来源：《新科学家》
原文刊登日期：2020年11月26日
本文适合做完型填空的选文
Tree leaves may fall earlier in autumn due to climate change, rather than later as previously thought. The finding suggests forests will store significantly less carbon than expected as temperatures rise, and earlier leaf-fall may have knock-on effects on insects and other species.
由于气候变化，秋天树叶可能会提早掉落，而不是像之前认为的晚些。这一发现表明，随着气温上升，森林储存的碳将明显少于预期，而提早落叶可能会对昆虫和其他物种产生连锁反应。
Constantin Zohner at ETH Zurich in Switzerland and his colleagues looked at autumn leaf-fall data from 1948 to 2015 for six temperate tree species, including common oak, across nearly 4000 sites in central Europe. They then ran two experiments to see what role CO2 and sunlight play in leaf-fall’s timing. The first compared trees in chambers at close to today’s atmospheric CO2 levels with those at double that amount, while the second tested the impact of shade.
瑞士苏黎世联邦理工学院的Zohner和他的同事研究了中欧近4000个地点的六种温带树种(包括常见的橡树)1948年至2015年的秋季落叶数据。然后，他们进行了两个实验，看看二氧化碳和阳光在落叶的时间上扮演什么角色。第第一个实验比较了室内树木在接近当今大气二氧化碳水平时与两倍于此水平时的情况，而第二个实验则测试了遮荫的影响。
Putting the results together, they modelled what would happen by 2100 if humanity’s carbon emissions stay high. Instead of the established expectation that warmer autumns will bring a longer growing season with leaf-fall occurring about 2 to 3 weeks later than today, Zohner’s team found it would probably happen 3 to 6 days earlier than now. “The key finding is this huge difference to when autumn happens compared to previous models,” says Zohner.
综合这些结果，他们模拟了如果人类的碳排放量保持在高位，到2100年将会发生什么。以往的预期是，更温暖的秋季将带来更长的生长季节，落叶将比今天晚2到3周发生，而Zohner的团队发现，落叶可能会比现在早3到6天发生。Zohner说：“关键的发现是，与之前的模型相比，秋季发生的时间存在巨大差异。”
The team’s experiments and the 67-year tree record suggest higher CO2 levels, temperatures or light levels are driving the leaves to be more productive in spring and summer, accelerating their deaths in autumn. “What we think is happening is plants seem have this internal limit to how productive they can be,” says Zohner. Though the study looked at European trees, he thinks the results will hold true for temperate trees in North America and Asia too.
该团队的实验和67年的树木记录表明，更高的二氧化碳水平、更高的温度或更高的光照水平，都促使树叶在春夏两季更具生产力，加速了它们在秋季的死亡。Zohner说:“我们认为，植物似乎有这种内在的生产力限制。”虽然这项研究着眼于欧洲树木，但他认为这一结果也适用于北美和亚洲的温带树木。
If proved right, this reversal has big global consequences beyond when tourists flock to see leaf-fall and for phenologists studying the interactions between trees and animals and other plants. Zohner calculates that the switch from a delay to an advance in leaf-fall amounts to about 1 gigatonne less carbon stored globally each year by temperate forests, roughly a tenth of what humanity emits annually. “It’s a quite huge number,” he says.
如果这被证明是正确的，这种逆转将产生巨大的全球影响，不仅是当游客蜂拥去看落叶时，也会对物候学家研究树木与动物和其他植物之间的相互作用产生影响。佐纳计算出，从落叶延迟到落叶加速的转变，每年全球温带森林的碳储量减少了约10亿吨，大约是人类每年排放量的十分之一。“这是一个相当大的数字，”他说。