Linking xylem network failure with leaf tissue death.

Global warming is expected to dramatically accelerate forest mortality as temperature and drought intensity increase. Predicting the magnitude of this impact urgently requires an understanding of the process connecting atmospheric drying to plant tissue damage. Recent episodes of forest mortality worldwide have been widely attributed to dry conditions causing acute damage to plant vascular systems. Under this scenario vascular embolisms produced by water stress are thought to cause plant death, yet this hypothetical trajectory has never been empirically demonstrated. Here we provide foundational evidence connecting failure in the vascular network of leaves with tissue damage caused during water stress. We observe a catastrophic sequence initiated by water column breakage under tension in leaf veins which severs local leaf tissue water supply, immediately causing acute cellular dehydration and irreversible damage. By highlighting the primacy of vascular network failure in the death of leaves exposed to drought or evaporative stress our results provide a strong mechanistic foundation upon which models of plant damage in response to dehydration can be confidently structured.