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.
A method for rapidly estimating the rootlet volume and mass in sugar maple groves was developed in relation with the rootlet size. Soil samples were obtained with corers and cut in 2-cm thick slices. The number of rootlets of diameter classes <0.3, 0.3–0.5, 0.5–0.8, and 0.8–1.0 mm were determined under microscope (× 150) on the upper surface of slices. Rootlet surface for each class was measured on thin sections of soil, with an optic microscope connected to a digitalizing board. Mean rootlet surface [Formula: see text] showed a small standard deviation within each diameter class. The rootlet surface (S) on a surface of soil St can be estimated as [Formula: see text], where N is the number of rootlets observed in nc fields of observation, each field having a surface So. If two soil slices are located at depths h1 and h2, respectively, and if the rootlet surfaces of those slices are S1 and S2, the rootlet volume V of the first slice corresponds approximately to the volume of a truncated cone, and can be calculated as V = [S1 + S2 + (S1S2)0,5] (h2–h1)/3. The rootlet density (g•cm−3 of root) was also determined for each diameter class. The standard deviation from [Formula: see text], the mean density for each diameter class was small. Thus, the rootlet mass M was determined as [Formula: see text]. Estimated and real rootlet volume and mass values were compared. A difference of about 10% was found between estimated and real values.
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