School of Biological Sciences, University of Utah, Salt Lake City, UT 84112;
School of Natural Resources and the Environment, University of Arizona, Tucson, AZ 85721.
Proc Natl Acad Sci U S A. 2019 Dec 3;116(49):24662-24667. doi: 10.1073/pnas.1821387116. Epub 2019 Nov 18.
Forests play a major role in the global carbon cycle. Previous studies on the capacity of forests to sequester atmospheric CO have mostly focused on carbon uptake, but the roles of carbon turnover time and its spatiotemporal changes remain poorly understood. Here, we used long-term inventory data (1955 to 2018) from 695 mature forest plots to quantify temporal trends in living vegetation carbon turnover time across tropical, temperate, and cold climate zones, and compared plot data to 8 Earth system models (ESMs). Long-term plots consistently showed decreases in living vegetation carbon turnover time, likely driven by increased tree mortality across all major climate zones. Changes in living vegetation carbon turnover time were negatively correlated with CO enrichment in both forest plot data and ESM simulations. However, plot-based correlations between living vegetation carbon turnover time and climate drivers such as precipitation and temperature diverged from those of ESM simulations. Our analyses suggest that forest carbon sinks are likely to be constrained by a decrease in living vegetation carbon turnover time, and accurate projections of forest carbon sink dynamics will require an improved representation of tree mortality processes and their sensitivity to climate in ESMs.
森林在全球碳循环中起着重要作用。以前关于森林固存大气 CO 的能力的研究主要集中在碳吸收上，但碳周转时间及其时空变化的作用仍知之甚少。在这里，我们利用来自 695 个成熟森林样地的长期清单数据（1955 年至 2018 年），量化了热带、温带和寒带气候区活植被碳周转时间的时间变化趋势，并将样地数据与 8 个地球系统模型（ESM）进行了比较。长期样地数据一致显示，活植被碳周转时间缩短，这可能是由于所有主要气候区的树木死亡率增加所致。森林样地数据和 ESM 模拟均显示，活植被碳周转时间的变化与 CO 富集呈负相关。然而，活植被碳周转时间与降水和温度等气候驱动因素之间的关系在样地数据和 ESM 模拟之间存在分歧。我们的分析表明，森林碳汇可能受到活植被碳周转时间缩短的限制，而准确预测森林碳汇动态将需要在 ESM 中改进对树木死亡率过程及其对气候的敏感性的表示。
