Diazotrophic communities shift with organic fertilizer substitution and growth stages in tomato field soil

Abstract

Applying organic fertilizers can improve soil quality, promote the growth of nitrogen-fixing bacteria, and reduce dependence on chemical fertilizers. Here we investigated the effects of different organic fertilization treatments (organic fertilizer substituting 20 %, 40 % or 60 % of chemical nitrogen fertilizer and increased organic fertilizers at the rate of 45, 90 and 135 t ha⁻¹) on soil diazotrophic communities at different growth stages (seedling, flowering, fruiting and maturity) of tomato. The results indicated that both organic fertilizer treatments and growth stages significantly affected the diversity and compositions of soil diazotrophic community, and organic fertilizer had a greater effect than growth stages. Compared to chemical fertilizer, the organic substitution overall increased the relative abundances of Bradyrhizobium, Skermanella, Paenibacillus and Azospirillum. Increased organic fertilizers raised the relative abundances of Methylocaldum and Hyphomicrobium. Organic substitution treatments increased the network complexity and microbial interactions of diazotrophic communities, but increased organic fertilizers reduced the alpha diversity and network complexity. Organic fertilizer affected the diazotrophic community structure and key taxa mainly through altering soil available nutrients and pH. The key diazotrophic genera varied at different growth stages. Azospirilum and Skermanella played an important role in diazotrophic community assembly in the flowering stage, additionally, Sinorhizobium, Paenibacillus, and Zoogloea were important in the fruiting stage. This study provided a deep understanding of the roles of organic fertilizer in regulating soil diazotrophic communities in tomato field.