| Maintenance and improvement of soil fertility quality is the basic task for forest sustainable management. By suffering the frequent human disturbance, the soil site capacity of Phyllostachys Pubescens forest gradually decreased. To realize the sustainable and healthy management of Phyllostachys Pubescens, evaluation of soil fertility quality is particularly important. The biological fertility characterized by soil biota which drive the soil ecology system is in central and core position. Soil of the core zone of Phyllostachys Pubescens forest in south Sichuan was set as the research object.8 indexes including soil microbial biomass carbon (Cmic), microbial biomass nitrogen (Nmic), the ratio between microbial biomass carbon and microbial biomass nitrogen (Cmic/Nmic), soil invertase, acid phosphatase, urease, catalase and soil respiration were selected as the evaluation indexes. Soil samples in layer 0-20 cm and 20-40 cm were determined. The whole level and variation law during inter day of soil respiration rate was observed and the spatial paterns of soil microbial biomass and soil enzyme were analyzed through both geo-statistical and traditional statistical methods. On this basis, using principal component analysis and fuzzy mathematics, a index evaluation model of soil biological fertility quality was carried out to evaluate the soil biological fertility quality of Phyllostachys Pubescens forest, in order to provide data support for sustainable management of Phyllostachys Pubescens forest and construct a reasonable evaluation system of soil fertility quality. The results were showed as the followings:(1) Variation of the biological indexes were relatively high and in layer 20-40 cm were higher than that in layer 0-20cm. With the increase of soil depth, Cmic/Nmic increased while the other indexes decreased.(2) Soil respiration rates in different sites had a little difference. The whole level of soil respiration rates in study area was high. During the inter-day observation period, soil respiration rates increased a little and the variation trend was same with soil temperature.(3) Spatial autocorrelation analysis showed that the autocorrelation distances of Cmic, Nmic, Cmic/Nmic, soil invertase, urease and catalase in layer 0-20 cm were 1.8,1.5,2.4,1.3, 1.7,1.62 km and in layer 20-40 cm were 2.0,1.75,2.72,0.85,0.95,1.45 km respectively. The autocorrelation distance of acid phosphatase in layer 0-20 cm was 1.95 km. The spatial autocorrelation coefficient of Cmic/Nmic and acid phosphatase in layer 0-20 cm and Nmic and Cmic/Nmic in layer 20-40 cm changed to negative with the increase of spatial distance and showed significant negative correlation.(4) Semi-variation function analysis showed that the best fitting model of Cmic, Nmic, Cmic/Nmic, soil urease, catalase and acid phosphatase were Gaussians and the determination coefficient were between 0.670-0.896 with better accuracies. While the best fitting model of soil invertase was Spherical with the determination coefficient being less than 0.4 and the fitting effect was relatively bad. Every index in two layers exhibited intensive spatial autocorrelation within major range, which meant the spatial variability was mainly caused by the structure. The major range of every Index was between 1.01-2.22 km.(5) Principal component analysis showed that in 0-20 cm layer the first principal component were catalase, Nmic and urease and the second principal component were Cmic/Nmic and Cmic. In 20-40 cm layer the first principal component were catalase, invertase and Nmic and the second principal component were Cmic/Nmic and acid phosphatase. The contribution to soil fertility of every index was different in different layers and the important components included all indexes.(6) The evaluation results of soil biological fertility quality showed that the soil fertility in study area was mainly third grade, respectively covering the 37.32% and 46.64% of total area in different layers. Then were the forth and second grade. The first grade was small and accounts for 7.5% and 15.16% of the total in the different two layers. The fifth grade was minimum, only accounts for 1.04% and 2.67% of the total. The third and less fertility grades in the study area covered 69.63% and 69.91%. The soil fertility in central area was generally higher than in edge area. |
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