Understanding canola root morphology and microbiomes in response to soil phosphorus fertility

Project Summary

Overview

Canola plant roots assemble or recruit a community of microorganisms to help with nutrient uptake, and that community – the root-associated microbiome – changes depending on what the plant needs.

This study looked at the root-associated microbiome in soils with low and high levels of phosphorus (P). It aimed to determine how canola root architecture and the root-associated microbiome impact the plant’s ability to forage for phosphorus. This research combined field and laboratory experiments to see how soil phosphorus fertility affects canola roots and their microbiome in order to develop strategies for overcoming phosphorus deficiency in canola production.

Researchers ran field studies at the Agriculture and Agri-Food Canada research farm at Scott, Saskatchewan and at the Conservation Learning Centre at Prince Albert, Saskatchewan. They also ran growth room experiments using Scott soil as a medium. Canola growing in narrow clear “rhizoboxes” allowed them to observe root growth patterns in the soil. Background levels of soil available P were considered minimally sufficient (with around 25 ppm of P).

Results and conclusions

In general, as researchers added P to canola growing in controlled-condition rhizoboxes, microorganism diversity in the microbiome went down. Because sufficient P is there, plant roots perhaps don’t recruit as much variety in the bacteria and fungi they associate with.

Interestingly, rhizobox studies showed that early canola growth was higher in plants where half of the root system was exposed to fertilized soil and the other half to unfertilized soil. Each half of the root system had a distinct root microbiome indicating that the root-microbiome system may confer the best advantage in soil where P availability is variable – as would be found in most field soils. This also supports the common practice of putting starter P in the seed row to give the crop an early jump and then letting lateral roots gather P from the soil.

Researchers also observed that the abundance of fungal pathogens that cause blackleg and sclerotinia were correlated with the no-P application. The no-P application appeared to make plants more susceptible to these pathogens, although disease symptoms were not assessed.

Overall, the plant microbiome response to P was inconsistent in the field, reflecting the complex factors contributing to soil P availability and canola uptake. Higher baseline levels of P may have been a factor. Expected associations may not occur when P is not the most limiting factor in plant growth and the root-associated microbiome.

Related content

Learn more about the canola microbiome by listening to this Canola Watch Podcast: Ep. 92 – Plants need their microbiome.