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The objective of this study was to assess canopy broadband spectral reflectance for turfgrasses under drought stress. Optimum turf quality (TQ) and leaf firing (LF) models were developed and compared based on two, three, and five wavelength bands. Sods of bermudagrass (Cynodon dactylon L. x C. transvaalensis Burtt-Davy), seashore paspalum (Paspalum vaginatum Swartz), zoysiagrass (Zoysia japonica Steud.), and St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze], and seeded tall fescue (Festuca arundinacea Schreb.) were used in this study with three cultivars each of bermudagrass, seashore paspalum, and tall fescue. Traditional vegetation indices (Vis) based on two bands within 660 to 950 nm were not as sensitive as three to five broadband models using a wider band range of 660 to 1480 nm. Optimum models were cultivar specific models, even within a species. The broadband wavelength at R900 and R1200 should be considered in drought sensitive spectral models since they were most often observed and exhibited high partial R~ values. These results suggest that mobile broadband spectral devices to map turfgrass responses to drought stress would benefit by the availability of three to five broadbands that could be user selected for optimum, cultivar specific models.

Antioxidant enzymes protect plant cells from oxidative injury induced by hypoxia. The objective of this study was to identify the responses of antioxidant enzymes to different depths of waterlogging (WL) in creeping bentgrass (Agrostis stolonifera L.) roots. 'Penncross' and 'G-6' were subjected to 21 d of WL at 1 cm (WL-1) and 15 cm (WL-15) below the soil surface, respectively. The turf quality of Penncross was not acceptable under both WL conditions, while G-6 had an acceptable quality of 6.5 under WL-15. The activity of superoxide dismutase (SOD) increased by 32 and 26% for Penncross and 83 and 44% for G-6 under WL-15 and WL-1, respectively. One isoform of Mn-SOD and three isoforms of Cu/Zn-SOD were identified in both cultivars under all treatments. The activity of ascorbate peroxidase (AP) significantly decreased by 46 and 40% for Penncross, while AP activity decreased 25% and increased 9% for G-6 under WL-1 and WL-15, respectively. One isoform of AP was identified with strong intensity in both cultivars under all treatments. The content of hydrogen peroxide ([H.sub.2][O.sub.2]) and malondialdehyde (MDA, 1,1,3,3-tetramethoxy-propane) and the activities of glutathione reductase (GR) and peroxidase (POD) were not affected by WL for both cultivars. These results indicated that SOD and AP were mainly involved in WL-induced antioxidant responses, and the partial WL could also significantly affect root antioxidant activities, particularly in WL-sensitive cultivar.

Oxygen deficiency is one of the primary root stresses in waterlogged or flooded soils. The objective of this experiment was to identify growth, physiological, and anatomical traits of creeping bentgrass (Agrostis stolonifera L.) associated with tolerance to different depths of waterlogging (WL). Five cultivars (L-93, A-4, G-6, Penncross, and Pennlinks) were subjected to the four WL treatments for 21 d: (i) drained control; (ii) water level at 15 cm (WL-15); (iii) water at 5 cm (WL-5); and (iv) water at 1 cm (WL-1) below the soil surface, respectively. Waterlogging reduced turf quality (TQ), root dry weight (RDW), root water soluble carbohydrate content (RWSC), and root soluble protein content (RPRO), while no significant reductions in RWSC, RDW, or RPRO were observed among three depths of WL. Turf quality and chlorophyll content (Chl) decreased with increasing water level from 15 to 1 cm. At WL-1, Chl, RDW, RWSC, and RPRO were reduced 27, 20, 44, and 22%, respectively, compared In the control. Cultivar differences in TQ, RDW, shoot water soluble carbohydrate content (SWSC), and RPRO were observed under WL. G-6 and L-93 had better quality than A-4, Penncross, and Pennlinks under WL conditions. The formation of aerenchyma was enhanced at WL-15 and WL-5. Mitochondrial swelling occurred under WL, particularly at WL-1. The results suggest that even partial WL (WL-15 and WL-5) could substantially affect turfgrass growth and physiological activities and cultivar variation in WL tolerance could potentially be used for enhancing breeding programs.

Low light (LL) stress is a major problem that influences turfgrass quality. Low light tolerance of seashore paspalum (Paspalum vaginatum Swartz) has not been assessed and information is needed to develop management strategies and to maximize turf performance. The objectives of this study were to: (i) evaluate responses of seashore paspalum to reduced light intensity and to identify the most tolerant entries; (ii) compare low light responses between paspalum and hybrid bermudagrass (Cynodon dactylon L. x C. transvaalensis Burtt Davy) cultivars. Eight entries of seashore paspalum and two hybrid bermudagrass cultivars were evaluated under full sunlight control (FL), and constant 70% and 90% LL provided by shade shelters in the field from August to October in 2001 and July to September in 2002 at Griffin, GA. Significant differences in turf quality, color, density, canopy photosynthetic rate (Pn), canopy chlorophyll index (Chl), canopy spectral reflectance, and leaf dry weight were observed in paspalum entries and hybrid bermudagrass cultivars under 70 and 90% LL treatments. Among all grasses, turf quality declined 9 (the best) to 22% (the worst) under 70% LL and 13 to 28% under 90% LL, respectively, compared with the control with FL. Canopy photosynthetic rate was reduced 10 to 43% under 70% LL and 27 to 67% under 90% LL; and normalized difference vegetation index (NDVI) decreased 14 to 31% and 20 to 45% for 70% LL and 90% LL treatments, respectively. Mast paspalum entries exhibited better low light tolerance than hybrid bermudagrasses under 70 and 90% LL, and 'Sea Isle 1' paspalum ranked as the most tolerant cultivar under both LL conditions. The ranking for the most low light tolerant entries under two LL conditions were: 'Sea Isle 1' paspalum (best) > Cloister paspalum = 'Sea Isle 2000' paspalum > Temple 1 paspalum = 'Salam' paspalum > Q 36313 paspalum = 561-79 paspalum = Hybrid 5 paspalum > 'TifSport' bermudagrass = 'TifEagle' bermudagrass (worst). Large variations observed among paspalum entries and bermudagrass cultivars in response to LL conditions could potentially be used for enhancing management practices., VARIOUS KINDS of shade, such as tree shade or shade of structures, can influence turf quality, persistence, and the traffic tolerance of turfgrasses. The estimated turf area under shade conditions [...]

Drought stress may alter protein synthesis in turfgrasses. The objectives of this study were to investigate physiological changes associated with the synthesis of dehydrin and a cytosolic-heat shock protein (HSC 70) in response to drought stress in two tall fescue (Festuca arundinacea L.) cultivars, `Southeast' and `Rebel Jr.'. The effects of abscisic acid (ABA) application on the drought tolerance of the cultivars also were evaluated. The cultivars were subjected to three treatments in growth chambers: well-watered control, drought stress, and drought stress following ABA treatment. Turf quality and leaf relative water content (RWC) decreased and electrolyte leakage (EL) increased during drought stress for both cultivars. The ABA-treated plants maintained higher turf quality and RWC, and lower EL than untreated plants under drought stress conditions. Levels of 20- and 29-kDa polypeptides increased during drought stress, and a 35-kDa polypeptide was noted in both cultivars only when subjected to drought stress either with or without ABA treatment. Immunoblot analysis indicated that dehydrin-like polypeptides of about 23-60 kDa were induced by progressive water deficit in both cultivars. The 53 kDa dehydrin polypeptide was present in Southeast with or without ABA treatment at 10 d of drought stress, whereas the 40 kDa dehydrin polypeptide accumulated in Rebel Jr. in both treatment. The 23- and 27-kDa dehydrin polypeptides were present at 10 d in drought-stressed and ABA-treated plants in both cultivars, but were more pronounced in the drought-stressed plants without ABA. A cytosolic-heat shock protein (HSC 70) was detected in plants in all treatments including well-watered plants of both cultivars, but its levels were higher in drought-stressed and ABA-treated plants. No single dehydrin polypeptide was induced by ABA treatment under drought stress, however, the promotive effects of ABA on the reduced drought stress paralleled the delayed induction of protein synthesis in tall fescue., NUMEROUS PHYSIOLOGICAL and biochemical changes occur in response to drought stress in various plant species. The alteration of protein synthesis or degradation is one of the fundamental metabolic processes that [...]

Prior exposure to drought stress (drought preconditioning) affects turfgrass tolerance to subsequent heat stress. The study was designed to examine whether these effects for Kentucky bluegrass (Poa pratensis L.) are associated with osmotic adjustment and root growth. Plants were subjected to two cycles of drying and rewatering, and turf quality was then allowed to recover to the well watered control level before being exposed to 21 d of heat stress (35 °C/30 ° C) in growth chambers. Compared with nonpreconditioned plants, drought-preconditioned plants had 13 and 21% higher turf quality, 6 and 10% higher leaf relative water content, and 17 and 48% higher osmotic adjustment at 14 and 21 d of heat stress, respectively. Total ion ([K.sup.+], [Ca.sup.2+], [Na.sup.+], [Ma.sup.2+], [Cl.sup.-], and P) concentration of cell sap increased during heat stress and was 11 to 16% higher in drought-preconditioned plants than nonpreconditioned plants. The concentration of [K.sup.+] accounted for 59 to 65% of total ion solutes in both groups of plants during heat stress. Soluble carbohydrate content (WSC) of leaves increased during heat stress and was about 21 and 44% higher in drought-preconditioned plants than nonpreconditioned plants at 14 and 21 d, respectively. Heat stress decreased root dry weight (DW) and WSC, but significant higher DW and WSC content of roots in the 40-60 cm soil layer were observed for preconditioned plants than nonpreconditioned plants before and after heat stress. The results demonstrated that drought preconditioning enhanced heat tolerance in Kentucky bluegrass, which could be related to the maintenance of higher osmotic adjustment associated with accumulation of ion solutes and water soluble carbohydrates and development of extensive roots deeper in the soil profile., TURFGRASSES are constantly subjected to changing nd interactive environmental stresses. Previous growing conditions can influence responses and adaptation of plants exposed to subsequent environmental stresses (Ackerson, 1980; Bennett and Sullivan, [...]

Drought and high temperature are two major factors limiting the growth of cool-season turfgrasses during summer in many areas. The objective of the study was to examine whether the adverse effects of drought and heat alone or in combination on tall fescue (Festuca arundinacea L.) and Kentucky bluegrass (Poa pratensis L.) involve oxidative stress. Grasses were exposed to drought (withholding irrigation), heat (35 ° C/30 ° C), and the combined stresses for 30 d in growth chambers. Turf quality (TQ), leaf relative water content (RWC), and chlorophyll content (Chl) decreased with prolonged drought, heat, and combined stresses for both species, but the severity of decline varied with stress type and duration. Transient increases in superoxide dismutase (SOD), ascorbate peroxidase (AP), and glutathione reductase (GR) activities occurred at 6 or 12 d of drought and the combined stresses in both species; however, the activities of all three enzymes decreased with extended periods of drought and the combined stresses. The SOD activity was not affected by heat stress alone. The activities of AP and GR were reduced after 18 d of heat stress for both species, but reductions were less than under the combined stresses. The catalase (CAT) activity continued to decrease to below the control level, beginning at 12 d for drought-stressed or heat-stressed plants and 6 d for plants exposed to the combined stresses. Lipid peroxidation occurred after 18 d of stresses in both species, as indicated by the increase in malondialdehyde (MDA) content. The results suggested that injuries of drought, heat, or the combined stresses to both tall fescue and Kentucky bluegrass, as manifested by declines in TQ, RWC, and Chl, could be associated with a decrease in antioxidant enzyme activities and an increase in membrane lipid peroxidation., COOL-SEASON TURFGRASSES often suffer from extended periods of drought stress, heat stress, or both during summer months in the transitional zone. Drought and heat stresses cause declines in turf quality [...]

Cool-season turfgrasses are frequently subjected to heat and drought stresses during summer months. This study was conducted to determine physiological responses of Kentucky bluegrass (Poa pratensis L.) to drought and heat alone or together, and the effects of drought preconditioning on plant responses to subsequent heat stress. Kentucky bluegrass (cv. Mystic) was subjected to drought and/or heat stress (35 ° C/30 ° C, day/night) in growth chambers for 40 d. Canopy photosynthetic rate ([P.sub.n]) and leaf photochemical efficiency (Fv/Fm) decreased under drought and heat stress. The decline in [P.sub.n] was more severe under heat than under drought stress during the first 12 d of treatment. The reduction in Fv/Fm ratio was more severe under drought stress than under heat stress after 20 d of treatment. The combined heat and drought stresses (H+D) caused more dramatic reductions in [P.sub.n] and Fv/Fm than either heat or drought alone, starting at 3 and 9 d after treatment, respectively. Drought or heat alone, or H+D, significantly reduced root dry weight. However, reduction was more severe under heat alone than under drought stress, particularly in the top 20 cm of soil. Drought preconditioning enhanced plant tolerance to subsequent heat stress but had no influence on plant tolerance to H+D. Drought-preconditioned plants maintained higher water status, stomatal conductance, and transpiration rate, and had significantly higher [P.sub.n] and root dry weight than non-preconditioned plants during subsequent heat stress. No significant difference in Fv/Fm was observed between drought-preconditioned and non-preconditioned plants under either heat alone or H+D. The results indicated that simultaneous drought and heat stresses were more detrimental than either stress alone. Drought preconditioning could improve Kentucky bluegrass tolerance to subsequent heat stress., KENTUCKY BLUEGRASS is a cool-season grass widely used for home lawns and commercial landscapes in temperate climates. The optimum temperature for shoot growth of Cool-season grasses is 15 to 23 [...]

An averaging procedure is presented for analysis of plain-weave-fabric composites with material nonlinear behavior. A representative volume cell is assumed. The cell is divided into many subcells, and averaging is performed again. The effective stress-strain relations of the subcell are obtained. Using iso-stress and iso-strain assumptions, the constitutive equations are averaged along the thickness direction. As a result, a linear system of equations is formed and subsequently solved to distribute the global average strains to each subcell. In this manner, given the average strains, the global average stresses can be determined. Numerical results are generated for plain-weave composite with material nonlinear behavior.