Higher diversity of Rhizobium leguminosarum biovar viciae populations in arable soils than in grass soils

The bacterial genetic diversity after long-term arable cultivation was comp ared with that under permanent grassland using replicated paired contrasts, Pea-nodulating Rhizobium leguminosarum populations were sampled from pairs of arable and grass sites at four locations in Yorkshire, United Kingdom, isolates were characterized using both chromosomal (16S-23S ribosomal DNA i nternal transcribed spacer PCR-restriction fragment length polymorphism) an d plasmid (group-specific repC PCR amplification) markers. The diversities of chromosomal types, repC profiles, and combined genotypes were calculated using richness in types (adjusted to equal sample sizes by rarefaction), S hannon-Wiener index, and Simpson's index. The relative differences in diver sity within each pair of sites were similar for all three diversity measure s, Chromosomal types, repC profiles, and combined genotypes were each more diverse in arable soils than in grass soils at two of the four locations. T he other comparisons showed no significant differences. We conclude that rh izobial diversity can be affected by differences between these two manageme nt regimens. Multiple regression analyses indicated that lower diversity wa s associated with high potential nitrogen and phosphate levels or with acid ity.