Plant water use under heat

Climate change is regularly confronting us with new heat records. Heat waves, often combined with drought, are now three times as frequent and on average 2.3 C hotter than before. Such combined events are particularly hard on plants. Plants transpire to cool themselves, but if they don`t have enough water, this air-conditioning system fails. During dry periods the stomata of the leaves close to prevent them from drying out. As a result, however, the leaf can heat up massively and is then usually much hotter than the surrounding air. The first heat damage occurs from around 40 C. But even when this air conditioner is switched off, the leaves still lose small amounts of water because the leaf skin is not completely waterproof and even becomes leakier when it is hot. The causes of increasing water leakage of the leaf skin under heat are being investigated in the present project. Modern imaging methods are used to make molecular and structural changes in the leaf skin visible. At the same time, various stress physiological methods are employed by which the heat-induced loss of function of the leaf skin can be measured. The leaf skin contains cutin and waxes that melt when exposed to heat - it is not known whether the becoming more permeable to water is reversible and whether a hardening can take place in this regard. It is also the dose that makes the poison. There are practically no studies on the effect of the duration of exposure to heat on plants and the temperature-dependent changes in the water permeability of the leaf skin. The damaging heat dose and the main causes for the heat-induced, increased water permeability of the leaf skin are therefore still largely unknown. Plants from habitats that differ in heat dose are examined. Pronounced short-term midday heat is a phenomenon of the mountain habitat and occurs above all in low statured plant species. Dwarf shrubs, tree seedlings and glacier foreland plants are examined there. In contrast, in the Nepalese tropics, where the heat prevails for months, selected trees and herbs are analyzed. This study includes numerous field tests and laboratory experiments and ranges from the molecular level to the individual level. It therefore promises comprehensive, new knowledge about the heat resistance of plants. The results are of great importance for estimating the future heat risk both for cultivated plants and for plants of natural habitats in a globally warmer world.