Bahn Michael, Schmitt Michael, Siegwolf Rolf, Richter Andreas, Brüggemann Nicolas
Institute of Ecology, University of Innsbruck, Sternwartestr. 15, 6020 Innsbruck, Austria.
Paul Scherrer Institute, 5232 Villigen PSI, Switzerland.
New Phytol. 2009;182(2):451-460. doi: 10.1111/j.1469-8137.2008.02755.x. Epub 2009 Feb 11.
Soil respiration is the largest flux of carbon (C) from terrestrial ecosystems to the atmosphere. Here, we tested the hypothesis that photosynthesis affects the diurnal pattern of grassland soil-respired CO(2) and its C isotope composition (delta(13)C(SR)). A combined shading and pulse-labelling experiment was carried out in a mountain grassland. delta(13)C(SR) was monitored at a high time resolution with a tunable diode laser absorption spectrometer. In unlabelled plots a diurnal pattern of delta(13)C(SR) was observed, which was not explained by soil temperature, moisture or flux rates and contained a component that was also independent of assimilate supply. In labelled plots delta(13)C(SR) reflected a rapid transfer and respiratory use of freshly plant-assimilated C and a diurnal shift in the predominant respiratory C source from recent (i.e. at least 1 d old) to fresh (i.e. photoassimilates produced on the same day). We conclude that in grasslands the plant-derived substrates used for soil respiratory processes vary during the day, and that photosynthesis provides an important and immediate C source. These findings indicate a tight coupling in the plant-soil system and the importance of plant metabolism for soil CO(2) fluxes.
土壤呼吸是陆地生态系统向大气输送碳（C）的最大通量。在此，我们检验了光合作用影响草地土壤呼吸释放的二氧化碳（CO₂）日变化模式及其碳同位素组成（δ¹³C(SR)）这一假设。在一片山地草地进行了遮荫与脉冲标记相结合的实验。利用可调谐二极管激光吸收光谱仪以高时间分辨率监测δ¹³C(SR)。在未标记的样地中观察到了δ¹³C(SR)的日变化模式，该模式无法用土壤温度、湿度或通量速率来解释，且包含一个与同化物供应无关的成分。在标记样地中，δ¹³C(SR)反映了新同化的植物碳的快速转移和呼吸利用，以及主要呼吸碳源从近期（即至少1天前）到新鲜（即当天产生的光同化物）的日变化。我们得出结论，在草地中，用于土壤呼吸过程的植物衍生底物在白天会发生变化，并且光合作用提供了重要且即时的碳源。这些发现表明植物 - 土壤系统中存在紧密耦合，以及植物代谢对土壤CO₂通量的重要性。
