Survival of 2 ecologically distinct bacteria (flavobacterium and arthrobacter) in unplanted and rhizosphere soil - field studies

The survival of two ecologically distinct bacteria, Arthrobacter sp. A109 and Flavobacterium sp. P25, in planted and unplanted field soils, was monitored and compared with the results of previous experiments in laboratory soil microcosms. In separate inoculations, A109 (autochthonous) survived for longer and in greater numbers than P25 (zymogenous) in both planted and unplanted soil in three separate field experiments (Autumn 1988, Spring 1989 and Spring 1990). In both field and laboratory experiments, the numbers of A109 and P25 were greater in rhizosphere soils than in unplanted soils. However, the rate of decline of inoculum was generally slower in field soils compared with laboratory soils, e.g. P25 fell below quantifiable limits (BQL) within 8 days in unplanted laboratory soil, but took between 29 days (Spring 1989) and 87 days (Autumn 1988) to fall BQL in field soils. A109 numbers were at least 1 x 10(3) cfu g-1 in planted or unplanted soils at the end of each field experiment (up to 300 days in the Autumn 1988 field experiment). There was no significant effect of prior inoculation of A109 on the survival of P25 introduced at a later date (21 days) in field soils, planted or unplanted. Likewise, there was no significant effect of prior inoculation of P25 on the survival of A109. All inocula of P25, whether as the sole inoculant, mixed with A109, or introduced before or after A109, declined BQL at similar times in unplanted field soil, or at similar rates in planted field soil. Similarly, rates of decline for A109 inoculum were not significantly different between the planted field soil treatments, or between the unplanted field soil treatments. In general, the same trends observed in laboratory experiments for A109 and P25 inoculum survival were observed in field soils.