The effect of within-vineyard variability in vigour and water status on carbon discrimination in Vitis vinifera L. cv Merlot

[摘要] ENGLISH ABSTRACT: Within-vineyard variability in vigour and water status commonly occurs in South Africanvineyards. Different soil types found over short distances are probably the main cause of vigourvariability, while differences in grapevine water status are commonly induced by lateral waterflow in the vineyard, blocked irrigation emitters and differences in soil water-holding capacity.These factors can cause heterogeneous ripening and differences in fruit quality betweendifferent parts of the vineyard, an aspect that needs to be avoided as far as possible in order toproduce quality wines. Measurements of carbon isotope discrimination (CID) have proved to bea tool to assess grapevine physiology in order to study the effects of environmental parameterson leaf carbon dioxide (CO2) gas exchange and stomatal conductance (gs). Grapevine waterdeficit stress/strain in reaction to these environmental conditions can then be determined byobserving the amount of 13C absorbed by plant material after discrimination of 13C has takenplace, and this is influenced by the grapevine stress condition and can indicate water-useefficiency.In this study, the variability of grapevine water status and vigour was determined in order toquantify these parameters in different parts of the vineyard. Two separate trials were conducted,the first at Wellington, South Africa, where different irrigation regimes resulted in variability ingrapevine water status between plots. The second trial was at Stellenbosch, South Africa,where plots were divided among different vigour classes and irrigation was applied in differentquantities for different irrigation treatments. Within-vineyard variability in water status(Wellington and Stellenbosch) and vigour (Stellenbosch) were then quantified and the effects onsome grapevine physiological parameters and berry composition were measured.The treatments in the Wellington trial led to differences in grapevine water status, whichcould be quantified by measurements of stem water potential (SWP) and leaf water potential(LWP). Soil variability also led to differences in grapevine vigour, which were quantified bymeasurements of pruning mass, leaf area and shoot length. The effect of the variability ingrapevine water status on grapevine physiology was assessed by measuring CID, which wasthe main focus of the study. Other physiological measurements, such as gs and leaf andcanopy temperature, were also conducted. The effect of these conditions on grape berrycomposition was also studied.In the Stellenbosch trial, soil water content, plant water status measurements (SWP, predawnLWP and LWP), physiological measurements (CID and gs) and berry size measurementswere used to classify plots into water status treatments ('wet and 'dry treatments). The effectof vigour differences was analysed separately from these treatments by using pruning mass asa covariate in the statistical analyses. The effect of vigour variability on the measurements wasstudied by looking at the effect of the covariate on the measurements, while shoot growth rate,shoot length and leaf area measurements were conducted as vegetative growth measurements.Differences in measurements were then studied between the treatments and between thevigour levels of the different plots.In the Wellington trial, plant water status was determined by irrigation, showing increasedstress for treatments that received less irrigation. The differences in plant water status thencaused differences in grapevine physiology between the treatments, leading to increased gs for increased irrigation. This of course influenced leaf internal CO2 and therefore CID, although CIDwas also clearly influenced by berry development. Berry size was influenced by irrigation, withlarger berries found in wetter treatments, while berry chemical composition was influenced bythe irrigation regime, with increased irrigation leading to increased pH and leading to trendsshowing increased total soluble solids and malic acid, and reduced total and tartaric acid andcolour intensity.In the Stellenbosch trial, plots with higher vigour had increased shoot growth rate, longershoots and increased leaf area, although topping influenced this. Wet treatment vines alsoshowed slightly longer shoots and larger leaf areas. There were differences in soil water contentbetween the wet and dry treatments, and this led to differences in plant water status. Vigouralso influenced pre-dawn LWP, especially in the 2007 season, as higher-vigour vines struggledmore to rehydrate through the night.Differences in plant water potential led to differences in grapevine physiology, withincreased gs for vines from the wet treatment, while higher-vigour vines had slightly increasedgs. The differences in gs led to gas exchange differences and therefore differences in CID,meaning that water status and vigour influenced CID. CID measurements illustrated the longterm effect of water status on plant physiology, while measurements such as SWP illustratedthe short term effects. CID measurements therefore proved to be accumulative over the season,in contrast to SWP measurements that were much more dependent on the current state ofgrapevine water status. Other physiological measurements showed that wet-treatment vineshad higher photosynthetic rates and evapotranspiration and lower leaf temperatures, whilehigher-vigour vines had slightly increased evapotranspiration and decreased leaf temperatures.Wet-treatment vines had larger berries, while a higher vigour also led to slightly larger berries.Berry composition was influenced by treatment, where wet-treatment vines had increased pHand total soluble solids, while higher-vigour vines had increased juice pH and, in the 2008season, decreased total soluble solids.Extremely stressed conditions did not show significant effects on plant water potential, butSWP measurements indicated slightly higher stress for the extremely stressed vines and LWPshowed slightly less stressed conditions for these vines. Measurements of gs showed slightlylower values for the extremely stressed vines, while measurements of CID showed largesignificant differences, with the extremely stressed vines having measurements showing highstress. The measurement therefore indicated highly stressed conditions accurately, while otherphysiological measurements, such as photosynthetic rate, evapotranspiration and leaftemperatures, only showed trends and no significant differences. Measurements of stomatalconductance reacted to plant water status measurements throughout the diurnal measurementdays, while CID only reacted slightly with gs changes during these days and was perhapsinfluenced more by berry chemical composition and development at this early stage of theseason.Vigour and water status therefore influenced grapevine physiology, with a more direct effectby water status and an indirect effect by vigour due to microclimatic differences. This alsoinfluenced berry composition and therefore quality. In future studies, CID measurements should be done on juice from which organic acids havebeen removed in order to eliminate the effect of seasonal berry composition on themeasurement.Measurements of CID proved to be an integrative, but sensitive, indicator of grapevinestress, especially at the end of the season. It might at best be useful as a post-harvestmanagement tool for producers or grape buyers, especially for irrigation control, as has alsobeen stated by Van Leeuwen et al. (2007).

[发布机构] Stellenbosch University