1 To whom reprint requests should be addressed. This work was supported by U.S. Dept. of Agr. Hatch Grant NYC 161422 (DWW). We thank S. McKay for assistance in preparation of the field plots and J. Melkonian for assistance with leaf water potential
Application of a low-relative-humidity treatment (LHT) to seedlings can reduce water stress on cuttings harvested from the seedlings, after the cuttings are planted. Effects of illumination during LHT and LHT duration on leaf water potential and leaf conductance in cucumber (Cucumis sativus L.) seedlings used as the model plant material and on growth of harvested cuttings were investigated to determine optimal LHT conditions. The seedlings received LHT for 12 or 24 h in a lighted or dark growth chamber at air temperatures of 28 to 31 °C and relative humidity of 12% to 25%. Cuttings including a foliage leaf and two cotyledons were harvested by cutting the hypocotyl of the seedlings immediately after the treatment, and then the cuttings were planted in vermiculite medium. Four days after planting, the total fresh weight of the cuttings from seedlings that had received LHT in the lighted chamber was 2.2 times that of cuttings from seedlings that had not received LHT, whereas the total fresh weight of those that had received LHT in the dark increased by 1.3 to 1.8 times. Significant effects of illumination during LHT were also observed in the transpiration rate and growth of the cuttings, harvested following the treatment, after they were planted. By varying LHT duration, it was also found that leaf water potential and leaf conductance of the seedlings decreased as LHT duration increased up to 18 h. Thus, illumination during LHT increased the growth of cuttings taken following the treatment, and optimal treatment duration of around 18 h was estimated from the seedlings' leaf conductance and leaf water potential.
Plant development, leaf morphology, leaf cuticular wax content, and leaf water relations were determined for seven tree species exposed to consecutive cycles of drought. The objective of the experiment was to identify plant taxa suitable for landscapes prone to drought. On the day drought treatments began, plant development traits and leaf morphology varied among species. Leaf cuticular wax content was different among species and ranged from 0.053 mg·cm–2 in California white oak (Quercus lobata Née), to 0.200 mg·cm–2 in Texas red oak (Quercus buckleyi Buckl.). Was content in Bur oak (Quercus macrocarpa Michx.) and Shumard oak (Quercus shumardii Buckl.) averaged 0.105 and 0.11 mg·cm–2, respectively. At harvest, Texas red oak plants treated with drought had the highest root-to-shoot dry weight ratio which averaged 3.1. In contrast, plants of Arizona ash (Fraxinus velutina Torr.) and California white oak that were frequently irrigated had the lowest root-to-shoot dry weight ratio. Drought did not affect stem elongation, total lamina area, leaf dry weight, and specific leaf weight. Abaxial leaf surfaces of Arizona ash were the most pubescent and averaged1836 trichomes/cm2. Drought-stressed plants of golden rain tree (Koelreuteria paniculata Laxm.) had the most negative midday leaf water potential, which averaged –2.5 MPa. Plants of Chinkapin oak (Quercus muehlenbergii Engelm.) that were irrigated frequently had the least negative predawn leaf water potentials. Predawn leaf water potentials tended to be more negative for Arizona ash and golden rain tree than for the oak species. These results suggest that some species of oak might perform well in landscapes prone to drought.
Proline content, leaf water potential (LWP), and leaf diffusive resistance (LDR) were determined for eight sweetpotato genotypes underwater stress conditions. Changes in fatty acid compositions of leaf polar lipids were determined in two sweetpotato genotypes during declining soil moisture. Proline did not accumulate and LWP did not decrease until soil moisture dropped below 10%, but LDR increased as soil moisture decreased. Genotypic differences in proline accumulation and LWP were found. Changes in fatty acid compositions occurred more in glycolipids than in phospholipids. Fatty acid changes were more pronouned in genotype MS20-2 than in “Vardaman”
Two tree species, Acer rubrum `October Glory' (October Glory red maple) and Quercus phellos (willow oak) were planted in Columbus, GA and Mobile, AL. Variables evaluated were location (park vs residential) and tree size (1.5 vs 3.0 inch caliper). Greater shoot elongation occurred with 1.5 inch red maples and willow oaks than with 3.0 inch caliper trees. First year growth differences were not related to photosynthesis, night respiration, leaf water potential, or foliar nitrogen levels. Little height or caliper change occurred with either species. Red maple shoot elongation was greater in Mobile than into Columbus. Growth was not affected by location within either city.
Storage of Rhododendron catawbiense Michx. ‘Roseum Elegans’ cuttings in moist burlap bags at 21° or 2°C for 21 days did not consistently reduce the percentage of rooting or rootball size. During storage, leaf water potential (ψw) of the cuttings increased from −0.47 MPa initially to −0.27 MPa after 14 days, regardless of storage temperature. Carbohydrate concentrations in the bases of the cuttings changed with time and storage temperature, but apparently neither these changes nor changes in ψw were large enough to influence subsequent rooting.
The purpose of this study was to determine if over-the-row mechanical shake-catch harvesting affected root development, leaf water stress, and yield of young ‘Golden Delicious’/M.7A and ‘Law Rome’/MM.111 apple (Malus domestica Borkh.) trees. Leaf water potential and temperature differential (canopy-air temperatures) were not significantly altered by mechanical harvesting. A minirhizotron technique did not detect changes in root distribution or root morphology. The fruit yield was unaffected by mechanical harvesting for four harvest years. No deleterious effects were detected as a result of over-the-row shake-catch harvesting.
Abbreviations: CSTR, continuously stirred tank reactor; PLA, planar leaf area; π osmotic potential; ψ leaf , leaf water potential. 1 Current address: 620 Shadywood Lane, Raleigh, NC 27603. This paper is a portion of a thesis submitted by J.M.P. in
Peach [(Prunus persica (L.) Batsch., `Rutgers Redleaf'] trees were grown for two seasons in a greenhouse with three pruning treatments (none, shoot tips removed, and half the shoots removed) and three grass treatments (no grass competition; perennial ryegrass, Lolium perenne L., `Linn'; and tall fescue, Festuca arundinacea Schreb, `Kentucky 31'). Competing grass reduced shoot growth, leaf area, and weight of fine roots in shallow soil, but did not affect the growth response to pruning. Regrowth from pruned trees was such that the shoot: root ratio was restored to that of unpruned trees. Leaf water potential, stomatal conductance, and photosynthesis had decreased markedly by 48 hours after irrigation ceased in trees without competition (larger trees) and to a similar level by 96 hours in trees with competition (smaller trees). Apparently, the reduced leaf area of peach trees grown with grass competition delayed water stress. Leaf abscisic acid levels were not directly affected by grass competition but increased as leaf water potential decreased. Grass competition modified morphology and reduced tree size, but did not affect shoot growth following pruning.
Two experiments were conducted on Acer rubrum L. to determine the influence of root severance on sap flow, stomatal conductance, leaf water potential (ψ), and stem xylem embolism. Experiment 1 utilized 3-year-old trees, and experiment 2 utilized 2-year-old trees. Sixteenmm sap flow gauges were installed on both groups. Trees for experiment 1 were harvested on 31 May 1996 with a root ball diameter of 30.5 cm. Sap flow was reduced within one day after plants were harvested and was still lower 1 week after harvest. On 7 June 1996, harvested trees had lower stomatal conductance measurements, compared to not-harvested trees, but ψ were similar. A second experiment was initiated on 20 Aug. 1996, using the same protocol as in experiment 1. Sap flow was reduced within 2 h after harvest for harvested trees compared to not-harvested trees. Leaf stomatal conductances were reduced within 4 h of harvest. Leaf water potentials were not influenced on the day that the trees were harvested. Embolism levels were increased by harvest within 24 h. These results indicate that transplant stress begins shortly after harvest and not at the actual time of transplant.