基于涡度协方差法和生理生态法对落叶松林CO2通量的初步研究

 该文利用涡度协方差法和生理生态学方法（不同分量的累积和）获得的通量观测数据，对老山落叶松(Larix gmelinii)林(45°20′N, 127°34 ′E)的碳收支进行了分析。通过对每0.5 h所测数据进行的分析表明，能量平衡达到75％，说明涡度协方差法适应于本站的研究。较阴天气情况 下，林分光照利用效率显著高于晴朗天气，可能归因于阴天较多的散射光。以单位土地面积计算发现，通过涡度协方差法计算的落叶松林生态 系统的总初级生产力在20～50 μmol?m^-2?s^-1之间，远高于冠层叶片的总光合速率9.8～23.4μmol?m^-2?s^-1 (平均值16.2μmol?m^-2?s^-1 )，而 当综合考虑冠层光合和林下植物光合作用时，两种方法测定结果吻合性较好，说明林下植物对落叶松林碳平衡有重要影响。在估计森林生态系 统呼吸方面，以有风夜晚净生态系统交换量（NEE）来代表生态系统呼吸总量（3～9μmol?m^-2?s^-1）低估了生态系统呼吸总量，粗略估计较生 理生态学方法（不同呼吸分量的累积和）低估了50%左右（14.2μmol?m^-2?s^-1）。结果发现两种方法在估计森林碳平衡方面存在一定的差异， 呼吸量的估计差异应是今后研究的重点。

PRELIMINARY STUDY OF CO2 FLUX OF A LARCH FOREST BY EDDYCOVARIANCE AND ECOPHYSIOLOGICAL METHODS

Abstract Aims The two main methods for estimating CO₂ flux from forests are the eddy covariance micrometeorological method and the ecophysiological component summation method. Eddy covariance is a standard method for long-term, direct measurement of forest CO₂ and is used in studying large-scale terrestrial carbon budgets, while the ecophysiological method can estimate each component (e.g., stem , leaves, branches, roots, as well as soil microbes) of total CO₂ flux of forests. Because forest CO₂ flux study, including eddy covariance measurement, is a recent development in China, it is important to compare results from these two methods for understanding scaling-up of forest carbon budgets. We did a preliminary comparison during a typical month of the strongest sink capacity (June 2002). Our aim was to determine how the methods differed in carbon budget estimation and evaluate implications for future research. Methods A micrometeorological tower with the eddy covariance system was used to directly estimate net ecosystem exchange of a larch (Larix gmelinii) plantation at Laoshan station (45°20′N, 127°34′E). Ecophysiological measurements by a Li_ 6400 system were used to measure leaf photosynthesis and respiration of the tree canopy and herbaceous understory, stem respiration, branch respiration and soil respiration. Root respiration, soil microbe respiration and litter respiration were measured by the pre-installed trenched box and litter exclusion method. We converted each photosynthesis and respiration value from an organ-area base to a soil-area base using leaf area index measured by LAI_2000 and stem area index and branch area index estimated by standard tree sampling. Important findings Energy balance was estimated to be 75% using half-hourly flux data, but improved when 5 days of accumulated data were used, indicating that the eddy covariance method is suitable for this site. In relative cloudy weather (mean photosynthetic active radiation, PAR<400μmol?m^-2?s^-1) , light use efficiency was much higher than on days with a mean PAR>500μmol?m^-2?s^-1. This may be related to diffuse light on cloudy days. Expressed on a soil area base, gross primary productivity (GPP) of the larch plantation was20-50μmol?m^-2?s^-1 estimated by the eddy covariance method. This value was much higher than the total photosynthetic capacity of dominant canopy leaves of 9.8-23.4μmol?m^-2?s^-1 (mean of 16.2　μmol?m ^-2?s^-1); however, it was equivalent to the summation of dominant canopy and understory photosynthesis, indicating the critical importance of under story photosynthesis in the carbon balance of the studied plantation. Ecosystem respiration estimated by eddy covariance on a windy night was 3-9μmol?m^-2?s^-1, which is about 50% lower than estimated by the ecophysiological method (14.2　μmol?m^-2?s^-1). This large discrepancy between the two methods would lead to a large difference in carbon sink estimation. Therefore, methods of estimating respiration need additional study.