Organ-level evaluation of the carbon starvation hypothesis in deciduous broad-leaved Catalpa bungei plants undergoing drought-induced mortality

The carbon starvation hypothesis (CSH) is one of the current leading hypotheses regarding the mechanism of plant death, although it has not been sufficiently validated due to a lack of evidence. To help verify the role of carbon starvation in plant mortality, we measured the non-structural carbohydrate (NSC) concentration ([NSC]) in different organs (roots, stems, and leaves) of plants of Catlapa bungei clone 9-1 after the cessation of photosynthesis and death due to drought and in well-watered controls. Drought in- duced the loss of NSC reserves, which was observed in all organs at death, and carbon starvation appeared to begin after the cessation of photosynthesis. The [NSC] dynamics, occurrence time of carbon starvation, and survival time varied among the organs, and even within the same organs at different stem heights. Overall, our findings are compatible with the CSH in that carbon starvation occurs in roots, stems, and leaves and concurs with plant death during prolonged drought.