JOURNAL OF NANJING FORESTRY UNIVERSITY ›› 2019, Vol. 43 ›› Issue (5): 113-120.doi: 10.3969/j.issn.1000-2006.201806032

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Diurnal and seasonal changes of fluxes over a poplar plantation in Hongze Lake basin

ZHANG Yue1(), FENG Huili1, WANG Weifeng1, XUE Jianhui1,2,*(), WU Yongbo1, YU Shuiqiang1   

  1. 1. College of Biology and the Environment, Co-Innovation Center of the Sustainable Forestry in the Southern China, Nanjing Forestry Univeristy, Nanjing 210037, China
    2. Institute of Botany, Jiangsu Province and Chinese Academy of Sciences, Nanjing 210014, China
  • Received:2018-06-25 Revised:2018-11-05 Online:2019-10-08 Published:2019-10-08
  • Contact: XUE Jianhui E-mail:649669013@qq.com;jhxue@njfu.com.cn

Abstract:

【Objective】 The frequent exchange of carbon water between forest ecosystems and the atmosphere has a significant effect on carbon sequestration, which plays an important role in the regulation and mitigation of global climate change. It is important to study the carbon water exchange of forest ecosystems, in order to elucidate the carbon water cycle and carbon sequestration capacities of forest ecosystems. Furthermore, few studies have investigated the carbon water flux of poplar plantations in the Hongze Lake basin. Therefore, the aim of the present study was to investigate the diurnal and seasonal variations of carbon water flux in the poplar plantation ecosystem of the Hongze Lake basin, in order to establish a basis for evaluating the carbon sequestration capacity of the poplar plantation ecosystem. This study determined the carbon cycle of the poplar plantation ecosystem, as well as the response of the ecosystem to external meteorological factors, and established a basis for enhancing the carbon sequestration capacity of forest ecosystems. 【Method】 The present study investigated the diurnal and seasonal variations of carbon water flux in the poplar plantation ecosystem of the Hongze Lake basin, using the eddy covariance technique and micro-meteorological observation to document the long-term and continuous flux and meteorological environments. The original observation data from May 2017 to April 2018 were selected to remove and interpolate the abnormal data, and two coordinate rotation, frequency loss revision and WPL density effect were carried out on the flux data using the Express Mode module in EddyPro, which is eventually converted to the data of the 30 min. The diurnal and seasonal dynamics of CO2, CH4, and latent heat flux between the poplar plantation ecosystem and the atmosphere, as well as their correlation with external meteorological factors, were analyzed. 【Result】 ① The carbon flux of the poplar plantation ecosystem exhibited significant diurnal and seasonal variation, and CO2 flux was a strong carbon sink and source during the day and night, respectively. The ecosystem was a carbon sink throughout the year, with an annual net ecosystem exchange (NEE) of -506.9 g/(m2·a). The daily changes exhibited a U-shaped curve during both the growing and non-growing seasons, and the carbon absorption during the growing season was significantly greater than that during the non-growing season. During the growing season, the NEE exhibited a significant logarithmic relationship with photosynthetically active radiation (PAR), whereas during the non-growing season, NEE exhibited a significant exponential relationship with nocturnal soil temperature (Ts). ② The latent heat (LE) of the poplar plantation ecosystem exhibited significant diurnal and seasonal variation, with a “single peak-type” curve during both the growing and non-growing seasons, and in the growing season greater than the non-growing season. Both LE and vapor pressure deficit (VPD) exhibited a significant linear positive correlation between the growing and non-growing seasons. ③ There was no significant diurnal or seasonal variation in CH 4 flux during either the growing or non-growing season; CH4 was weakly absorbed during the growing season and, at best, weakly emitted during the non-growing season. In addition, the whole year was shown as the weak CH4 sinks. 【Conclusion】 The poplar plantation ecosystem of the Hongze Lake basin possesses a high carbon sequestration capacity. Indeed, CO2 and LE flux exhibited significant diurnal and seasonal variation, whereas CH4 flux was not significant, and the carbon water flux of the ecosystem was significantly influenced by environmental factors. This work provides a reference for improving the carbon sequestration ability of poplar plantations and indicates that the poplar plantation ecosystem of the Hongze Lake basin could continue to function as strong CO2 sink and weak CH4 sink here after. Therefore, planting trees, such as poplar, could be an effective way to sequester carbon and to mitigate climate change in the near future.

Key words: poplar plantation, carbon and water flux, environmental factor, diurnal change, seasonal change, Hongze Lake basin

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