树木年轮没有提供证据表明加拿大西部古老的亚高山森林有二氧化碳施肥效应,Global Change Biology

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树木年轮没有提供证据表明加拿大西部古老的亚高山森林有二氧化碳施肥效应
Global Change Biology ( IF 10.8 ) Pub Date : 2019-02-01 , DOI: 10.1111/gcb.14561
Oleksandra Hararuk _{1,

2} , Elizabeth M Campbell ₃ , Joseph A Antos ₄ , Roberta Parish ₅

Affiliation

大气中的 CO ₂浓度现在是工业化前值的 1.7 倍。尽管假设光合速率会随着大气中 CO ₂浓度的升高而增加，但原位实验的结果并不支持 CO ₂树木生长的施肥效应。树木年轮数据提供了树木生产力的历史记录，可用于评估树木生长的长期反应。我们使用来自加拿大西部古老的亚高山森林的树木年轮数据，这些森林数百年来没有发生林分置换干扰，以确定在 19 世纪和 20 世纪的生长是否有所增加。我们的样本包括 5,858 棵树木，属于五个物种，分布在沿海地区的两个地点和内陆大陆性气候的两个地点。我们计算了树木断面面积的年度增量，根据树木的大小和年龄调整了这些增量，并测试了 19 世纪和 20 世纪树木生长是否存在可检测的时间趋势。我们在所有地点的所有物种中发现了 20 世纪增长趋势的类似模式。19 世纪的增长大多稳定或增加，但沿海地区之一除外，那里的树木生长略有下降；而 20 世纪的增长持续下降。20 世纪增长的意外下降表明没有 CO₂施肥对光合作用的影响。我们将四个站点的增长趋势与七个地球系统模型模拟的趋势进行了比较，发现大多数模型都没有预测到这些增长下降。总的来说，我们的结果表明，这些古老的森林不太可能增加其碳储存能力以应对大气中 CO ₂的升高，因此不太可能对抵消未来的碳排放做出重大贡献。

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Tree rings provide no evidence of a CO2 fertilization effect in old‐growth subalpine forests of western Canada

Atmospheric CO₂ concentrations are now 1.7 times higher than the preindustrial values. Although photosynthetic rates are hypothesized to increase in response to rising atmospheric CO₂ concentrations, results from in situ experiments are inconsistent in supporting a CO₂ fertilization effect of tree growth. Tree‐ring data provide a historical record of tree‐level productivity that can be used to evaluate long‐term responses of tree growth. We use tree‐ring data from old‐growth, subalpine forests of western Canada that have not had a stand‐replacing disturbance for hundreds of years to determine if growth has increased over 19th and 20th centuries. Our sample consisted of 5,858 trees belonging to five species distributed over two sites in the coastal zone and two in the continental climate of the interior. We calculated annual increments in tree basal area, adjusted these increments for tree size and age, and tested whether there was a detectable temporal trend in tree growth over the 19th and 20th centuries. We found a similar pattern in 20th century growth trends among all species at all sites. Growth during the 19th century was mostly stable or increasing, with the exception of one of the coastal sites, where tree growth was slightly decreasing; whereas growth during the 20th century consistently decreased. The unexpected decrease in growth during the 20th century indicates that there was no CO₂fertilization effect on photosynthesis. We compared the growth trends from our four sites to the trends simulated by seven Earth System Models, and saw that most of the models did not predict these growth declines. Overall, our results indicate that these old‐growth forests are unlikely to increase their carbon storage capacity in response to rising atmospheric CO₂, and thus are unlikely to contribute substantially to offsetting future carbon emissions.

更新日期：2019-02-01

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