Rob R. Walker

Regulation of canopy conductance and transpiration and their modelling in irrigated grapevines

Whole-vine transpiration was estimated for well-watered nine-year-old Sultana grapevines (Vitis vinifera L. cv. Sultana) from xylem sap flow measured with Graniers heat-dissipation probes. Canopy conductance of the grapevine was calculated by inverting the Penman-Monteith equation. Transpiration from grapevine canopies was strongly controlled by the canopy conductance. Canopy conductance decreased exponentially with increasing vapour pressure deficit (VPD) except in the morning when solar radiation was less than 200 W m-2 and the canopy conductance was predominantly limited by the solar radiation. A non-linear model of canopy conductance as a function of the solar radiation and VPD explained > 90% of the variation observed in canopy conductance. Under contrasting VPD conditions (daytime maximum of 3 kPa vs 8 kPa), grapevines were able to regulate their canopy conductance from 0.006 to 0.001 m s-1 to maintain a near constant transpiration. Whole-canopy transpiration calculated from modelled canopy conductance using the Penman-Monteith equation was highly correlated with the measured transpiration (sap flow) values over the range of 0-0.20 mm h-1 (R2 > 0.85). Cross-validation shows that these mechanistic models based on solar radiation and VPD provide good predictions of canopy conductance and transpiration under the conditions of the study.

Partitioning of seasonal evapotranspiration from a commercial furrow-irrigated Sultana vineyard

Abstract Seasonal partitioning of evapotranspiration (ET) between transpiration by grapevines (Vitis vinifera) (Tgp) and by cover crops of a ryegrass/clover mixture (Tcc), and soil evaporation (Es) was performed for a furrow-irrigated vineyard during the 1994/1995 and 1995/1996 growing seasons in south-eastern Australia. ET, determined with a water balance approach, averaged 622 mm. The ET rate averaged over the two seasons increased from 2 mm day–1 in spring (September to November), when it was dominated by Tcc, to peak rates of around 5 mm d–1 in summer (December to February) when it was dominated by Es. Tgp, determined with either heat-pulse sensors or the Penman-Monteith equation, attained peak rates of 0.75 and 0.98 mm d–1, or 6.2 and 8.1 l vine–1 day–1 in the first and second seasons, respectively. Total seasonal Tgp of 109.1 mm (900 l vine–1) in 1994/1995 and 118.8 mm (980 l vine–1) in 1995/1996 constituted just 18 – 19% of total ET. Tcc totalled 214 mm (34% of ET) in the first season, when pasture cover was sparse and present for 5 months of the growing season (September to February), and 196 mm (30% of ET) in the second season when pasture cover was heavy but present for only 3 months (September to November). Es averaged 49% of total ET over both seasons. At least 30% of water used for ET was contributed by antecedent soil water in both seasons. The crop factor (Kc) was largely constant throughout the season with an average value of 0.48. The depletion pattern of soil water indicated that the vine explored the soil profile well beyond 1.0 mm depth and almost evenly up to a distance of 1.5 m from the trunk. Water use efficiencies for fresh fruit yield (WUE), i. e., the ratio of fruit weight to total water use at harvest,were 13.3 and 40.5 kg ha–1 mm–1 when based on ET in 1994/1995 and 1995/1996, respectively, and 84.0 and 211.1 kg ha–1 mm–1, respectively, when based on Tgp. The Tgp data were used to verify three models of vine transpiration developed in an earlier study. Models based on the green area index or on fraction of incident radiation intercepted by the vine canopy produced good agreement with Tgp. The model based on canopy resistance performed poorly, indicating the difficulty of extrapolating the stomatal response to environmental variables from one set of experimental conditions to another.

Determination of transpiration in irrigated grapevines: comparison of the heat-pulse technique with gravimetric and micrometeorological methods

Abstract The use of a heat-pulse technique to monitor sap flow from which transpiration can be deduced was evaluated in ungrafted grapevines (Vitis vinifera L., cv. Sultana) under glasshouse and field conditions. There was a significant degree of agreement between daily transpiration deduced from heat-pulse velocity (Thp) and that determined directly by gravimetry in the glasshouse and by calibration using the Penman-Monteith equation in the field. Comparison throughout the growing season of Thp to transpiration calculated with the full Penman-Monteith equation produced a high coefficient of determination (r2=0.69). A similar comparison of Thp with transpiration calculated with only the aerodynamic component of the Penman-Monteith equation produced a non-linear relationship, due to the equation over-estimating transpiration relative to Thp at high vapour pressure deficits (i.e. above 2.5 kPa). Values for total seasonal transpiration measured with heat-pulse sensors or calculated with either the full Penman-Monteith equation or with only the modified aerodynamic component of the equation were within 10% of each other. Transpiration (Thp) in grapevines with an adequate supply of soil water was shown to be coupled to ambient air conditions.

Cl– uptake, transport and accumulation in grapevine rootstocks of differing capacity for Cl–-exclusion

Mechanisms of chloride (Cl–) exclusion in rootstocks of grapevine (Vitis spp.) were studied using a strong Cl–-excluding rootstock (140 Ruggeri) and a poor Cl–-excluding rootstock (K51–40). Xylem Cl– concentration in potted whole grapevines of 140 Ruggeri treated with 50 mM Cl– was 6.8-fold lower than that in K51–40. Five-fold lower total shoot Cl– in salt-treated 140 Ruggeri grapevines relative to that in K51–40 after 50 days, when shoots were of similar biomass, was unrelated to water use. Unidirectional influx of 36Cl– into excised roots (up to 30 min), and uptake of 36Cl– in roots of intact rooted-leaves (up to 180 min) in 10 mM Cl– was similar between the genotypes. However, net accumulation of Cl– by excised roots of K51–40 up to 180 min in 10 mM Cl– was significantly higher than that of 140 Ruggeri. Intact rooted-leaves of 140 Ruggeri in 10 mM Cl– accumulated higher Cl– concentrations in roots, and had a lower percentage of total plant 36Cl– accumulation in the shoot (petiole plus lamina) than those of K51–40. The greater Cl– exclusion capacity of 140 Ruggeri appears to be associated with restricted entry of Cl– to xylem and lower root to shoot Cl– transport.

Characterisation of water use by Sultana grapevines (Vitis vinifera L.) on their own roots or on Ramsey rootstock drip-irrigated with water of different salinities

Abstract Seasonal evapotranspiration (ET) was determined for Sultana grapevines grown on their own roots (Own-rooted) or grafted onto Ramsey rootstock (Grafted), and irrigated with water of three salinity levels – low (0.4 dS m–1), medium (1.8 dS m–1) and high (3.6 dS m–1) – during the 1994/1995 growing season in south-eastern Australia. Transpiration (T) was determined from sap flux, soil evaporation (Es) with a model, and soil water (S) with a neutron probe. Total ET for the season was similar for both Own-rooted and Grafted, averaging 382 mm. However, Grafted partitioned a mean of 193.5 mm (50.8%) of the ET through T compared to 146.7 mm (38.4%) by Own-rooted. Daily rates of T were generally low and attained peaks of 1.2 mm (9.9 l per vine) for Grafted and 0.9 mm (7.5 l) for Own-rooted in late November, and changed very little until after harvest in February. In contrast to T, the Es rate was consistently higher for Own-rooted than for Grafted from November onwards, and at the end of the season totalled 237 mm for Own-rooted compared to 187 mm for Grafted. Differences between Own-rooted and Grafted in their partitioning of ET into T and Es were associated with their canopy development. Grafted had a higher rate of canopy development than Own-rooted, and in mid-season, the former intercepted about 50% more incident radiation than Own-rooted. The crop factors, i. e. ratio of water use to evaporative demand, based on ET were similar for both vine types with an average seasonal value of 0.25, but when based on T were 0.12 for Grafted and 0.10 for Own-rooted. The ratio of fresh fruit weight to total water used at harvest, i. e. crop water use efficiency (CWUE), based on ET, had a mean of 86 kg mm–1 ha–1 for Grafted and 43 kg mm–1 ha–1 for Own-rooted, and when based on T, was 165 and 115 kg mm–1 ha–1, respectively; however, supplementary data obtained during the 1993/1994 season, indicated a CWUE based on T of 294 and 266 kg mm–1 ha–1 for Grafted and Own-rooted, respectively. Salinity did not have significant effects on canopy development and water use for most of the 1994/1995 growing season. The study shows ET and crop factors for the drip-irrigated grapevines to be much lower than previously reported for this district.

Contrast in chloride exclusion between two grapevine genotypes and its variation in their hybrid progeny

Potted grapevines of 140 Ruggeri (Vitis berlandieri × Vitis rupestris), a good Cl− excluder, and K 51-40 (Vitis champinii × Vitis riparia ‘Gloire’), a poor Cl− excluder, and of a family obtained by crossing the two genotypes, were used to examine the inheritance of Cl− exclusion. Rooted leaves were then used to further investigate the mechanism for Cl− exclusion in 140 Ruggeri. In both a potting mix trial (plants watered with 50 mM Cl−) and a solution culture trial (plants grown in 25 mM Cl−), the variation in Cl− accumulation was continuous, indicating multiple rather than single gene control for Cl− exclusion between hybrids within the family. Upper limits of 42% and 35% of the phenotypic variation in Cl− concentration could be attributed to heritable sources in the potting mix and solution culture trials, respectively. Chloride transport in roots of rooted leaves of both genotypes appeared to be via the symplastic pathway, since addition of 8-hydroxy-1,3,6-pyrenetrisulphonic acid (PTS), an apoplastic tracer, revealed no obvious PTS fluorescence in the laminae of either genotype, despite significant accumulation of Cl− in laminae of K 51-40 during the PTS uptake period. There was no significant difference in either unidirectional 36Cl− flux (10 min) or 36Cl− uptake (3 h) into roots of rooted leaves exposed to 5, 10, or 25 mM Cl−. However, the percentage of 36Cl− transported to the lamina (3 h) was significantly lower in 140 Ruggeri than in K 51-40, supporting reduced Cl− loading into xylem and implicating the root stele in the Cl− exclusion mechanism.

Shoot chloride exclusion and salt tolerance in grapevine is associated with differential ion transporter expression in roots

BackgroundSalt tolerance in grapevine is associated with chloride (Cl−) exclusion from shoots; the rate-limiting step being the passage of Cl− between the root symplast and xylem apoplast. Despite an understanding of the physiological mechanism of Cl− exclusion in grapevine, the molecular identity of membrane proteins that control this process have remained elusive. To elucidate candidate genes likely to control Cl− exclusion, we compared the root transcriptomes of three Vitis spp. with contrasting shoot Cl− exclusion capacities using a custom microarray.ResultsWhen challenged with 50 MM Cl−, transcriptional changes of genotypes 140 Ruggeri (shoot Cl− excluding rootstock), K51-40 (shoot Cl− including rootstock) and Cabernet Sauvignon (intermediate shoot Cl− excluder) differed. The magnitude of salt-induced transcriptional changes in roots correlated with the amount of Cl− accumulated in shoots. Abiotic-stress responsive transcripts (e.g. heat shock proteins) were induced in 140 Ruggeri, respiratory transcripts were repressed in Cabernet Sauvignon, and the expression of hypersensitive response and ROS scavenging transcripts was altered in K51-40. Despite these differences, no obvious Cl− transporters were identified. However, under control conditions where differences in shoot Cl− exclusion between rootstocks were still significant, genes encoding putative ion channels SLAH3, ALMT1 and putative kinases SnRK2.6 and CPKs were differentially expressed between rootstocks, as were members of the NRT1 (NAXT1 and NRT1.4), and CLC families.ConclusionsThese results suggest that transcriptional events contributing to the Cl− exclusion mechanism in grapevine are not stress-inducible, but constitutively different between contrasting varieties. We have identified individual genes from large families known to have members with roles in anion transport in other plants, as likely candidates for controlling anion homeostasis and Cl− exclusion in Vitis species. We propose these genes as priority candidates for functional characterisation to determine their role in chloride transport in grapevine and other plants.

Grapevine and Arabidopsis Cation-Chloride Cotransporters Localize to the Golgi and Trans-Golgi Network and Indirectly Influence Long-Distance Ion Transport and Plant Salt Tolerance

A protein from grapevine that transports sodium, potassium, and chloride ions across endomembranes is important for normal growth and salt tolerance. Plant cation-chloride cotransporters (CCCs) have been implicated in conferring salt tolerance. They are predicted to improve shoot salt exclusion by directly catalyzing the retrieval of sodium (Na+) and chloride (Cl−) ions from the root xylem. We investigated whether grapevine (Vitis vinifera [Vvi]) CCC has a role in salt tolerance by cloning and functionally characterizing the gene from the cultivar Cabernet Sauvignon. Amino acid sequence analysis revealed that VviCCC shares a high degree of similarity with other plant CCCs. A VviCCC-yellow fluorescent protein translational fusion protein localized to the Golgi and the trans-Golgi network and not the plasma membrane when expressed transiently in tobacco (Nicotiana benthamiana) leaves and Arabidopsis (Arabidopsis thaliana) mesophyll protoplasts. AtCCC-green fluorescent protein from Arabidopsis also localized to the Golgi and the trans-Golgi network. In Xenopus laevis oocytes, VviCCC targeted to the plasma membrane, where it catalyzed bumetanide-sensitive 36Cl–, 22Na+, and 86Rb+ uptake, suggesting that VviCCC (like AtCCC) belongs to the Na+-K+-2Cl– cotransporter class of CCCs. Expression of VviCCC in an Arabidopsis ccc knockout mutant abolished the mutant’s stunted growth phenotypes and reduced shoot Cl– and Na+ content to wild-type levels after growing plants in 50 mm NaCl. In grapevine roots, VviCCC transcript abundance was not regulated by Cl– treatment and was present at similar levels in both the root stele and cortex of three Vitis spp. genotypes that exhibit differential shoot salt exclusion. Our findings indicate that CCC function is conserved between grapevine and Arabidopsis, but neither protein is likely to directly mediate ion transfer with the xylem or have a direct role in salt tolerance.

Whole-plant transpiration efficiency of sultana grapevine grown under saline conditions is increased through the use of a Cl--excluding rootstock

The aim of this study was to test the influence of salinity (1, 20, 40 and 80 mol m-3) on the transpiration efficiency (W = biomass / water transpired), lamina gas exchange and carbon isotope discrimination (Δ) of grapevine (Vitis vinifera L. cv. Sultana) grown on own roots or grafted to a Cl--excluding rootstock (Ramsey; Vitis champiniL.). Growth of own-rooted and Ramsey-rooted vines irrigated with a salinity of 40 mol m-3 was reduced by 55 and 12%, respectively, compared with vines irrigated with 1 mol m-3. At 1 mol m-3 W of Ramsey-rooted vines was 1.3-fold higher than own-rooted vines (3.9 and 3.0 g L-1, respectively). Salinity resulted in a decrease in W of own-rooted vines (31% reduction at both 40 and 80 mol m-3). In contrast, W of Ramsey-rooted vines increased by up to 1.25-fold under saline conditions. Consequently, at 80 mol m-3 W of Ramsey-rooted vines was 2-fold higher than own-rooted vines. To our knowledge this is the first demonstration of the potential of a rootstock to increase W of a crop species under saline conditions. The rootstock-dependent differences in grapevine W under saline conditions were not determined by differences in lamina gas exchange. Differences in W associated with rootstock may be attributed to differences in ion uptake and the energy requirements associated with ion partitioning and the formation of compatible solutes.

Management practices impact vine carbohydrate status to a greater extent than vine productivity

Light pruning and deficit irrigation regimes are practices which are widely used in high yielding commercial vineyards in the warm climate regions of Australia. Little information is available on their impacts on carbohydrate dynamics in vegetative organs within and between seasons, and on the resulting plant capacity to maintain productivity and ripen fruits. This study was conducted to address this gap in knowledge over five vintages on Vitis vinifera L. cv. Cabernet Franc, Shiraz, and Cabernet Sauvignon in the Sunraysia region of Victoria, Australia. Lighter pruning did not change the total carbohydrates concentration and composition in wood and roots within seasons in Cabernet Franc and Shiraz. However, the total carbohydrate pool (starch and soluble sugars) at the end of dormancy increased under lighter pruning, due to higher vine size, associated with retention and growth of old-wood (trunk and cordons). Water deficit negatively impacted trunk and leaf starch concentrations, over the day and within seasons in Cabernet Sauvignon. Soluble sugars concentrations in these tissues tended to be higher under limited water supply, possibly due to higher sugar mobilization as photosynthesis decreased. Trunk carbohydrate concentrations markedly varied within and between seasons, highlighting the importance of interactive factors such as crop load and climate on carbon status. The period between fruit-set and véraison was shown to be critical for its impact on the balance between carbon accretion and depletion, especially under water deficit. The lower leaf and trunk starch concentration under water deficit resulted in a decrease of yield components at harvest, while similar yields were reached for all pruning systems. The sugar allocated to berries at harvest remained remarkably stable for all practices and seasons, irrespective of vine yield and carbohydrate status in vegetative organs in Shiraz and Cabernet Sauvignon.