Sulfur dioxide gas injury to fruit trees. V.

Absorption of sulfur dioxide by citrus trees and its relation to leaf fall and mineral contents of leaves

Abstract

Absorption of sulfur dioxide by citrus trees and its relation to the injury and the content of nutrient elements of leaves were studied. Two-year-old trees were fumigated with constant flow of SO₂-air mixture in the cabinets reported previously.
1. In Satsuma orange (Citrus unshiu), Hassaku (C. Hassaku) and Natsudaidai (C. Natsudaidai) fumigated with 5, 1 and 0ppm concentrations for 2 hours per day from November 18 to December 23 (during 34 days), 1963, the leaf fall increased with the higher concentration of the fumigation, though the smoke lesion did not occur. The increase of sulfur content of the leaves coincided with the tendency of leaf fall rate.
2. Hassaku and Natsudaidai accumulated the greater amount of sulfur than Satsuma orange, but the leaf fall rate was markedly less than Satsuma orange.
3. Calcium content of leaves greatly decreased and potassium content a little decreased in all species with the fumigation of 5ppm sulfur dioxide as compared with those of the control.
4. In the growing season, from May to June, 1964, the same relationship was recognized, but the amount of absorption of sulfur was markedly greater than in the winter fumigation in spite of the short duration of fumigation, and the smoke lesion also did not occur.
5. Calcium content of leaves was not clearly connected with sulfur dioxide fumigation in growing season, but potassium content of fumigated trees was higher than the control. Nitrogen, phosphorus and magnesium contents were not concerned with sulfur dioxide fumigation in all species.
6. In November, 1965, the fumigating experiment was done in the controlled chamber, in which the temperature was 30°C and the illumination was about 18, 000lux. Trees were treated with SO₂-air mixtures of 0ppm, 2ppm-6 hours, 10ppm-12 hours, 5ppm-24 hours and 2.5ppm-48 hours respectively (each plot recieved 120ppm of sulfar dioxide gas accumulatively). As the result, the higher the concentration of sulfur dioxide, the more sever the injury of Satsuma orange. But the sulfur content of leaves did not coincide with the injury. Therefore, analysis of sulfur content of leaves may be useful for estimation of chronic injury, but in acute injury it may not be always useful method.