中文摘要：

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CO2浓度及其δ13C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CO2浓度及其δ13C值的差异，并探究其对气象因子的响应．结果表明：林内CO2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，其δ13C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CO2浓度随高度的升高而降低，林内0、2、5、8、12．5和18In处的日均值为386．5、369．9、368．2、367．8、367．9和367．9μmol·mol^-1，δ13C值呈现出随高度升高而升高的趋势，林内0、2、5、8、12．5和18m处的日均值为-16．O‰、-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CO2浓度及δ13C值的主要因子，饱和蒸汽压差（VPD）可以影响林内CO2浓度变化，风速可以影响林冠层CO2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CO2浓度及δ13c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CO2浓度及其δ13C值的变化．

英文摘要：

This research employed off-axis integrated cavity output spectroscopy technique to ob- serve CO2 concentration and δ13C values of planted Platycladus orientalis in Beijing mountainous area. We compared the variation between CO2 concentration and δ13C values in the plantation at dif- ferent heights observed by every 0.5 h to explore how the CO2 concentration and δ13C values respon- ded to the meteorological factors. The results showed that the CO2 concentration showed the pattern of ＂first decreased and then increased＂ after sunrise. The lowest value （ 352.5 μmol ·mool^-1 ） ap- peared at 16：00-16：30, while the maximum value （402.0 μmol·mol^-1） was observed at about 5：00. However, the change of δ13C value was not significant and regular, which increased firstly and then decreased in the surface layer while opposite for the canopy. Atmospheric CO2 concentra- tion decreased with the increasing height. In the height of 0, 2, 5, 8, 12.5 and 18 m, the average daily value was 386.5, 369.9, 368.2, 367.8, 367.9 and 367.9 μmol · mol^-1, respectively. In con- trast, the δ13C values tended to rise correspondingly with height with the average daily value being -16.0‰, -13.7‰, -13.5‰, -13.5‰, -13.1‰and -13.3‰at 0, 2, 5, 8, 12.5 and 18 m, respectively. The stepwise regression analysis showed that temperature and humidity were the main factors for the changes of atmospheric CO2 concentration and δ13C values. The saturated vapor pres-sure difference （VPD） affected the concentration of on the canopy. However, soil moisture, soil electric CO2 concentration and 8~3C values in surface layer. CO2 in the forest and wind speed could affect it conductivity and net solar radiation affected the All these environmental factors influenced CO2 concentration and δ13C values through their influences on the photosynthesis and respiration