Fig. 4

Bacterial concentration in the front-, middle-, and rear-ends of artificial cores A, B, C and D. Core A, B, C and D correspond to core A, B, C and D in Fig. 3 and Tables 3, 4. Black, blue, and red columns represent the bacterial concentration in the front-, middle-, and rear-ends, respectively. The results represent means from three replicates in the same experiments. *p < 0.05; **p < 0.01. A-F, the front-end of core A; A-M, the middle-end of core A; A-R, the rear-end of core A; B-F, the front-end of core B; B-M, the middle-end of core B; B-R, the rear-end of core B; C-F, the front-end of core C; C-M, the middle-end of core C; C-R, the rear-end of core C; D-F, the front-end of core D; D-M, the middle-end of core D; D-R, the rear-end of core D