TABLE 1.

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

MicroorganismsPlant speciesNo. of subsamples analyzedMean no. of colonies/g (dry wt) of soil (SD)
0-20 cm20-40 cm40-60 cm0-20 cma20-40 cm40-60 cm
PCB degraders (103)Ash4447.3 (5.2) Aab25.0 (27.0) Aa27.0 (43.0) ABa
Birch2406.7 (0.01) Aa3.3 (2.0) AaNDc
Black locust4448.1 (5.2) Aa17.0 (15.0) Aa2.6 (1.0) ABa
Pine2408.0 (0.3) Aa68.0 (27.0) BbND
Willow6452.2 (1.8) Aa1.3 (0.8) Aab120.0 (96.0) Ab
Grass or no roots8483.3 (3.5) Aa1.2 (1.2) Aa3.9 (4.9) Ba
Total heterotrophs (106)Ash4445.7 (5.1) DEd17.0 (7.8) Dd8.9 (5.0) DEd
Birch2401.4 (0.1) DEd4.1 (3.6) EFdND
Black locust4449.8 (6.2) DEd18.0 (1.6) De11.0 (2.7) Dde
Pine24012.0 (12.0) Dd14.0 (7.2) DFdND
Willow6453.0 (2.2) DEd2.5 (1.2) Ed5.4 (2.9) Ed
Grass or no rootsd8482.5 (1.9) Ed1.5 (0.4) Ede0.5 (0.2) Fe
  • a Beneath all trees there were grass and forb roots at a depth of 0 to 20 cm.

  • b 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).

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

  • d Grass roots were limited to the upper 0 to 20 cm of soil; hence, the soil obtained from 20 to 40 and 40 to 60 cm was considered non-root-containing control soil.