Search Results
Abstract
Three of 6 antitranspirants significantly reduced winter injury 1 of 5 years when applied 1 and 2 times to Ilex × attenuata Ashe ‘Foster's No. 2’. No reduction of winter injury was observed during 1979 and 1980 even though leaf water potentials recorded during winter stress periods indicated that Exhalt 4-10, Vapor Gard, Wilt Pruf, Folicote, and Foligard significantly reduced transpirational loss of water in midwinter. Two applications of Folicote and Exhalt 4-10 increased water potential more than the single fall application, but did not reduce winter injury significantly. Clear Spray did not increase leaf water potential and appeared to crack and peel within 3 weeks aftef application. Scanning electron micrographs indicated better coverage of leaf surfaces by dipping them by spraying and verified the rapid cracking of Clear Spray.
Abstract
A study was conducted to investigate environmental factors which affect leaf water potential (LWP) response of chrysanthemums (Chrysanthemum × morifolium Ramat). Meteorological parameters, including air temperature (TEMP), relative humidity (HUM), total solar radiation (RAD), and photosynthetically active radiation (PAR) were measured simultaneously as LWP determinations were made diurnally for plants grown with 5 different irrigation rates. Stepwise multiple regression analyses using the meteorological parameters as independent variables and LWP as the dependent variable showed that models developed for each irrigation rate included TEMP, HUM, and PAR as statistically significant (P = 5%) independent variables. Coefficients of determination (R2) for the models ranged from 0.83–0.87. A combined model, including irrigation rate (R) as an independent variable along with the meteorological parameters, revealed that TEMP, PAR, HUM, and R were statistically significant at P = 1% and had an R2 = 0.84. Results reveal environmental factors which must be considered in studies involving LWP measurements for chrysanthemums in order to avoid misinterpretation of data.
Abstract
The relationship between stomatal conductance and leaf water potential in field-grown apple trees (Malus domestica Borkh.) was determined throughout one growing season. Between May and September the leaf water potential required to close stomates decreased (became more negative) by about 25 bars, indicating decreasing sensitivity of the stomates to leaf water stress. A good linear correlation was found between stomatal conductance and net photosynthesis in trees grown under a wide range of water stress conditions. In September net photosynthesis of excised leaves of field trees was not reduced to zero until leaf water potentials reached −50 to −60 bars. The results emphasize the importance of pre-conditioning and time of season in plant water relations studies.
Abstract
Regression models of potato (Solanum tuberosum L. cv. Russet Burbank) leaf water potential (ψleaf) were developed for irrigated conditions using concurrent measurements of total solar irradiance (Rs), air vapor pressure deficit (VPD), air temperature (Ta) and windspeed. Estimates of potential evaporation (Ep) also were related to ψleaf. The data were collected over a 3-year period from two locations in southern Idaho. Of the variables tested, Rs had the highest simple correlation with ψleaf (r = 0.93), although a slightly higher correlation was obtained for log-transformed values of VPD (1n VPD). Potato ψleaf was best described by the equation ψleaf = -0.3672 - 0.1959 In VPD – 0.0005 Rs, where ψleaf, VPD, and Rs are expressed in units of MPa, kPa and W·m–2, respectively. The model accounted for 95% of the variation in ψleaf for well-watered ‘Russet Burbank’ potatoes. When the model was tested on an independent data set, it estimated diurnal changes in ψleaf for several different cultivars to within ±0.1 MPa of the measured values. The relationship between ψleaf and Ep was nonlinear and was described by an exponential function. Estimates for the Ep model were nearly identical to those for the VPD Rs model when ψleaf values were below -0.3 MPa.
Abstract
Tomato plants (Lycopersicon esculentum Mill.) were grown under 4 irrigation treatments. In the first three an attempt was made to maintain soil water at a different level for each treatment. The fourth treatment was an approximation of the varied moisture levels that would be encountered with furrow irrigation. Leaf water potential (ΨL) was affected more during a day by atmospheric factors than by soil water availability. Hourly changes in ΨL and air water potential (Ψ air) were highly correlated (range .94*** and .99***). ΨL decreased as the plant aged, apparently due to decreasing soil water availability, decreasing root activity, and increasing resistance to water flow in stems and leaves. The stress factor, (which is an integration of the area below −6 bars; a critical level for tomatoes) was determined from the second degree polynomial regression of time versus ΨL and is proposed as a useful integration of ΨL. By using stepwise regression it was found that plant water status as evaluated by tensiometer reading, stress factor, the ratio of soil water/soil water at field capacity, and daily pan evaporation had the greatest effect on yield and total soluble solids content of tomato fruit.
Relationships between midday (Ψmd) and predawn (Ψpd) leaf water potential, stomatal conductance (gs), and net CO2 assimilation rate (A) were determined at different fruit growth stages and for 2 years with different fruit loads in a `Sudanell' peach [Prunus persica (L) Batsch] plot subjected to two regulated deficit irrigation (RDI) strategies plus a control irrigation treatment. A postharvest RDI (PRDI) treatment was irrigated at 0.35 of the control after harvest. The second treatment (SPRDI) applied RDI during Stage II, the lag phase of the fruit growth curve, at 0.5 of the control and postharvest at 0.35 of the control. The control treatment and the PRDI and SPRDI when not receiving RDI were irrigated at 100% of a modified Penman crop water use calculation (ETo) in 1994, a full crop year, and 80% in 1995, a year of nearly zero crop. In 1995, with 80% of the 1994 irrigation rate and no crop, the Ψmd was higher, probably because of the lower crop load, while Ψpd was lower, probably because less water was applied to the soil. The relationship of gs and A with Ψmd during Stage II was steeper than during postharvest. Low Ψmd was not indicative of a depression in gs and A in Stage III. Osmotic leaf water potential at turgor loss (Ψπ 0) as derived from pressure-volume curves was more negative during Stage III and postharvest (about -2.9 MPa) than in Stage II (about -2.7 MPa). The Ψmd measurements together with Ψπ 0 determinations seemed to be more useful to characterize peach tree water status than Ψpd under soil water deficits because of their better relationship to midday stomatal closure.
Abstract
The effects of ambient temperatures between 15° and 43°C were determined on net photosynthesis of ‘French’ prune (Prunus domestica L. cv. Agen) trees maintained under a non-limiting soil water supply. The temperature optimum for photosynthesis was about 30° and net CO2 assimilation decreased rapidly above 35° even when water vapor pressure differences (VPD) were only 5 to 10 mb. Leaf resistance (r1) remained very low (2 to 3 sec cm-1) although leaf temperature reached 47° and the leaf water potential (ψ) decreased to -25 bars. Thus, non-stomatal photosynthetic inhibition was responsible for the 80% decline in net CO2 assimilation. Canopy wetting prevented the decline in net CO2 assimilation by reducing leaf temperature 8° (vs. control) and maintaining the ψ 14 bars higher than the non-misted control.
Abbreviations: BBL, `Bush Blue Lake 274'; DAP, days after planting; g,, leaf conductance; LN, `Luna'; Pn, photosynthesis; ψ L , leaf water potential. 1 Current address: Fakultas Pertanian, Universitas Sriwijaya, Palembang 30139, Indonesia. 3 Dept
Abstract
‘Olympus’ strawberries (Fragaria × ananassa (Duch.) with and without black polyethylene mulch were compared in terms of leaflet elongation and diurnal water potential (ψ) of leaves at 2 levels of drip irrigation. Mulch increased leaflet elongation at both irrigation levels, but had no appreciable effect on soil water potential at 20 cm depth, nor on leaf ψ or leaf turgor. Leaflet elongation with black polyethylene may have been favored by the increased soil temperature throughout the upper 20 cm. At the 10-cm depth, mulched, high-moisture soil was an average of 3.0°C warmer during a diurnal cycle. Greatest warming was in late afternoon and late evening in low and high moisture soil, respectively.
, chlorophyll fluorescence (Fv:Fm ratio), and predawn leaf water potential did not indicate the presence of stress in field-grown Passiflora ligularis during standard growing conditions. Water stress affects plant growth because cell growth is one of the most