Diurnal changes in water relations and abscisic acid in field grown Vitis vinifera cvs. I. Leaf water potential components and leaf conductance under humid temperate and semiarid conditions

Diurnal changes of water potential (Ψw) and its components (Ψs, Ψp) and leaf conductance were analysed under the humid temperate climate of Germany (Geilweilerhof) and the semiarid climate of South Australia (Adelaide) comparing the two cultivars, Riesling and Silvaner, which appear to differ in their adaptation to drought.At Geilweilerhof predawn water potential was close to 0 and leaf conductance very low. Stomata opened during the morning as light intensity and temperature increased. At 3 p. m. stomata started to close, leaf conductance declining earlier in Silvaner than in Riesling. Ψw of Silvaner was slightly lower during the day than that of Riesling except during the late afternoon.Under the semiarid conditions of Adelaide predawn Ψw. was -6 bar (Riesling) and -7bar (Silvaner); it decreased rapidly to -14 bar (Riesling) and -16 bar (Silvaner) at 10 a. m.; leaf conductance at thattime had reached its maximum which in Riesling was distinctly higher than in Silvaner. lt rapidly declined thereafter in Riesling and more slowly in Silvaner. Ψw remained low until the late afternoon, Silvaner always having lower values than Riesling.While there were no distinct diurnal changes in the osmotic potential (Ψs), turgor potential (Ψp) decreased during the day, Ψp of Silvaner always being lower than that of Riesling. After 10 a. m. under semiarid conditions, Ψp of Silvaner was close to 0.4. The osmotic potential of leaves was generally lower under semiarid conditions indicating osmotic adjustment. In Riesling, the osmotic potential was generally lower and tissue elasticity higher than in Silvaner.Under semiarid conditions fruitload increased Ψs and lowered Ψp in the leaves of Silvaner but not in Riesling.Der Tagesgang des Wasserhaushaltes und der Abscisinsäure bei Vitis-vinifera-Sorten im FreilandI. Die Komponenten des Blattwasserpotentials und die stomatäre Leitfähigkeit unter gemäßigt humiden und semiariden BedingungenUnter den gemäßigt humiden Klimabedingungen Deutschlands (Geilweilerhof) und im semiariden Klima Südaustraliens (Adelaide) wurden der diurnale Verlauf des Wasserpotentials (Ψw) und seiner Komponenten, das osmotische Potiential (Ψs) und das Turgorpotential (Ψp), sowie die stomatäre Leitfähigkeit untersucht; hierzu wurden die Sorten Riesling und Silvaner miteinander verglichen, die sich offenbar hinsichtlich ihrer Anpassungsfähigkeit an Trockenheit unterscheiden.Auf dem Geilweilerhof lag das Ψwvor Sonnenaufgang nahe bei 0 bar, und die stomatäre Leitfähigkeit war sehr niedrig. Mit zunehmender Lichtintensität und Temperatur öffneten sich die Stomata am Vormittag. Um 15 Uhr begannen die Stomata sich zu schließen, wobei die stomatäre Leitfähigkeit bei Silvaner rascher abnahm als bei Riesling. Mit Ausnahme des späten Nachmittags lag das Ψw des Silvaners im Tagesverlauf geringfügig unter dem des Rieslings.Unter den semiariden Bedingungen Adelaides betrug das Ψw vor Sonnenaufgang -6 bar (Riesling) bzw. - 7 bar (Silvaner); es nahm um 10 Uhr rasch auf -14 bar (Riesling) bzw. -16 bar (Silvaner) ab; die stomatäre Leitfähigkeit hatte zu dieser Zeit Maximalwerte erreicht, die bei Riesling deutlich höher lagen als bei Silvaner. Danach nahm die stomatäre Leitfähigkeit bei Riesling rasch, bei Silvaner etwas langsamer ab. Die Ψw-Werte blieben bis zum späten Nachmittag niedrig, wobei Silvaner stets geringere Werte aufwies als Riesling.Während Ψs keine deutlichen Veränderungen im Tagesverlauf erkennen ließ, nahmen die ljlpWerte insgesamt ab; die Ψp-Werte des Silvaners lagen hierbei stets unter denen des Rieslings. Unter semiariden Bedingungen lag Ψp bereits ab 10 Uhr nahe bei 0 bar.Unter semiariden Bedingungen waren die Ψs-Werte der Blätter grundsätzlich vermindert, was auf eine osmotische Anpassung hindeutet. Bei Riesling war das osmotische Potential niedriger und die Gewebeelastizität höher als bei Silvaner.Unter semiariden Bedingungen löste der Traubenbehang einen Anstieg der Ψs-Werte und eine Abnahme der Ψp-Werte bei Silvaner, nicht jedoch bei Riesling aus

Stomatal patchiness of field-grown sultana leaves: Diurnal changes and light effects

Unirrigated, field-grown Sultana vines were used to study diurnal changes of stomatal patchiness under the natural ambient conditions of South Australia. Non-homogenous aperture of stomata (patchiness) was determined by an infiltration technique and by counting infiltrated patches. Stomatal conductance was linearly related to the number of patches with open stomata (r2 = 0.622). Both parameters increased in the early morning (maxima at 8 a.m.) and decreased thereafter. In the afternoon stomatal conductance and the number of patches with open stomata remained at a low level. When dark adapted leaves were exposed to sun light (900 -1000 mu mol quanta . m-2 . s-1) the number of patches with open stomata increased from 23 to 143 cm-2 within 15 min, indicating that besides several stress factors light induces non-homogenous stomatal opening. It is assumed that stomatal action of single patches is autonomous, i.e. stomata of single patches will regulate water loss and CO2 uptake according to local changes of ambient and endogenous conditions

Grapevine shoot growth and stomatal conductance are reduced when part of the root system is dried

Split-root plants, where the root system was divided between two containers, were used to study the effect of partial drying of the root system on shoot growth and stomatal conductance of grape cultivars Chardonnay and Shiraz (syn. Syrah). When part of the root system was allowed to dry while the other part was well-watered, shoot growth was significantly reduced. Changes in both shoot growth and stomatal conductance in response to half-drying took place in the absence of any change in shoot water status suggesting the involvement of a non-hydraulic signal in mediating this response. Recovery of both shoot growth rate and stomatal conductance appeared to start before rewatering of the dried half of the root system, and coincided with the time when there was no further decrease of soil water content in the dried container. This appears to be first report of a significant decrease in shoot growth in response to partial drying of the root system of grapevines

Partial drying of the rootzone of grape. I. Transient changes in shoot growth and gas exchange

Split-root  plants, where  the  root  system was  divided between  two containers, were used  to  study  the effect  of  partial  drying  of  the  root  system  on  shoot growth and gas exchange of Shiraz  (syn. Syrah)  (Vitis vinifera), Kober 5 BB  (Vitis berlandieri x Vitis  riparia) and 110 Richter (Vitis berlandieri x Vitis rupestris). The initial decrease  in both shoot growth rate and gas exchange  in  response  to half-drying  coincided with  the decrease  in  soil water content of  the dried half of  the root  system. Recovery  of  shoot  function  of half-dried grapevines  occurred without  rewatering  of  the dried half  of  the  root  system,  and  commenced when  there was no  further decrease  in  soil water  content. There was no effect of half-drying on  leaf water potential at the  times  of  greatest  inhibition  of  shoot  growth  rate and stomatal conductance relative to control; this suggests  the  involvement of a non-hydraulic  signal originating  from  the  roots  in drying  soil. Changes  in  stomatal  conductance  in  response  to  half-drying were strongly  correlated with  shoot  growth  rate

Partial drying of the rootzone of grape. II. Changes in the pattern of root development

Split-root plants, where the root system was divided between two containers, were used to study the effect of partial drying of the root system on gas exchange and root growth of 110 Richter (Vitis berlandieri x Vitis rupestris). The initial decrease in gas exchange in response to half-drying coincided with the decrease in soil water content of the dried half of the root system. Recovery of gas exchange of half-dried grapevines occurred without any further change in soil water content of the dried half of the root system, and coincided with the point at which there was no further decrease in soil water content. For half-dried plants, there was a relative increase in root development in moist soil layers, both in the wet container as a whole or in the lower part of the dry container. Recovery of gas exchange of half-dried plants occurred at the time when there were no more roots dried in the dry container. We propose that, for half-dried plants, the part of the root system in dry soil can survive because water moves from wet roots to dry roots

Thermal acclimation of leaf and root respiration: an investigation comparing inherently fast- and slow-growing plant species

We investigated the extent to which leaf and root respiration W differ in their response to short- and long-term changes in temperature in several contrasting plant species (herbs, grasses, shrubs and trees) that differ in inherent relative growth rate (RGR, increase in mass per unit starting mass and time). Two experiments were conducted using hydroponically grown plants. In the long-term (LT) acclimation experiment, 16 species were grown at constant 18,23 and 28degreesC. In the short-term (ST) acclimation experiment, 9 of those species were grown at 25/20degreesC (day/night) and then shifted to a 15/10degreesC for 7 days. Short-term Q(10) values (proportional change in R per 10degreesC) and the degree of acclimation to. longer-term changes in temperature were compared. The effect of growth temperature on root and leaf soluble sugar and nitrogen concentrations was examined. Light-saturated photosynthesis (A(sat)) was also measured in the LT acclimation experiment. Our results show that Q(10) values and the degree of acclimation are highly variable amongst species and that roots exhibit lower Q(10) values than leaves over the 15-25degreesC measurement temperature range. Differences in RGR or concentrations of soluble sugars/nitrogen could not account for the inter-specific differences in the Q(10) or degree of acclimation. There were no systematic differences in the ability of roots and leaves to acclimate when plants developed under contrasting temperatures (LT acclimation). However, acclimation was greater in both leaves and roots that developed at the growth temperature (LT acclimation) than in pre-existing leaves and roots shifted from one temperature to another (ST acclimation). The balance between leaf R and A(sat) was maintained in plants grown at different temperatures, regardless of their inherent relative growth rate. We conclude that there is tight coupling between the respiratory acclimation and the temperature under which leaves and roots developed and that acclimation plays an important role in determining the relationship between respiration and photosynthesis

Evaluating the Potential for Smoke from Stubble Burning to Taint Grapes and Wine

Published: 13 December 2021It has been well established that bushfire/wildfire smoke can taint grapes (and therefore wine), depending on the timing and duration of exposure, but the risk of smoke contamination from stubble burning (a practice employed by some grain growers to prepare farmland for sowing) has not yet been established. This study exposed excised bunches of grapes to smoke from combustion of barley straw and pea stubble windrows to investigate the potential for stubble burning to elicit smoke taint. Increased levels of volatile phenols (i.e., chemical markers of smoke taint) were detected in grapes exposed to barley straw smoke (relative to control grapes), with smoke density and the duration of smoke exposure influencing grape volatile phenols. However, the sensory panel did not perceive wine made from grapes exposed to low-density smoke to be tainted, despite the presence of low levels of syringol providing compositional evidence of smoke exposure. During the pea stubble burn, grapes positioned amongst the burning windrows or on the edge of the pea paddock were exposed to smoke for ~15–20 and 30–45 min, respectively, but this only resulted in 1 µg/kg differences in the cresol and/or syringol concentrations of smoke-affected grapes (and 1 µg/L differences for wine), relative to controls. A small, but significant increase in the intensity of smoke aroma and burnt rubber flavor of wine made from the grapes positioned amongst the burning pea stubble windrows provided the only sensory evidence of any smoke taint. As such, had vineyards been located immediately downwind from the pea stubble burn, it is unlikely that there would have been any smoke contamination of unharvested grapes.Kerry Wilkinson, Renata Ristic, Imogen McNamara, Beth Loveys, WenWen Jiang and Mark Krsti

Regulation of abscisic acid concentration in leaves of field-grown pearl millet (Pennisetum americanum (L.) Leeke): the role of abscisic acid export

Diurnal changes in the ABA concn. in leaves of droughted, field-grown plants of P. americanum were not always correlated with changes in bulk leaf water potential. A rapid decline in ABA content of the leaves following its rise to a peak level in mid-morning, was observed in several time-course studies despite continued water stress. The possibility that the reduction in ABA in leaves was due to an elevated rate of its export was examined by measuring ABA concn. in developing panicles (possible sinks for leaf-produced ABA) and in leaves, and by comparing the amounts of ABA in ungirdled leaves and in leaves heat-girdled at the base of the lamina to block export. ABA concn. in panicles generally paralleled those in leaves, though the peak concn. of ABA in the morning in panicles occurred later than in the leaves in some samplings. Although girdling initially increased ABA concn., it did not prevent a subsequent fall which generally paralleled the decline observed in untreated leaves. The decrease in ABA that occurred despite the block to export and despite continuing stress was attributed to changes in the synthesis or metabolism of ABA within the leaf. The probable rate of export of ABA from leaves, calculated from the changes in its concn. due to girdling, was highest at the time of most rapid ABA accumulation and declined thereafter. The percentage export of recently assimilated C declined similarly. However, the probable absolute rate of export of photosynthate, computed from stomatal conductance and [14C]-export measurements, was not uniquely related to that of AB