The Net Ecosystem Carbon Exchange and Its Environmental Factors in a Tropical Rubber Plantation Ecosystem in Hainan Island
The rubber plantation in the northwest of Danzhou, Hainan area was used as the study object with the eddy covariance technique for long-term CO2 flux observations, Hainan rubber forest ecosystem carbon flux dynamic characteristics were obtained, and the responses on the environmental factors were analyzed in the research. The results showed as follows:(1) The daily dynamic of net ecosystem carbon exchange(NEE) of rubber plantation ecosystem was an " U" shaped curve; and rubber trees absorbed carbon during the daytime( NEE negative), released carbon nighttime( NEE positive). All the monthly NEE values throughout the year except February were negative(rubber trees absorb carbon); and the NEE values from April to October during the rainy season were large, from January to March, November to December during the dry season little. Rubber plantation ecosystem had the strong carbon sequestration capability, and the yearly NEE values were more than 11.0 t C/(hm2·a).( 2) The NEE of rubber plantation ecosystem and all the environmental factors such as photosynthetically active radiation( PAR), the average atmosphere temperature within the canopy( Ta),-5 cm soil temperature( T_-5 cm),vapor pressure deficit( VPD) and-5 cm soil volume water content( VWC_-5 cm) were negatively correlated with different intensity, and PAR was the most significantly related factor. NEE was also associated with the rubber plantation itself stand conditions and ambient atmospheric CO2 concentration. The results could provide a reference for tropical plantation ecosystems carbon estimates and offer basic data reduction for the government trade negotiations.