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

Dry weight and nitrogen (N) partitioning of sand-cultured youngjack pine (Pinus banksianaLamb.) seedlings under controlledenvironments were studied 3, 6, 9, 12 and/or 15 weeks afterthe initiation of six dynamic N supply treatments. The supplyof other nutrients was maintained at optimal levels. Total dryweight varied widely among treatments and whole plant totalN concentration ranged from 10 to 32 mg g^-1d. wt at most samplingintervals. Whole plant N concentration changed, with time, accordingto three distinct patterns: (1) stable; (2) rapidly increasing;or (3) gradually declining. Regardless of N treatment and samplinginterval, whole plant N concentration was linearly and positivelycorrelated with root, needle and stem N concentration. Dry weightand N weight ratios of needles declined, whereas those of rootsincreased linearly with decreasing whole plant N concentration(r²=0.43 to 0.76) regardless of N regime. Dry matter partitioningto stems, however, was better explained by developmental stagethan by whole plant N concentration. With the decline in internalN status, N was increasingly concentrated in roots at the expenseof needles and stems. These results suggest: (1) dry weightand N partioning may be largely a function of the internal Nstatus of plant rather than root and shoot activities; (2) bothshoot and root specific activities may have a close, positiveassociation with whole plant N concentration; (3) N-partitioningmay be an active process itself and may warrant separate considerationfrom dry weight; and (4) developmental stage may be a significantdeterminant of partitioning, particularly to stems.Copyright1998 Annals of Botany Company Developmental stage; dry weight; internal N status; jack pine; modelling; nitrogen; partitioning;Pinus banksiana; substrate N supply.