THE EFFECT OF PHOTOPERIOD AND NITROGEN ON THE GROWTH AND DEVELOPMENT OF SEEDLINGS OF JACK PINE

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Abstract
Nine seed lots of Pinus banksiana Lamb. and one of P. contorta var. latifolia Engelm. were grown for 115 days on five nitrogen levels and two photoperiods. The nitrogen levels were: zero N—no nitrogen, [Formula: see text], [Formula: see text], 1N—203 p.p.m., and 2N—406 p.p.m. The two photoperiods were a long-night photoperiod (10-hour day) and a broken-night photoperiod (9.5-hour day followed by 0.5-hour light break in the middle of the dark period). The plants, five per vessel, were analyzed for their response to treatments in terms of growth, development, and nitrogen content.(1) The breaking of the night doubled the height, total dry weight, and leaf weight and increased root weight and nitrogen absorption, but it lowered the number of fresh, active root tips, the proportion of the plant in root tissue, and the nitrogen concentration, inhibited production of secondary leaves, and delayed winter bud formation.(2) The increase in nitrogen level in the medium lowered the percentage of fresh, active root tips, the proportion of the plant in root tissue, and the production of winter buds; it increased the content and concentration of nitrogen in the plants. Up to a certain maximum (about [Formula: see text]), it increased the dry weight and height of the plants.(3) The interrelation of growth and developmental stimuli is discussed. It is suggested that growth is an important factor in controlling development.

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