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KMID : 0903620040450030143
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Journal of the Korean Society for Horticultural Science
2004 Volume.45 No. 3 p.143 ~ p.148
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Comparative Photosynthetic Characteristics of Well-Watered and Water-Stressed ‘Rancocas’ Highbush Blueberry Leaves
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Kim Su-Jin
Kim Ji-Hyo
Kim Tae-Choon
Lee Byoung-Yil
Lee Hee-Jae
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Abstract
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Photosynthetic characteristics of ‘Rancocas’ highbush blueberry (Vaccinium corymbosum) leaves were monitored under well-watered and water-stressed conditions. Two-year-old trees in 4-L pots were daily irrigated (well-watered) or not irrigated for 7 days (water-stressed). Soil water potentials in well-watered and water-stressed conditions were measured to be approximately -0.22 and -0.99 ㎫, respectively, whereas leaf water potentials in well-watered and water-stressed blueberries were about -1.07 and -1.79 ㎫, respectively. The CO₂ assimilation rates of well-watered and water-stressed blueberries were both saturated at about 500 μmolㆍm?²ㆍs?¹ photosynthetic photon flux density (PPFD) following the initial linear increases with increasing PPFD up to about 200 μmolㆍm?²ㆍs?¹. Well-watered blueberry exhibited higher CO₂ assimilation rate than water-stressed blueberry by 3-5 μmolㆍm?²ㆍs?¹ depending on PPFD ranged from 0 to 2,000 μmolㆍm?²ㆍs?¹. Maximum CO₂ assimilation rates of well-watered and water-stressed blueberries were 8.8 and 4.6 μmolㆍm?²ㆍs?¹, respectively. Apparent quantum yields appeared to be similar in well-watered and water-stressed blueberries, but both light compensation point and dark respiration rate were higher in water-stressed blueberry. Stomatal conductance in well-watered blueberry in response to incident PPFD showed linear increase at low PPFD and saturation at high PPFD, but no clear asymptote was observed in water-stressed blueberry. The relationship between net CO₂ assimilation rate and stomatal conductance was linear (r² = 0.96**) in well-watered blueberry, but curvilinear (r² = 0.90**) in water-stressed blueberry, demonstrating the involvement of non-stomatal factors in photosynthesis under water stress condition. Net CO₂ assimilation rates during the day were always higher in well-watered than in water-stressed blueberry. In water-stressed blueberry, the diurnal time course of net CO₂ assimilation rates showed a sustained decrease until midday followed by afternoon recovery. However, such change was less apparent in well-watered blueberry. Stomatal conductance and transpiration rate during the day were always higher in well-watered than in water-stressed blueberry, being decreased until midday and then increased. Their diurnal changes were more apparent in well-watered than in water-stressed blueberry. However, the differences in stomatal conductance and transpiration rate between well-watered and water-stressed blueberries were diminished until midday and then became larger thereafter.
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KEYWORD
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apparent quantum yield, CO₂ assimilation, dark respiration, photoinhibition, stomatal conductance, transpiration
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