On the variability of respiration in terrestrial ecosystems:: moving beyond Q10
On the variability of respiration in terrestrial ecosystems:: moving beyond Q10
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DOI：
10.1111/j.1365-2486.2005.01065.x
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发表时间：
2006-02-01
影响因子：
11.6
通讯作者：
Luo, YQ
中科院分区：
文献类型：
--
作者：
Davidson, EA;Janssens, IA;Luo, YQ
呼吸是生态系统中仅次于总初级生产力的第二重要的碳通量，在生态地球化学模型中通常由简单的温度依赖方程表示。这些方程建立于19世纪，自那时以来几乎没有修改。最近应用这些方程的土壤呼吸数据产生了高度可变的表观温度敏感性。本文寻找这种变化的原因，从生化反应到生态系统规模的基质供应。对于遵循Michaelis-Menten动力学的简单膜结合酶系统，最大酶活性（V-max）的温度敏感性和反映酶对底物的亲和力的半饱和常数（K-m）可以彼此抵消，从而不产生酶的净温度依赖性。或者，当衬底的扩散与温度共变时，则组合的温度灵敏度可以高于每个单独工艺的温度灵敏度。我们还提出的例子表明，可溶性碳基质供应可能是重要的尺度范围从跨膜运输，通过土壤水膜扩散，分配到地上和地下植物组织，碳分配和生长的物候模式，和站点间的生产力差异。稳健的土壤呼吸模型需要将基质供应、温度和干燥胁迫的直接影响与温度和土壤含水量对基质扩散和有效性的间接影响分开。我们推测，呼吸的表观Q（10）值显著高于约2.5，可能表明某些未识别的底物供应过程与观察到的温度变化相混淆。
Respiration, which is the second most important carbon flux in ecosystems following gross primary productivity, is typically represented in biogeochemical models by simple temperature dependence equations. These equations were established in the 19th century and have been modified very little since then. Recent applications of these equations to data on soil respiration have produced highly variable apparent temperature sensitivities. This paper searches for reasons for this variability, ranging from biochemical reactions to ecosystem-scale substrate supply. For a simple membrane-bound enzymatic system that follows Michaelis-Menten kinetics, the temperature sensitivities of maximum enzyme activity (V-max) and the half-saturation constant that reflects the affinity of the enzyme for the substrate (K-m) can cancel each other to produce no net temperature dependence of the enzyme. Alternatively, when diffusion of substrates covaries with temperature, then the combined temperature sensitivity can be higher than that of each individual process. We also present examples to show that soluble carbon substrate supply is likely to be important at scales ranging from transport across membranes, diffusion through soil water films, allocation to aboveground and belowground plant tissues, phenological patterns of carbon allocation and growth, and intersite differences in productivity. Robust models of soil respiration will require that the direct effects of substrate supply, temperature, and desiccation stress be separated from the indirect effects of temperature and soil water content on substrate diffusion and availability. We speculate that apparent Q(10) values of respiration that are significantly above about 2.5 probably indicate that some unidentified process of substrate supply is confounded with observed temperature variation.