Substantial non-growing season carbon dioxide loss across Tibetan alpine permafrost region.

One of the major uncertainties for projecting permafrost carbon (C)-climate feedback is a poor representation of the non-growing season carbon dioxide (CO 2 ) emissions under a changing climate. Here, combining in situ field observations, regional synthesis and a random forest model, we assessed contemporary and future soil respired CO 2 (i.e., soil respiration, R s ) across the Tibetan alpine permafrost region, which has received much less attention compared with the Arctic permafrost domain. We estimated the regional mean R s of 229.8, 72.9 and 302.7 g C m -2  year -1 during growing season, non-growing season and the entire year, respectively; corresponding to the contemporary losses of 296.9, 94.3 and 391.2 Tg C year -1 from this high-altitude permafrost-affected area. The non-growing season R s accounted for a quarter of the annual soil CO 2 efflux. Different from the prevailing view that temperature is the most limiting factor for cold-period CO 2 release in Arctic permafrost ecosystems, precipitation determined the spatial pattern of non-growing season R s on the Tibetan Plateau. Using the key predictors, model extrapolation demonstrated additional losses of 38.8 and 74.5 Tg C from the non-growing season for a moderate mitigation scenario and a business-as-usual emissions scenario, respectively. These results provide a baseline for non-growing season CO 2 emissions from high-altitude permafrost areas and help for accurate projection of permafrost C-climate feedback.