Ecology and Genetics Unit, University of Oulu, P.O. Box 3000, FI-90014, Finland.
Botany Unit, Finnish Museum of Natural History LUOMUS, University of Helsinki, P. O. Box 7, FI-00014, Finland.
Tree Physiol. 2019 Jun 1;39(6):961-970. doi: 10.1093/treephys/tpz013.
Deciduous trees prepare for winter by breaking up chlorophyll and other nitrogen-rich compounds, which are resorbed for storage. Timing is important as senescence too early will waste growing season, while senescence too late risks the loss of the leaf resources to frost. While plants of temperate and boreal regions use decreasing day length as a cue of approaching winter, we show that decreasing temperature may also play a role in the variability of leaf senescence. We investigated the timing of autumnal decrease in photosynthetic efficiency and the concentration of chlorophyll and total carotenoids in nine common lilac (Syringa vulgaris L.) trees over two consecutive years. Day length explained a greater proportion of photosynthetic efficiency, but temperature had a significant additional role, which seems to be related to individual differences. Precipitation and cloudiness did not explain photosynthetic efficiency. Photosynthetic efficiency was higher outside the canopy and at high and middle elevations than inside and low elevations of the canopy. Late onset of senescence led to a steeper decline in photosynthetic efficiency than early senescence. The onset of decline in photosynthetic efficiency differed between years, but there was no difference in the steepest rate of change in photosynthetic efficiency with respect to sampling year or location. Contributions of day-length vs temperature to leaf senescence have important consequences for the adaptability and invasibility of deciduous trees in a changing climate, especially at the edge of species distributions.
落叶树通过分解叶绿素和其他富含氮的化合物为储存而进行吸收来为冬季做准备。时机很重要，因为过早衰老会浪费生长季节，而过晚衰老则有遭受霜害损失叶片资源的风险。虽然温带和北方地区的植物使用昼长的缩短作为冬季即将到来的提示，但我们表明，温度的降低也可能在叶片衰老的可变性中发挥作用。我们在连续两年中调查了九种普通丁香树（Syringa vulgaris L.）秋季光合效率和叶绿素及总类胡萝卜素浓度下降的时间。昼长解释了更大比例的光合效率，但温度有显著的额外作用，这似乎与个体差异有关。降水和阴天对光合效率没有解释作用。树冠外、高海拔和中海拔处的光合效率高于树冠内和低海拔处。衰老开始较晚导致光合效率下降比衰老开始较早更陡峭。光合效率下降的开始在不同年份有所不同，但在采样年份或地点上，光合效率变化率的最陡斜率没有差异。昼长和温度对叶片衰老的贡献对落叶树在气候变化中的适应性和入侵性有重要影响，尤其是在物种分布的边缘。
