Abstract
Excessive nitrogen (N) fertilizer input to agroecosystem fundamentally alters soil microbial properties and subsequent their ecofunctions such as carbon (C) sequestration and nutrient cycling in soil. However, between soils, the rhizobacterial community diversity and structure in response to N addition is not well understood, which is important to make proper N fertilization strategies to alleviate the negative impact of N addition on soil organic C and soil quality and maintain plant health in soils. Thus, a rhizo-box experiment was conducted with soybean grown in two soils, i.e. soil organic C (SOC)-poor and SOC-rich soil, supplied with three N rates in a range from 0 to 100 mg N kg−1. The rhizospheric soil was collected 50 days after sowing and MiSeq sequencing was deployed to analyze the rhizobacterial community structure. The results showed that increasing N addition significantly decreased the number of phylotype of rhizobacteria by 12.3%, and decreased Shannon index from 5.98 to 5.36 irrespective of soils. Compared to the SOC-rich soil, the increases in abundances of Aquincola affiliated to Proteobacteria, and Streptomyces affiliated to Actinobacteria were greater in the SOC-poor soil in response to N addition. An opposite trend was observed for Ramlibacter belong to Proteobacteria. These results suggest that N addition reduced the rhizobacterial diversity and its influence on rhizobacterial community structure was soil-specific.
Highlights
Worldwide, large amounts of nitrogen (N) are being applied into farmland ecosystems with frequently more than 100 kg N ha−1 1
Since biogeographical distribution of bacterial communities varies in the Mollisol region, and this variation is greatly attributed to the soil organic C (SOC) distribution along the latitude of this region[13], we expected that the impact of N addition on bacterial community would be different in Mollisols differing in SOC
Nitrogen addition resulted in the increase in NH4+ concentration in the rhizosphere of soybean grown in both soils (Table 1)
Summary
Large amounts of nitrogen (N) are being applied into farmland ecosystems with frequently more than 100 kg N ha−1 1. The mean N application rate per crop has reached 155 kg N ha−1 with the total N input of 24 Mt year−1, which accounts for about 30% of the world’s total consumption[2,3]. Specifying the bacterial response to N addition in the rhizosphere of crops is important for developing N-strategies in farming soils that consider microbial ecoservices such as soil carbon (C) dynamics and plant health. This study aimed at the comparison of rhizobacterial diversity and structure in response to N addition between two major farming Mollisols in Northest China. This soil region is the world’s fourth largest contiguous bodies of Mollisols which are fertile for crop production[12]. Since biogeographical distribution of bacterial communities varies in the Mollisol region, and this variation is greatly attributed to the soil organic C (SOC) distribution along the latitude of this region[13], we expected that the impact of N addition on bacterial community would be different in Mollisols differing in SOC
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