Large influence of soil moisture on long-term terrestrial carbon uptake
Large influence of soil moisture on long-term terrestrial carbon uptake
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DOI：
10.1038/s41586-018-0848-x
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发表时间：
2019-01-24
期刊：
影响因子：
64.8
通讯作者：
Gentine, Pierre
中科院分区：
文献类型：
--
作者：
Green, Julia K.;Seneviratne, Sonia I.;Gentine, Pierre
虽然陆地生物圈吸收了约25%的人类二氧化碳排放量，但陆地碳吸收率仍高度不确定，导致气候预测的不确定性（1、2）。因此，了解限制或驱动土地碳储存的因素对于改善气候预测非常重要。土地碳吸收的一个潜在限制因素是土壤水分，它可以通过生态系统水分胁迫减少总初级生产（3，4），导致植被死亡（5），并进一步加剧由于土地-大气反馈（6）的极端气候。以前的工作已经探讨了土壤水分的可用性对过去碳通量变化的影响（3，7，8）。然而，土壤水分变化和趋势对长期碳汇的影响以及相关碳损失的机制仍然不确定。在这里，我们使用四个地球系统模型（9）从一系列实验中输出的数据来分析陆地净生物群落生产力对土壤水分变化的响应，发现土壤水分的变化和趋势在整个21世纪诱导了大量的CO2通量（每年约2至3千兆吨碳;与陆地碳汇本身（1）相当）。由于光合作用和净生态系统交换对土壤-水供应的非线性反应，以及陆地-大气相互作用造成的温度和蒸汽压力赤字增加，亚季节和年际土壤-水分变化产生CO2。土壤湿度的变化减少了目前的陆地碳汇，预计若干区域的土壤湿度增加和干燥趋势将进一步减少土壤碳汇。我们的研究结果强调，大陆作为未来的碳汇的能力，关键取决于土壤水分和陆-气相互作用的碳通量的非线性响应。这表明，碳吸收率的增长趋势可能无法持续到本世纪中叶，并可能导致大气二氧化碳增长加速。
Although the terrestrial biosphere absorbs about 25 per cent of anthropogenic carbon dioxide (CO2) emissions, the rate of land carbon uptake remains highly uncertain, leading to uncertainties in climate projections(1,2). Understanding the factors that limit or drive land carbon storage is therefore important for improving climate predictions. One potential limiting factor for land carbon uptake is soil moisture, which can reduce gross primary production through ecosystem water stress(3,4), cause vegetation mortality(5) and further exacerbate climate extremes due to land-atmosphere feedbacks(6). Previous work has explored the impact of soil-moisture availability on past carbon-flux variability(3,7,8). However, the influence of soil-moisture variability and trends on the long-term carbon sink and the mechanisms responsible for associated carbon losses remain uncertain. Here we use the data output from four Earth system models(9) from a series of experiments to analyse the responses of terrestrial net biome productivity to soil-moisture changes, and find that soil-moisture variability and trends induce large CO2 fluxes (about two to three gigatons of carbon per year; comparable with the land carbon sink itself(1)) throughout the twenty-first century. Subseasonal and interannual soil-moisture variability generate CO2 as a result of the nonlinear response of photosynthesis and net ecosystem exchange to soil-water availability and of the increased temperature and vapour pressure deficit caused by land-atmosphere interactions. Soil-moisture variability reduces the present land carbon sink, and its increase and drying trends in several regions are expected to reduce it further. Our results emphasize that the capacity of continents to act as a future carbon sink critically depends on the nonlinear response of carbon fluxes to soil moisture and on land-atmosphere interactions. This suggests that the increasing trend in carbon uptake rate may not be sustained past the middle of the century and could result in accelerated atmospheric CO2 growth.