A Comparison of Carbon and Water Vapor Gas Exchange Characteristics Between a Diploid and Highbush Blueberry

Abstract

Abstract CO2 assimilation (A), leaf conductance to water vapor (gl), mesophyll conductance (gm), and water use efficiency (WUE) were compared for two cultivars of highbush (Vaccinium corymbosum L.) and a wild diploid lowbush blueberry species (Vaccinium darrowii Camp.) in response to PPF, CO2, temperature, and vapor pressure deficit (VPD) to determine if apparent tolerance of V. darrowii to high temperature and drought conditions resulted from differences in gas exchange characteristics. Cultivar differences between ‘Bluecrop’ and ‘Jersey’ in A were not significant when expressed on a leaf area, leaf dry weight, or total chlorophyll basis. Maximum CO2 assimilation rates for V. darrowii were about 35%, 50%, or 40% lower than highbush cultivars when expressed on a leaf area, leaf dry weight, or total chlorophyll basis, respectively. Differences between ‘Bluecrop’ and ‘Jersey’ were also non-significant for mesophyll conductance, transpiration, CO2 compensation points, and water use efficiency. CO2 assimilation maximized between 600-800 µmol·s–1·m–2 photosynthetic photon flux (PPF) for all three genotypes and the temperature optima ranged between 18° and 26°C for ‘Jersey’, 14° and 22° for ‘Bluecrop’, and 25° and 30° for V. darrowii. As temperature was increased from 20° to 30°, leaf conductance (gl) to water vapor was lower and water use efficiency was higher for V. darrowii, compared to ‘Bluecrop’ but not ‘Jersey’. There was a 50-65% reduction in gl as VPD was increased, but only 10–20% reduction was observed in A. Leaf conductance to water vapor was reduced for V. darrowii, which restricted intercellular CO2. Since crosses are possible between highbush and V. darrowii, it is possible that heat tolerance and/or drought resistance could be improved in Highbush blueberry through the incorporation of genes from V. darrowii.