Limits to the growing season The length of the growing season in temperate forests has been increasing under recent climate change because of earlier leaf emergence and later leaf senescence. However, Zani et al. show that this trend might be reversed as increasing photosynthetic productivity begins to drive earlier autumn leaf senescence (see the Perspective by Rollinson). Using a combination of experimental, observational, and modeling studies based on European forest trees, the researchers conclude that leaf senescence will advance by 3 to 6 days by the end of the 21st century rather than lengthening by 1 to 3 weeks as current phenological models have predicted. In turn, this predicted phenological pattern will limit the capacity of temperate forests to mitigate climate change through carbon uptake. Science, this issue p. 1066; see also p. 1030 Physiological constraints on the growing season and productivity may limit the capacity of temperate forests to retain carbon. Changes in the growing-season lengths of temperate trees greatly affect biotic interactions and global carbon balance. Yet future growing-season trajectories remain highly uncertain because the environmental drivers of autumn leaf senescence are poorly understood. Using experiments and long-term observations, we show that increases in spring and summer productivity due to elevated carbon dioxide, temperature, or light levels drive earlier senescence. Accounting for this effect improved the accuracy of senescence predictions by 27 to 42% and reversed future predictions from a previously expected 2- to 3-week delay over the rest of the century to an advance of 3 to 6 days. These findings demonstrate the critical role of sink limitation in governing the end of seasonal activity and reveal important constraints on future growing-season lengths and carbon uptake of trees.

中文翻译：

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生长季节生产力的提高推动了温带树木的秋季叶片提前衰老

生长季节的限制 由于较早的叶子出现和较晚的叶子衰老，温带森林的生长季节长度在最近的气候变化下一直在增加。然而，扎尼等人。表明随着光合生产力的增加开始推动秋季叶片提前衰老，这种趋势可能会逆转（参见 Rollinson 的观点）。研究人员结合基于欧洲森林树木的实验、观察和建模研究得出结论，到 21 世纪末，叶片衰老将提前 3 到 6 天，而不是像目前的物候模型那样延长 1 到 3 周。预料到的。反过来，这种预测的物候模式将限制温带森林通过碳吸收缓解气候变化的能力。科学，这个问题 p。1066; 另见第 1030 生长季节和生产力的生理限制可能会限制温带森林保留碳的能力。温带树木生长季节长度的变化极大地影响了生物相互作用和全球碳平衡。然而，由于对秋季叶片衰老的环境驱动因素知之甚少，因此未来的生长季节轨迹仍然高度不确定。使用实验和长期观察，我们表明，由于二氧化碳、温度或光照水平升高，春季和夏季生产力的增加会导致更早的衰老。考虑到这种影响，衰老预测的准确性提高了 27% 至 42%，并将未来预测从先前预期的本世纪剩余时间的 2 至 3 周延迟逆转为提前 3 至 6 天。