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Ronald S. Thomas and Jack E. Staub

Abbreviations: CWSI, crop water stress index; OVR, overall fruit quality rating; P, photosynthesis; PFD, pillowy fruit disorder; RH, relative humidity; SMT, soil moisture tensions; SR, stomatal resistance; VPD, vapor pressure deficit. 1 Former

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Pedro Perdomo, James A. Murphy, and Gerald A. Berkowitz

Understanding the factors influencing the performance of Kentucky bluegrass (Poa pratensis L.) cultivars under summer stress is necessary for developing criteria for identifying resistant germplasm. The objectives of this study were to evaluate two Kentucky bluegrass cultivars for leaf water (ψl) and osmotic potential (ψπ), stomatal resistance (Rs), leaf: air temperature differential (ΔT) and determine the relationship of these parameters to drought and heat tolerance. Stress-resistant (`Midnight') and susceptible (`Nugget') cultivars were evaluated in a field study during 1993 and 1994 under moisture-limiting conditions. Leaf water potential for `Nugget' was higher than for `Midnight' in 1993 and similar in 1994. `Midnight' had lower ψπ than `Nugget' during the evaluation period in 1994. `Midnight' maintained more open stomata (lower Rs) and lower ΔT than `Nugget' at the end of the dry down period when `Nugget' was showing visual signs of stress. `Midnight' and `Nugget' had similar root weight at the 0- to 45-cm depth zone in 1994. Lower basal osmotic potential (i.e., higher solute concentration) may be the physiological mechanism allowing larger stomatal aperture in `Midnight'. Greater transpirational cooling in `Midnight' relative to `Nugget' was correlated with higher turf quality for `Midnight'.

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Atilla B. Goknur and Theodore W. Tibbitts

The magnitude of dark opening of stomata on leaves of Irish potato (Solanum tuberosum L.) was studied to determine if this opening was related to the high sensitivity of these plants to air pollutants. Stomatal opening was studied over diurnal periods both in the field and in controlled environments. In both environments, stomatal conductance decreased rapidly at the initiation of dark to 0.1 cm·s-1 but then increased to 0.2 cm·s-1 over the dark period. However conductance was always less in the dark than in the light (0.3 to 0.9 cm·s-1). During the early part of the dark period, stomatal conductance in controlled environments was not as great as in the field, but conductance was similar in both environments over the latter part of the dark period. Cultivars Norchip and Kennebec had smaller conductances during the first hours of the dark than Haig or Katahdin, and all cultivars increased in conductance over the dark period. `Haig' showed slightly higher conductance than the other three during the last 4 hours of the dark period. Injury to `Haig' from 3-hour fumigations with sulfur dioxide (SO2) or ozone (O3) demonstrated that exposures during the day generally produced more injury than during the night, although exposures with SO2 during the last 3 hours of the light period produced similar injury to exposures at the end of the dark period. Thus, although partial opening during the dark may be permitting some pollution injury, it is concluded that previous published reports of similar opening of stomata on Irish potatoes during the light and dark periods, and equal or greater pollution injury during the dark compared with the light period, were not substantiated and apparently resulted from procedural artifacts.

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Iro Kokkinou, Nikolaos Ntoulas, Panayiotis A. Nektarios, and Dimitra Varela

1330 hr with a handheld SPAD meter (SPAD-502 Chlorophyll meter; Konica Minolta, Japan). For each measurement, the youngest of fully developed leaves were selected. Leaf stomatal resistance. Leaf stomatal resistance measurements were performed every 3

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George Kotsiris, Panayiotis A. Nektarios, and Angeliki T. Paraskevopoulou

their increased stomatal resistance compared with the plants in deeper substrates (30 cm) ( Fig. 7 ). Differences were negated after September rainfall events ( Figs. 1 and 7 ). Regarding substrate types, substrate Pum 65 :C 30 :Z 5 exhibited

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Chiara Cirillo, Youssef Rouphael, Rosanna Caputo, Giampaolo Raimondi, and Stefania De Pascale

’, B. ‘Lindleyana’ ( =B. ‘Aurantiaca’ )] trained to two canopy shapes (globe and pyramid). For this, plant growth, ornamental quality, WUE, mineral composition, stomatal resistance, and water relations were measured during the growing cycle. These

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Youssef Rouphael, Giampaolo Raimondi, Rosanna Caputo, and Stefania De Pascale

; Dionex, Sunnyvale, CA). Nitrate, potassium, and phosphate losses were also measured by cumulating the amounts of NO 3 − , K + , and PO 4 3− that were leached during each flushing event from the semiclosed soilless system. Stomatal resistance was measured

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Carlos Vinicius Garcia Barreto, Rhuanito Soranz Ferrarezi, Flávio Bussmeyer Arruda, and Roberto Testezlaf

; leaf water potential at 36, 55, 67, 75, and 90 DAS; and leaf temperature, transpiration, and stomatal resistance at 36, 55, and 90 DAS. We sampled three plants per plot for each sampling date. The gaseous exchange measurements from the porometer LI-1600

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Lamprini Tassoula, Maria Papafotiou, Georgios Liakopoulos, and Georgios Kargas

experimental module was taken as a sample. The substrate was carefully washed off the root biomass under running tap water and over a fine mesh to collect possible roots that might break off during washing. Physiological parameters. Leaf stomatal resistance ( R