Effect of inoculating aciduric rhizobia on rhizospheric microecology of the leguminous hosts in acid soil

ObjectivesExisting studies proved that inoculating aciduric rhizobium to the rhizosphere could improve the ability of leguminous host to survive in acid soils. In this paper, the PLFA and other methods were used to study the effect of inoculating rhizobium on rhizospheric soil in order to understand the mechanism of the improvement.

MethodsA pot experiment was conducted using acid soil of pH 4.8. Aciduric kudzu rhizobium strains 068, 389, and 390 and alfalfa rhizobium strains 91522, 91512 and 91532 were inoculated to the corresponding leguminous host plants. Rhizospheric soil samples were collected on the 30^th, 60^th, 90^th, 120^th and 150^th day after the inoculation. Soil nutrients, culturable microorganisms and microbial community diversity were measured in the samples.

Results1) Inoculating acid-tolerant rhizobia improved rhizospheric soil pH from 4.8 to 6.0, significantly improved the contents of soil organic matter, NH₄⁺-N, NO₃^–-N, available P and available K in rhizosphere (P < 0.05). The peak contents of soil available P, NH₄⁺-N, NO₃^–-N and organic matter in the inoculating treatments were at the 120^th d, they were 23.16–48.68 mg/kg, 61.21–81.96 mg/kg, 65.05–86.38 mg/kg and 11.85–12.87 g/kg, with increase of 24.8%–162.4%, 16.6%–56.2%, 145.4%–225.8%, 1.4%–10.1%, comparing with those of the control. 2) The population of soil microorganisms increased significantly during the cultural period (P < 0.05). The peak microbial community appeared at the 120^th d samples, the culturable bacteria, fungi and actinomycetes in the treatments were 48.00 × 10⁷–133.3 × 10⁷ cfu/g, 20.11 × 10⁴–155.9 × 10⁴ cfu/g, and 3.21 × 10⁴–9.59 × 10⁴ cfu/g, increased by 61.5% to 348.4%, 3.4% to 441.7%, 18.9% to 255.2% respectively, comparing with those of the control. 3) PLFA analysis showed that although the types of microbial PLFAs in rhizospheric soil were not significantly different between the inoculation treatments and the control, the ratio of heterogeneous PLFA/anti heterogeneous PLFA was reduced significantly, showing effective reduction of acid stress on rhizosphere microorganisms.

ConclusionsInoculating the related aciduric rhizobium strains to the leguminous hosts planted in acid soil could improve the rhizospheric soil pH, organic matter, and available nutrients significantly, and hence improve the ability of rhizopheric micro-organisms to deal with soil acidity stress.