Industry concerns in Australia about the impacts of climate change have, to date, focused on the effects of warming, particularly shorter maturation periods. The effects of elevated CO 2 concentration (eCO 2 ) on C 3 plant physiology have been extensively studied and suggest that eCO 2 impacts on viticulture could affect grapevine shoot growth, fruit production and fruit composition. We previously used open top chambers (OTC) with an active heating system to study the effects of elevated air temperature (eTemp) on mature grapevines in the field. This system was augmented with the ability to elevate atmospheric CO 2 and established in a mature Shiraz vineyard in a factorial combination of eTemp and eCO 2 . Three seasons of observations on the eTemp only treatment corroborated our previous study; all aspects of phenology were advanced, but leaf function was largely unaffected. In contrast, the effects of eCO 2 on phenology were small in the first season, but increased over the subsequent two seasons. Interactive effects of the treatments on gas exchange were observed; photosynthesis rates were significantly higher in the eCO 2 +eTemp treatment, compared to eCO 2 alone, suggesting that the likely future climate will have a larger impact on viticulture than might be predicted from experiments examining only one of these factors.

<p style="text-align: justify;"><strong>Abstract:</strong> Industry concerns in Australia about the impacts of climate change have, to date, focused on the effects of warming, particularly shorter maturation periods. The effects of elevated CO₂ concentration (eCO₂) on C₃ plant physiology have been extensively studied and suggest that eCO₂impacts on viticulture could affect grapevine shoot growth, fruit production and fruit composition. We previously used open top chambers (OTC) with an active heating system to study the effects of elevated air temperature (eTemp) on mature grapevines in the field. This system was augmented with the ability to elevate atmospheric CO₂and established in a mature Shiraz vineyard in a factorial combination of eTemp and eCO₂. Three seasons of observations on the eTemp only treatment corroborated our previous study; all aspects of phenology were advanced, but leaf function was largely unaffected. In contrast, the effects of eCO₂ on phenology were small in the first season, but increased over the subsequent two seasons. Interactive effects of the treatments on gas exchange were observed; photosynthesis rates were significantly higher in the eCO₂+eTemp treatment, compared to eCO₂ alone, suggesting that the likely future climate will have a larger impact on viticulture than might be predicted from experiments examining only one of these factors.</p>

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Abstract. Global mean temperature is likely to rise by more than 2°C by the end of the century and carbon dioxide concentration ([CO2]) is expected to increase from 408 µmol mol-1 in 2018 to 650 µmol mol-1 by 2060-2070. Previous studies and industry experience suggest that there has already been an effect of warmer temperatures on grapevine phenology; harvest dates have advanced and vintages have become shorter over the past 30 years in Australia. In addition, increasing [CO2] in the atmosphere will likely alter grapevine growth, development, and grape quality. Understanding the interactive effects of [CO2] and temperature on grapevines is essential to determine the potential impact of future climate on grape phenology, grape composition, and final wine quality. Open-top chambers (OTC), capable of maintaining air temperature 2°C above ambient throughout the diurnal cycle using an active heating system and fan-assisted air circulation, were established in an experimental vineyard managed to current commercial practice. A system was then developed to elevate atmospheric [CO2] to 650 µmol mol-1 around the grapevines within the OTC. The main engineering goal of the system was to maintain an even temporal and spatial distribution of CO2. Monitoring showed that the mean daytime [CO2] at the center of each OTC varied between 620 and 665 µmol mol-1, maintaining [CO2] at or above 95.4% of the target [CO2] and not exceeding the target by more than 2.3%, meeting the performance criteria of within ±10% of the target concentration. Both the temporal and spatial distributions of [CO2] were more even in heated OTCs than non-heated OTCs. In all heated OTCs, the [CO2] was at or above 90% of the target and within ±10% of the target at all locations assessed (spatial distribution). The mean [CO2] was between 80% and 86% of the target at 40% of locations in OTCs without heating; however, the overall mean [CO2] in the OTCs was 97.5% of the target. The system performed satisfactorily over a wide range of temperatures (20°C to 50°C), with overall standard deviation varying between 85 and 112 µmol mol-1. This indicates that the CO2 injection system showed satisfactory performance in controlling [CO2] at the center of each OTC and providing confidence in the results that will be generated from experiments using the system. On average, the heating system maintained a higher temperature (about 2.0°C in both day and night) than the ambient control plots. Keywords: Australia, CO2 injection in grapevines, Elevated CO2, Grapevines, Open-top chamber, Temperature.

(formerly DPI-Mildura); as well as Jenny Gordon (DPI-Mildura), who undertook sample collection and processing and Debra Partington (DPI-Hamilton), who assisted with statistical analyses and interpretation of results.