Dry weight and N partitioning in relation to substrate N supply, internal N status and developmental stage in jack pine (Pinus banksiana Lamb.) seedlings: Implications for modelling

Abstract

Dry weight and nitrogen (N) partitioning of sand-cultured young jack pine (Pinus banksiana Lamb.) seedlings under controlled environments were studied 3, 6, 9, 12 and/or 15 weeks after the initiation of six dynamic N supply treatments. The supply of other nutrients was maintained at optimal levels. Total dry weight varied widely among treatments and whole plant total N concentration ranged from 10 to 32 mg g-1 d. wt at most sampling intervals. Whole plant N concentration changed, with time, according to three distinct patterns: (1) stable; (2) rapidly increasing; or (3) gradually declining. Regardless of N treatment and sampling interval, whole plant N concentration was linearly and positively correlated with root, needle and stem N concentration. Dry weight and N weight ratios of needles declined, whereas those of roots increased linearly with decreasing whole plant N concentration (r2 = 0.43 to 0-76) regardless of N regime. Dry matter partitioning to stems, however, was better explained by developmental stage than by whole plant N concentration. With the decline in internal N status, N was increasingly concentrated in roots at the expense of needles and stems. These results suggest: (1) dry weight and N partioning may be largely a function of the internal N status of plant rather than root and shoot activities; (2) both shoot and root specific activities may have a close, positive association with whole plant N concentration; (3) N-partitioning may be an active process itself and may warrant separate consideration from dry weight; and (4) developmental stage may be a significant determinant of partitioning, particularly to stems.