John Stewart Turner

Acacia saligna (Labill.) H.Wendl, a potential crop for forage and wood production, is considered highly drought-resistant. The aim of this study was to characterise some of the physiological traits contributing to drought resistance in A. saligna. Two experiments were conducted: (i) 4-year-old A. saligna were grown in the field under dryland and irrigated treatments and (ii) 6-month-old A. saligna were grown in pots and irrigated to replenish 100% of the transpiration demand (control), or 75% 50% or 25% of the control. Soil-water deficits in the field elicited an increase in osmotic potential in phyllodes. Stomatal conductance was negatively correlated with air vapor pressure deficit under drought conditions in both experiments, whereas under irrigation in the field it was correlated with solar radiation. In the field, dry matter (DM) production under irrigation was only 14% greater (not significant) than under dryland. In the pot experiment, DM production was significantly reduced, and water use efficiency (WUE) and chlorophyll content increased with reduced availability of water. The greater WUE induced by drought could have resulted from stomatal regulation and increased chlorophyll content. Carbon isotope ratios were correlated with the WUE, and may be utilised for selection to further improve the WUE of A. saligna under drought conditions.

Drought Resistance and Water Use Efficiency in Acacia saligna

Acacia saligna (Labill.) H.Wendl, a potential crop for forage and wood production, is considered highly drought-resistant. The aim of this study was to characterise some of the physiological traits contributing to drought resistance in A. saligna. Two experiments were conducted: (i) 4-year-old A. saligna were grown in the field under dryland and irrigated treatments and (ii) 6-month-old A. saligna were grown in pots and irrigated to replenish 100% of the transpiration demand (control), or 75% 50% or 25% of the control. Soil-water deficits in the field elicited an increase in osmotic potential in phyllodes. Stomatal conductance was negatively correlated with air vapor pressure deficit under drought conditions in both experiments, whereas under irrigation in the field it was correlated with solar radiation. In the field, dry matter (DM) production under irrigation was only 14% greater (not significant) than under dryland. In the pot experiment, DM production was significantly reduced, and water use efficiency (WUE) and chlorophyll content increased with reduced availability of water. The greater WUE induced by drought could have resulted from stomatal regulation and increased chlorophyll content. Carbon isotope ratios were correlated with the WUE, and may be utilised for selection to further improve the WUE of A. saligna under drought conditions.

Using Canopy Temperature Measurements to Evaluate Drought Tolerance of Potato Genotypes

Field studies were conducted in 1986 and 1987 to evaluate the potential of using canopy temperature measurements to evaluate the relative drought tolerance of potato genotypes. In both years, 14 potato genotypes representing a relatively wide range of Solarium tuberosum L. germplasm were grown under well-watered [irrigation ≈100% potential evapotranspiration (ET) and stressed (irrigation ≈40% to 50% potential ET) coditions. Irrigation differences were imposed with a line source irrigation system. Canopy temperatures of the 14 genotypes were measured between 0900 and 1430 hr on 7 clear days during tuber bulking. A general linear relationship between canopy minus air temperature (ΔT) and air vapor pressure deficit (VPD) was determined for each year by regressing all ΔT data onto corresponding VPD values. The relative sensitivity of each genotype to changes in VPD was determined by regressing observed ΔT values onto the estimated ΔT from the general equation for that year. Genotypes with higher than average temperatures under well-watered conditions were generally less sensitive to changes in VPD than those with lower than average temperatures. Warmer genotypes under well-watered conditions were also generally less susceptible to drought than cooler genotypes. Thus, ΔT measurements from well-watered plots can be effectively used to assess the relative drought tolerance of potato genotypes.

Stomatal conductance patterns and environment in high elevation phreatophytes of Wyoming

High-elevation (2305 m) phreatophytes (cottonwood, Populus angustifolia James, and willows, Salix monticola Nutt. and Salix exigua Bebb) in southeastern Wyoming commonly showed a pattern of increasing stomatal conductance (g1) throughout the day, despite minimum leaf water potentials (ψ1) as low as −2.7 MPa. Diurnally, light and leaf temperature were the most important variables influencing g1, but there were also threshold values of ψ1 and leaf-to-air vapor pressure deficit for stomatal closure. Seasonally, maximum daily g1 (gmax) was similar between species, was positively related to minimum air temperature the previous night, and showed a threshold response to soil temperature. Two types of evidence existed for large soil-to-leaf conductances (gs–l) and for liquid water being available to the roots. The first was no change in ψ1 despite increasing transpiration during the afternoon. The second was rapid evening recovery of ψ1 often to values higher than mean soil water potential to 60-cm depth. The combination of low atmospheric pressures at high elevation, large gs–l, and access to a water table may explain how these phreatophytes attained gmax of 0.8–0.9 mol m−2 s−1, much higher than gmax of low-elevation phreatophytes or high-elevation nonphreatophytes. Key words: Populus, Salix, phreatophyte, stomatal conductance, xylem pressure potential.