TABLE 2.

Numbers of organisms in the rhizosphere in relation to plant species and soil depth (November)

MicroorganismsPlant speciesNo. of subsamplesMean no. of colonies/g (dry wt) of roots (SD)
0-20 cm20-40 cm40-60 cm0-20 cm20-40 cm40-60 cm
PCB degraders (106)Ash4641.6 (0.9) Aaa1.0 (0.9) ABa0.3 (0.2) Aa
Birch040NDb2.0 (1.5) ABND
Black locust4345.2 (5.1) Aa0.1 (0.1) Aa0.7 (0.4) Aa
Pine6602.4 (1.8) Aa3.0 (1.8) BaND
Willow4430.95 (0.9) Aa1.4 (0.3) ABa5.3 (3.1) Bb
Grass800160.0 (210.0) ANDND
Total heterotrophs (109)Ash4642.8 (1.3) Dd2.6 (2.1) DEd4.0 (1.3) Dd
Birch040ND1.0 (0.5) DND
Black locust4348.6 (7.2) DEd0.4 (0.3) Dd1.4 (0.6) Ed
Pine6603.1 (3.5) Dd5.8 (3.1) EeND
Willow4432.2 (1.3) Dd2.8 (1.2) DEde2.9 (0.3) DEe
Grass80017.0 (7.5) ENDND
  • a Uppercase letters indicate significant differences in the same column, and lowercase letters indicate differences in the same row (P < 0.05, as determined by ANOVA).

  • b ND, not determined because a sample was not available.