Nitrogen fixation and growth of annual Medicago-Sinorhizobium associations at low temperature

Abstract Annual Medicago (medics) represents a great potential of forage production in areas suffering from shortage of livestock feed; however, low winter temperature delays the growth and reduces the nitrogen fixation of medics in Mediterranean dry areas with cool to cold winter. In this context, the identification of medics able to fix nitrogen and produce dry matter at low temperature is necessary to extend the grazing period. The experiment was carried out in controlled growth chambers at two low temperatures 7 and 9 °C, temperature known to limit growth and N 2 fixation of Medics in the field. Three accessions were used, two of Medicago aculeata , accessions 80 (A) and 5099 (B) and one of M. rigidula , accession 716 (R). Each accession was inoculated with Sinorhizobium strains appropriate for nodulation under low temperature ( Sinorhizobium meliloti strain M620 with accession A, strain M508 with B and strain BZI with R). The percentage of nitrogen in the shoots derived from atmosphere was quantified using 15 N dilution technique with barley as reference plant. Results demonstrated that responses of accessions depend on temperature, nitrogen and inoculated strain. Among the accessions tested, M. aculeata 5099 was more adapted to temperature and grew faster than the others at the lowest temperature. Strain M53 performed better with M. rigidula 716 than with M. aculeata 80 and strain M620 with M. aculeata 5099 than with M. aculeata 80 for yield and N nutrition of plants. M508 for M. aculeata 5099 and BZI for M. rigidula 716 leaded to more N fixed per plant. Nitrogen fixation in inoculated treatment of accession M. aculeata × M508 accounted for 88 and 78% of total plant N at 9 and 7 °C versus 49 and 51% for accession M. rigidula × M53. It was concluded that the selection of associations medics × Sinorhizobium is a promising way to improve yield and N 2 fixation at low temperature in areas where N fertilization cannot be possible.