As a widespread phenomenon affecting terrestrial ecosystems worldwide, the extent and spatio-temporal scales at which the increasing number of reported events of climatechange-induced tree mortality could affect the ecology and carbon (C) sink capacity of terrestrial soils, remains unknown. We here study how regional-scale drought-induced tree mortality events registered after a very dry 2012 year in the Carpathians mountain range (Romania), which affected three of the most widely distributed conifer species: Scots pine, Black pine, and Silver fir, resulted in hot-spots of biogenic soil CO 2 emissions (soil respiration; R s ). Four to five years after the main mortality event, R s -related soil CO 2 emissions under dead trees were, on average, 21% higher than CO 2 emissions under living trees (ranging from 18 to 35%). Total (R s ) and heterotrophic (R H )-related soil CO 2 emissions were strongly determined by the soil environmental alterations following tree mortality (e.g. changes in quantity and quality of soil organic matter, microclimate, pH or fine root demography). Moreover, the massive mortality event of 2012 ultimately resulted in a stronger dominant role of successional vegetation (broadleaf seedlings, shrubland and grasses) in controlling those environmental factors that either directly or indirectly affected biotic soil fluxes (R s and R H ). We, therefore, show that apart from the well-known direct effects of climate change over soil CO 2 emissions, cascading effects triggered by climatechange-induced tree mortality could also exert a strong indirect impact over soil CO 2 emissions, altering the magnitude and the environmental controls of R s and hence determining ecosystem C budget and their response to climate.

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