Differences in root traits influence the amount of C rhizodeposited in soil across five canola (Brassica napus L.) lines under two nitrogen fertilizer rates.

Root traits play a key role in determining how much and where rhizodeposits are transferred to soil, which in turn can contribute to the formation and stabilization of soil organic matter (SOM). Studying these traits in canola is particularly relevant because it is one of the world’s most important oilseed crops and a leading crop in Canada. To examine how root traits influence carbon (C) transfer  to SOM, this greenhouse study used 13CO₂ pulse-labeling approach to quantify rhizodeposit C in soil across five canola lines with contrasting root morphologies at low N (60 kg N ha⁻¹) and recommended N (120 kg N ha⁻¹) rates. At harvest, roots were collected and scanned to determine the root surface area and total root length. The total C and N and 13C enrichment in soil and root samples was quantified using EA-IRMS.  Long root lines (NAM 10 and NAM 39), had greater root biomass, total root length, and 13C-rhizodeposition than short root lines (NAM 1 and NAM 12) and NAM 10 exhibited significantly higher rhizodeposition, releasing approximately 30% more C than the other four lines. The recommended N rate increased root biomass and overall soil rhizodeposition. These results indicate that genotypic variation in root system size is a key driver of rhizodeposition, while N supply at the recommended rate may enhance this effect by promoting root growth. Our results also indicate that for canola, root biomass was a better predictor of rhizodeposition in soil than root surface area or total root length.