| The plantation of Chinese fir is one of the important fast-growing timber species in our country, with the increasing demand for Chinese fir forest, the growing area of the cultivation area and the gradual shortening of the rotation period, the gradual decline of the strength of Chinese fir forest land and the primary productive forces are also declining. In this paper, we took the 27-year-old Chinese fir plantation as the research object in Ⅲ catchment area in Huitong, Hunan Province. Measured and calculated C, N, P content and stoichiometric ratio of leaf, branch, root, litter and soil at the end of each quarter. Record the environmental factors when we collect the plant and soil. Analysed the ecological stoichiometry of leaf, branch, root, litter and soil in different season, and suggested the limiting factor of controlling the process of nutrient cycling, and revealed the synergistic trend of the "organ-litter-soil" system. The results showed that as follows:(1) The C content of plant organs expressed, leaf> root>branch. The N、P content of different organs expressed, leaf>branch>root. But there was no great changes of C and P concentrations.the C:N、C:P and N:P ratio expressed, root> branch> leaf. The C、N、P of plant organ was showing rise then falling after rise again In the growing season. It indicated that during the spring and autumn the Chinese fir forest was growing fast. A nd analyzed the relativity of leaf, branch and root were showing leaf and branch closely.(2) The C content of litter was showing the same rule of plant organ, while N:P ratio was opposite. The N,P content showed rudece then rise.while C:N、C:P ratio were opposite. The N:P ratio was lower at April, in April the litter nutrients decomposition rate increased and nutrient return to soil most. We can adequate fertilization as the C:N ratio during the future management measures.(3) The C, N content of soil increased with the soil depth. And there was no changes in different soil layer. The C content of soil was higher at April, the N content was higher at October, but P as a kind of sedimentary minerals in the soil, the content was no great change. The C:N, C:P ratio showed the same rule with C content, and the N:P ratio was the same with N content. By the C:N ratio, we can know the nutrient of soil. The correlation analysis showed we can change the C, P content to control the C:N ratio.(4) The growth of Chinese fir in III catchment area was mainly limited by N, and mineral weathering rate is higher of soil in this area, so increased the content of organic matter of soil, and the N of plant growth required was mainly come from the decomposition of the litter. At the same time, litter content of Chinese fir was relatively few, further influence nutrient elements content in plant organs like N, P and so on. There are certain positive correlation in C, N, P content and ecological stoichiometry of leaf, branch and root in Chinese fir, and the background value, temperature, light and moisture of the nutrient element content in the soil had certain effect to the ecological stoichiometric characteristics of plant organs; Ecological stoichiometry characteristics of plant organs presented the corresponding change with the constraints of nutrient factors in environment, the adaptability could be expatiated through growth of plant and the functions characters of different organs. We need to further analyze the seasonal dynamics characteristics of Chinese fir forest ecosystem, then to more comprehensive reveal the regulation mechanism of nutrient elements, finally to take a more scientific management measures to improve the economic and ecological benefits of Chinese fir forest. |
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