Physiological Effects of Leaf Color and Artificial Shading on Leaf Gas Exchange and Growth in Rabbiteye Blueberry (Vaccinium ashei)
Date Issued
2016
Date
2016
Author(s)
Tsai, Ming-Hsuan
Abstract
The rabbiteye blueberry (Vaccinium ashei.) is a promising new fruit crop in Taiwan’s subtropical lowland. However, mid-day temporarily wilting of young shoot tips often occurs in the high summer heat and irradiance. This thesis investigated that 1) how leaf color of diffent genotypes responses to heat and light stress and 2) can artificial shading avoid overload of solar energy but maintain light above the saturation point of leaf photosynthesis to improve photosynthesis and vegetative growth in rabbiteye blueberry. Leaf temperature (TL) and gas exchange of ‘Blueshower’ open-pollinated seedlings with leaves of different shades of green were monitored. Leaf-air temperature differences (∆T) in genotypes with dark green leaves were greater than those with light green leaves before solar noon but were undistinguishable among genotypes after solar noon. There was no special correlation between leaf lightness and leaf stomatal conductance (gs) or net assimilation rate (An). Maximum An was recorded at leaf temperature around 35˚C in all genotypes. Mid-day transpiration rates (E) in genotypes with dark green leaves were higher than those with light green leaves. Consequently, water use efficiency (WUE) in genotypes with dark green leaves was lower than that with light green leaves. Container grown 3-year-old rabbiteye blueberries were lightly (20%) or moderately (35%) shaded with white knitted shade cloth and compared with the unshaded control during the summer heat. Leaf gas exchange, chlorophyll content, chlorophyll fluorescence, vegetative growth, and fruit yield of the following year were measured. On hot sunny days, the dark-adapted photosystem II efficiency (Fv/Fm) and quantum efficiency of photosystem II electron transport (ΦPSII) of mature exposed leaves decreased. The decreases in Fv/Fm and ΦPSII in midday were slightly smaller for ‘Blueshower’ plants under shading but were not statistically differed from the unshaded control, indicating no severe photoinhibition. The lower TL and smaller leaf-to-air vapor pressure deficit (VPDL-air) of ‘Tifblue’ under the 35% shading treatment improved leaf An and gs by 30% higher than those of the control. WUE was imporved by shading although E was not affected. the positive physiological effects of shading were only obvious in conditions with high irradiance and air temperature above 35°C. Therefore, the benefits of shading did not reflect on seasonal vegetative growth or yield of rabbiteye blueberries in northern Taiwan with a hot but frequently cloudy weather condition in the summer.
Subjects
leaf color
leaf temperature
transpiration
water use efficiency
light intensity
net assimilation rate
leaf-to-air vapor pressure deficit
stomatal conductance
chlorophyll fluorescence
SDGs
Type
thesis
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