THE VERTICAL CHARACTERISTICS OF SOIL CARBON AND NITROGEN AT DIFFERENT RUBBER PLANTATION AGES IN XISHUANGBANNA, SOUTHWEST CHINA

The tropical rainforest of Xishuangbanna (XSBN) in the southern Yunnan province is the most intact tropical rainforest of the high-latitude and high-altitude areas in China, and the only oasis at the latitude of 21 degrees north. However, large-scale rubber planting has seriously damaged the ecological environment in recent decades. The relationship between the carbon (C) and nitrogen (N) contents of soil and the stand age has been discussed based on the organic carbon (SOC) and nitrogen (STN) content of soil, the C/N variation in rainforests, and rubber plantation at different stand ages (10a, 22a, 30a). Furthermore, we analysed the factors influencing the variation of soil carbon and nitrogen. The results showed that the contents of SOC, STN, and C/N decreased with the depth of the soil profile in the study area at the same stand age. The order of the SOC content of different rubber stand ages at the same depth was generally as follows: 22a >30a >10a. The STN pattern from 30 cm depth to the top was 22a >10a >30a and the variation regularity was not significant below 30 cm. However, the value of C/N increased gradually with the age of the rubber trees. This indicates that the SOC and STN contents are significantly affected by the soil depth and stand age. Compared with the rainforest in the same region, the lower SOC and STN concentrations and the higher C/N of the rubber plantation demonstrated the effect of the rubber plantation on the carbon storage and nutrient utilization, which is much lower than that of virgin forest. Human activities (such as tapping) further intensified the loss of nitrogen in the soil.