Carbon Storage And Soil CO₂ Efflux Of Tropical Seasonal Rain Forest, Rubber Tree Plantation And Paddy Soil In Xishuangbanna, Southwest China

Global change, with great impacts on natural ecosystems and human society, is a great concern of scientists, common people and governments around the world. The increasing CO2 concentration in atmosphere, induced from fossil fuel burning and land use/land cover change, is one of the main factors related to global warming. The research on soil respiration and carbon sequestration in vegetation is important for understanding carbon cycle in terrestrial ecosystem.Based on the biomass data from previous studies and the dada collected in this study, we estimated the carbon stock in the biomass of tropical seasonal rain forests, secondary forests and rubber tree plantation of different age. The carbon stock in the biomass of tropical seasonal rain forest was 180.46 tC hm-2,and that of rubber tree plantation at the age of 7, 15, 22 and 40-year-old was 18.36, 75.36, 169.75 and 362.18 tC hm-2, respectively. The mean carbon increase rate of rubber tree plantation was 7.78 tC hm-2 a-1.The carbon stock in the soil at the depth of 1m of tropical seasonal rain forest, 15-year-old rubber tree plantation and paddy soil was 80.1, 144.3 and 103.0 tC hm-2, respectively.The diurnal change of soil respiration rate of tropical seasonal rain forest was small, but the seasonal change was great, in relation to temperature, soil moisture and plant phenology. The annual CO2 emission from soil, soil with litter, and soil with litter & seedlings treatment was 9.5, 12.7 and 14.6 tC hm-2 a-1,respectively. Q10 value was 2.03, 2.36 and 2.08, respectively.The soil respiration rate of rubber tree plantation changed seasonally, with no close relationship to temperature and soil moisture. The annual CO2 emission from soil was 10.97 tC hm-2 a-1. Q10 was 1.65 to 1.86.The diurnal change of soil respiration rate and rice ecosystem respiration rate were obvious. In growing season, soil respiration rate and rice ecosystem respiration rate related negatively to depth of water. In the relative dry period before rice transplanting, soil respiration rate related positively to soil moisture. In the wet period after rice harvest, soil respiration rate was mainly affected by temperature. Q10 was 2.46 to 3.67. The annual CO2 emission from rice ecosystem with normal nitrogen fertilizer dosage was 6.37 tC hm-2 a-1. NEE was 2.24 tC hm-2 a-1. This rice ecosystem served as a carbon sink.We studied carbon flux in tropical seasonal rain forest by eddy covariance technique. NEE changed obviously at diurnal, seasonal and inter-annual scale. The temporal change of NEE was shaped by local specific climate and related plant phenology, balance between photosynthesis and plant respiration, soil respiration, litter decomposition, fine root decomposition. The result showed that the tropical seasonal rain forest in Xishuangbanna was a carbon sink from 2003 to 2006, and changed seasonally, as a carbon source in wet season (from April to August), a carbon sink in other seasons.