Fluctuations of soil bacterial communities under potato cropping

It is important to understand the underlying factors that lead to shifts in soil microbial communities, not simply for the characterization of these complex biotic systems, but also to understand the impact that changes in microbial community composition may have on terrestrial ecosystems. In this study, the impact of genetically different potato (Solanum tuberosum) plants growing in arable soil on the soil bacterial community composition was investigated. It was hypothesized that the modifications in the tuber starch content of these plants might lead to changes in root exudation, resulting in changes in bacterial composition near the roots. In a crop rotation schedule, including potato-barley-potato, plants of different potato cultivars were grown, including one genetically modified (GM) line that was modified in its tuber starch content. Thus, to establish the normal operating range (NOR) of soil bacterial community make-up in the production system, the variability of the bacterial communities in soil under the subsequent cropping regimes was determined. The results showed that the effect of the GM potato line on soil bacteria fitted within the NOR. The bacterial community structure of the potato rhizosphere samples was mainly affected by plant growth stage. Besides, clone library and PCR-DGGE analyses indicated that the bulk soil community fluctuated over the three growth seasons, concomitant with the crop rotation and fertilization regime. Some bacterial species found in the bulk soil were specific for the plant species under investigation (barley and potato) or plant growth stage. Arthrobacter, Streptomyces, Rhodanobacter and Dokdonella were only found at flowering potato plants in both seasons, whereas Rhodoplanes and Sporosarcina were only observed in the bulk soil with barley.