Genetic structure and activity of the nitrate-reducers community in the rhizosphere of different cultivars of maize

In this study, the structure and activity of the nitrate-reducers community were analysed in bulk and rhizospheric soils from three different non-isogenic transgenic cultivars of maize (two Bacillus thuringiensis maize and one glyphosate-resistant maize) in a long-term field experiment. DNA was extracted from both rhizospheric and non-rhizospheric soil sampled at three different development stages of the plants and amplified using primers targeting the genes encoding the␣membrane-bound nitrate reductase (narG). Nitrate-reducers community structure was analysed by generating fingerprints and sequencing of narG clone libraries. The season seems to be the most important factor controlling the genetic structure of the nitrate-reducers community. Smaller differences in the narG fingerprints were also observed between bulk and rhizospheric soils suggesting that presence of maize roots was the second important factor affecting the structure of this functional community. Similarly, a rhizosphere effect was observed on the nitrate reductase activity with a 2–3-fold increased in the rhizospheric soil compared to the non-rhizospheric soil. However, for both structure and activity of the nitrate-reducers community, no effect of the maize cultivar was observed. This study suggests that the effect of the cultivar and/or of the agricultural practices associated with the cultivation of transgenic maize is not significant compared to the effect of other environmental factors.