Leaf litter decomposition characters and impact on soil organic carbon/nitrogen in different vegetation restorations of karst rocky desertification: An example of the Zhongliang mountain in Chongqing

Restoring vegetation and improving soil quality is key to the control of rocky desertification. Soil organic carbon/nitrogen is not only the key component of soil quality, but also the basic role in the soil fertility system. In this study the Shiqing village in Nanchuan, a typical man-made vegetation restoration base, and the Zhongliang mountain in Beibei, a typical natural vegetation restoration pattern, were chosen as the study sites. In these areas, some typical sample plots were selected based on the field investigation and leaf litter of dominant plant species was collected. Then the treated leaf litter was filled into litter bags and was buried in the respective sample plots. At the same time, some 0-10 cm layered soil samples were collected in the vicinity of buried litter bag site in every experimental plot. In order to probe into leaf litter decomposition characters in the process of vegetation recovery, and the impact of leaf litter decay on soil organic carbon/nitrogen accumulation and nitrogen supply in karst rocky desertification areas, leaf litter decomposition rate of dominant plant species and organic carbon/nitrogen release rate were examined using the litter bag burying method, and the correlation between leaf litter decomposition and soil organic/nitrogen was analyzed in this study. On the basis of this analysis, this work discussed the key aggregate-size in the process of organic/nitrogen accumulation. The main results are as follows, the coefficient k of leaf litter decomposition varies from 0.73 to 1.33. On different sampling lands, the k value shows a tendency of grass land < brush land < arbor land < brush-arbor land .The k value of Cinnamomum camphora tree land is greater than arbor land and less than shrub-arbor land. With the extension of vegetation recovery, leaf litter decomposition rate increases. At the same time, organic carbon of leaf litter shows a releasing status during the decomposition period; and the release rate of organic carbon varies in 58.5%-72.9%, while the release rate of organic nitrogen varies in 21.2%-63.9%. The study results also show that the leaf litter decomposition rate and organic carbon/nitrogen release rates are controlled mainly by the initial nitrogen content and C/N ratio of leaf litter. Furthermore, there is a significantly positive relationship between the leaf litter decomposition rate and the light fraction organic carbon/nitrogen contents of the soil aggregate of 0.25-1 mm and <0.25 mm classes. Accordingly, the light fraction organic carbon/nitrogen is preference of the process to smaller aggregate-sizes in the leaf litter decomposition period. So in the process of accumulation, active organic carbon and nitrogen are in superior to the smaller sizes of aggregate, and the smaller size aggregates play an important role in this process. Therefore, the leaf litter decomposition is an important role in the vegetation recovery process. On one hand, the litter decomposition could provide nutrients for plant growth; on the other hand, it could promote the formation and accumulation of soil organic matters. In the process of vegetation succession, the work of soil and water conservation should be strengthened, so as to improve the capacity of absorption and storage of soil nutrients.