Rhizosphere interactions under diverse canola genotypes: a key component in seed nitrogen use efficiency

Belowground
dynamics between soil-plant-microbial interactions impact crop nitrogen use
efficiency (NUE), but current research focuses on aboveground crop management
and breeding, leaving belowground dynamics scarcely studied. Canola (Brassica napus L.) is an agriculturally
relevant crop in Canada, with relatively high N requirement and largely unknown
soil-plant-microbial impact. We
explored canola genotypic and temporal changes in soil N concentrations, root
morphology, and rhizosphere and root microbiomes to identify belowground traits
important to canola NUE. Sixteen canola genotypes were grown on a Dark
Brown Chernozem in Saskatchewan, Canada, in a randomized complete block design with
three blocks. Soil and plant were sampled five times over the growing season
from 32- 81 days after sowing (DAS), and seeds sampled at 81 DAS. Soil moisture
and NO3--N were negatively correlated with canola NUE, with
genotype specific changes possibly related to genetically inherited traits that
controlled soil moisture and N cycling. Root length and surface area were
highest under seed ripening (67 DAS) and root surface area was negatively
correlated with soil NO3--N concentrations. This suggests
that root morphology changed to facilitate greater soil mineral N absorption,
with genetically driven changing controlled by plant inherited traits.
Rhizosphere microbial diversity and community structure were largely predicted
by soil NH4+-N and pH respectively; and root microbial
diversity and community structure predicted by soil moisture and pH, and soil NO3--N
respectively. We determined canola genotypes had a significant influence on
rhizosphere and root microbial assemblages, and plant-microbial interactions likely
shaped these microbiomes, making them distinct between genotypes. This research
helps us understand belowground predictors on canola seed NUE that can benefit
agronomic practices for greater canola productivity and NUE metrics.