THE EFFECT OF NITROGEN AND POTASSIUM LEVELS IN TUNG SEEDLINGS ON GROWTH, APPARENT PHOTOSYNTHESIS, AND CARBOHYDRATE COMPOSITION

Abstract

Three levels of N and of K in factorial combinations were obtained in leaves of tung seedlings growing in sand culture. The percentages of N desired in the leaves were 2.5, 1.75, and 1.25; those obtained at the last harvest date were 2.59, 1.95, and 1.38. The percentages of K desired in the leaves were 1.2, 0.8, and 0.4; those obtained were 1.4, 0.93, and 0.5. When the N content of the leaves of N1 plants fell to about 2%, a change in color of the foliage was noted, and both rate of apparent photosynthesis and rate of growth declined. When at a later date the N content of the leaves of the N2 plants approached 2%, similar effects were observed. In plants, the leaves of which contained only about 1.6 to 1.4% of N, photosynthesis was at a very low level, linear growth stopped, many leaves abscised and increase in dry wt. was nearly at a standstill. Decline of the K content of the leaves to about 0.55% failed to produce symptoms in the leaves and reduced the rates of apparent photosynthesis and growth to a lesser extent than did the low levels of N reported above. N deficiency reduced the rate of apparent photosynthesis to about the same extent morning and afternoon, but K deficiency depressed photosynthesis to a greater extent in the afternoon. A low level of K was associated with a decrease in rate of photosynthesis and of growth and there was a concomitant increase in reducing sugars and decrease in nonreducing sugars, particularly marked in the roots. A low level of N in the leaves tended to be associated with low levels of nonreducing sugars and high levels of reducing sugars in the leaves, but the effects on stems and roots were less consistent. Starch in the leaves appeared to accumulate most rapidly in the low N high K and in the high N low K plants. Apparently a low level of one of these elements in the presence of a high level of the other checked growth more than photosynthesis, with the result that starch tended to accumulate.