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Thomas E. Marler and Patrick D. Lawton

Temperature and chlorophyll fluorescence characteristics were determined on leaves of various horticultural species following a dark adaptation period where dark adaptation cuvettes were shielded from or exposed to solar radiation. In one study, temperature of Swietenia mahagoni (L.) Jacq. leaflets within cuvettes increased from ≈36C to ≈50C during a 30-minute exposure to solar radiation. Alternatively, when the leaflets and cuvettes were shielded from solar radiation, leaflet temperature declined to 33C in 10 to 15 minutes. In a second study, 16 horticultural species exhibited a lower variable: maximum fluorescence (Fv: Fm) when cuvettes were exposed to solar radiation during the 30-minute dark adaptation than when cuvettes were shielded. In a third study with S. mahagoni, the influence of self-shielding the cuvettes by wrapping them with white tape, white paper, or aluminum foil on temperature and fluorescence was compared to exposing or shielding the entire leaflet and cuvette. All of the shielding methods reduced leaflet temperature and increased the Fv: Fm ratio compared to leaving cuvettes exposed. These results indicate that heat stress from direct exposure to solar radiation is a potential source of error when interpreting chlorophyll fluorescence measurements on intact leaves. Methods for moderating or minimizing radiation interception during dark adaptation are recommended.

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Eric Watkins, Bingru Huang, and William A. Meyer

related to rainfall differences, although it will not grow in arid regions with severe drought ( Davy, 1980 ). When compared with tall fescue, tufted hairgrass seedlings were shown to have lower photochemical efficiency at high temperatures ( Steiner et al

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Jia Li, Liyun Liu, Huanqi Zhou, and Meng Li

-control software (PAMWin 3.0). The photochemical quenching (qP) = (F m – F s )/(F m ′ – F o ′), nonphotochemical quenching (NPQ) = (F m – F m ′)/F m ′, maximum photochemical efficiency of PSII (F v /F m , F v = F m – F o ), and actual photochemical efficiency

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Julián Miralles-Crespo, Juan Antonio Martínez-López, José Antonio Franco-Leemhuis, and Sebastián Bañón-Arias

photochemical efficiency of photosystem II (PSII) (F v /F m ) in N. oleander ‘Yellow’; ( B ) F v /F m in N. oleander ‘Pink’; ( C ) quantum yield of PSII (éPSII) in N. oleander ‘Yellow’; ( D ) éPSII in N. oleander ‘Pink’; ( E ) non

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Jieshan Cheng, Peige Fan, Zhenchang Liang, Yanqiu Wang, Ning Niu, Weidong Li, and Shaohua Li

bag removal” treatment at 1100 hr and 1000 to 1100 hr , respectively ( Fig. 2, E and F ). Fig. 2. Diurnal changes in ( A ) maximal quantum yield of photosystem II (F v /F m ), ( B ) actual photochemical efficiency of photosystem II (ΦPSII

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Yiming Liu, Hongmei Du, Kai Wang, Bingru Huang, and Zhaolong Wang

was measured at 663 and 645 nm with a spectrophotometer (Helios Alpha, thermospectronic, Rochester, NY) and total chlorophyll concentration was calculated as described by Arnon (1949) . Leaf photochemical efficiency (Fv/Fm) was estimated by measuring

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Xunzhong Zhang and Erik H. Ervin

. Turfgrass quality or injury was rated based on a visual scale of 1 to 9 with 9 indicating the best quality or no injury and 1 indicating the worst quality or most injury (chlorosis). Canopy photochemical efficiency measurement. The photochemical efficiency

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Zipeng Tian, Bingru Huang, and Faith C. Belanger

samples were then dried in the oven at 80 °C for 72 h and dry weight (DW) of tissues was measured. Relative water content was calculated as (FW – DW)/(TW – DW) × 100 ( Barrs and Weatherley, 1962 ). Leaf photochemical efficiency was determined as an

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Stephen E. McCann and Bingru Huang

canopy ( Turgeon, 1999 ). A rating of 6 was considered the minimal acceptable turf quality level. Leaf photochemical efficiency was estimated by measuring the variable to maximum fluorescence ratio (F v /F m ) in the nonenergized state accomplished by

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Ming Ding, Beibei Bie, Wu Jiang, Qingqing Duan, Hongmei Du, and Danfeng Huang

was calculated using the extinction coefficient of 155 m m/ cm. Measurements of leaf photochemical efficiency and photosynthesis. Leaf photochemical efficiency of watermelon seedlings during storage was estimated by measuring chlorophyll fluorescence