PHYSIOLOGICAL AND MORPHOLOGICAL RESPONSES TO NITROGEN LIMITATION IN JACK PINE-SEEDLINGS - POTENTIAL IMPLICATIONS FOR DROUGHT TOLERANCE

The morphological and physiological responses to nitrogen (N) limitati on in jack pine (Pinus banksiana Lamb.) seedlings were studied followi ng the initiation of four different dynamic N treatments for six and 1 5 weeks. The N treatments produced needle N concentrations from 11 to 31 mg g(-1) dry weight, and seven-fold difference in dry weight at 15 weeks. Low-N jack pine seedlings: 1) had an higher root/shoot ratio; 2 ) extended their tap root more rapidly; 3) were better able to maintai n turgor when shoot water potential declined; and 4) had a larger dry weight fraction and apoplasmic fraction than seedlings with higher fol iar N concentrations. These responses may contribute collectively to e nhance drought tolerance in N-limited plants, thereby affecting seedli ng quality. Modifying nursery fertilization regimes, other than optima l as usually applied, may thus be needed to produce stock for use on p articularly droughty sites. Knowledge of the nature of drought at a pa rticular site could be an important consideration when making decision s related to fertilization.