Row orientation effects on whole-canopy gas exchange of potted and field-grown grapevines

The effects of canopy orientation (North-South vs. East-West) on total cano py assimilation (TCA) and transpiration (TCE) were evaluated on potted grap evines mounted on wheeled platforms for full swivel relation. Eight vines w ere assembled in pairs to form four canopy walls 2 m long, 1.1 m tall and 0 .25-0.30 m wide. TCA and TCE readings were also taken in the field on four NS-oriented, hedgerow cordon-trained grapevines. Diurnal trends of TCA reco rded on potted vines showed little variability when related to row orientat ion. The TCE pattern for EW followed essentially that of light intensity, w hereas a NS orientation induced a marked decrease in TCE at midday before r ecovering in mid-afternoon. As a result, water use efficiency (WUE) in NS r ows was higher during the midday hours. Total canopy water loss in NS was l inearly correlated with estimates of intercepted light, suggesting that wat er use was a function of both, light intensity and canopy geometry (i.e. mo re light lost to the ground at noon, hence less transpiration). The results for the NS-oriented field-grown canopies differed to some extent from thos e of the pot experiments. TCA showed a more marked afternoon decline and TC E flattened at noon, though with no apparent decrease. WUE efficiency was l owest at the highest evaporative demand. The daily water loss of field vine s could not be predicted by total light interception estimates only, indica ting a more complex regulation of canopy transpiration than recorded on pot ted plants.