| With the population growing and the socio-economic rapid developing, continuously increasing of land use and development has led to changes of global biogeochemical cycle and speed up the rate of the soil properties (such as soil nutrients, soil moisture, etc.) change.Thereby land use change affected many ecological processes of the soil, lead to decreased soil quality and accelerated soil erosion and soil degradation. Thus effect of land use change on soil ecological environment has been the main issue of research in the earth surface system interface process and environmental effects.Subtropical mountain areas of China are large. Because of high mountains, steep slopes, thin soil organic and poor soil resisted erosion, soil and water loss easily happen. Mountain ecosystems has great potential frangibility. However, subtropical mountain has rich light, heat, water, soil, biological resources, and good water and heat conditions, so that land use types are manifold. Land use change has significantly changed the structure, function and pattern of systems in a subtropical mountain and will affect the direction and the magnitude of soil ecology environmental change.Research plots are set up in the Shuitou Town, Nanan city, Fujian of the subtropical region. The object of the study is the secondary broad-leaved forest,consistent with the conditions of the background,plantation, economic forest, cultivated field and mine land. This paper studies effects of land use change on soil moisture physical structure and water storage characteristics,soil organic carbon and nutrients distribution,anti-erosion properties of the soil.Based on field sampling and laboratory analysis in 2008, a comprehensive evaluation has made on soil quality and soil anti-erosion to further clarify the mechanism of land use change influence on soil quality and anti-erosion performance in sub-tropical. To provide scientific basis for scientifically adjusting the land use patterns and improving soil quality for the subtropical mountain. It has the important theoretical and practical significance to promote regional sustainable development. The results show that:(1) Soil bulk density increased, porosity decreased and the soil structure tended to tighten from secondary broad-leaved forest to plantation, economic forest, farmland, mine land. Effects of land use change on surface soil were significantly higher than the underlying soil. Soil bulk density increased by 8.03%～25.89% because of land use change, total porosity decreased by 6.58%～34.57% and the total water storage capacity reduced by 7.0%～41.22% in 0-60cm soil layer. Ventilation degree of farmland is slightly better than that of secondary broad-leaved forest. Capillary porosity of Eucalyptus robusta plantation increased by 20.34% than that of the secondary broad-leaved forest, but the non-capillary porosity decreased 69.92%. The capillary porosity is the main gap in total gap. From the perspective of soil and water conservation, soil non-capillary porosity reflect the size of the soil moisture retention and water conservation and reduction of the flood, therefore water conservation function and reducing the flood peak capacity of Eucalyptus robusta plantations decreased significantly.(2) Soil organic carbon content of different land use types decreased with soil depth and exponential trend, the ratio of decrease in secondary broad-leaved forest and Eucalyptus plantations is greater than that in the economic forest and farmland. Soil organic carbon contents of secondary broad-leaved forest and other land use types were significantly different (P<0.05) between different soillayers. The average soil organic carbon content in secondary broad-leaved forest is 10.78 g·kg-1 and carbon storage is 83.48t·hm-2 in 0-60cm soil depth. The soil organic carbon content decreased by 16.51%～63.47%, organic carbon storage decreased 9.79%～93.62% from secondary broad-leaved forest into other land use types. The ratio of soil organic carbon of 0～10cm layer to 0-60cm soil layer is about 31.22%～32.65% in secondary broad-leaved forest and Eucalyptus plantations, as the main storage of organic carbon level. While the ratio of soil organic carbon storage of 0～20cm to 0～60cm is 36.97%～45.72% in the economic forest and farmland, therefore 0～20cm is the main storage of organic carbon levels. The impact of land use change on soil organic carbon content under 40cm layer is minimal. Soil organic C behaves significant accumulation characteristics in the top soil. This explains to some extent that the secondary broad-leaved forest has unparalleled advantage of carbon sequestration with other land use types.(3) Soil TN and TP were significantly decreased from secondary broad-leaved forest to plantation, economic forest, farmland, mine land.TN decreased 11.61%～92.05%, N reserves declined 12.85%～44.40%; TP down 23.36%～56.93%, P reserves fell by 22.03%～60.79%. TK of soil mainly is from soil minerals and less affected by land use change. Average TK levels of mine land is the largest, that of secondary broad-leaved forest and economic forest is second, and that of Eucalyptus plantations and the farmland is lowest. Soil N accumulation characteristics of the topsoil is significant, while that of K and P in topsoil is not obvious.(4) Soil available N of farmland(68.96 mg·kg-1) and that of secondary broad-leaved forest (70.83 mg·kg-1) is relatively close affected by artificial fertilization. The effect of artificial fertilization and degree of mineralization on soil available phosphorus content is significant. Available P content in farmland is high to 37.15 mg·kg-1, the economic forest for the 4.38 mg·kg-1, that in mine land is the relatively high for the 1.94 mg·kg-1, while P content in the secondary broad-leaved forest and Eucalyptus plantation is only 1.83% and 1.59%of the farmlad, is 13.47%,and 15.53% of the economic forest. From secondary broad-leaved forest to Eucalyptus plantation, economic forest, farmland and mine land, soil available K decreased by 6.64%～37.97%.(5) From secondary broad-leaved forest to the plantation, forest, slope cultivation, mine land leads to the trend of degradation of soil quality. This paper uses soil quality index (ISQI) and soil degradation index (ID) to evaluate the soil quality of different land use patterns, evaluation results and the actual availability of soil nutrients is consistent. Soil quality of secondary broad-leaved forest, fewer human disturbance, is the best, followed by Eucalyptus plantations and economic forest, farmland soil of poor quality, and the most serious soil degradation in mine land. A good linear relationship between ISQI and ID (P<0.01). This indicated that the soil degradation index, index of soil quality and soil Nemerow index can also be used to evaluate effect of land use changes on soil quality in the study area. The secondary broad-leaved forests of natural recovery helps to improve soil quality.(6) Secondary broad-leaved forest to other land use types, large aggregates, clay content, MWD decreases, the aggregates content of smaller size and sand content increased, aggregate breakage rate and dispersion rate increase, and soil anti-erosion index decreased. But the degree and the basic conditions of aggregate in Eucalyptus robusta plantation are better than that in the secondary broad-leaved forest, the distribution ratio is slightly smaller than that of the secondary broad-leaved forest. Evaluation of soil anti-erosion and soil quality evaluation results were consistent, the secondary broad-leaved forest strongest, Eucalyptus robusta plantations and Forest's second, cultivated soil of anti-erosion poor, while the mine land worst.(7) Obtaining soil erosion resistance comprehensive index A. A of Secondary broad-leaved forest, Eucalyptus robusta plantation, the economic forest, farmland and mine land is 12.62,10.44,3.46,-2.61 and-9.51, respectively.Secondary broad-leaved forest into plantations, soil with high content of capillary gap in Eucalyptus robusta plantation, its favorable for roots to absorb a large amount of water from the soil, a large number of rainwater infiltration too late, easy to form a strong surface runoff, increased soil erosion occurring because of low levels of non-capillary gaps in the rainfall-rich sub-tropical regions. Land use change significantly reduced the function of soil carbon sinks, especially the large area exposed to mine land,we should actively take artificial measures, appropriate plant selection, the rapid formation of the vegetation types adapted to the environmental conditions, vegetation coverage increasing may improve the soil carbon pool at the same time, in order to absorb more CO2, emitting more O2.lt has very important significance to mitigate climate warming. Soil phosphorus in farmland and economic forest is relatively high, so to control non-point source pollution, controlling the output of soil phosphorus of farmland and economic plantation may be more important.That soil properties response to the land use change is effected by the time largly,so the comparison of multiple time periods is needed to be really clear the soil real change under different use patterns. The future study should combine with new theoretical models and techniques such as spatial analysis to propose sensitive indicators of soil quality evaluation system. To provide a theoretical foundation for the spatial variation and rapid assessment of soil quality.
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