| The soil organic carbon (SOC) pool is an important component of global C reservoir. there could have a major impact on global terrestrial carbon cycling, eco-system construction and material recycling because of a slight changes in SOC. SOC is sensitive to a range of factors such as soil, climate, and anthropogenic conditions, etc. and various factors are restricted each other. Horizontal distribution characteristics of SOC mainly influenced by climate, and the vertical distribution on soil profile is mainly affected by vegetation types on a global scale. Different vegetation types which have different habitat conditions have formed the different way of SOC input and output, thus affect the reserves of SOC, So far, only few studies have estimated impact of plant diversity on SOC, and less investigations have evaluated how different hierarchies of forest affect SOC. There is also a very big difference between different research results. Low efficiency stands of Cuprssus funebris in the central Sichuan hilly region are important ecological barriers which have very important science value and realistic meaning to preventing soil erosion and water environment deterioration in the upper reaches of the Yangtze River. Moreover, they have great impact on SOC. But they have slow growth, poor quality, low total vegetation cover, and soil structure was severely eroded. Therefore, it is necessary to reconstruct and research low efficiency stands of Cuprssus funebris.Bambusa pervariabilis×Dendrocalamopsis daii (CZ), Cupressus funebris Endl.+Bambusa pervariabilis×Alnus cremastogyne Burk.+Alnus cremastogyne Burk. (BZQ), Cupressus funebris Endl.+Quercus acutissima Carruth (BL), Cupressus funebris Endl.+Bambusa pervariabilis×Dendrocalamopsis daii (BZ) were selected in 2002 to reconstruct low efficiency stands of Cuprssus funebris in Jingyang district, Deyang city, Sichuan province. CZ patter was reconstructed on the basis of 4 m X 4 m after clear cutting,and the other patters were reconstructed after intermediate cutting. We choosed 3 sample plots of 20 m×20 m in each patter which had basically the same site conditions in 2012 to study SOC content, SOC density, easily-oxidized carbon (EOC), water-soluble organic carbon (WSOC), soil microbial biomass carbon (SMBC) and plant diversity. The results were found as follows:(1) Contents of SOC and its fractions were decreased with increasing soil depth, with the most decrease in SOC content and the least in EOC; SOC density in topsoil (0—10cm) accounted for 45.7% to 64.4% of the whole sampling profile with obvious surface accumulation.(2) SOC content, SOC density, EOC, WSOC and SMBC content in 0—40cm were in the order of BZQ>BZ>CB>BL>CZ, with significant differences (p<0.05). Compared with CB, the increase rates of SOC content, SOC density, EOC, WSOC and SMBC content were 37.8%,33.5%,36.6%,52.5% and 23.2%, respectively, and BZQ had the most obvious effect on SOC.(3) The species dominance index, species diversity index, species evenness index and species richness index were roughly BZQ>BZ>CB>BL>CZ. There were significant positive correlation between SOC content, SOC density, EOC, WSOC and SMBC content and the plant diversity of shrub and herbaceous layers; while the correlation were not significant between SOC and its fractions and the plant diversity of tree layer. It indicated that the effects of the diversity of herbaceous and shrub layers on SOC were greater than the tree layers. The most obvious influence of improving SOC content was BZQ patter; we proposed to promote this patter. Due to the transformation of the region is still in its initial stage, Vegetation succession will continue, therefore, it will be more effective to provide a theoretical basis for the transformation of low efficiency stands of Cupressus funebris to track changes in the plant diversity of this region.(4) Contents of soil total N, total P, total K, organic matter content and soil moisture under different reconstructing patterns in low efficiency stands of Cuprssus funebris were decreased with increasing soil depth.BZQ mode and BZ mode were better to improvement the soil, which BZQ mode works best, but BL mode and CZ mode reduced the soil fertility. Comprehensive various soil properties, BZQ mode under different reconstructing patterns in low efficiency stands of Cuprssus funebris was best to improve soil physical and chemical properties, BZ model followed, but BL mode and CZ mode for improved soil fertility effect is not obvious.(5) SOC content and total N, total P, total K, organic matter content and soil moisture showed a significant positive correlation (p<0.01), the activity of different soil organic carbon and total N, total P, total K, organic matter content and soil moisture were a positive correlation; pH with SOC and different soil active organic carbon fractions were correlation significant, while soil bulk density and SOC, SMBC and WSOC were significant correlation (p<0.01), with the EOC and POC correlation were not significant (p> 0.05); soil temperature and SOC, EOC and POC content correlation were not significant, and SMBC content was significantly positively correlated (p<0.01), while the WSOC content was significantly negatively correlated (p<0.01). This indicated that the activity was closely related to SOC and soil organic carbon and soil physical and chemical properties, but the activity could change over in SOC indication of soil fertility, there has a guiding role to further evaluate the effectiveness of the reconstructing patterns.(6) Seasonal dynamics of SOC contents were basically consistent under different reconstructing patterns in low efficiency stands of Cuprssus funebris. SOC content of the autumn and winter seasons were generally greater than the the spring and summer seasons; EOC content of the autumn and spring seasons were generally greater than the winter and summer seasons; POC content of the autumn and winter seasons were generally greater than the spring and summer seasons; SMBC content of the winter and autumn seasons were generally greater than the summer and spring seasons; WSOC content of the winter and spring seasons were generally greater than the summer and autumn seasons. Significant difference was found in different forms of organic carbon in different quarter peak, which showed that the soil temperature and humidity variation of different seasons were one of the main influence factors. |
