Fig. 4

Microbiota richness a and diversity b as measured by Chao and Shannon indexes observed in the different fumigation years. P values was from two-tailed Student’s t test (P < 0.05). 0.01 < P ≤ 0.05, one star; 0.001 < P ≤ 0.01, two stars; P ≤ 0.001, three stars. NF non-fumigation, F_1 chloropicrin-fumigation for 1 year, F_3 continuous chloropicrin-fumigation for 3 years