| 摘 要： |
Droughts significantly impact land carbon uptake by reducing the gross primary productivity (GPP). Projections suggest an increase in severe and extreme droughts in the twenty-first century. Despite the importance of droughts on carbon uptakes, it remains unclear about the GPP responses under different drought severity and its changes under current climate changes. Using four state-of-the-science GPP products, we showed that moderate (-1 <= SPEI < -1.5), severe (-1.5 <= SPEI < -2), and extreme (SPEI < -2) droughts caused on average 5%, 7%, and 9% GPP reductions, respectively, across the globe during the recent decades. Although the mean reductions varied among GPP products, we observed similar spatial patterns. The reductions increased significantly along the severity gradient, while the sharpest increases were observed in semi-arid and grassland ecosystems. On a biome level, we found that the reductions increased nonlinearly with increasing drought severities for almost all vegetation types, but the trends and slopes varied significantly. In addition, we found that the mean drought-induced GPP reductions had increased in dry ecosystems but decreased in humid ecosystems from 2001-2008 to 2009-2016. The result highlights the potential increase of drought-induced land carbon sink loss responding to more extreme climates and offers new perspectives to improve the prediction of global carbon fluxes in a changing climate. |
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