Wang Bin, Jin Haiyan, Li Qi, Chen Dongdong, Zhao Liang, Tang Yanhong, Kato Tomomichi, Gu Song
Key Laboratory of Marine Ecosystem and Biogeochemistry, Second Institute of Oceanography, State Oceanic Administration, Hangzhou, China.
College of Life Science and Agriculture and Forestry, Qiqihar University, Qiqihar, China.
PLoS One. 2017 Jan 27;12(1):e0170963. doi: 10.1371/journal.pone.0170963. eCollection 2017.
Carbon dioxide (CO2) exchange between the atmosphere and grassland ecosystems is very important for the global carbon balance. To assess the CO2 flux and its relationship to environmental factors, the eddy covariance method was used to evaluate the diurnal cycle and seasonal pattern of the net ecosystem CO2 exchange (NEE) of a cultivated pasture in the Three-River Source Region (TRSR) on the Qinghai-Tibetan Plateau from January 1 to December 31, 2008. The diurnal variations in the NEE and ecosystem respiration (Re) during the growing season exhibited single-peak patterns, the maximum and minimum CO2 uptake observed during the noon hours and night; and the maximum and minimum Re took place in the afternoon and early morning, respectively. The minimum hourly NEE rate and the maximum hourly Re rate were -7.89 and 5.03 μmol CO2 m-2 s-1, respectively. The NEE and Re showed clear seasonal variations, with lower values in winter and higher values in the peak growth period. The highest daily values for C uptake and Re were observed on August 12 (-2.91 g C m-2 d-1) and July 28 (5.04 g C m-2 day-1), respectively. The annual total NEE and Re were -140.01 and 403.57 g C m-2 year-1, respectively. The apparent quantum yield (α) was -0.0275 μmol μmol-1 for the entire growing period, and the α values for the pasture's light response curve varied with the leaf area index (LAI), air temperature (Ta), soil water content (SWC) and vapor pressure deficit (VPD). Piecewise regression results indicated that the optimum Ta and VPD for the daytime NEE were 14.1°C and 0.65 kPa, respectively. The daytime NEE decreased with increasing SWC, and the temperature sensitivity of respiration (Q10) was 3.0 during the growing season, which was controlled by the SWC conditions. Path analysis suggested that the soil temperature at a depth of 5 cm (Tsoil) was the most important environmental factor affecting daily variations in NEE during the growing season, and the photosynthetic photon flux density (PPFD) was the major limiting factor for this cultivated pasture.
大气与草原生态系统之间的二氧化碳（CO₂）交换对全球碳平衡非常重要。为了评估CO₂通量及其与环境因子的关系，于2008年1月1日至12月31日，采用涡度协方差法对青藏高原三江源地区某人工草地生态系统净CO₂交换量（NEE）的日变化和季节动态进行了观测。生长季NEE和生态系统呼吸（Re）的日变化均呈单峰型，CO₂吸收的最大值和最小值分别出现在中午和夜间；Re的最大值和最小值分别出现在下午和清晨。NEE和Re的小时最低值分别为-7.89和5.03 μmol CO₂ m⁻² s⁻¹。NEE和Re呈现明显的季节变化，冬季较低，生长盛期较高。碳吸收和Re的日最高值分别出现在8月12日（-2.91 g C m⁻² d⁻¹）和7月28日（5.04 g C m⁻² d⁻¹）。年总NEE和Re分别为-140.01和403.57 g C m⁻² a⁻¹。整个生长季表观量子效率（α）为-0.0275 μmol μmol⁻¹，草地光响应曲线的α值随叶面积指数（LAI）、气温（Ta）、土壤含水量（SWC）和水汽压差（VPD）的变化而变化。分段回归结果表明，白天NEE的最适Ta和VPD分别为14.1℃和0.65 kPa。白天NEE随SWC增加而降低，生长季呼吸温度敏感性（Q10）为3.0，受SWC条件控制。通径分析表明，5 cm土壤温度（Tsoil）是影响生长季NEE日变化的最重要环境因子，光合有效辐射（PPFD）是该人工草地的主要限制因子。
