Department of Renewable Resources, University of Alberta, 4-42 Earth Sciences Building, Edmonton, AB, T6G 2E3, Canada.
Forest Sciences Department, University of British Columbia, 4605 - 2424 Main Mall, Vancouver, BC, V6T 1Z4, Canada.
New Phytol. 2013 Apr;198(1):139-148. doi: 10.1111/nph.12129. Epub 2013 Jan 25.
Climate models suggest that more frequent drought events of greater severity and length, associated with climate change, can be expected in the coming decades. Although drought-induced tree mortality has been recognized as an important factor modulating forest demography at the global scale, the mechanisms underlying drought-induced tree mortality remain contentious. Above- and below-ground growth, gas exchange, water relations and carbon reserve accumulation dynamics at the organ and whole-plant scale were quantified in Populus tremuloides and P. balsamifera seedlings in response to severe drought. Seedlings were maintained in drought conditions over one growing and one dormant winter season. Our experiment presents a detailed description of the effect of severe drought on growth and physiological variables, leading to seedling mortality after an extended period of drought and dormancy. After re-watering following the dormant period, drought-exposed seedlings did not re-flush, showing that the root system had died off. The results of this study suggest a complex series of physiological feedbacks between the measured variables in both Populus species. Further, they reveal that reduced reserve accumulation in the root system during drought decreases the conversion of starch to soluble sugars in roots, which may contribute to the root death of drought-exposed seedlings during the dormant season by compromising the frost tolerance of the root system.
气候模型表明，未来几十年，与气候变化相关的更频繁、更严重和更长时间的干旱事件预计将会增加。虽然干旱导致的树木死亡已被认为是调节全球森林动态的一个重要因素，但干旱导致树木死亡的机制仍存在争议。为了应对严重干旱，我们在颤杨和银白杨幼苗中定量研究了地上和地下生长、气体交换、水分关系以及器官和整个植株水平的碳储备积累动态。幼苗在一个生长季和一个休眠季中都维持在干旱条件下。我们的实验详细描述了严重干旱对生长和生理变量的影响，导致幼苗在长时间干旱和休眠后死亡。休眠期后再浇水时，暴露于干旱中的幼苗没有重新生长，表明根系已经死亡。本研究的结果表明，在这两个杨树物种中，所测量的变量之间存在一系列复杂的生理反馈。此外，它们表明，干旱期间根系中储备积累的减少会降低根系中淀粉向可溶性糖的转化，这可能会通过削弱根系的抗冻能力，导致休眠季节中干旱暴露的幼苗的根死亡。
