© 1990 Heron Publishing—Victoria, Canada
Whole-tree carbon and nitrogen partitioning in young hybrid poplars
Kurt S. Pregitzer, Donald I. Dickmann, Ron Hendrick and Phu V. Nguyen
Department of Forestry, Michigan State University, East Lansing, MI 48824-1222, USA /
Summary
The effects of water, nitrogen (N), and genotype on whole-tree carbon and nitrogen partitioning were examined in two Populus genotypes grown from cuttings in large pots set in the ground. Four replicate trees from each genotype/water/N treatment
combination were harvested in either August, September, or November of their first year of growth. Aboveground biomass was
linearly related to total leaf area. Clones allocated photosynthate differently. Populus tristis × P. balsamifera cv. Tristis #1 produced 14.5 cm of fine roots (< 0.5 cm diameter) per cm2 of foliage, whereas P. × euramericana cv. Eugenei only produced 4.0 cm of fine roots per cm2 of foliage. The large diameter structural roots of Eugenei grew rapidly late in the growing season so that large-root biomass
was 3.8 to 7.5 times greater in November than in mid-August. In both clones, the root system grew twice as fast as the stem
and branches late in the year. During August, about 75% of total tree N was in the canopy, but at least 80% of the September
N content was still present in November following leaf fall. The major site of N storage was the large diameter structural
roots. Nitrogen concentrations in these roots doubled following bud set.
