Marchin Renée M, Dunn Robert R, Hoffmann William A
Centre for Carbon, Water and Food, University of Sydney, Camden, NSW, 2570, Australia,
Oecologia. 2014 Dec;176(4):1161-72. doi: 10.1007/s00442-014-3074-8. Epub 2014 Sep 26.
In the eastern United States, winter temperature has been increasing nearly twice as fast as summer temperature, but studies of warming effects on plants have focused on species that are photosynthetically active in summer. The terrestrial orchid Tipularia discolor is leafless in summer and acquires C primarily in winter. The optimum temperature for photosynthesis in T. discolor is higher than the maximum temperature throughout most of its growing season, and therefore growth can be expected to increase with warming. Contrary to this hypothesis, experimental warming negatively affected reproductive fitness (number of flowering stalks, flowers, fruits) and growth (change in leaf area from 2010 to 2012) in T. discolor. Temperature in June-July was critical for flowering, and mean July temperature greater than 29 °C (i.e., 2.5 °C above ambient) eliminated reproduction. Warming of 1.2 °C delayed flowering by an average of 10 days and fruiting by an average of 5 days. Warming of 4.4 °C reduced relative growth rates by about 60%, which may have been partially caused by the direct effects of temperature on photosynthesis and respiration. Warming indirectly increased vapor pressure deficit (VPD) by 0.2-0.5 kPa, and leaf-to-air VPD over 1.3 kPa restricted stomatal conductance of T. discolor to 10-40% of maximum conductance. These results highlight the need to account for changes in VPD when estimating temperature responses of plant species under future warming scenarios. Increasing temperature in the future will likely be an important limiting factor to the distribution of T. discolor, especially along the southern edge of its range.
在美国东部，冬季气温的上升速度几乎是夏季气温的两倍，但关于变暖对植物影响的研究主要集中在夏季进行光合作用的物种上。地生兰花二色竹芋在夏季无叶，主要在冬季获取碳。二色竹芋光合作用的最适温度高于其大部分生长季节的最高温度，因此预计随着气候变暖其生长会增加。与这一假设相反，实验性变暖对二色竹芋的繁殖适合度（花茎、花朵、果实的数量）和生长（2010年至2012年叶面积的变化）产生了负面影响。6月至7月的温度对开花至关重要，7月平均温度高于29℃（即比环境温度高2.5℃）会导致无法繁殖。升温1.2℃平均使开花延迟10天，结果延迟5天。升温4.4℃使相对生长率降低约60%，这可能部分是由于温度对光合作用和呼吸作用的直接影响。变暖间接使水汽压差（VPD）增加了0.2 - 0.5 kPa，叶 - 气VPD超过1.3 kPa时，二色竹芋的气孔导度限制在最大导度的10% - 40%。这些结果凸显了在未来变暖情景下估计植物物种温度响应时考虑VPD变化的必要性。未来气温升高可能会成为二色竹芋分布的一个重要限制因素，尤其是在其分布范围的南部边缘。
