A portable whole canopy gas exchange system for several mature field-grown grapevines

Abstract

Six flow-through chambers (8 m³ volume) were built to measure gas exchange (CO₂ and H₂O) of whole vines under deficit irrigation regimes that imposed water stress at different stages of berry development. Chamber design and materials were selected to minimize environmental effects, 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 mid-canopy height, 1.6 m, air temperature inside the chamber was no more than 2.5 °C higher than at the same height in the canopy of an unchambered vine. Over 24 h, solar radiation inside the chamber was 90 % of ambient. For vines irrigated according to standard industry practice, maximum values of net CO₂ exchange approached 12 μmol m^-2 s^-1, whereas in water-stressed vines the maxima approached only 6.5 μmol m^-2 s^-1. Transpiration among water-stressed plants was reduced, with maximum rates at 1 mmol m^-2 s^-1 while vines under standard irrigation were at 2.5 mmol m^-2 s^-1. Apparent light saturation for canopy photosynthesis was approximately 1200 μmol m^-2 s^-1 PPFD (photosynthetic photon flux density) for vines under standard irrigation, and about 800 μmol m^-2 s-1 PPFD for vines under water stress.