Impact of warming on CO2 emissions from streams countered by aquatic photosynthesis
Impact of warming on CO2 emissions from streams countered by aquatic photosynthesis
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DOI：
10.1038/ngeo2807
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发表时间：
2016-10-01
影响因子：
18.3
通讯作者：
Freitag, Thomas E.
中科院分区：
文献类型：
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作者：
Demars, Benoit O. L.;Gislason, Gisli M.;Freitag, Thomas E.
溪流和河流是二氧化碳排放的重要来源(1)。这些排放的一个重要控制因素是光合作用（将二氧化碳转化为有机碳）和呼吸（将有机碳转化为二氧化碳）之间的代谢平衡（参考文献2、3）。河流的碳排放量可能会随着变暖而增加，与有机碳输入无关，因为预计呼吸作用的表观活化能高于光合作用(4,5)。然而，生理性 CO2 浓缩机制可能会阻止光呼吸的增加，从而限制随变暖而发生的光合作用(6)。在这里，我们报告了北美、冰岛和堪察加半岛地热区溪流水温在 4 至 70 摄氏度之间的水生光合作用的热响应。基于酶动力学的热力学理论，我们表明，水生生态系统光合作用的表观活化能在 4 至 45 摄氏度的温度范围内约为 0.57 电子伏特 (eV)，这与呼吸作用相似(4,5,7-9)。这一结果以及全球 222 条溪流的综合表明，变暖不会因变暖引起的光合作用和呼吸之间的不平衡而导致溪流和河流二氧化碳排放量增加。然而，如果生态系统呼吸独立于总初级生产，温度可能会影响溪流的年二氧化碳排放量，并且可能会通过增加有机碳供应而放大。
Streams and rivers are an important source of CO2 emissions(1). One important control of these emissions is the metabolic balance between photosynthesis, which converts CO2 to organic carbon, and respiration, which converts organic carbon into CO2 (refs2,3). Carbon emissions from rivers could increase with warming, independently of organic carbon inputs, because the apparent activation energy is predicted to be higher for respiration than photosynthesis(4,5). However, physiological CO2-concentrating mechanisms may prevent the increase in photorespiration, limiting photosynthesis with warming(6). Here we report the thermal response of aquatic photosynthesis from streams located in geothermal areas of North America, Iceland and Kamchatka with water temperatures ranging between 4 and 70 degrees C. Based on a thermodynamic theory of enzyme kinetics, we show that the apparent activation energy of aquatic ecosystem photosynthesis is approximately 0.57 electron volts (eV) for temperatures ranging from 4 to 45 degrees C, which is similar to that of respiration(4,5,7-9). This result and a global synthesis of 222 streams suggest that warming will not create increased stream and river CO2 emissions from a warming-induced imbalance between photosynthesis and respiration. However, temperature could affect annual CO2 emissions from streams if ecosystem respiration is independent of gross primary production, and may be amplified by increasing organic carbon supply.