洪泽湖地区杨树人工林碳水通量昼夜和季节变化特征

【目的】通过对洪泽湖地区杨树人工林生态系统碳水通量的昼夜变化和季节变化特征进行分析,为评估该杨树人工林生态系统的固碳能力提供必要的基础数据,揭示杨树人工林生态系统碳循环及对外部气象环境因子的响应,同时为增强森林生态系统固碳能力提供依据。【方法】以洪泽湖地区杨树人工林生态系统为研究对象,利用涡度相关技术和微气象观测系统进行长期且连续的通量以及气象环境观测。选取2017年5月至2018年4月期间的原始观测数据,对异常数据进行剔除和插补处理,同时,利用EddyPro软件中的Express Mode模块对通量数据进行二次坐标旋转、频率损失订正以及WPL密度效应修正,最终转化为30 min数据。分析杨树人工林生态系统与大气间的二氧化碳(CO₂)、甲烷(CH₄)和潜热(latent heat, LE)通量的季节动态变化和昼夜变化特征及其与外部气象环境因子的相互关系。【结果】洪泽湖地区杨树人工林生态系统碳通量均有显著的昼夜和季节变化,净生态系统碳交换(net ecosystem exchange, NEE)白天为较强的碳汇,夜晚为较弱的碳源,整年表现为固碳作用,年通量为-506.9 g/(m²·a)。其日变化在生长季和非生长季均呈“U”形曲线,生长季的碳吸收明显大于非生长季;在生长季白天,NEE与光合有效辐射(photosynthetically active radiation, PAR)呈显著的对数关系;而在非生长季,NEE与夜间土壤温度(soil temperature,T_s)呈显著的指数关系。洪泽湖地区杨树人工林生态系统LE的昼夜和季节变化显著,在生长季和非生长季均呈“单峰型”曲线,且在生长季大于非生长季,LE与饱和水汽压差(vapor pressure deficit, VPD)在生长季和非生长季均呈显著的线性正相关关系。洪泽湖地区杨树人工林生态系统CH₄通量在生长季和非生长季均无显著的昼夜变化,在生长季为较弱的CH₄吸收,非生长季为中性至微弱的CH₄排放,全年可能表现为较微弱的CH₄汇。【结论】洪泽湖地区杨树人工林生态系统整体具有较高的固碳能力,CO₂和LE通量具有显著的昼夜变化和季节变化规律,而CH₄通量季节和昼夜变化并不显著,生态系统碳水通量受环境因子的影响较显著,可以为今后提升杨树人工林的固碳能力提供参考。因此,营造杨树人工林将是短期内吸收大气中的CO₂和CH₄并缓解气候变化的有效途径。

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

【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 (T_s). 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.