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  • Author or Editor: Richard L. Garcia x
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Eureka lemon (Cirrus limon L. `Eureka') trees were grown in factorial combinations of low (L) or high (H) temperature [day/night temperature regimens of 29.4C/21.1C or 40.5C/32.2C] and ambient (C380) or enriched (C680) atmospheric CO2 concentrations [380 umol mol-1 or 680 umol mol-1, respectively]. After growth under these conditions for 5 months, morning and afternoon leaf carbon assimilation measurements were made with a temperature-controlled cuvette attached to a portable photosynthesis system. Net (P3) and gross (Pg) photosynthesis were measured at 30 umol mol-1 intervals as leaves were exposed to cuvette CO2 drawndowns from 700 to 300 umol mol-1 at 21% and 1% O2, respectively. Photorespiration (Rp) was estimated as the difference between Pg and Pn. Generally, Rp increased as cuvette CO2 decreased. Morning and afternoon Rp of leaves adapted to LC380 conditions were similar. Morning Rp was higher than afternoon Rp for leaves adapted to LC680 conditions. Morning Rp was higher for leaves adapted to HC380 conditions as compared to HC680-adapted leaves. In contrast, afternoon Rp was higher for leaves adapted to HC680 conditions than for H&,-adapted leaves.

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Eureka lemon (Citrus limon L. `Eureka') trees were inoculated with ecotypes of VAM fungi isolated from either a subtropical desert (HVAM) or a temperate grassland (LVAM), and grown for five months at 40.5C/32.2C (high) or 29.4C/21.1C (low) day/night, respectively. Diurnal measurements of leaf carbon assimilation (A), transpiration (E) and stomatal conductance (gs) were then made with a portable photosynthesis system. At high temperatures, afternoon A, E and gs were highest for trees inoculated with LVAM and lowest for trees inoculated with HVAM. At low temperatures, afternoon A, E and gs were highest for trees inoculated with HVAM and lowest for trees inoculated with LVAM. Compared to controls, trees inoculated with HVAM and LVAM displayed rapid mid-day fluctuations in stomatal conductance. At low temperatures, water use efficiency (WUE) during the morning was lowest for trees inoculated with LVAM; whereas, afternoon WUE was not affected by HVAM or LVAM. HVAM and LVAM did not affect WUE at high temperatures. Results indicate that long-term physiological adaptations of lemon trees to temperature are uniquely affected by different VAM fungal ecotypes.

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Paclobutrazol at 0 and 750 μl·liter–1 was sprayed on shoots of Feijoa sellowiana O. Berg. and Ligustrum japonicum Thunb. grown under similar production regimes in central Arizona (subtropical desert) and southern Georgia (humid temperate). Five months after application, Feijoa and Ligustrum leaves were generally smaller and thicker in Arizona than in Georgia. Arizona leaves were thicker than those in Georgia because of more layers of palisade and spongy mesophyll cells. Compared with leaves from control plants, paclobutrazol 1) increased Feijoa leaf area in Georgia, 2) decreased Ligustrum leaf area at both locations by ≈50%, and 3) decreased leaf thickness of both species in Arizona. Arizona Feijoa leaves had trichomes on adaxial and abaxial surfaces, whereas Georgia Feijoa leaves had trichomes on abaxial surfaces only. Paclobutrazol increased trichome frequency on adaxial surfaces of Arizona Feijoa leaves. Stomatal frequency of Georgia Feijoa leaves was about doubled by paclobutrazol. Reflectance of near-infrared radiation by paclobutrazol-treated Feijoa leaves was 1.4 times higher than that of nontreated leaves in Georgia and 1.9 times in Arizona. Near-infrared reflectance by Georgia Ligustrum leaves was 1.3 times higher than by Arizona Ligustrum leaves and was not affected by paclobutrazol. Leaf reflectance of photosynthetically active radiation (PAR) by Arizona Feijoa was higher than by Georgia Feijoa. Paclobutrazol increased PAR reflectance by Arizona Feijoa leaves. In contrast, Georgia Feijoa PAR reflectance was decreased by paclobutrazol. Paclobutrazol or location did not affect Ligustrum PAR reflectance. Chemical name used: (2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)pentan-3-ol (paclobutrazol).

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Same-source rooted cuttings of Feijoa Sellowiana Hort. and Ligustrum japonicum L. were grown under identical production systems in Tempe, AZ, USA or Tifton, GA, USA during the Spring and Summer 1992. Leaf area was largest and specific leaf weight was lowest for all Georgia-grown plants. Scanning electron microscopy revealed that Arizona Feijoa leaves had trichomes on both the abaxial and adaxial leaf surfaces, whereas, leaves of Georgia Feijoa had trichomes on the abaxial surface only. Arizona Feijoa leaves also had increased abaxial surface pubescence compared to leaves of Georgia Feijoa. Both Feijoa and Ligustrum grown in Arizona had a higher density of palisade and spongy mesophyll cell layers compared to their Georgia counterparts. When placed under the same irradiance source, adaxial leaf surface temperatures of Georgia-grown Ligustrum and Feijoa were approximately 4.2 and 0.2C, respectively, higher than for those grown in Arizona. Higher leaf temperatures of Georgia-grown plants were correlated with darker leaf color compared to the Arizona-grown plants.

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