Photosynthetic Acclimation of Leaves of Three Apple Cultivars as Affected by Growth Under Different Light Regimes

Abstract

Photosynthetic acclimation of leaves of young ‘Delicious,’ ‘Golden Delicious,’ and apple trees ( Malus domesticaBork.) as affected by growth under full sun or 15% sun and subsequent transfer to the contrasting light regime was studied. Photosynthetic capacity was reduced in ‘Granny Smith,’ ‘Golden Delicious’ and ‘Delicious’ apple leaves when grown under 15% sun. Leaf nitrogen per area (N) was highly correlated with CO ₂assimilation (A), CO ₂assimilation at saturating CO ₂(A _max), and carboxylation efficiency (g’ _m). The highest N was in leaves grown under the highest photosynthetic photon flux (PPF). Photosynthetic capacity under 15% sun was reduced to a greater extent in ‘Granny Smith’ compared to ‘Golden Delicious’ or ‘Delicious.’ ‘Granny Smith,’ however, acclimated photosynthetically to shade-to-sun transitions, whereas ‘Delicious’ did not acclimate. Since photosynthetic capacity was greatly reduced by shade in ‘Granny Smith’ and since ‘Delicious’ and ‘Golden Delicious’ did not acclimate to shade-to-sun transitions, the greatest photosynthetic productivity in these apple cultivars would be obtained by exposing the greatest portion of the canopy to full sun throughout the season.