Leaf Transpiration Efficiency of Some Drought-Resistant Maize Lines

Field measurements of leaf gas exchange in maize (Zea mays L.) often indicate stomatal conductances higher than required to provide substomatal carbon dioxide concentrations saturating to photosynthesis. Thus maize leaves often operate at lower transpiration efficiency (TE) than potentially achievable for species with C, metabolism. I tested whether several maize lines described as drought resistant or drought tolerant operated with higher leaf TE than less drought-adapted lines. Field measurements of leaf TE were conducted over two seasons for five reputedly drought-resistant lines of maize and three locally grown lines not regarded as drought resistant. Midday photosynthesis, transpiration, stomatal conductance, and substomatal carbon dioxide concentration measurements were made under the ambient field conditions of air temperature and humidity in Beltsville, MD Soil moisture was not limiting. Consistent and significant differences among the lines occurred for stomatal conductance, substomatal carbon dioxide concentration, and TE, but no significant differences among the lines occurred in photosynthesis. One drought-tolerant line had higher TE than all others tested, and one of the local lines had the lowest TE, but the drought-tolerant lines as a group did not have significantly higher TE. It is concluded that significant genotypic variation in leaf TE exists in maize, and that TE could be improved without reducing photosynthesis.