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本研究采用离轴积分腔输出光谱技术对北京山区侧柏人工林进行了大气CO_2浓度及其δ~(13)C值的原位观测,在半小时尺度上对比了林内不同高度处大气CO_2浓度及其δ~(13)C值的差异,并探究其对气象因子的响应.结果表明:林内CO_2浓度自日出后经历先降低后升高的变化趋势,最低值出现在16:00—16:30,浓度为352.5μmol·mol~(-1),最大值出现在5:00左右,达到402.0μmol·mol~(-1),其δ~(13)C值变化趋势微弱且较为复杂,呈现出近地层先降低后升高、林冠层先升高后降低的趋势;研究日期内,林内CO_2浓度随高度的升高而降低,林内0、2、5、8、12.5和18 m处的日均值为386.5、369.9、368.2、367.8、367.9和367.9μmol·mol~(-1),δ~(13)C值呈现出随高度升高而升高的趋势,林内0、2、5、8、12.5和18 m处的日均值为-16.0‰、-13.7‰、-13.5‰、-13.5‰、-13.1‰和-13.3‰;逐步回归分析表明,温度和湿度是影响林内大气CO_2浓度及δ~(13)C值的主要因子,饱和蒸汽压差(VPD)可以影响林内CO_2浓度变化,风速可以影响林冠层CO_2浓度变化,而土壤含水率、电导率和地面净辐射则是影响近地层CO_2浓度及δ~(13)C值的环境因子.这些环境因子通过增强或减弱生态系统内光合作用和呼吸作用来影响林内CO_2浓度及其δ~(13)C值的变化.
In this study, atmospheric CO 2 concentration and δ 13 C values of Platycladus orientalis plantations in Beijing mountainous area were measured by off-axis integrated output spectroscopy. The atmospheric CO 2 concentrations at different altitudes in the forest were compared on a semi-hour scale And δ ~ (13) C values were measured and their response to meteorological factors was explored.The results showed that CO 2 concentration in forest changed from low to high and then increased after sunrise, the lowest value appeared at 16: 00-16 : 30, the concentration was 352.5μmol · mol -1, the maximum appeared at about 5:00, reached 402.0μmol · mol -1, the δ 13 C value tended to be weak and complex, The results showed that the near-surface layer decreased first and then increased, and the canopy at first increased and then decreased. During the study period, the CO 2 concentration in the forest decreased with the increase of height, and at 0, 2, 5, 8, 12.5 and 18 m The daily average values were 386.5, 369.9, 368.2, 367.8, 367.9 and 367.9 μmol · mol -1, and the δ 13 C values showed a trend of increasing with increasing height. The daily mean values at 12.5 and 18 m were -16.0 ‰, -13.7 ‰, -13.5 ‰, -13.5 ‰, -13.1 ‰ and -13.3 ‰, respectively. The stepwise regression analysis showed that temperature and humidity were the main factors influencing the atmospheric CO2 And the main factors of δ ~ (13) C value. The saturated vapor pressure difference (VPD) can affect the change of CO_2 concentration in the forest. The wind speed can affect the change of CO_2 concentration in the forest canopy, while the soil water content, conductivity and net radiation CO2 concentration in the formation and δ ~ (13) C, which affect the CO2 concentration in the forest and the δ ~ (13) C value by increasing or decreasing the photosynthesis and respiration in the ecosystem.