EFFECTS OF 2 COLLEMBOLA SPECIES ON NODULE OCCUPANCY BY 2 BRADYRHIZOBIUM-JAPONICUM STRAINS

Is the competition between indigenous and introduced bradyrhizobia influenced by soil invertebrates? This question was investigated in pots and the field by testing effects of two collembola species, Folsomia candida and Tullbergia granulata, on nodule occupancy by Bradyrhizobium japonicum strains 110 and 123. Pot experiments were performed by inoculating soybeans with 10(9)' cells of both B. japonicum strains 110 and 123 plus 300 F. candida, 300 T. granulata or 150 of each species. In the field, the same treatments were applied to pairs of commercially-planted soybean. Collembola were contained in soil around soybeans with 24-cm dia cylinders sunk 30 cm deep. The single strongest collembolan effect was increased nodule occupancy by indigenous strains of B. japonicum associated with F. candida in both pots and field soil. B. japonicum strain 110 occupied more nodules singly in presence of T. granulata in pots. Overall, collembola determined the occupancy of 16% of the nodules in pot experiments and 20% in field experiments in the simplest models that fit the experimental data.