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

Abstract

Summary 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.

What’s past is past, mostly: Brassicaceae host plants mask the feedback from the previous year’s soil history on bacterial communities, except when the Brassicaceae hosts experience drought

“…S1B). For further details of this well-described experiment, its design, and treatments, see Hossain et al (2019), and Wang et al (2020.…”

“…The subsequent Test Phase Brassicaceae plant hosts were subjected to the same standard management practices as the Conditioning Phase, including pre-seed 'burn off', in-season herbicide and fungicide treatments as needed, and fertilized as recommended by soil tests (Table S4; Hossain et al 2019, and Wang et al 2020. Additionally, all Brassicaceae crops, except B. napus, were treated with Assure II mixed with Sure-Mix or Merge surfactant (0.5% v/v) for post-emergence grass control: Liberty (glufosinate, 593 g a.i.…”

“…Conditioning and Test Phase crops were grown and maintained according to standard management practices, as previously described by Hossain et al (2019), Liu et al (2019), and Wang et al (2020). A pre-seed 'burn off' herbicide treatment using glyphosate (Roundup, 900 g acid equivalent per hectare, a. e. ha −1 ) was applied to all plots each year to ensure a clean starting field prior to seeding.…”

“…when 50% of the flowers on the main raceme were in bloom, as described by the Canola Council of Canada (Canola Encyclopedia: Canola Growth Stages, 2017). Four plants from two different locations within each subplot were excavated and pooled together as a composite sample (Hossain et al, 2019;Liu et al, 2019, Wang et al, 2020. In the field, each plant had its rhizosphere soil divided from the root material by gently scraping it off using bleach sterilized utensils into fresh collection trays.…”

“…Recent work on the canola (Brassica napus L. or B. juncea L.) bacterial community has begun to correct this knowledge deficit (Lay et al, 2018;Floch et al, 2020;Taye et al, 2020;Wang et al, 2020;Morales Moreira et al, 2021). Brassicaceae oilseed-based rotations are common throughout the world, as demand for vegetable oil and biofuels increase (Yang et al, 2021).…”