Dominant associations of Ensifer medicae-Medicage polymorpha and Ensifer meliloti-Medicago lupulina in farmland and natural ecosystem

Abstract

Aims The nitrogen-fixing rhizobia associated with Medicago polymorpha and M. lupulina in Yunnan, China have been poorly documented. This study aims to analyze the diversity of rhizobia isolated from these two Medicago species and investigate the impact of abiotic (soil properties) and biotic (plant hosts) factors on Medicago-associated rhizobia in this region. Methods 91 rhizobial isolates were characterized by RFLP of 16S rDNA and 16S–23S IGS, BOX-PCR fingerprinting, nodulation assays and phylogeny analyses based on housekeeping and symbiosis genes. The genetic diversity of the rhizobial isolates was assessed by the BOX AIR pattern and Shannon index. Additionally, the correlation of soil properties and rhizobial distribution was determined by the constrained analysis of principle coordinates (CAP) based on Bray-Curtis distance of presence/absence (PA) transformed species data. Results All the tested strains fell in the genus Ensifer and divided into two species, E. medicae and E. meliloti. Both host plants and soil properties contributed to the rhizobial diversity. For either E. meliloti or E. medicae, isolates from native host plants tended to be more genetically diverse than those of the same species from non-native hosts. The soil edaphic factor analysis elucidated that nitrogen, organic matter as well as Ca2+ and Na+ are the key factors to shape the biogeographical distribution of rhizobia. Conclusions This study evidenced the microsymbiont preference of M. polymorpha to E. medicae and M. lupulina to E. meliloti, but also revealed the considerable impacts of both plant hosts and soil factors on the rhizobial diversity and biodistribution.