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Jason J. Griffin, Thomas G. Ranney, and D. Mason Pharr

Tolerance to high solar irradiation is an important aspect of stress tolerance for landscape plants, particularly for species native to understory conditions. The objective of this study was to evaluate differential tolerance to high solar irradiation and underlying photosynthetic characteristics of diverse taxa of Illicium L. grown under full sun or 50% shade. Eleven commercially available taxa of Illicium were evaluated for light tolerance by measuring light-saturated photosynthetic capacity (Amax), dark-adapted quantum efficiency of photosystem II (Fv/Fm), and relative chlorophyll content using a SPAD chlorophyll meter. Comparisons of Amax indicated that three of the 11 taxa (I. anisatum L., I. parviflorum Michx. ex Vent., and I. parviflorum `Forest Green') maintained similar rates of light-saturated carbon assimilation when grown in either shade or full sun. All other taxa experienced a significant reduction in Amax when grown in full sun. Chlorophyll fluorescence analysis demonstrated that Fv/Fm was similar between sun and shade plants for the same three taxa that were able to maintain Amax. These taxa appeared to experience less photoinhibition than the others and maintained greater maximum photochemical efficiency of absorbed light. SPAD readings were not significantly reduced in these three taxa either, whereas most other taxa experienced a significant reduction. In fact, SPAD readings were significantly higher in I. parviflorum `Forest Green' when grown under full sun, which also maintained the highest Amax of all the taxa. These results suggest that there is considerable variation in light tolerance among these taxa, with I. parviflorum `Forest Green' demonstrating superior tolerance to high light among the plants compared. A more rigorous examination of I. parviflorum `Forest Green' (high light tolerance) and I. floridanum Ellis (low-light tolerance) demonstrated that I. parviflorum `Forest Green' had a considerably higher Amax, a higher light saturation point, greater potential photosynthetic capacity, reduced susceptibility to photoinhibition as indicated by superior PSII efficiency following light exposure, greater capacity for thermal de-excitation as indicated by a higher rate of nonphotochemical quenching (NPQ) under full sun, greater apparent electron transport rate (ETR) at mid-day, and higher concentrations of the free-radical scavenger myo-inositol. All of these factors contribute potentially to a greater capacity to use light energy for carbon fixation while minimizing photodamage.

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Juan Carlos Díaz-Pérez

., Ramsey, NJ). Leaf gas exchange and photosystem II efficiency. Simultaneous measurements of leaf gas exchange (net photosynthesis, g S , transpiration, and internal CO 2 concentration) and fluorescence determined as photosystem II (PSII) efficiency were

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Eva Bacaicoa and Jose María García-Mina

method described in Séstak et al. (1971) . Chl fluorescence measurements. The effect of Fe deficiency on plant photosynthetic efficiency was evaluated through the determination of the photosystem II (PSII) efficiency in dark-adapted (F v /F m

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Juan Carlos Díaz-Pérez and Touria E. Eaton

., Ramsey, NJ). Leaf gas exchange and PSII efficiency. Simultaneous measurements of leaf gas exchange (net photosynthesis, g S , transpiration, and internal CO 2 concentration), and fluorescence were determined as PSII efficiency were made with an infrared

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Rongpei Yu, Ying Cheng, Yanfei Pu, Fan Li, and Shugang Lu

Rapparini et al. (2015) . The chlorophyll fluorescence parameters of hydrated, dehydrated, and rehydrated plants were tested by Chlorophyll Fluorescence Imager (Technologica Inc., Essex, UK). The maximum photosystem II (PSII) efficiency at open centers ( F v

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Renée L. Eriksen, Laban K. Rutto, James E. Dombrowski, and John A. Henning

-6400XT version 6 manual); all other LCF settings complied with the manufacturer’s suggested settings for determining PSII efficiency (Ф PSII ). Following survey measurements, a rapid A/C i curve was performed at each temperature on one plant of the

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David H. Suchoff, Penelope Perkins-Veazie, Heike W. Sederoff, Jonathan R. Schultheis, Matthew D. Kleinhenz, Frank J. Louws, and Christopher C. Gunter

fluorescence ( Allen and Ort, 2001 ; Kingston-Smith et al., 1997 ; Lynch, 1990 ; Maxwell and Johnson, 2000 ). F v / F m is a measure of intrinsic PSII efficiency and, because PSII efficiency reduces with suboptimal temperatures, values of F v / F m can

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Juan Carlos Díaz-Pérez and James E. Hook

chlorophyll meter (Chlorophyll Meter SPAD-502; Minolta Co., Ltd., Ramsey, NJ). Leaf gas exchange and photosystem II (PSII) efficiency. Simultaneous measurements of leaf gas exchange (net photosynthesis, g S , transpiration, and internal CO 2 concentration

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Augusto Ramírez-Godoy, María del Pilar Vera-Hoyos, Natalia Jiménez-Beltrán, and Hermann Restrepo-Diaz

applications of synthetic elicitors on stomatal conductance ( g S ), leaf temperature, chlorophyll content, and PSII efficiency in Tahiti lime trees. Fig. 3. Effect of foliar applications of synthetic elicitors on the relative growth rate in flush shoots of

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Mengmeng Gu, James A. Robbins, and Curt R. Rom

) were taken at 1300 hr (CDST). The maximum PSII efficiency of dark-adapted leaves was calculated as: F v / F m = ( F m – F o )/ F m ( van Kooten and Snel, 1990 ). The efficiency of excitation transfer to open PSII reaction centers under