ROOT-SYSTEM OF SUGAR MAPLE GROVES IN QUEBEC .2. ROOT-GROWTH IN RELATION TO MICRORELIEF AND PARENT MATERIAL

The root systems of two sugar maple groves, one on acidic parent material, the other on calcareous parent material, were studied in Quebec. The microrelief of both sites consisted of bumps and holes. Bumps represented 65% of the area. On acidic parent material, the roots >1 cm in diameter were more than 5 m long. On calcareous parent material, they rarely exceeded 4 m in length. These larger roots branched out into many smaller roots in all directions in the bumps, and in the upper soil horizons of the holes. In the acidic site, the rootlet mass was smaller (about 16 t.ha-1) than that observed in calcareous site (about 19 t.ha-1). In both sites, rootlet mass was higher in the bumps (14-17 t.ha-1) than in holes (2-4 t.ha-1). In bumps, 80 and 69% of these rootlets grew in the B horizons in acidic and calcareous sites, respectively. In the holes, rootlets were concentrated (>65%) in the F and Ah horizons. In the acidic site, rootlets <0,5 mm in diameter were longer, more entangled, and more densely packed (7-11 mg.cm-3) in the F and Ah horizons than in the B horizons (1-2 mg.cm-3); F and Ah horizons of the bumps also produced the highest density of rootlets <0,3 mm in diameter (about 50 and 20 mg.cm-3, respectively). In the other horizons of this site, as well as in all horizons of the calcareous site, the rootlets were short and developed in tufts. In the calcareous site, rootlets <0,3 mm in diameter were less abundant in the Ah horizons of bumps (about 10 mg.cm-3). This site contained more rootlets 1-2 mm in diameter than the acidic site.