Changes of Atmospheric CO2, Photosynthesis of the Grass Layer and Soil CO2 Evolution in a Typical Temperate Deciduous Forest Stand in the Mountainous Areas of Beijing
作 者 ：Jiang Gao-ming, Han Xing-guo and Zhou Guang-sheng
Abstract:Middle-sized chambers (40 cmx 40 cmx20 cm) and an infrared gas analyzer (IRGA)were used for the measurement of net photosynthesis of the grass layer and soil CO2 evolution, in Quercus liaotungensis Koidz. forest, which is a typical temperate forest ecosystem in the mountainous areas of Beijing. Changes of CO2 concentrations in both the atmosphere (2 m above canopy) and the forest canopy (2 m below the top of the canopy) together with those of net photosynthesis and soil CO2 evolution were also examined, in order to find the characteristics of CO2 exchange between the different components of the temperate forest ecosystem and the atmosphere. Atmospheric CO2 averaged (323 ±10) and (330± 1) μmol‘mo1-1 respectively in summer and autumn. During the 24-hour measurements, large differences as much as – 46 and – 61 μmol ·mol- 1 respectively in the atmosphere and forest were found. Net photosynthesis of the grass layer in summer was (2.59 ± 1.05) μmol CO2·m-2·s-1, two times of that in autumn, (1.31±0.39) μmol CO2·m-2·‘s-1. In summer, there was much more CO2 evolved from soil than in autumn, averaging (5.18 ± 0.75) μmol CO2·m- 2·s- 1 and ( 1.96 ± 0.57) tanol CO2· m- 2· s- 1, respectively. A significant correlation was found between soil CO2 evolution and ground temperature, with Y = –0.864 2 + 0.310 1X, r =0.7164, P < 0.001 (n = 117). Both the minimal atmospheric CO2 level and the maximum net photosynthesis occurred around 14:00; and an increase in atmospheric CO2 and of soil CO2 evolution during night times were also found to be remarkable.