Dry Weight and N Partitioning in Relation to Substrate N Supply, Internal N Status and Developmental Stage in Jack Pine (Pinus banksianaLamb.) Seedlings: Implications for Modelling

Abstract

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 ( r 2 =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.