Influence of rootstock and soil moisture on leaf photosynthesis of apple trees on JM1, JM7, JM8, and m.9 rootstocks.

摘要

JM1, JM7 and JM8 apple (Malus x domestica) rootstocks, bred from a M. prunifolia var. ringo x M.9 (M. pumila var. paradisiaca) cross, show similar/weaker tree vigor and smaller fruit yield compared with M.9 rootstock. To elucidate rootstock effects on photosynthesis, we studied differences in leaf net photosynthesis of apple trees between the various rootstocks and investigated photosynthetic responses to various soil moisture statuses. Field-grown 'New Jonagold' apple trees grafted onto JM1, JM7, JM8, and M.9 rootstocks were subjected to sheet mulching using moisture-permeable waterproof fabric in order to control soil moisture status. Diurnal changes of photosynthetic and transpiration rates and stomatal conductance were determined. Without mulching, soil water potential was higher (-4.9 kPa) and photosynthetic rates were relatively high on JM8 and M.9, intermediate on JM7, and significantly lower on JM1 rootstocks; maximum values were 15.3, 12.7, 8.2, and 5.9 micro mol m-2 s-1, respectively. With mulching, soil water potential was lower (-10.3 kPa), photosynthetic rates on all rootstocks remained at low levels (maximum values ranged between 5.3 and 8.1 micro mol m-2 s-1), and there was less variation due to rootstocks. The same tendencies could be seen in transpiration rates and stomatal conductance. Trees on JM1 rootstock were significantly less vigorous than those on JM7, JM8, and M.9 rootstocks as indicated by reduced tree height, canopy diameter, trunk circumference, and shoot length. These findings imply that leaf photosynthesis of apple trees on JM1 rootstock is consistently low regardless of soil moisture status, resulting in the lack of tree vigor on JM1.