Dynamic Response of Ammonia-Oxidizers to Four Fertilization Regimes across a Wheat-Rice Rotation System.

Jichen Wang,Geoff Rhodes,Lei Ni,Yang Song,Qiwei Huang,Qirong Shen,Jing Li

doi:10.3389/fmicb.2017.00630

Abstract

Ammonia oxidation by microorganisms is a rate-limiting step of the nitrification process and determines the efficiency of fertilizer utilized by crops. Little is known about the dynamic response of ammonia-oxidizers to different fertilization regimes in a wheat-rice rotation system. Here, we examined ammonia-oxidizing bacteria (AOB) and archaea (AOA) communities across eight representative stages of wheat and rice growth and under four fertilization regimes: no nitrogen fertilization (NNF), chemical fertilization (CF), organic-inorganic mixed fertilizer (OIMF) and organic fertilization (OF). The abundance and composition of ammonia oxidizers were analyzed using quantitative PCR (qPCR) and terminal restriction fragment length polymorphism (T-RFLP) of their amoA genes. Results showed that fertilization but not plant growth stages was the best predictor of soil AOB community abundance and composition. Soils fertilized with more urea-N had higher AOB abundance, while organic-N input showed little effect on AOB abundance. 109 bp T-RF (Nitrosospira Cluster 3b) and 280 bp T-RF (Nitrosospira Cluster 3c) dominated the AOB communities with opposing responses to fertilization regimes. Although the abundance and composition of the AOA community was significantly impacted by fertilization and plant growth stage, it differed from the AOB community in that there was no particular trend. In addition, across the whole wheat-rice rotation stages, results of multiple stepwise linear regression revealed that AOB played a more important role in ammonia oxidizing process than AOA. This study provided insight into the dynamic effects of fertilization strategies on the abundance and composition of ammonia-oxidizers communities, and also offered insights into the potential of managing nitrogen for sustainable agricultural productivity with respect to soil ammonia-oxidizers.

Highlights

Ammonia oxidation by microorganisms is the first step of nitrification
By using a multiple stepwise linear regression, bacterial amoA gene abundance was the best predictor for soil potential nitrification rate (PNR) explaining 48.7% (P < 0.001) of the PNR variation, whereas archaeal amoA gene abundance only accounted for 6.7% of the variation; soil properties of soil organic carbon content (SOC), NH+4, NO−3, soil moisture and soil pH played significant (P < 0.05) roles in the variation of PNR, which accounted for 11.5, 7.9, 1.6, 1.3, and 1.9%, respectively
The results showed that soil electrical conductivity (EC), pH, SOC, AK, total N content (TN), NO−3, and NH+4 contents were the important (P < 0.05) soil properties influencing the ammonia-oxidizing bacteria (AOB) community composition, and the AOA composition were driven by all the soil properties

Summary

Introduction

Ammonia oxidation by microorganisms is the first step of nitrification. It is a rate-limiting step of the nitrification process and influences the efficiency of fertilizer utilized by crops (Kowalchuk and Stephen, 2001). Ammoniaoxidizing bacteria (AOB) of the β- and γ- subclasses of Proteobacteria were thought to be the exclusively contributor to this key process. This view was challenged by the discovery of the function and transcription of the amoA gene in archaeal ammonia-oxidizer (AOA) (Könneke et al, 2005; Treusch et al, 2005; Prosser and Nicol, 2008). AOA might play a dominant role in the nitrification process in soils with low ammonia content, high acidity, or low oxygen conditions (Zhang et al, 2010, 2012), while AOB may contribute more to the nitrification process in neutral of alkaline soils, or in soils with a higher ammonia content (Shen et al, 2012; Ke et al, 2013)

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Results

Discussion

Conclusion