Leaf epicuticular waxes and its effects on the energy balance of sorghum

Epicuticular waxes are thought to enable plants to cope with drought. Increased reflectivity of solar radiation and decreased conductance of water vapor from the leaf to the atmosphere are the mechanism hypothesized to aid plants to conserve water. Alone, increased reflectivity should reduce canopy temperature and water use, but lower conductance could counteract that effect due to restrictions in evaporative cooling. It is not clear how these competing effects exert control over water use in a crop such as sorghum [Sorghum bicolor (L.) Moench]. To better understand the role of epicuticular waxes on the energy balance of sorghum, experiments were conducted to determine the effects of waxes on field-scale energy fluxes using near-isogenic lines of grain sorghum having different levels of epicuticular wax loading. We found that increased canopy reflectivity played a minor role in controlling energy fluxes in the field. Instead, for the plant materials we tested, our data suggests that the primary mechanism through which waxes affect the energy balance of sorghum is by means of reduced conductance.