Long-term phosphorus application to a maize monoculture influences the soil microbial community and its feedback effects on maize seedling biomass

Both indigenous arbuscular mycorrhizal (AM) fungi and phosphate solubilizing bacteria (PSB) are involved in phosphorus (P) mobilization and turnover in agroecosystems. Understanding the diversity and community structure of AM fungi and PSB is important for potentially optimizing their role in mining P for sustainable agriculture. Yet the characteristics of both AM fungi and PSB in response to P input, in particular the influence of different indigenous microbial communities on plant growth has been little studied. Here, we collected soil samples from the top 20 cm of the profile of a soil receiving three fertilizer P rates, comprising nil, optimal (44kgPha(-1)) and excessive (131 kgPha(-1)) P to evaluate the AM fungal community structure and abundance of relevant PSB groups at three sampling times (June, July and September) using 454 pyrosequencing and quantitative-PCR (q-PCR), respectively. In addition, a pot experiment was conducted to investigate the feedback effects of different fractions of indigenous soil microbes on maize seedling growth. The results showed that overall sampling time had a greater impact than P application rate on the community structure of AM fungi and PSB abundance. At each sampling time the AM fungal communities were significantly affected by the fertilizer P rate. The overall abundance of soil microbes and selected taxa were slightly affected by sampling time but not by fertilizer P. Shoot biomass and P nutrition were significantly affected by the microbial community fraction but not by the fertilizer P rate. Changes in AM fungal communities did not lead to significant differences in maize growth. However, long-term absence of P inputs tended to build up microbial communities which greatly suppressed maize growth. Shoot biomass showed a mean decline of 24.4% when grown in inoculated soil compared to sterilized soil. Our results indicate that current P management has not led to negative influences on soil microbial communities. Evidence highlights the need to understand the interactions between plants and microbiome in mining P in order to make maximum use of the most effective indigenous soil microbes for sustainable agriculture.