Marchand Fleur L, Mertens Sofie, Kockelbergh Fred, Beyens Louis, Nijs Ivan
Research Group Plant and Vegetation Ecology, Department of Biology, University of Antwerp (UA), Campus Drie Eiken, Universiteitsplein 1, B-2610 Wilrijk, Belgium.
Research Group Polar Ecology, Limnology and Paleobiology, Department of Biology, University of Antwerp (UA), Campus Middelheim, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium.
Glob Chang Biol. 2005 Dec;11(12):2078-2089. doi: 10.1111/j.1365-2486.2005.01046.x. Epub 2005 Oct 20.
Arctic ecosystems are known to be extremely vulnerable to climate change. As the Intergovernmental Panel on Climate Change scenarios project extreme climate events to increase in frequency and severity, we exposed High Arctic tundra plots during 8 days in summer to a temperature rise of approximately 9°C, induced by infrared irradiation, followed by a recovery period. Increased plant growth rates during the heat wave, increased green cover at the end of the heat wave and higher chlorophyll concentrations of all four predominating species (Salix arctica Pall., Arctagrostis latifolia Griseb., Carex bigelowii Torr. ex Schwein and Polygonum viviparum L.) after the recovery period, indicated stimulation of vegetative growth. Improved plant performance during the heat wave was confirmed at plant level by higher leaf photochemical efficiency (F /F ) and at ecosystem level by increased gross canopy photosynthesis. However, in the aftermath of the temperature extreme, the heated plants were more stressed than the unheated plants, probably because they acclimated to warmer conditions and experienced the return to (low) ambient as stressful. We also calculated the impact of the heat wave on the carbon balance of this tundra ecosystem. Below- and aboveground respiration were stimulated by the instantaneous warmer soil and canopy, respectively, outweighing the increased gross photosynthesis. As a result, during the heat wave, the heated plots were a smaller sink compared with their unheated counterparts, whereas afterwards the balance was not affected. If other High Arctic tundra ecosystems react similarly, more frequent extreme temperature events in a future climate may shift this biome towards a source. It is uncertain, however, whether these short-term effects will hold when C exchange rates acclimate to higher average temperatures.
北极生态系统被认为极易受到气候变化的影响。政府间气候变化专门委员会的情景预测显示，极端气候事件的频率和强度将会增加，因此我们在夏季将北极高纬度冻原地块暴露于红外线照射诱导的约9°C的温度升高下8天，随后进入恢复期。热浪期间植物生长速率加快、热浪结束时绿色覆盖增加以及恢复期后所有四种优势物种（北极柳、北极虎尾草、大果苔草和珠芽蓼）的叶绿素浓度升高，表明营养生长受到刺激。热浪期间植物性能的改善在植物层面表现为叶片光化学效率（Fv/Fm）更高，在生态系统层面表现为冠层总光合作用增加。然而，在极端温度过后，受热的植物比未受热的植物压力更大，这可能是因为它们适应了较温暖的条件，而将恢复到（较低的）环境温度视为一种压力。我们还计算了热浪对该冻原生态系统碳平衡的影响。地下和地上呼吸分别受到瞬时变暖的土壤和冠层的刺激，超过了总光合作用的增加。因此，在热浪期间，受热地块与未受热地块相比，碳汇较小，而之后碳平衡不受影响。如果其他北极高纬度冻原生态系统也有类似反应，未来气候中更频繁的极端温度事件可能会使这个生物群落转变为碳源。然而，当碳交换率适应更高的平均温度时，这些短期影响是否仍然存在尚不确定。
