Submitted to: Vitis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2003
Publication Date: 5/1/2004
Citation: Pena, P.J., Tarara, J.M. A portable whole canopy gas exchange system for multiple mature field-grown grapevines. Vitis. 43(1) p. 7-14. Interpretive Summary: Photosynthesis is the ultimate source of sugar that a grapevine accumulates in its fruit (grapes). When grapevines are subjected to water stress or drought, photosynthesis generally declines. Excessive water stress or drought may reduce photosynthesis enough to adversely affect how the fruit ripens, when it ripens, and its ultimate quality. However, mild water stress often improves quality in wine grapes, particularly the varieties used to make red wines. In the semi-arid inland Pacific Northwest, grape growers are required to use irrigation to produce grapes commercially. These growers welcome insight on how to manage irrigation in such a way as to induce the right amount of water stress to improve the quality of their grapes without harming the vine or decreasing the vineyard's longevity through excessive drought stress. A first step to assisting growers with these irrigation decisions is to measure photosynthesis on entire vines that are grown in commercial vineyards under the scheme of managed water stress. One cannot buy whole-vine photosynthesis chambers commercially, so a custom, mobile field system was designed, tested, and run in a commercial vineyard. Vines were deliberately subjected to one of three levels of water (drought) stress and photosynthesis per vine was measured. During the season, samples of the photosynthesizing leaves were analyzed for chlorophyll, the green pigment in the leaves, plus sugar and starch. This research project was part of a larger, collaborative study involving scientists from USDA-ARS, Washington State University, and private industry.
Technical Abstract: Six flow-through chambers (8 m3 volume) were built for the measurement of gas exchange (co2 and H20v) from whole vines under deficit irrigation that was meant to impose water stress at different stages of berry growth. Chamber design criteria and materials used were selected to minimize environmental effects of the enclosure, and to accommodate the trellis of a mature, field-grown vine. A framed design allowed the chambers to withstand sustained winds up to 13 m s 1, overcoming one disadvantage of the balloon-type chambers. At canopy height, air temperature was no more than 2.5 °C higher than at the same height in an unchambered canopy. Over 24 h, solar radiation inside the chamber was 90% of ambient. For vines irrigated according to standard industry practice, maximum values of next C02 exchange approached 12 'mol m 2 s 1, whereas in deliberately water-stressed vines the maxima approached only 6.5 'mol m 2s 1. Likewise, the chamber system detected reduced transpiration among water stressed plants, where maximum rates averaged 1 mmol m 2 s 1 as opposed to vines under standard irrigation, at 2.5 mmol m 2 s 1. Apparent light saturation for canopy photosynthesis was approximately 1200 'mol m 2 s 1 PPFD (photosynthetic photon flux density) for vines under standard irrigation, and about 800 'mol m 2 s 1 PPFD for vines under additional water stress.