Significant dose effects of fertilizers on soil diazotrophic diversity, community composition and assembly processes in a long-term fertilization field experiment

In this study, we collected soil samples from a rice paddy field with long-term fertilization (since 1998) in southern China. The fertilization treatment included three doses of mineral fertilizers at same ratio (NPK, 2(NPK), and 3(NPK)), three ratios of mineral fertilizers (N2PK, NP2K, and NPK2), and manure (M) addition. Thus, it provides an excellent platform to investigate the response of diazotrophic communities to different fertilizer doses and ratios. Here, we proposed two hypotheses: 1) long-term fertilization would strongly influence diazotrophic diversity and community composition, and there would be significant dose effect of fertilizer; 2) deterministic processes play a dominant role in diazotrophic community assembly after long-term fertilization.