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Abstract
Mature bearing pear [Pyrus communis L. ‘Beurre d’Anjou’ (‘Anjou’)] trees in an arid climate were irrigated weekly at 125% of pan evaporation (wet), biweekly at 100% of pan evaporation (normal), or irrigated only twice (dry) during the summer (1980, 1981), and were fertilized with and without 0.9 kg of supplemental N. Prior to final fruit harvest in 1981, depletion of available soil moisture (ASM) averaged 10%, 16.7%, and 89% for the wet, normal, and dry treatments, respectively. Mid-day leaf water potential (ψL) was correlated with the level of ASM only on bright days of high vapor pressure deficit. Stomatal conductance (κs) and transpirational flux density (F) of dry treatment leaves was lower than that of either wet or normal treatment leaves ψL exceeded −1.4 to −1.7 MPa. Resistance to vapor (water) transport (Rν) of fruit was independent of irrigation regime. Terminal buds had set on shoots from all 3 irrigation regimes at 58 days after full bloom (AFB) in 1981, but resumed growth on normal and wet treatment shoots at 87 days AFB. On 7 of 10 sampling dates during 1981, dry treatment fruit weighed less than normal or wet treatment fruit.
Abstract
The effect of temperature, soil moisture, and diurnal variations in plant water content on pollen viability (PV) in bean (Phaseolus vulgaris L.) genotypes was investigated under field conditions in 1981 and 1982. Each year PV, relative water content (RWC), and leaf water potential (LWP) of each cultivar at mean soil moisture tensions (MSMT) of −0.05 and −0.10 MPa were reduced significantly between 0700 hr and 1400 hr. At a MSMT of −0.05 MPa, PV and RWC of both cultivars significantly increased between 1400 hr and 1900 hr. During the same period, the LWP of ‘California Light Red Kidney’ increased to the 0700-hr level, but remained at the 1400-hr level in ‘Gloria’. At a MSMT of −0.10 MPa, PV significantly increased in ‘Gloria’ but failed to increase in ‘California Light Red Kidney’ between 1400 hr and 1900 hr. RWC remained at the 1400-hr level in both cultivars. LWP of ‘California Light Red Kidney’ remained at the 1400-hr level, but continued to decline below the 1400-hr level in ‘Gloria’ during the same period. PV declined as both RWC and LWP decreased. A relative value for the simultaneous contribution of both high ambient temperature and the water status of bean plants to loss of PV was calculated.
Abstract
Trees of peach (Prunus persica (L.) Batsch) and pear (Pyrus communis L.) were grown without irrigation and received only 86-mm rainfall during the growing season. Many peach trees died after experiencing leaf water potentials below −30 bars in July and August. Defoliation began in July, fruit growth was arrested, flavor was astringent, and flower buds failed to differentiate. Pear trees survived under similar conditions although tops died back or grew poorly and flowering was reduced. Regrowth came from trunks and lower scaffolds. Heavy pruning (“dehorning”) delayed the appearance of drought symptoms until very late in the season and resulted in 100% survival of both peach and pear trees. Heavy thinning of peaches in early June did not affect current season's symptoms but apparently reduced dieback and death of trees.
Boltonia asteroides L. `Snowbank' (Snowbank boltonia), Eupatorium rugosum L. (eastern white snakeroot), and Rudbeckia triloba L. (three-lobed coneflower) were subjected to drought for 2, 4, and 6 days during the fall and spring. Leaf gas exchange, leaf water potential, growth, and carbohydrate partitioning were measured during drought and throughout the following growing season. Leaf gas exchange of B. asteroides was not affected by drought treatment in the fall, not until day 6 of spring drought, and there were no long-term effects on growth. Transpiration and stomatal conductance of R. triloba decreased when substrate moisture decreased to 21% after drought treatment during both seasons. Assimilation of drought-treated R. triloba decreased when substrate moisture content decreased to 12% during spring but was not affected by drought in the fall. There was a decrease in the root-to-shoot ratio of R. triloba that had been treated for 4 days, which was attributed to an increase in the shoot dry weight (DW) of treated plants. Reductions in spring growth of E. rugosum were observed only after fall drought of 6 days, and there were no differences in final DWs of plants subjected to any of the drought durations. Spring drought had no effect on growth index or DW of any of the perennials. Boltonia asteroides and R. triloba had increases in low-molecular-weight sugars on day 4 of drought, but E. rugosum did not have an increase in sugars of low molecular weight until day 6 of drought. Differences in drought response of B. asteroides, E. rugosum, and R. triloba were attributed to differences in water use rates.
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).
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).
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
Abstract
Cherry (Prunus avium L.) and prune (P. domestica L.) trees were trickle irrigated daily or weekly at 100%, 50%, and 15% of evaporation from a standard Class “A” pan, adjusted to the area of the tree canopy (Ec), for one full growing season. Soil moisture remained above the wilting point throughout the soil profile with 100% Ec but reached the wilting point except for a wetted zone near the emitters for 50% Ec and 15% Ec. Leaf water potential of shaded cherry leaves at midday averaged near -14 bars for 100% Ec, near -20 bars for 15% Ec, reaching as low as -28 bars for prunes in late July and August. Growth of fruit and vegetative parts was reduced by severe stress but the trees survived on 15% Ec. Prunes recovered to normal yield and growth by the second year after treatment. Peripheral branches of cherries died back during the year of treatment and in the following year. Cherries grew and fruited normally by the third year after treatment except for reduced bearing surface.
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
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