Canopy Water Use Research Articles

Effects of Contrasting Climate and Paclobutrazol on the Growth and Water Use of Two Container-Grown Landscape Plants

Abstract A study was conducted under contrasting climates [southwestern Georgia (humid, temperate) and central Arizona (arid, Sonoran desert)] to evaluate the effects of paclobutrazol on the growth and water use of container-grown Feijoa Sellowiana O. Berg and Ligustrum japonicum Thunb. Plants grown in Georgia were taller, had approximately twice as many leaves and five times more canopy leaf area, a lower shoot:root ratio, and generally higher water use compared to plants grown in Arizona. Differences in meteorological factors such as higher maximum and minimum temperatures and increased solar radiation in Arizona compared to Georgia were coincident with smaller plant size and lower water use of plants grown in Arizona compared to those grown in Georgia. Paclobutrazol inhibited height growth of plants grown in Arizona; however, this growth inhibition was not affected by application concentration. In Georgia, paclobutrazol inhibited height growth of all plants; however, Ligustrum treated with 250 ppm paclobutrazol appeared to begin to overcome growth suppression after five months. Paclobutrazol reduced canopy leaf area and water use for all plants except for Arizona Feijoa.

Water relations of the canopy species in a Banksia woodland, Swan Coastal Plain, Western Australia

Abstract Diurnal and seasonal water relations were measured in selected species of a Banksia woodland at a site with groundwater at a depth of 6–7 m. The canopy co‐dominants Banksia attenuata and Banksia menziesii exhibited similar patterns of variation in water relations, both diurnally and seasonally. Stomatal conductance was usually 0.4–0.5 cm s−1 diurnally and seasonally and, generally, did not respond to water deficit and other factors. Transpiration was correlated positively with factors indicative of atmospheric evaporative demand, especially total global radiation and pan evaporation, and was highest in summer when canopy water use reached 2.1 mm d−1. Xylem pressure potential at dawn averaged −0.25 MPa in both species throughout the year. Minimum xylem pressure potential varied seasonally and was negatively correlated with transpiration. Seasonal means of minimum xylem pressure potential varied from −1.0 MPa in winter to −1.5 MPa in early summer. Both Banksia species appeared to function as phreatophytes, utilizing groundwater which enabled them to maintain high rates of water use in late summer. Water use over a 12 month period totalled 635 mm, of which the canopy and understorey contributed 61% and 39%, respectively. Water use in the woodland was dominated by the canopy in late summer and the understorey at other times.

A model of canopy photosynthesis and water use incorporating a mechanistic formulation of leaf CO 2 exchange

A model of the carbon uptake and water balance of forest stands is described where leaf photosynthesis is represented by a mechanistic model of photosynthesis by C 3 plants. Data are presented to support an empirical relationship linking stomatal conductance, photosynthesis, relative humidity and ambient CO 2 concentration. The model was applied to stands of Pinus radiata subject to extremes of water and nutrient availability. Simulated water storage in the root zone agreed with measurements conducted over a 5 year period. Simulated and measured seasonal patterns of water use reached maximum rates of approximately 7 mm day −1 in summer for irrigated stands with projected leaf area indices of approximately 8. Simulated annual net photosynthesis (net of photorespiration and day-time foliar respiration) ranged from approximately 17 Mg C ha −1 year −1 for control stands to approximately 45 Mg C ha −1 year −1 for irrigated and fertilised stands.

Canopy conductance, carbon assimilation and water use in wheat

Chambers were used to investigate changes in assimilation ( A) and evaporation ( E) rates in the field on a diurnal and a daily basis in rainfed and irrigated crops of wheat. Measurements were made in crops at growth stages between ear emergence and physiological maturity. Leaf area index ranged from a maximum of ∼8 to a minimum of ∼0.2. Assimilation and canopy conductance, g C, decreased rapidly in rainfed treatments during grain filling, with midday values of g C becoming progressively smaller than morning values as stress progressed. Hysteresis was also evident in well-watered crops, indicating that E was adversely affected by the increase in evaporative demand during the day. Evaporative fluxes were analysed in terms of the sensitivity (α) of leaf conductance to solar radiation. Changes in α implied both long-term and diurnal effects of stress on E. The estimate of α in the middle of the day was ∼0.02 mm s −1 (W m −2) −1 in well-watered crops and so corresponded with the upper limit of the slope, leaf conductance vs. net radiation, reported elsewhere for wheat. Estimates of α were generally larger in the morning than at noon. Diurnal changes in g C and A indicated that the diffusive component in the assimilation pathway was the more sensitive to stress. The mean rate of assimilation during the day, A , was curvilinearly related to g C such that the A: g C ratio decreased with an increase in g C . These changes suggested that stress increased relative stomatal control over CO 2 assimilation and increased water use efficiency. Daily carbon assimilation was poorly associated with daily light interception in these data. However, the strength of the relationship between A and g C was sufficient to postulate that estimates of light use efficiency, derived from measurements of A and light interception or, less directly, growth and light interception, may be used to infer effects of stress on canopy conductance to CO 2 and H 2O under conditions of water stress in wheat.

Water use of plum trees ( Prunus salicina) trained to four canopy arrangements

Water supply is a limiting factor in the production of stone fruit in the Mediterranean climate of South Western Australia. Fruit growers are adopting intensive orchard systems and are using a variety of canopy training methods. To establish whether the training system was likely to have a strong influence on water use, we studied the soil water balance and plant water status of 6-year-old plum trees (cultivars ‘Laroda’ and ‘Santa Rosa’) trained to Lincoln, Vase, Palmette and Tatura trellis systems, and growing on a loamy sand. When trickle irrigated at 110% class A pan evaporation rate, the Tatura trellis used more water than the other systems, but the differences were small, being 9–12% between training systems. Trees with a high crop load used slightly more water than those with a low crop load. There were no significant differences between the two cultivars in their water use. When irrigated after harvest at 40% of A pan, the Vase system used more water than the other systems, but again differences were small (∼ 18%). When water was withheld for a week in a period of high evaporative demand (7.3 mm day −1), the Tatura and Palmette systems used more water than the Lincoln trees. This was associated with their ability to extract water from deeper layers in the soil. When well watered, the trees used 75–99% of the intercepted net radiation for evaporation of water. As differences in canopy water use were not large, but yield differences were considerable (34 t ha −1 for the Vase cf. 62 t ha −1 for the Tatura trellis), the efficiency of water use will be greatest on those canopies giving the greatest yield.

Effects of short-term variation in weather on diurnal canopy CO 2 flux and evapotranspiration of a juvenile douglas-fir stand

Using a modified Bowen ratio method, measurements of canopy energy balances and CO 2, flux densities ( F c) of a 22-year-old low productivity Douglas-fir stand, were made successfully at a remote site, during wet and dry growing seasons. Canopy conductances ( g c) were calculated from canopy evapotranspiration rates ( E) using the Penman-Monteith equation, and used to estimate mean sink level intercellular CO 2 concentration ( c i). Canopy responses of g c, E 1 F c and c i were related to variations in weather conditions. As observed in other work, g c was found to be strongly influenced by variation in vapour pressure deficit ( D) caused by changes in air temperature. Night-time F c measurements indicated that canopy respiration rates were often very high and also strongly dependent on air temperature. Hence air temperature was concluded to be a major factor limiting overall forest productivity. Variation in solar irradiance ( S) appeared to have little direct effect on g c, while no simple relationship was apparent between S and F c at the canopy level. In general, F c was not limited by g c although these two variables were often correlated. Highest F c and canopy water use efficiency ratios were observed on cloudy days with low air temperature and low D, suggesting maximum productivity occurred under these conditions.

Effects of Ozone and Water Stress on Canopy Temperature, Water Use, and Water Use Efficiency of Alfalfa

AbstractOzone (O3) and soil water deficit are two environmental stresses that significantly affect the growth and yield of alfalfa (Medicago sativa L). However, little is known of the responses of field‐grown alfalfa to O3, and the effects of the interaction between O3 and water stress on canopy temperature and water relations of alfalfa have not been previously reported. The objective of this 2‐yr study was to determine the interactive effects of O3 and soil water deficits on canopy temperatures, water use, and water use efficiency (WUE) of alfalfa. Alfalfa (cv. WL‐514) was grown in 30‐3‐ by 5.5‐m plots on Wasco sandy loam (coarse‐loamy, mixed, nonacid, thermic Typic Torriorthents) in Shafter, CA, and was exposed in open‐top chambers to five levels of O3 for 12 h daily, from March to October of 1984 and 1985. Ozone treatments ranged from charcoal‐filtered air (CF) to twice ambient O3 concentrations. Each plot received either normal amounts of irrigation (NI) or 30% less than normal (WS). Canopy temperature‐air temperature differentials (Tc‐Ta) were significantly reduced by water stress an average of 27.9% in 1984 and 44.0% in 1985. Ozone also significantly reduced Tc ‐ Ta by 31% in NI and 37% in WS plots in 1984, but in 1985 O3 had no effect on Tc ‐ Ta. Water use, rate of soil water depletion, or depth of effective rooting zone were not affected by O3, hereas water stress significantly reduced all three. Water use efficiency was significantly reduced by O3, averaging 12% lower in nonfiltered compared with CF plots. The effects of O3 on WUE were attributed to premature senescence and abscission of older alfalfa leaves.

Diurnal patterns of canopy photosynthesis, evapotranspiration and water use efficiency in chickpea (Cicer arietinum L.) under field conditions

Diurnal changes in net photosynthetic rate (PN), evapotranspiration rate (ET) and water use efficiency (WUE=PN/ET) of field grown chickpea (Cicer arietinum) L. cv. H-355 were studied from the vegetative phase through maturirty at Haryana Agricultural University Farm, Hissar, India. The maximum photosynthetic rate (PN max) increased from the initial vegetative phase to pod formation and declined at a rapid rate from pod filling to maturity. The response of PN to photosynthetic photon flux density (PPFD) (400-700 nm) was temperature-dependent during the day, i.e. on cool days the PN rates were lower for certain quanta of PPFD during the first half than during the second half of day, and vice versa on warm days. ET was affected both by crop cover and evaporative demand up to flowering, but thereafter it was independent of crop cover and followed the course of evaporative demand. ET was related to air temperature during the day while PN was related to PPFD. There was a lag of two to three hours between PNmax (around noon) and ETmax (around 2 p.m.). WUE increased from the vegetative stage through flowering but decreased thereafter to maturity.

Interactive effects of water and nitrogen stresses on carbon and water vapor exchange of corn canopies

Water and nitrogen stresses often reduce the yield of corn ( Zea mays L.). Crop responses to low soil nitrogen are similar in many ways to crop responses to soil water deficits. Interaction between nitrogen and water stresses is also common. The objective of this study was to examine the interactive effects of water and nitrogen stresses on canopy photosynthesis, evapotranspiration, and water use efficiency of field corn canopies. Corn was grown on a Kendrick fine sand soil (a member of the loamy, siliceous, hyperthermic family of arenic Paleudults) and subjected to three irrigation treatments (optimal, vegetative water stress, and rainfed). Two nitrogen (N) levels were imposed within each irrigation treatment (low, 62 kg ha −1; high, 255 kg ha −1). During the vegetative water stress period, hourly measurements were made of canopy carbon dioxide exchange rate (CER) and canopy evapotranspiration (ET) on the optimal and vegetative water stress treatments in combinations with both N levels. In addition to decreases in ET caused by water stress, the corn canopies exhibited a decrease in ET when subjected to N stress. Part of this decrease was explained by the lower leaf area indexes (LAI) of the low-N canopies. On day 14 of the vegetative water stress, a curvilinear relationship existed between CER and photosynthetic photon flux density (PPFD) for both the irrigated high- and low-N plants although low-N plants exhibited decreased sensitivity to PPFD during midday hours. In contrast, two distinctly different hysteretic loops were obtained for low- and high-N water stress plants. Instantaneous water use efficiency (CER/ET) varied considerably with time of day and treatment combination. We conclude that most of this variation was the result of different vapor pressure dificits (VPD). Canopy CER was linearly related to ET/VPD regardless of N and water stress and the slope of the line ( k′ = 0.024) was in close agreement with the theoretical value predicted by Tanner and Sinclair (1983) for corn.

Responses of Soybean Canopy Photosynthesis and Transpiration to Whole‐Day Temperature Changes in Different CO2 Environments1

AbstractResponse of plants to increased temperatures, as well as increased CO2, is one of the concerns about the global consequences of continued burning of fossil fuel. In this study, soybeans [Glycine max (L.) Merr. cv. Bragg] were grown in controlled‐environment chambers located outdoors and acclimated to two environmental CO2 levels, 330 and 800 µmol mol−1. Canopies were exposed to different day‐long dry bulb temperature treatments that were maintained for a few days. Comparisons of CER‐light response curves and daytime total CO2 exchange from both low and high CO2 treatments indicated that canopy CER was not significantly affected by dry bulb temperature in the range 28°C to 35°C (nighttime temperature was 23°C). Canopy water use increased significantly in both CO2 treatments as dry bulb temperature was increased and the dewpoint temperature was kept at 21°C. Calculated total canopy resistances were constant throughout the temperature treatments in each of the CO2 treatments. This indicated that between dry bulb treatments, changes in canopy water use resulted strictly from temperature‐driven changes in the vapor pressure gradients within the canopy. Characteristic ratios of internal to external canopy CO2 concentrations were calculated and found to be similar among all temperature treatments and in both CO2 treatments. Across all temperature treatments, cumulative daytime transpiration was nearly equal between the two CO2 treatments, however, water‐use efficiency (WUE) decreased in both CO2 treatments as dry bulb temperature increased. Since CER response in both CO2 treatments was unaffected by air temperature across the range of 28 to 35°C, the decrease in WUE with increasing temperature was due solely to increasing transpiration.

Ecological optimality in water‐limited natural soil‐vegetation systems: 2. Tests and applications

The long‐term optimal climatic climax soil‐vegetation system is defined for several climates according to previous hypotheses in terms of two free parameters, effective porosity and plant water use coefficient. The free parameters are chosen by matching the predicted and observed average annual water yield. The resulting climax soil and vegetation properties are tested by comparison with independent observations of canopy density and average annual surface runoff. The climax properties are shown also to satisfy a previous hypothesis for short‐term optimization of canopy density and water use coefficient. Using these hypotheses, a relationship between average evapotranspiration and optimum vegetation canopy density is derived and is compared with additional field observations. An algorithm is suggested by which the climax soil and vegetation properties can be calculated given only the climate parameters and the soil effective porosity. Sensitivity of the climax properties to the effective porosity is explored.

Canopy Temperatures, Water Use, and Water Use Efficiency of Corn Genotypes1

AbstractIt is desirable to describe and characterize physiological properties of corn (Zea mays L.) genotypes that will permit a basis for selecting genotypes. The objective of this field study was to compare two hybrids (Mo17 ✕ B73, A619 ✕ A632) and their respective inbred parents under irrigated and nonirrigated conditions. Measurements of canopy temperature, stomatal diffusive resistance, xylem water potential, leaf area index, ear dry weight, and grain yield were determined. Water use was determined from neutron moderation measurements of the soil‐water profile. The soil was a fine silty, mixed mesic, Pachic Haplustoll that holds approximately 250 mm of plant available water.Hybrids had higher grain yield, water use, and water use efficiency than the inbred parents under both irrigated and nonirrigated conditions. Estimates of water use by both hybrids and inbreds were greater for irrigated than for nonirrigated treatments. Early ear dry weight appeared to be an indicator of final ear weight, and in this particular study, was an indicator of final grain weight. Canopy temperatures were cooler for hybrids than for the inbreds which is consistent with greater water use by the hybrids. Stomatal resistance and xylem water potential were not significantly different among genotypes.