林木树干呼吸变化及其影响因素研究进展

 树干呼吸是森林生态系统碳平衡的重要组成部分，它每年消耗碳同化总量（NPP）的11%～33%。受测定技术所限，过去对树干呼吸的研究未能引起足够的重视。近十几年来，由于大气CO₂温室气体浓度的持续升高，树干呼吸已成为研究的热点。测定树干呼吸的方法较多，早期一般采用气体交换法和密闭方法，最近利用便携式光合测定系统（Li-Cor6400）或土壤碳通量测量系统（Li-8100）对树干呼吸采用开路系统测定方法。大量研究结果表明 ：1）树干呼吸的日变化呈双峰型曲线，即从早晨开始，树干呼吸速率随温度的上升而增加，到午间有所降低，之后逐渐增加，达到峰值后又逐渐降低。2）树干呼吸的季节动态为：生长季的树干呼吸速率明显高于非生长季，即从春季到夏季树干呼吸速率呈持续升高态势，高峰值出现在7或8月，尔后逐渐下降。树干呼吸活动是一个复杂的生物学过程，其影响因子较多。直接影响因子有气象因子（如温度、湿度和CO₂浓度）和生物因子（如树种、树龄、径阶、边材积和树干氮含量等）；而纬度、海拔和地形因子通过影响气象因子或生物因子而间接影响树干呼吸。诸多因子中，树干温度对树干呼吸的贡献最大（Q₁₀可描述树干呼吸对温度升高的敏感性）。树干呼吸机理及其影响因子乃是今后研究的主要内容，一方面要采用统一的测量方法和技术，另一方面要综合考虑影响树干呼吸的内外因素，建立树干呼吸的相关模型，为构建森林生态系统碳循环模型、了解森林生态系统碳收支状况及其对大气CO₂浓度变化的贡献和对全球变化的响应提供理论依据。

STEM RESPIRATION AND ITS CONTROLLING FACTORS IN FOREST ECOSYSTEMS

Stem respiration is an important part of the annual carbon balance of forest ecosystems and consumes ca. 11%-33% of total net daytime carbon assimilation. Because of difficulties in measurement, little attention was paid to stem respiration studies in the past. However, with increasing atmospheric CO2 concentration, studies of stem respiration have become popular. Several methods were applied in earlier studies, including gas exchange measurements and closed method. An open flow system is employed in recent studies. Results from recent research show that the diurnal pattern of stem respiration is bimodal with a midday depression and those rates are the greatest in the growing season. Controlling factors include meteorological factors (e.g., stem temperature, CO₂ concentration and humidity) and biological factors (tree species, tree age, and diameter at breast height, sapwood size and nitrogen content in stem). Latitude, altitude and topographic factors indirectly influence respiration rates through meteorological or biological factors, in particular stem temperature. Stem respiration rate is positively correlated with stem temperature. The mechanism of stem respiration and its controlling factors will continue to be subjects of future research. Integration of meteorological and biological factors into models of stem respiration will provide insight into contribution of stem respiration to the carbon balance of forest ecosystems, role of forest ecosystems in reducing CO₂ concentration elevation in the atmosphere, response of forest ecosystems to global changes, and development of carbon cycle models of forest ecosystems. These issues and measurement techniques remain challenging and fruitful areas for future research.