LIGHT DISTRIBUTION IN AND PHOTOSYNTHESIS OF APPLE TREE CANOPIES

Light distribution within canopies of mature apple trees changed rapidly during the pre and post bloom period.
Light was limited in the bottom third and middle of the trees (4 m tall) trained to a central leader within 30 days from bud break.
Leaves in the shaded portions of the canopy had thinner palisade layers, less leaf starch and higher soluble carbohydrate content.
Fruit set was least in the lower portions of the tree canopy.
Light penetration within the canopies related to spur and fruit quality.
In controlled studies, limiting light (<900 umoles/m²/s) either before or after bloom reduced fruit set and tended to reduce fruit size.
Shade during the middle of the season or late in the season tended to reduce fruit size and fruit quality.

Net photosynthesis (Pn) of spur leaves is 10–20% less than leaves on vegetative shoots.
Pn was similar between vegetative shoots and vegetative spurs.
Fruit on spurs did not affect spur leaf Pn.
Early in the season, spur leaf Pn may be limiting to fruit set and early fruit development.
Maximum Pn was reduced in N deficient trees.
Similarly, light saturation of N deficient trees occurred at a lower level.

III International Workshop on Temperate Zone Fruits in the Tropics and Subtropics

Curt R. Rom

https://doi.org/10.17660/ActaHortic.1990.279.33