engleski

Influence of different Sinorhizobium meliloti inocula on abundance of genes involved in nitrogen transformations in the rhizosphere of alfalfa (Medicago sativa L.)

The inoculation of seeds with Rhizobium is known to increase nodulation, nitrogen uptake, growth and yield response of crop plants. However the effective symbiosis does not depend only on the capacity to fix elemental nitrogen from the air, but also on the internal nitrogen turnover in root – rhizosphere complex. In the present study, a greenhouse experiment was set up to test the influence of inoculation with two indigenous Sinorhizobium meliloti strains, with different efficiency in terms of plant growth promotion, on nitrogen turnover processes in the rhizosphere during the growth of alfalfa. Quantification of six target genes (bacterial amoA, nirK, nirS, nosZ, nifH and archaeal amoA) was performed by real-time PCR in rhizosphere samples that have been taken before nodules formation, at the bud development stage as well as at the late flowering stage. The results clearly demonstrate that efficiency of rhizobial inocula is highly related to abundance of nifH genes in the late flowering phase of alfalfa. Low copy numbers of genes involved in ammonia oxidation as well as in denitrification at the same plant development stage indicate that the formed ammonia by the rhizobia at this time point is mostly used by the plant and is not transferred to the rhizosphere.

S.meliloti; alfalfa; nitrogen fixation; N cycle; denitrification; nitrification

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