NEDKYLNING HOS VANLIG BÖNA, PHASEOLUS VULGARIS

Abstract

Beans are a global source of plant-based protein, and in some countries, they constitute a primary source of protein intake. With ongoing climate change, including rising temperatures, it is necessary to adapt beans to ensure a reliable food supply. An important mechanism that many plants have, to cope with high temperatures, is cooling through transpiration. During transpiration, stomata open and release water vapor. Water molecules use heat energy from the leaf to convert into gas, thereby cooling the leaf. The aim of this study was to investigate the extent of cooling in common bean, Phaseolus vulgaris, and how cooling differs between various bean varieties. This was done by comparing differences in leaf and air temperatures from existing field data from Rwanda and a selection of five bean varieties in a laboratory setting. Additionally, the lab examined how an increase in air temperatures and an increase in light intensity affect the cooling process. In both the field and lab studies, the plants were watered so that water availability did not limit transpiration. Both field and lab results show that common beans lower leaf temperature by an average of 3.3°C relative to air temperature and that cooling is greater at higher air temperatures than at lower ones. This is likely due to increased VPD (Vapor Pressure Deficit) and increased stomatal conductance. The lab results also showed that cooling decreased with increased light intensity. In the field data, no significant differences between the bean varieties were observed. The lab data did not provide conclusive results but showed a trend where one variety often cooled better than the others. The study demonstrates that transpirational cooling is an important mechanism in common beans to avoid high temperatures. The increased cooling protects against the harmful effects of heat and allows continued photosynthesis even at high air temperatures.