Abstract
Fertilization is one of the most common agricultural practices to achieve high yield. Although microbes play a critical role in nutrient cycling and organic matter decomposition, knowledge of the long-term responses of the soil bacterial community to organic and inorganic fertilizers is still limited. This study was conducted to evaluate the effects of century-long organic (manure), inorganic (NPK), and no fertilization (control) treatments on soil bacterial community structure under continuous winter wheat (Triticum aestivum L.) cultivation. Fertilization treatments altered the richness, diversity and composition of the soil bacterial community. Compared with the control, manure significantly increased the operational taxonomic units (OTUs), Chao 1 and Shannon indices, and taxonomic groups, while NPK significantly decreased these parameters. Fertilization treatments did not alter the types of dominant phyla but did significantly affect their relative abundances. Acidobacteria and Proteobacteria were the most dominant phyla in all treatments. Manure led to enrichment of most phyla, with a diazotrophic group, Cyanobacteria, being an exception; NPK reduced most phyla, but enriched Chloroflexi; control led to promotion of Cyanobacteria. Soil pH and NO3− were two dominant parameters influencing the bacterial community structure. Soil pH positively correlated with the relative abundances of Proteobacteria and Gemmatimonadetes but negatively correlated with those of Acidobacteria and Chloroflexi; NO3− negatively correlated with the relative abundance of Cyanobacteria, which was 14–52 times higher in control than the fertilized soils. Cyanobacteria, especially M. paludosus and L. appalachiana, could be the key players in maintaining wheat productivity in the century-long unfertilized control.
Highlights
Understanding the soil microbial community structure presents understated challenges, largely due to the complex nature of the system and the enormous abundance and diversity of the community residing within [1]
Bacterial rarefaction curves of the observed operational taxonomic units (OTUs) numbers approached plateaus in all treatments (Figure 1), indicating that the number of 16S rRNA sequences obtained in each treatment was sufficient to reveal detectable genotypes in the community
NPK had a greater impact on soil bacterial community structure, which was evidenced by the lower percentage of bacterial groups shared between NPK and control than the percentage of bacterial groups shared between manure and control at all taxonomic levels (Figure 2), as well as the larger distance in microbial community structure between NPK and control than the distance between manure and control in the non-metric multi-dimensional scaling (NMDS) plot (Figure 3)
Summary
Understanding the soil microbial community structure presents understated challenges, largely due to the complex nature of the system and the enormous abundance and diversity of the community residing within [1]. With as many as one billion bacterial cells and an estimated 8.3 million species in each gram of soil [4], the challenges in revealing and understanding the richness, diversity and composition of soil microbial community are thought-provoking. Numerous studies have demonstrated that healthy soil harbors abundant and diverse microbes, while environmental perturbation and management practices could lead to changes in microbial community structure that impact soil health and productivity [5,6,7,8,9]. Long-term manure application resulted in enrichment of soil organic matter and microbial abundance [5,10,11,12,13], it did not always translate into higher crop yield than soils supplemented with inorganic fertilizers [5,14]
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