Abstract: Warming and drought will occur with increased frequency and intensity along with global climate change. In recent years, extensive tree mortality and forest declines have been reported in response to drought and rising temperature. Despite an enormous body of empirical evidence, the underlying physiological mechanisms of the changes still remain unclear. At present, the study on the drought-induced tree mortality mechanisms is still a hot spot. Three hypotheses concerning the physiological mechanisms leading to tree mortality during drought have been proposed: hydraulic failure hypothesis, proposing that low water potential due to drought impedes long-distance water transport within plants and results in dehydration of plant tissues; carbon starvation hypothesis, suggesting that a prolonged stomatal closure during drought constrains carbon uptake and leads to a depletion of available carbohydrats; and biotic attack hypothesis, considering that trees subjected to drought are prone to attacks by insects and pathogens. Each of the hypotheses can interpret certain phenomena of drought-induced tree mortality, but cannot universally interpret all phenomena of drought-induced tree mortality under whatever drought conditions. Lately more attention has been paid to the combined action or interaction of the different mortality mechanisms, especially the coupling of hydraulic failure and carbon starvation. This paper mainly reviewed experimental evidence and existing problems of the three hypotheses. Meanwhile, the limitations of current researches and possible research direction in the future in this field were also discussed.

Key words: Frankliniella occidentalis, life table, developmental duration, sublethal concentration, biopesticide