Effect of acid soil chemical properties on nodulation and competition ofRhizobium trifolii

Abstract

Abstract Soils in the Appalachian region are acidic and many have chemical properties which may inhibit the initiation of clover‐Rhizobium leguminosarum biovar trifolii symbiosis. The influence of soil properties on nodulation by, and competition between, an introduced strain (162X95) and a naturalized strain (WV22) of Rhizobium trifolii were studied in limed and unlimed portions of 10 subsoil horizons. Rhizobial strains were inoculated alone or in a 1:1 mixture in liquid form on germinating subterranean clover (Trifolium subterraneum L.). Nodulation by both strains was inhibited in soils with a combination of toxic properties: pH (1:1 H2O) 4.37 to 4.46, Ca saturation 1.1 to 9.2 %, and Al saturation 54.2 to 82.6 %. In the competition experiment strain 162X95 was detected in nodules by enzyme‐linked immunosorbent assay (ELISA) using a monoclonal antibody. Soil and soil solution chemical properties which were correlated with percent nodule occupancy by strain 162X95 were soil pH (1:1 H2O), soil solution pH, Al saturation, exchangeable Al, soil solution total Al, and soil solution reactive Al (as measured by 8‐hydroxyquinoline) (p ≤0.05). Soil pH gave the best estimate of nodule occupancy by strain 162X95 using a second order polynomial: % nodule occupancy = ‐481.40 + 176.05 soil pH ‐ 14.28 soil pH2 (r2 = 0.62**).