Net Photosynthesis, Chlorophyll, and Foliar Iron in Apple Trees After Injection with Ferrous Sulfate

Abstract

Abstract Severely chlorotic ‘Delicious’ apple ( Malus domestica Borkh.) trees growing in a calcareous soil were pressure-injected with a 1.0% (w/w) ferrous sulfate solution. Net photosynthesis (Pn) of iron-treated trees was at least 50% greater than controls within 10 days after injection and reached as high as 115% above controls during the first growing season. Chlorophyll (Chl) concentration closely paralleled Pn during the first growing season, but the correlation was not as strong thereafter. During the 3rd growing season after injection, Pn of injected trees declined, yet still remained greater than controls until September (last sampling date). Visual chlorosis reappeared in the young terminal leaves near the end of the 3rd growing season. Stomatal diffusive resistance was unaffected by the treatments. Foliar iron concentrations in treated trees increased above the controls for about 2 months after injection. Thereafter, foliar iron content gradually decreased until the end of the first growing season, after which concentrations were similar to controls. Results indicate that injection of iron into chlorotic apple trees can enhance Pn and Chl for at least 3 growing seasons.