Influence of long-term fertilization on the community structure and diversity of soybean rhizobia in black soil

Abstract

The objectives of this study were to explore the effects of long-term fertilization on the community structure and diversity of soybean rhizobia in black soil. BOX-PCR, IGS-PCR-RFLP and 16S rDNA gene sequencing methods were used to analyze the genetic diversity of the 254 soybean rhizobia isolated from 7 treatments at Heilongjiang Long-term Fertilization Experiment Station. The 7 treatments were as follows: no fertilization (CK), organic manure (OM), chemical nitrogen (N1), double chemical nitrogen (N2), chemical nitrogen-phosphorus (N1P1), double chemical nitrogen-phosphorus (N2P2), chemical nitrogen plus organic manure (N1+OM). Soil properties were measured and analyzed to test for relationships with the community and diversity of soybean rhizobia. All of the tested rhizobia belonged to Bradyrhizobium, of which the majority were closely related to B. japonicum and the others closely to B. liaoningense. BOX-PCR fingerprints 第 1 期 关大伟等: 长期施肥对黑土大豆根瘤菌群体结构和多样性的影响 69 showed that the tested rhizobia could be divided into 15 groups at 70% similarity level. These groups clustered into 3 communities that correspond to no chemical fertilizer treatments (CK, OM), chemical nitrogen fertilizer treatments (N1, N2, N1+OM), and chemical nitrogen-phosphorus treatments (N1P1, N2P2), respectively. Canonical correspondence analysis showed that pH, available N, and available P of the soil were significantly correlated with the community of rhizobia (P=0.002, 0.004, 0.002, respectively). Soybean rhizobia diversity indices varied significantly among fertilization treatments. Shannon-Wiener and species richness index were highest in N2P2 and Simpson index was highest in the OM treatment. The species richness, Shannon-Wiener and Simpson index in N1 and N2 were significantly lower than those in other treatments. The results of path analysis showed that the pH and available P had the greatest direct positive effects on the 3 indices, and that available N indirectly affected the 3 indices through pH. In conclusion, long-term chemical fertilization results in changes to community structure of soybean rhizobia in black soil, and application of chemical nitrogen fertilizer by itself reduces the diversity of soybean rhizobia, while application of nitrogenphosphorus has the opposite effect.