Leaf Litter Traits And Decomposition Of Main Woody Plants In Different Community Successional Stages In Karst Rocky Desertification Area In Zhongliang Mountain

Plant functional traits refer to the plant traits that can respond to the living environment changes and / or have certain effects on the ecosystem function. They emphasize the relationship between ecosystem processes and functions, which could predict the change of plant community and ecosystem function in the processes of ecological system development and provide a method to link environmental factors and species characteristics. Litter decomposition is the key link of nutrient cycling in terrestrial ecosystems. Litter decomposition rate determines soil nutrient supply capacity, and then affects the process of vegetation succession. Plant functional traits have been widely using in the study on litter decomposition of different plant species and the regularity of litter decomposition in the worldwide. Precipitation influences the water supply of the soil, which affects the leaching and activity of decomposer in the litter decomposition process, and then affects the decomposition of litter. In the karst rocky desertification area in southwestern China, due to the specific geological characteristics and the impacts of the excessive exploitation and production of human beings, humidity and nutrients become the extremely important limiting factors of ecological system function. In karst rocky desertification areas, how do plant functional traits change in different community successional stages? What are the changes of community litter decomposition in different community successional stages? What is the relationship between functional traits and litter decomposition? How do different rainfall patterns affect the decomposition of leaf litters? All these issues impede people to understand the formation mechanism of vulnerability of rocky desertification habitat. For the purpose, we chose the secondary succession communities in Zhongliang Mountain limestone area, which has been restored naturally about 50 years, 20 years and five years after human disturbance, and designed two experiments to reveal :(1) the relationships between main woody plant functional traits and leaf litter decomposition at different community successional stages in karst environments and(2) the responses of leaf litter decomposition to different rainfall patterns. To compare the changes of functional traits and their decomposition rules at the species level and community level, we performed statistical analysis of the main woody plant litter functional traits at different community successional stages and the mass loss of leaf litter in decomposition process. By calculating the mass loss and nutrient change of leaf litter during decomposition under different rainfall patterns, we explored what is the response of litter decomposition on different rainfall patterns. The results were as follows:1. With the development of community succession, community functional traits shifted from higher community specific leaf area(CSLA), community leaf nitrogen content(CLNC), community leaf phosphorus content(CLPC) and low community leaf dry matter content(CLDMC) to the lower ones. The community species composition changed from resource acquisitive components to resource conservative components.2. The leaf litter decomposition rate of the main woody plants at different successional stages went up first then went down. The decomposition rate of the 50 year recovery communities was lower than that of five year recovery community and 20 year recovery community. This means community nutrient using strategies turned to resource conservation along the succession series. The nutrient changes of leaf litter in decomposition process showed similar trends. This provided further evidence that with the development of succession, the community nutrient using strategies changed from resource acquisition to resource conservation. At species level, LDMC had a good linear relationship with litter decomposition when litter decomposed 90 days and 240 days. While LPC had a good linear relationship with litter decomposition after decomposed 160 days. At community level, CLPC showed a significant positive correlation with CML in the whole experimental stage and it performed best in 160 days of decomposition. The relationship between leaf litter mass loss and functional traits was changing and gradually becomed weak with the progress of decomposition at the species level and community level.3. Different rainfall patterns had different effects on leaf litter mass loss in decompositin. Increased rainfall did not significantly influence the litter decomposition of main woody plant in karst rocky desertification area, but rainfall frequency did. The effect of low frequency rainfall event(long duration and high intensity of rainfall, namely fewer larger rainfall events) on the leaf litter decomposition was negative gradually transformed into positive under the condition of same amount of precipitation supplied, and many-small events had a restrictive effect on litter mass loss. With the decomposition of leaf litter under different rainfall patterns, C content and K content decreased while N content and P content increased. The effect of increased rainfall(fewer larger rainfall event and many smaller rainfall event) on the increase of N content and P content was promoted significantly, especially P, but it had a slight influence on K content. C, N and K of litter in the decomposition process were shown as release pattern in all treatments and P of litter was also shown as release pattern except control group. Fewer larger rainfall groups first slowed release of N, C and then turn to promoting, while many smaller rainfall groups have been shown to slow down the release of C and N all the time. The change of P in fewer larger and many smaller rainfall groups transformed from the release of the control into the accumulation. However, rainfall patterns did not show a significant effect on the variation of K in decomposition process.In the karst rocky desertification area, the community species composition changed from resource acquisitive components to resource conservative components. The relationship between leaf litter mass loss and functional traits was changing and gradually becomed weak with the progress of decomposition at the species level and community level, and the leaf litter P concentration was the limiting factor for the vegetation in this area. The effect of the rainfall frequency on the decomposition of the litter is larger than that of the rainfall. The extreme rainfall events characterized by the increase of the interval of rainfall and the single rainfall may promote the decomposition of litter and the nutrient cycling of nitrogen and carbon in karst rocky desertification area but slow down the cycle of phosphorus. Therefore, the limitation of phosphorus in the area was enhanced to a certain extent. It means that further changes in the pattern of rainfall may exacerbate environmental problems in the region, so that the recovery of karst rocky desertification region will be more difficult.