%of total root system value in the0-20cm soil layer, and99%for Paspalum notatum,78%for cynodon dactylon in the0-10cm soil layer, so it can be concluded that the root system distribution of Medicago sativa and vetiver grass mainly gathered in0-20cm of soil layer, but in0-10cm of soil layer for Paspalum notatum, and cynodon dactylon.(2) With the increase of planting years, Four Herbaceous root rhizosphere soil mechanical composition are expressed as:clay gradually increased, sand gradually reduced, But there are differences of different herbs improvement of soil mechanical composition, The effect of improving is Medicago sativa> vetiver> Cynodon dactylon> Paspalum notatum. Correlation analysis showed that, There had very significant negative correlation between root length density and the coarse sand(1-0.5mm), There had very significantly positive correlation between root length density and the fine silt (0.005-0.002mm), There had very significantly positive correlation between root length density and the cosmid (<0.002mm), There had significantly negative correlation between the root surface density and the coarse sand(1-0.5mm), There had significantly positive correlation between the root surface density and the fine silt (0.005-0.002mm), There had significantly positive correlation between the root surface density and the cosmid (<0.002mm), There had significantly positive correlation between root weight density and the Coarse silt(0.05-0.01mm). But the herb different diameter root parameters to improve the effect of the soil mechanical composition differences, They were significantly negative correlation between the sand content and root length density in diameter of0.5mm<L≤1mm, Correlation coefficient of-0.522. They were significantly positive correlation between clay fraction of mechanical composition and root length density in diameter of0.5mm<L≤1mm, root length density in diameter of lmm<L^2mm, correlation coefficients were-0.531、-0.474,there were no significantly correlation between silt and different root length density, There had significantly correlation between particle Fractal dimension and root length density in diameter of L≤0.5mm、0.5mm<L≤1mm,1mm<L≤2mm. root length density in diameter of0.5mm<L<1mm for the influence of fractal dimension is most obvious, correlation coefficient of-0.416. Therefore,0.5mm<L≤lmm diameter roots constitute the largest contribution to reducing the sand content, increasing clay content, improve soil structure.(3) With the years of cultivation increasing, the structure of soil micro-aggregates of four kinds of herbaceous plant roots in rhizosphere all as followed:clay contents decreased while sand contents increased. But the improvement of different herbaceous roots on soil micro-aggregates were differences and the size of improvement effects showed:vetiver>Medicago sativa> Cynodon dactylon> Paspalum notatum. Correlation analysis showed that:the relationships among root length density, root weight density, root surface area density and soil clay contents were highly significant negative correlation and the correlation coefficient were-0.804,-0.512,-0.768, and coarse sand were highly significant positive correlation and the correlation coefficient were0.622,0.815,0.635. The greater the density of root length, root weight and root surface area, the lower clay contents in the micro-aggregates and soil structure were more steady. By analyzing the relationships between particles composed of micro-aggregates and different diameter root length density, it can concludes that the correlation coefficients between sand and different root diameter class root length density were first increased and then decreased, and clay and different root diameter root length density were first decreased and then increased. The diameter class in0.5mm<L≤of2mm root, there were the greatest contribution to increase sand contents, decrease the clay contents and promote the stability of soil structure. The relationships between fractal dimension of micro-aggregates and diameter class in L≤0.5mm,0.5mm<L≤lmm and lmm<L≤2mm root length density were highly significant negative correlation, the correlation coefficients were-0.801,-0.826,-0.760, so0.5mm<L≤1mm diameter roots and soil aggregate structure stability was most closely related.(4) The content of organic, total nitrogen, total phosphorus, valid nitrogen, valid phosphorus and valid potassium decrease as the increase of soil depth in the same year; And the organic content of all samples soil increase in the same soil layer as the increase of years, and it indicated that the organic content of Medicago sativa and vetiver grass was bigger than that of Paspalum notatum and cynodon dactylon, but the increase range in soil surface is bigger than that in bottom. Organic matter content of the overall size can be expressed as:Vetiver> Medicago sativa> Cynodon dactylon> Paspalum notatum. And different herbs root system on soil nutrient effect are also dissimilarity, the nutrient effect overall performance are as follows:Medicago sativa> vetiver grass> Cynodon dactylon> Paspalum notatum, the overall evaluation of plant root nutrient solid hold effect, Medicago sativa is the optimal herb. The root weight density have a significant positive correlation with soil organic content, available nitrogen, valid phosphorus, valid potassium under0.01level, and also with total nitrogen under0.05level, The density of root length, root surface density value have extremely significant positive correlation with organic content, available potassium under the0.01level. Root parameters have no significant correlation with total potassium content, but valid potassium content have significant correlation with root weight density, root length density and root surface density value, there are also differences herb different diameter root parameters retaining effect on soil nutrients, it indicated that bigger diameter of root have a close relationship with soil nutrients, such as root diameter2mm-4.5mm and>4.5mm, Influence on soil nutrients relative to is higher than fibrous roots. |
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