The water status of strawberry (Fragaria х ananassa Duchesne) was indicated by the occurrence of guttation. Guttation was present when pre-dawn leaf water potential (PLWP) was greater than -0.07 MPa and absent when PLWP was below – 0.11 MPa. Plants exhibiting guttation had greater stomatal conductivity and lower leaf – air temperature at midday, indicating a greater transpiration rate. Hydathodes on older leaves did not consistently express guttation; thus, the occurrence of guttation must be evaluated on young leaves.
To compare the effects of water deficits and restricted root volume, 1- and 2-year-old peach trees (Prunus persica L.) with roots divided among four 2.5-Iiter pots were irrigated daily with 30% (deficit irrigation) or 100% (non-deficit) replacement of water used the day before. The water was applied to one, two, or all four pots during the period of rapid terminal growth. After 7 weeks, all trees received 100% replacement of water used the previous day. After terminal growth ended, the root : shoot ratio of the 2-year-old trees was adjusted by 1) tripling available soil volume, 2) removing two-thirds of lateral branches, 3) both 1 and 2, 4) treatment 3 defoliated, or 5) left unchanged. Deficit irrigation reduced midday leaf water potential, leaf conductance, and terminal growth equally, regardless of irrigated soil volume, whereas in non-deficit irrigated trees these factors were proportional to the irrigated soil volume. After deficit irrigation ended, terminal growth resumed at rates above those of the trees with non-deficit irrigation applied to all four pots and proportional to the severity of growth reduction during deficit irrigation. Pruning and defoliation increased leaf conductance within 3 days. Increased soil volume increased leaf conductance after 4 weeks. Deficit irrigation nearly eliminated flowering for the following year. Tripling the soil volume overcame the effect of deficit irrigation on flowering, but pruning did not. Defoliation inhibited flowering. The effect of restricted irrigated soil volume was similar to that of deficit irrigation. Increasing root : shoot ratios by adjusting the soil volume or by pruning the shoot always increased leaf conductance.
Half or whole root systems of micropropagated `Gala' apple (Malus ×domestica Borkh.) plants were subjected to drought stress by regulating the osmotic potential of the nutrient solution using polyethylene glycol (20% w/v) to investigate the effect of root drying on NO3- content and metabolism in roots and leaves and on leaf photosynthesis. No significant difference in predawn leaf water potential was found between half root stress (HRS) and control (CK), while predawn leaf water potential from both was significantly higher than for the whole root stress (WRS) treatment. However, diurnal leaf water potential of HRS was lower than CK and higher than WRS during most of the daytime. Neither HRS nor WRS influenced foliar NO3- concentration, but both significantly reduced NO3- concentration in drought-stressed roots as early as 4 hours after stress treatment started. This reduced NO3- concentration was maintained in HRS and WRS roots to the end of the experiment. However, there were no significant differences in NO3- concerntation between CK roots and unstressed roots of HRS. Similar to the effect on root NO3- concentration, both HRS and WRS reduced nitrate reductase activity in drought-stressed roots. Moreover, leaf net photosynthesis, stomatal conductance and transpiration rate of HRS plants were reduced significantly throughout the experiment when compared with CK plants, but the values were higher than those of WRS plants in the first 7 days of stress treatment though not at later times. Net photosynthesis, stomatal conductance and transpiration rate were correlated to root NO3- concentration. This correlation may simply reflect the fact that water stress affected both NO3- concentration in roots and leaf gas exchange in the same direction.
The influence of deficit irrigation on predawn leaf water potential (Ψpd) and leaf gas-exchange parameters was analyzed in almond [Prunus dulcis (Mill.) D.A. Webb] and compared to hazelnut (Corylus avellana L.). Both species were planted in adjacent plots in which four irrigation treatments were applied: T-100%, T-130%, and T-70%, which were irrigated at full crop evapotranspiration (ETc), 1.3 × ETc, and 0.7 × ETc, respectively, and a regulated deficit irrigation (RDI) treatment, which consisted of full irrigation for the full season, except from middle June to late August when 0.2 × ETc was applied. Under nonstressful conditions, hazelnut had a lower net CO2 assimilation rate (A) (12.2 μmol·m-2·s-1) than almond (15.5 μmol·m-2·s-1). Reductions in net CO2 assimilation rate (A) induced by decreases in Ψpd were higher in hazelnut than in almond. Gas-exchange activity from early morning to midday decreased in hazelnut for all irrigation treatments, but in almond increased in the well-watered treatments and decreased slightly or remained constant in the RDI. Hazelnut had a higher A sensitivity to variations in stomatal conductance (gs) than almond, especially at low gs values. The Ψpd values in almond and hazelnut of the T-100% and T-130% treatments were affected by decreasing values in midsummer, but in hazelnut Ψpd was probably also affected by sink kernel filling. These facts indicate that hazelnut RDI management could be more problematic than in almond.
Understanding factors associated with drought resistance and recovery from drought stress in tall fescue (Festuca arundinaces Schreb.) is important for developing resistant cultivars and effective management strategies. Our objective was to investigate water relations, photosynthetic efficiency, and canopy characteristics of tall fescue cultivars (forage-type `Kentucky-31', turf-type `Mustang', and dwarf-type `MIC18') in responses to drought stress and subsequent recovery in the field and greenhouse. During drought stress under field conditions, `MIC18' had lower turf quality, more severe leaf wilting, and higher canopy temperature than `Mustang' and `Kentucky-31', indicating that `MIC18' was more drought-sensitive. The greenhouse study comparing `K-31' and `MIC18' showed that leaf water status, chlorophyll fluorescence, canopy green leaf biomass, and lead area index of both cultivars declined as soil dried. Reductions in relative water content, leaf water potential, chlorophyll fluorescence, canopy green leaf biomass, and leaf area index were more severe and occurred sooner during dry down for `MIC18' than for `Kentucky-31'. After rewatering following 14 days of stress, leaf water deficit and turf growth recovered, to a greater degree for `Kentucky-31' than for `MIC18'. However, soil drying for 21 days caused long-term negative effects on leaf photosynthetic efficiency and canopy characteristics for both cultivars.
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.
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.
‘Delicious’ and ‘Golden Delicious’ apples (Malus domestica Borkh.) on seedling rootstock were grown with trickle and sprinkler irrigation, both operated at high frequency of irrigation (daily). Trees with trickle irrigation developed lower leaf water potentials and produced less vegetative growth than trees with sprinkler irrigation, but fruit and productivity were similar. Apples from the trickle-irrigated trees had less water content and higher soluble solids than those from sprinkler-irrigated trees. Titratable acidity tended to be lower and both red color in ‘Delicious’ and yellow color in ‘Golden Delicious’ tended to be higher in fruit from trickle-irrigated trees than from sprinkled trees; firmness at harvest was similar regardless of irrigation procedure. Storage life was not influenced consistently by irrigation. Where differences did occur, the fruit from trickle-irrigated trees was softer after storage. Changes in fruit quality similar to those observed in trickle-irrigated trees were produced by imposing, through high frequency deficit irrigation with sprinklers, similar moisture deficits on apple trees, as measured by leaf water potential.
One-year-old gerbera plants subjected to 1 night at 5C had reduced leaf water losses and chlorophyll content and increased root hydraulic resistance, but stomatal conductance and leaf water potential did not change. After 3 nights, leaf water potential had decreased and leaf reflectance in the visible and the near-infrared had increased. Similarly, abscisic acid (ABA) in leaves had increased and cytokinins (CK) in leaves and roots had decreased, but ABA levels in roots did not change. After 4 days at 20C, root hydraulic resistance, reflectance and leaf water loss returned to their initial values, but leaf water potential and chlorophyll content remained lower. Leaf ABA levels reached values lower than the initial, while root ABA and leaf CK levels retained the initial values. These data suggest that in the gerbera plants studied, 3 nights at 5C produced a reversible strain but otherwise plants remained uninjured, so this gerbera variety could be cultured with low energetic inputs under Mediterranean conditions. The results may indicate that ABA and CK were acting as synergistic signals of the chilling stress. Spectral reflectance signals seemed to be useful as plant chilling injury indicators at ground level.
When grown in refined sand with one-twentieth normal K supply, cauliflower (Brassica oleracea L. var. botrytis L. cv. Pusi) had lower dry matter and tissue concentration of K than the controls and developed visible symptoms characteristic of K deficiency. In K-deficient plants, the specific leaf weight, diffusive resistance, and proline concentration in leaves were significantly higher and relative water content (RWC), leaf water otential (ψ), stomatal aperture, stomatal density, and transpiration rate were significantly lower than in control plants. When K-deficient plants were supplied additional Na to the extent K was deficient, Na concentration in the plants increased and the plants recovered from the K deficiency effect on free proline concentration, RWC, leaf water potential, stomatal aperture, stomatal density, specific leaf weight, diffusive resistance, and transpiration.