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Travis Culpepper, Joseph Young, David T. Montague, Dana Sullivan, and Benjamin Wherley

provided by turfgrasses capable of maintaining green cover, photosynthetic production, and reduced canopy temperatures under combined heat and soil water deficit resulting from summertime landscape irrigation restrictions. Physiological adaptation and

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Khalid F. Almutairi, David R. Bryla, and Bernadine C. Strik

fruit bud set ( Almutairi et al., 2017 ). The objective of the present study was to build on these findings and examine the effects of soil water deficits during various stages of fruit development on different cultivars of northern highbush blueberry

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Jeffrey Melkonian and David W. Wolfe

Cucumber (Cucumis sativus L. cv. Marketmore 80) plants were exposed to a soil water deficit and subsequently rewatered. Maximum stress intensity was -1.5 MPa midday leaf water potential compared to -0.6 to -0.8 MPa in the well watered control, eight days after withholding water. Midday stomatal conductance {ks), leaf turgor potential and water potential decreased in the stress treatment compared to the control beginning at the first sampling, two days after withholding water. The decrease in all three was approximately linear with time over the stress. Decreased leaf elongation was observed at the second sampling, three days after the initial decline in ks and five days after withholding water. At similar relative water content {RWC), osmotic potentials of the stress and control treatments were the same throughout most of the stress. Further, there was no difference in osmotic potential, at the same RWC, between the stress and control treatments 12 - 16 hours after rewatering. Split-root experiments were also conducted to examine a possible role of a non-hydraulic signal from roots in drying soil in the regulation of ks and leaf elongation in cucumber. No conclusive evidence of a signal was found despite significant decreases in soil water potential of one-half of the root system of the stress plants. However, fluctuating vapor pressure gradients (vpg) may have obscured evidence of a signal.

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Sarah E. Cathey, Jason K. Kruse, Thomas R. Sinclair, and Michael D. Dukes

characteristics Crop Sci. 28 328 331 Lecoeur, J. Sinclair, T.R. 1996 Field pea transpiration and leaf growth in response to soil water deficits Crop Sci. 36 331 335 Miller, G.L. 2000 Physiological response of bermudagrass gown in soil amendments during drought

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Matthew W. Fidelibus and Chris A. Martin

Four AM fungal isolates (Glomus sp.) from disparate edaphic conditions were screened for effects on leaf gas exchange of `Volkamer' lemon (Citrus volkameriana Ten. and Pasq.) plants of similar size under conditions of increased soil water deficit stress and recovery from stress. Mycorrhizal and non-mycorrhizal plants were grown in 8-L containers for 10 weeks under well-watered conditions in a glasshouse and then subjected to three consecutive soil-drying episodes of increased severity (mean soil water tension reached –0.02, –0.06, and –0.08 MPa, respectively). Gas exchange measurements were made on the last day of each soil-drying episode. Plants were irrigated after each soil-drying episode, and measurements were repeated on the following 2 recovery days, when soil remained moist. All measurements were made at mid-day with a LI-COR 6200 portable photosynthesis system. The effect of AM fungi on leaf gas exchange fluxes varied depending on the isolate and the intensity of soil water stress. Leaf gas exchange fluxes always were highest for plants colonized by Glomus mosseae (Nicol. & Gerde.) isolate 114C, except during the third soil-drying episode, when all mycorrhizal plants had similar, and lower, gas exchange fluxes compared with non-mycorrhizal plants. During recovery from the third soil-drying episode, Glomus mosseae isolate 51C had lower leaf gas exchange fluxes compared with all other plants. Our results show that AM fungi can alter leaf gas exchange fluxes of citrus, under conditions of optimal P nutrition, in an isolate-specific manner.

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R.B. Hutmacher, J.J. Steiner, J.E. Ayars, A.B. Mantel, and S.S. Vail

The influence of irrigation frequency and the severity and rate of development of soil water deficits on the vegetative growth and water status of carrots (Daucus carota L. var. sativa DC.) grown for seed were investigated in a fine sandy loam soil. Beginning with the period of rapid development of primary umbels, various irrigation frequencies [daily vs. intervals corresponding to 30 mm of accumulated crop evapotranspiration (ETc)] were investigated at irrigation rates ranging from 40% to 120% of estimated ETC. The magnitude and rate of development of soil water deficits markedly influenced carrot responses to developing water deficits. Stomata] conductance and leaf water potential (LWP) measurements exhibited some potential for use in irrigation scheduling and were the most sensitive and consistent indicators of plant water status. Under low-frequency continuous-deficit irrigation, a combination of moderate reductions in stomatal conductance and major reductions in peak leaf area and late-season maintenance of viable leaf area occurred. These responses were effective water-conserving mechanisms, allowing growth at a reduced rate and continued development of viable seed. In contrast, rapid development of soil water deficits resulted in nearly complete stomatal closure, cessation of growth, and rapid reductions in leaf area.

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P.W. Masinde, H. Stützel, S.G. Agong, and A. Fricke

Plant growth and osmotic adjustment of spiderplant were investigated in a glasshouse and under field conditions. Two fast-growing genotypes (P-landrace and P-commercial) and a slow-growing landrace (G-landrace) were grown under soil water deficit and watered conditions. The fraction of transpirable soil water (FTSW) was used as an indicator of water availability in pots. In the greenhouse, transpiration was determined by changes in daily pot weights and the ratio of transpiration of plants in soil water deficit to watered treatments expressed as normalized transpiration ratio (NTR). Water use in the field experiment was determined by gravimetric methods. The fast-growing genotypes had a higher rate of soil drying due to a higher rate of leaf area development. They were also more sensitive to soil water deficit with NTR beginning to decline at FTSW of 0.55-0.77 as compared to 0.29 for the slow-growing landrace. Also, the fast growing genotypes had FTSW thresholds for the stem elongation rate of 0.35-0.55 as compared to 0.20 for the slow growing landrace. The rate of leaf development declined when 40% to 60% of available water in the soil was removed, regardless of genotype. Leaf area of plants under field conditions decreased when the soil moisture was <60% field capacity. Under severe soil water deficit stress in pots, plants partitioned more biomass to roots than above ground; however, biomass partitioning between leaves and stems was not influenced by soil water deficit. Spiderplant showed limited osmotic adjustment (OA) in the range of 0.10-0.33 MPa at the highest soil water deficit (FTSW = 0). Thus, spiderplant is mainly a drought avoiding species. To achieve maximum growth, it is necessary to keep FTSW above 0.6.

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James Bunce

127 136 Warren, C.R. 2006 Estimating the internal conductance to CO 2 movement Funct. Plant Biol. 33 432 442 Warren, C.R. 2008 Soil water deficits decrease the internal conductance to CO 2 transfer but atmospheric water deficits do not J. Expt. Bot

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Christopher Vincent, Diane Rowland, and Bruce Schaffer

soil profile ( Rowland et al., 2012 ). However, this mechanism is only beneficial in deep soils under moderate or short-term soil water deficits, cases in which greater rooting depth actually confers increased access to soil water ( Tardieu, 2012

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

genotypes grown in two different shapes. For these reasons, the evaluation of DI as a possible technique to improve water productivity and the selection of genotypes that can better withstand soil water deficits are essential for sustainable production. The