Effects of Light Interception and Canopy Orientation on Grapevine Water Status and Canopy Gas Exchange
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An experiment was conducted in a vineyard planted with Vitis vinifera L. 'Riesling' in New York, USA. Vines were fully irrigated and were trained via vertical shoot positioning (VSP) giving a narrow curtain intercepting approximately 27% of the incident light. Vine rows were north-south oriented. In one experiment, the single curtain canopies were opened into a V-shape to increase light interception. Results showed that midday stem water potential decreased by approximately 20%, suggesting an increase in vine water use. In a second experiment, canopies were inclined towards the west for 20 min periods every 40 min in order to modify the daily pattern of vine light interception. The whole canopy gas exchange responses to these practices were measured with Mylar plastic chambers. During the afternoon, decreasing light interception by inclining the vine canopy towards the west, increased vine water use efficiency (WUE, canopy photosynthesis: transpiration) by 40% compared to when the vine canopy was in the vertical position. However, over the whole day WUE increased by only 8%. Overall this study supports the idea that vine gas exchange is driven more by vine light interception than by leaf area. Vines trained as VSP in north-south oriented rows offer a possibility for modifying daily patterns of gas exchange by changing canopy orientation to the sun. These strategies could be employed in order to either increase or decrease vine gas exchange depending on the environmental conditions and soil water status.