Expression of N-cycling genes of root microbiomes provides insights for sustaining oilseed crop production

Citation

Wang, L., Gan, Y., Bainard, L.D., Hamel, C., St-Arnaud, M., Hijri, M. (2020). Expression of N-cycling genes of root microbiomes provides insights for sustaining oilseed crop production. Environmental Microbiology, [online] 22(11), 4545-4556. http://dx.doi.org/10.1111/1462-2920.15161

Plain language summary

Production of crops in agricultural systems heavily relies on inputs of nitrogen. Soil microorganisms that live in the soil and in association with the crops, play a critical role in the cycling of nitrogen in agricultural systems. One potential strategy to improve the sustainability and availability of nitrogen in agricultural systems is through crop diversification. In this study, we assessed the nitrogen cycling gene expression patterns in the root and rhizosphere microbiomes of five oilseed crops (i.e., canola, Ethiopian mustard, oriental mustard, yellow mustard, and camelina) as influenced by a fallow treatment or two different crops grown the previous year (i.e., lentil or wheat). Among the five oilseed plants tested in our study, Ethopian mustard showed the best performance with the highest yield and lowest impact on potential greenhouse gas emissions. Camelina exhibited the opposite trend, with lower yield and greenhouse gas emissions potential. Our results also demonstrated that the preceding crop is an important factor to consider in crop production systems. Lentil, as a preceding crop for oilseed production, could help to increase biological nitrogen fixation, decrease nitrogen fertilization application and reduce the agricultural footprint on the environment. The outcome of our investigation brings a new level of understanding on how crop diversification and rotation sequences are related to nitrogen cycling in annual cropping systems.

Abstract

Agricultural production is dependent on inputs of nitrogen (N) whose cycle relies on soil and crop microbiomes. Crop diversification has increased productivity; however, its impact on the expression of microbial genes involved in N-cycling pathways remains unknown. Here, we assessed N-cycling gene expression patterns in the root and rhizosphere microbiomes of five oilseed crops as influenced by three 2-year crop rotations. The first phase consisted of fallow, lentil or wheat, and the second phase consisted of one of five oilseed crops. Expression of bacterial amoA, nirK and nirS genes showed that the microbiome of Ethiopian mustard had the lowest and that of camelina the highest potential for N loss. A preceding rotation phase of lentil significantly increased the expression of nifH gene by 23% compared with wheat and improved nxrA gene expression by 51% with chemical fallow in the following oilseed crops respectively. Lentil substantially increased biological N2 fixation and reduced denitrification in the following oilseed crops. Our results also revealed that most N-cycling gene transcripts are more abundant in the microbiomes associated with roots than with the rhizosphere. The outcome of our investigation brings a new level of understanding on how crop diversification and rotation sequences are related to N-cycling in annual cropping systems.

Publication date

2020-11-01

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