A CO2 Injection System Inside an Open-Top Chamber Enclosing Mature Field-Grown Grapevines: Design and Performance

Abstract

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.