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Yaling Qian and Jack D. Fry

Greenhouse studies were conducted on three warm-season turfgrasses, `Midlawn' bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy], `Prairie' buffalograss [Buchloe dactyloides (Nutt.) Engelm.], and `Meyer' zoysiagrass (Zoysia japonica Steud.), and a cool-season turfgrass, `Mustang' tall fescue (Festuca arundinacea Schreb.) to determine 1) water relations and drought tolerance characteristics by subjecting container-grown grasses to drought and 2) potential relationships between osmotic adjustment (OA) and turf recovery after severe drought. Tall fescue was clipped at 6.3 cm once weekly, whereas warm-season grasses were clipped at 4.5 cm twice weekly. The threshold volumetric soil water content (SWC) at which a sharp decline in leaf water potential (ψL) occurred was higher for tall fescue than for warm-season grasses. Buffalograss exhibited the lowest and tall fescue exhibited the highest reduction in leaf pressure potential (ψP) per unit decline in ψL during dry down. Ranking of grasses for magnitude of OA was buffalograss (0.84 MPa) = zoysiagrass (0.77 MPa) > bermudagrass (0.60 MPa) > tall fescue (0.34 MPa). Grass coverage 2 weeks after irrigation was resumed was correlated positively with magnitude of OA (r = 0.66, P < 0.05).

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Susan L. Steinberg, Jayne M. Zajicek, and Marshall J. McFarland

Growth of potted hibiscus (Hibiscus rosa-sinensis L.) was limited either by pruning or by a soil drench of `uniconazole at 3.0 mg a.i. per pot. Both treatments changed the water use of hibiscus. Five days after treatment with uniconazole, plants showed reduced water use, an effect that became more pronounced with time. Water use of pruned plants was reduced immediately after pruning, but soon returned to the level of the control due to the rapid regeneration of leaf area. Pruned or chemically treated plants used 6% and 33% less water, respectively, than the control. Chemically treated plants had a smaller leaf area, and individual leaves had lower stomatal density, conductance, and transpiration rate than control plants. Under well-watered conditions, the sap flow rate in the main trunk of control or pruned plants was 120 to 160 g·h-1·m-2, nearly three times higher than the 40 to 70 g·h-1·m-2 measured in chemically treated plants. Liquid flow conductance through the main trunk or stem was slightly higher in chemically treated plants due to higher values of leaf water potential for a given sap flow rate. The capacitance per unit volume of individual leaves appeared to be lower in chemically treated than in control plants. There was also a trend toward lower water-use efficiency in uniconazole-treated plants. Chemical name used: (E)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-l-yl)-1-penten-3-ol (uniconazole).

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Renee H. Harkins, Bernadine C. Strik, and David R. Bryla

electric solenoid valves and an automatic timer. Irrigation was scheduled weekly based on estimates of crop evapotranspiration (ET) but adjusted as needed each week to maintain similar leaf water potentials among treatments. Crop ET was calculated by

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Emily K. Dixon, Bernadine C. Strik, Luis R. Valenzuela-Estrada, and David R. Bryla

each week to maintain similar leaf water potentials (LWP) among treatments. Crop ET was calculated by multiplying reference ET by a crop coefficient for blackberry that was downloaded daily along with weather data, including air temperature and

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Bharat P. Singh, Kevin A. Tucker, James D. Sutton, and Harbans L. Bhardwaj

Abbreviations: E, transpiration; g s , stomatal conductance; Pn, net photosynthesis; ψ, leaf water potential. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations

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Thomas J. Tworkoski and D. Michael Glenn

Competitive effects of different grass species were evaluated on growth, yield, leaf N, and leaf water potential of 8-year-old peach [Prunus persica (L.) Batsch.] trees and on weed abundance. Two cultivars (`Loring' on Lovell rootstock and `Redhaven' on Halford rootstock) of peach trees were planted in separate orchards in 1987. Nine orchard floor treatments were installed beneath the peach trees in 1995: Festuca arundinacea Schreber (tall fescue); Lolium perenne L., var. Manhattan II (perennial ryegrass); Lolium perenne L., var. Linn; Agrostis gigantea Roth (red top); Dactylis glomerata L. (orchardgrass); Phleum pratense L. (timothy); Bromus carinatus Hook. and Arn. (brome); weedy control; and herbicide weed control (simazine, glyphosate). In general, grasses reduced vegetative growth and yield in both cultivars. Orchardgrass was one of the most competitive species and reduced vertical water sprout length by 15% to 27% and lateral shoot length on fruit-bearing branches by 19% to 30% compared with herbicide treatments. Orchardgrass reduced yield by 37% and 24% in `Loring' and `Redhaven', respectively. All grasses were not equally competitive; `Linn' perennial ryegrass did not significantly reduce growth or yield in `Redhaven'. Control treatments with weeds also did not differ from herbicide treatments in peach tree growth and yield. Grass and weed ground covers consistently reduced peach tree leaf N by at least 10%, compared to herbicide treatment, possibly due to reduced root growth. `Redhaven' root density in the top 10 cm of soil was ≈12 cm·cm-3 in herbicide strips vs. 1 cm·cm-3 in weedy or ground-covered strips. Peach leaf water potential was not affected by grass and weeds. Weed weights were significantly reduced by all grasses compared with weedy control. The results indicate that peach cultivars respond differently to grass competition, but the relative competitiveness of each grass species was similar for both cultivars. Grass competition reduced growth, yield, and pruning weights of mature peach trees, but the reduction in vegetative growth did not significantly reduce pruning time per tree. Grasses that are less inhibitory to peach yield may be useful for weed management in orchards.

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D. Joseph Eakes, Robert D. Wright, and John R. Seiler

inhibition of photosynthesis; WUE, water-use efficiency; ψ L , leaf water potential. 1 Former Graduate Student. Present address: Dept. of Horticulture, Auburn Univ., AL 36849. 2 Professor. 3 Assistant Professor, Dept. of Forestry. Technical guidance and

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Zhongchun Wang and Gary W. Stutte

Abbreviations: ψ P , leaf turgor potential; ψ s , leaf osmotic potential; ψ W , leaf water potential; DPM, disintegration per minute; MEOH, methanol; Pn, photosynthesis; RWC, relative water content; Rs, stomatal resistance. 1 Current address

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Peter Nitzsche, Gerald A. Berkowitz', and Jack Rabin

Horticulture and Crops Dept., Cook College. Author to whom reprint requests should be addressed. Abbreviations: Ψ w, leaf water potential; r L , leaf resistance; SLW, specific leaf weight. 1 Horticulture and Crops Dept., Cook College. 3 Rutgers

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D. Michael Glenn, Nicola Cooley, Rob Walker, Peter Clingeleffer, and Krista Shellie

., 2000a , 2000b ). Changes in root growth and development may subsequently influence soil water extraction and translocation of root-derived signals ( Rogiers et al., 2010 ). Moriana et al. (2003) found that the leaf water potential and stomatal