Negative impacts of excessive nitrogen fertilization on the abundance and diversity of diazotrophs in black soil with monocropping maize

Abstract

Background: Excessive nitrogen fertilizer input and low nitrogen fertilizer use efficiency in maize in China are serious ecological and economic problems, which might affect the procedures in the nitrogen cycle. To reveal the effects of long-term excessive nitrogen fertilization on diazotrophs in maize rhizosphere and bulk soil, we performed a long-term (five-year) N-input experiment (N rates from 0 to 300 kg N ha -1 ) in black soil maize in northeast China. The effect of N fertilizer application rates on the abundance, structure and compositions of diazotrophic community in both the bulk soil and rhizosphere of maize were investigated by Real-time quantitative PCR and high-throughput sequencing, and a structural equation model was constructed based on this study.Results: 1) Excessive N fertilization significantly reduced the abundance and diversity of diazotrophs. 2) The accumulation of Sphingobium was correlated positively with soil nitrate concentration and soil EC, and negatively with soil pH. The contrast correlation was found in Burkholderia . 3) Diazotrophs were enriched in maize rhizosphere, but the diversity and compositions of diazotrophic community were less affected by maize rhizosphere effect. 4) The enriched Bradyrhizobium and Methylobacterium in maize rhizosphere showed a significant positive correlation with of maize plant biomass. Conclusions: Our results suggest that through affecting soil pH, nitrate and EC values, long-term excessive N input increase Sphingobium accumulation and reduce the abundance of beneficial diazotrophs such as Bradyrhizobium and Burkholderia ，which contribute to the decreased nitrogen use efficiency.

Bacterial endophytes: Molecular interactions with their hosts

“…A series of genes/gene clusters in Bacillus velezensis F21 associated with plant growth promotion including siderophore synthesis, production of growth-promoting, volatile organic compounds and growth-promoting hormones, and nutrition utilization was identified [20,123,247]. The siderophore bacillibactin favors plant growth and contributes to protect plants against pathogenic infections by complexing iron and making iron less available to pathogens.…”

Impacts of maize hybrids with different nitrogen use efficiency on root‐associated microbiota based on distinct rhizosphere soil metabolites

“…Beneficial root‐associated microbes have positive effects on plant growth through enhancing nutrient availability, phytohormone biosynthesis, and protecting plants from biotic or abiotic stresses (Bakker et al, 2018; Hu et al, 2022; Xiong & Lu, 2022). Studies have shown that root‐associated microbiota are affected by biotic and abiotic factors, such as plant genotype, developmental stage, and nutrient status (Bakker et al, 2018; Bulgarelli et al, 2013; Chen, Hao, et al, 2021; Chen, Li, et al, 2021). However, the underlying relationship between root‐associated microbiota and maize NUE in the context of rhizosphere metabolites is largely unclear.…”

“…In modern breeding, maize is typically grown under high N input conditions (Moose & Below, 2009; Wissuwa et al, 2009), which could result in the loss of some beneficial plant–microbe interactions relative to nutrient acquisition in maize during long‐term screening (Chen, Li, et al, 2021; Wissuwa et al, 2009). A previous study showed that rhizosphere microbiota recruited by recent germplasm have fewer functions in N provision and more functions in N losses (Favela et al, 2021).…”