Department of Applied Ecology, Ghent University, Ghent, Belgium.
Glob Chang Biol. 2013 Feb;19(2):517-28. doi: 10.1111/gcb.12044. Epub 2012 Nov 7.
The frequency and intensity of heat waves are predicted to increase. This study investigates whether heat waves would have the same impact as a constant increase in temperature with the same heat sum, and whether there would be any interactive effects of elevated [CO2 ] and soil moisture content. We grew Quercus rubra seedlings in treatment chambers maintained at either ambient or elevated [CO2 ] (380 or 700 μmol CO2 mol(-1) ) with temperature treatments of ambient, ambient +3 °C, moderate heat wave (+6 °C every other week) or severe heat wave (+12 °C every fourth week) temperatures. Averaged over a 4-week period, and the entire growing season, the three elevated temperature treatments had the same average temperature and heat sum. Half the seedlings were watered to a soil water content near field capacity, half to about 50% of this value. Foliar gas exchange measurements were performed morning and afternoon (9:00 and 15:00 hours) before, during and after an applied heat wave in August 2010. Biomass accumulation was measured after five heat wave cycles. Under ambient [CO2 ] and well-watered conditions, biomass accumulation was highest in the +3 °C treatment, intermediate in the +6 °C heat wave and lowest in the +12 °C heat wave treatment. This response was mitigated by elevated [CO2 ]. Low soil moisture significantly decreased net photosynthesis (Anet ) and biomass in all [CO2 ] and temperature treatments. The +12 °C heat wave reduced afternoon Anet by 23% in ambient [CO2 ]. Although this reduction was relatively greater under elevated [CO2 ], Anet values during this heat wave were still 34% higher than under ambient [CO2 ]. We concluded that heat waves affected biomass growth differently than the same amount of heat applied uniformly over the growing season, and that the plant response to heat waves also depends on [CO2 ] and soil moisture conditions.
预计热浪的频率和强度将会增加。本研究旨在探讨热浪是否会产生与恒定增温（相同热总量）相同的影响，以及是否存在[CO2]升高和土壤湿度含量升高的交互作用。我们在环境或升高的[CO2]（380 或 700 μmol CO2 mol(-1)）条件下，在处理室中种植红栎幼苗，温度处理为环境温度、环境温度+3°C、中度热浪（每隔一周升高 6°C）或严重热浪（每隔四周升高 12°C）。在 4 周的时间内和整个生长季节内，三种升高温度处理的平均温度和热总量相同。一半的幼苗浇到接近田间持水量的土壤水分，一半浇到这个值的 50%左右。在 2010 年 8 月应用热浪之前、期间和之后的上午和下午（9:00 和 15:00 小时）进行叶片气体交换测量。在五个热浪周期后测量生物量积累。在环境[CO2]和充分浇水条件下，+3°C 处理的生物量积累最高，+6°C 热浪处理居中，而+12°C 热浪处理最低。这种响应被升高的[CO2]缓解。土壤湿度低显著降低了所有[CO2]和温度处理的净光合速率（Anet）和生物量。在环境[CO2]下，+12°C 热浪使下午的 Anet 降低了 23%。尽管在升高的[CO2]下，这种降低相对较大，但在热浪期间的 Anet 值仍比在环境[CO2]下高 34%。我们得出结论，热浪对生物量生长的影响不同于整个生长季节均匀施加相同热量的影响，并且植物对热浪的响应还取决于[CO2]和土壤湿度条件。
