LI Zihan1,2, LUO Weijun1,3, DU Hu4,5, SONG Tongqing4,5, PENG Haijun1, WANG Yanwei1,2, WANG Shijie1,3
（1. State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang , 550002, China;
2.University of Chinese Academy of Sciences, Beijing 100049, China;
3. Puding Karst Ecosystem Research Station, Chinese Academy of Sciences, Puding Guizhou 562100, China;
4. Key Laboratory of Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, 410125, China;
5.Huanjiang Observation and Research Station for Karst Ecosystems, Chinese Academy of Sciences, Huanjiang Guangxi 547100, China）
Abstract: The variation of net ecosystem CO2 exchange (NEE) and the environmental factors was analyzed preliminarily in a karst evergreen deciduous broad-leaf mixed forest ecosystem, Mulun National Nature Reserve in Guangxi, SW China, in dry season to estimate the carbon sinks of the ecosystem during the study period and try to provide a basis for accurately estimating the annual carbon sinks of this ecosystem, in addition, values obtained from other ecosystems under similar climatic conditions were compared . Open-path eddy covariance system was used to continuously measure the CO2 flux in a dry season from October 1st, 2018 to March 31st, 2019. Meanwhile, environmental factors such as precipitation (P), photosynthetic active radiation (PAR), air temperature (Tair), soil temperature (Tsoil), and soil water content (SWC) were also monitored. CO2 flux and concentration have obvious diurnal variation of single-valley shape. NEE is highest at 12:00 with -0.309±0.330 mg CO2/(m2·s), and is lowest at 18:30 with 0.074±0.061 mg CO2/(m2·s). The accumulated NEE, Ecosystem Respiration (Re), and Gross Ecosystem Productivity (GEP) during the study period are -121.4, 209.2 and 330.6 g C/m2, respectively. The carbon sink capacity of this ecosystem is strongest in February 2019, while, Re and GEP reach the maximum in October 2018. PAR is the main controlling factor for the change of daytime NEE (R2=0.40, p＜0.01), and air temperature exponentially correlates with nighttime NEE (R2 = 0.1267, p <0.01). Precipitation has an inhibitory effect on the carbon sink capacity of the ecosystem. Overall, this ecosystem in dry season performs as a carbon sink with 1.214 t C/ha, that significantly lower than other ecosystems under similar climate conditions.
Key words: eddy covariance method; karst hilly area; mixed evergreen and deciduous forest; net ecosystem CO2 exchange; carbon sink capacity
EARTH AND ENVIRONMENT Vol.48, No.5, Tot No.337, 2020, Page 525-536
