Diurnal and Seasonal Variations of CO2 Fluxes and Their Climate Controlling Factors for a Subtropical Forest in Ningxiang

• Published in: Advances in atmospheric sciences Vol. 32; no. 4; pp. 553 - 564
• Main Authors: Jia, Binghao, Xie, Zhenghui, Zeng, Yujin, Wang, Linying, Wang, Yuanyuan, Xie, Jinbo, Xie, Zhipeng
• Format: Journal Article
• Language: English
• Published: Heidelberg Science Press 01.04.2015; Springer Nature B.V; State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics,Institute of Atmospheric Physics,Chinese Academy of Sciences,Beijing 100029%State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics,Institute of Atmospheric Physics,Chinese Academy of Sciences,Beijing 100029; University of Chinese Academy of Sciences,Beijing 100049
• Subjects: Atmospheric Sciences; Carbon dioxide; Carbon sinks; Climate change; CO2通量; Drought; Earth and Environmental Science; Earth Sciences; Ecosystems; Geophysics/Geodesy; Greenhouse gases; Growing season; Meteorology; Moisture content; Rainforests; Seasonal variations; Soil water; Solar radiation; Summer; Vapor pressure; Water content; Winter; 二氧化碳通量; 亚热带森林; 季节变化; 控制因素; 日变化; 气候因素; 生态系统呼吸; East Asian monsoon region; net ecosystem exchange; diurnal and seasonal variations; climate controlling factors; subtropical mixed forest
• ISSN: 0256-1530; 1861-9533
• DOI: 10.1007/s00376-014-4069-4

In this study, the diurnal and seasonal variations of CO2 fluxes in a subtropical mixed evergreen forest in Ningxiang of Hunan Province, part of the East Asian monsoon region, were quantified for the first time. The fluxes were based on eddy covariance measurements from a newly initiated flux tower. The relationship between the CO2 fluxes and climate factors was also analyzed. The results showed that the target ecosystem appeared to be a clear carbon sink in 2013, with integrated net ecosystem CO2exchange（NEE）, ecosystem respiration（RE）, and gross ecosystem productivity（GEP） of-428.8, 1534.8 and1963.6 g C m^-2yr^-1, respectively. The net carbon uptake（i.e. the-NEE）, RE and GEP showed obvious seasonal variability,and were lower in winter and under drought conditions and higher in the growing season. The minimum NEE occurred on12 June（-7.4 g C m^-2d^-1）, due mainly to strong radiation, adequate moisture, and moderate temperature; while a very low net CO2 uptake occurred in August（9 g C m^-2month^-1）, attributable to extreme summer drought. In addition, the NEE and GEP showed obvious diurnal variability that changed with the seasons. In winter, solar radiation and temperature were the main controlling factors for GEP, while the soil water content and vapor pressure deficit were the controlling factors in summer. Furthermore, the daytime NEE was mainly limited by the water-stress effect under dry and warm atmospheric conditions, rather than by the direct temperature-stress effect.