川西贡嘎山峨眉冷杉成熟林生态系统CO2通量特征

成熟森林的碳收支对陆地生态系统碳循环研究具有重要意义。目前,我国关于西南亚高山暗针叶林成熟林碳通量的研究还相对较少,尚不明确对碳循环的作用。以涡度相关技术为基础,对川西贡嘎山东坡峨眉冷杉成熟林生态系统尺度的CO_2通量进行长期定位观测。利用2015年6月至2016年5月观测数据,分析了峨眉冷杉成熟林净生态系统CO_2交换量(NEE)、生态系统呼吸(Re)和总生态系统生产力(GPP)的季节变异特征及其源汇状况,并结合环境因子,分析CO_2通量的主要控制因子。结果表明:(1)峨眉冷杉成熟林NEE具有明显的日变化特征,呈现"U"形变化,白天为负值,夜间为正值,中午前后CO_2通量达到最大;各月间日平均NEE变化差异显著,NEE峰值最大出现在2015年6月(-0.64 mg CO_2m~(-2)s~(-1)),峰值最小出现在2016年1月(-0.08 mg CO_2m~(-2)s~(-1));日平均NEE由正值变为负值的时间夏季最早,冬季最晚,NEE由负值变为正值的时间冬季最早,夏季最晚。(2)峨眉冷杉成熟林NEE、Re和GPP具有明显的月变化。2015年6月和12月NEE分别达到最大值(-46.02 g C m~(-2)月~(-1))和最小值(-1.42 g C m~(-2)月~(-1));Re呈现单峰变化,最大和最小值分别出现在2015年6月(84.78 g C m~(-2)月~(-1))和2016年1月(12.82 g C m~(-2)月~(-1));GPP最大值和最小值分别出现在2015年6月(130.81 g C m~(-2)月~(-1))与2016年1月(16.15 g C m~(-2)月~(-1))。(3)空气温度(T_a)、5 cm土壤温度(T_(s5))和光合有效辐射(PAR)是影响峨眉冷杉成熟林CO_2通量的主要环境因子。T_a与CO_2通量呈指数相关(R~2=0.5283,P0.01);白天CO_2通量与PAR显著相关(R~2=0.4373,P0.01);夜晚CO_2通量与T_(s5)显著相关(R~2=0.4717,P0.01)。(4)全年NEE、Re和GPP分别为-241.87、564.81 g C m~(-2)和806.68 g C m~(-2),表明川西贡嘎山峨眉冷杉成熟林具有较强的碳汇功能。

Carbon dioxide flux characteristics in an Abies fabri mature forest on Gongga Mountain, Sichuan, China

Carbon budgets for mature forests are important when studying carbon cycling in terrestrial ecosystems. To date, there has been little research on the carbon flux of a mature coniferous forest in the dark coniferous forest of Southwest China, and the role of the carbon cycle is not clear. In this study, the CO₂ flux of an Abies fabri mature forest was observed over a long period of time on Gongga Mountain in western Sichuan Province, China by using the eddy covariance technique. The data from June 2015 to May 2016 were used to analyze the variations in net ecosystem CO₂ exchange (NEE), ecosystem respiration (Re), and gross primary productivity (GPP) so that the carbon sources and sink conditions could be better understood. The data were combined with the environmental factors so that the main control factors affecting CO₂ flux could be analyzed. The results showed that (1) NEE had obvious diurnal variation characteristics and this produced a "U" shaped curve. The NEE was negative during the daytime, positive during the night, and reached its maximum around noon. The average daily NEE changes for each month were significantly different. The maximum peak for NEE appeared in June (-0.64 mgCO₂ m^-2 s^-1) and the minimum peak appeared in January (-0.08 mgCO₂ m^-2 s^-1). The earliest time when NEE changed from positive to negative occurred in winter and the latest in summer. (2) The NEE, Re, and GPP values showed obvious monthly variation characteristics. The NEE reached a maximum (-46.02 gC m^-2 month^-1) in June 2015 and a minimum (-1.42 gC m^-2 month^-1) in January 2016. The Re had a single peak variation, and the maximum and minimum values appeared in June 2015 (84.78 gC m^-2 month^-1) and January 2016 (12.82 gC m^-2 month^-1). The maximum and minimum GPP values appeared in June 2015 (130.81 gC m^-2 month^-1) and January 2016 (16.15 gC m^-2 month^-1), respectively. (3) Air temperature (T_a),5 cm soil temperature (T_s5), and photosynthetically active radiation (PAR) were the main environmental factors affecting the carbon fluxes in the Abies fabri mature forest. Carbon dioxide flux and air temperature had an exponential correlation (R²=0.5283, P < 0.01); CO₂ flux was significantly correlated with PAR during the daytime (R²=0.4373, P < 0.01); and CO₂ flux was significantly correlated with soil temperature (R²=0.4717, P < 0.01). (4) The annual NEE, Re and GPP values were -241.87, 564.81 gC m^-2and 806.68 gC m^-2, respectively. The results showed that mature Abies fabri forest on Gongga Mountain still has a strong carbon sequestration function.