Water use and physiological responses of apple trees and grapevines to water stress and cultural practices

'Empire' apple trees grown in two-sided Plexiglas pots and 'Cabernet' grapevines grown in plastic pots were subjected to water stress early in the season during the cell division. This was to study the sensitivity of shoot growth, fruit growth, root growth and single leaf photosynthesis of apple tress to water stress and their recovery after rewatering; and to study the response patterns of whole canopy versus single leaf gas exchange of grapevines to different levels of water stress. Also seven-year-old 'Chardonnay' grapevines grown in the field, and 4-year-old potted 'Pinot Noir' grown in Cornell mix were trained on different trellis forms that were manipulated in different ways to influence radiation interception and water loss. For apple, the results during the stress period and after rewatering indicated that the sensitivity to water stress, starting with the most sensitive process, is in the following order: shoot growth, fruit growth, photosynthesis, root growth. When water stress developed during the middle of cell division stage, final fruit size and weight of stressed tress was less than that of the well-watered control trees significantly. But when water stress developed during the end of cell division and beginning of cell expansion stages, final fruit size and weight of the two treatments were similar. For grape, photosynthesis of well exposed single leaves and whole grapevines early in the season had a similar response to increasing water stress. Single leaf and whole-vine dark respiration were reduced less by mild water stress. Water stress reduced photosynthesis by 40% more than it reduced dark respiration. Most of whole-canopy respiration was respiration by leaves; therefore, the effect of water stress on respiration of fruits and actively growing shoot tips did not significantly affect the response pattern of whole vine photosynthesis to water stress. The reduction in single leaf photosynthesis under mild water stress was due to stomatal closure. But under severe water stress there was an increase in internal CO{dollar}sb2{dollar} consistent with non-stomatal inhibition of photosynthesis. Finally for trellis manipulation, training grapevines to different trellis forms had significant effects on radiation interception, and thus on vine diurnal stem water potential and water use during sunny days. Under diffuse light conditions, light hits canopies from all angles regardless of trellis form. Therefore, the effect of trellis forms on vine water use was not significant under diffuse light conditions. A north-south oriented vertical canopy tilted to the west to minimize early afternoon light interception reduced the mid-day stem water potential decline compared to a horizontal trellis. This suggests that tilted trellis forms could ameliorate the diurnal pattern of water stress in the grapevine.