Root system architecture of contrasted maize landraces under nitrogen deficit

Details

Supervisors

Draye, Xavier ; Guyot, Josephine

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en sciences agronomiques, à finalité spécialisée

Abstract

enNitrogen (N) is a critical limiting nutrient in crop production, and improving nitrogen use efficiency (NUE) in maize represents a major challenge for sustainable agriculture. Root system architecture (RSA) plays a central role in N acquisition, as it determines the plant's capacity to explore the soil and access spatially heterogeneous N resources. This study investigated how contrasting N conditions affect root architectural and biomass-related traits in a panel of 13 maize varieties, including eight European landraces classified as high or low NUE, and five hybrid varieties. Plants were grown on the aeroponic RootPhAir platform under two N treatments severe low N (0.5 mM) and moderate low N (3 mM) over a three-week period. Root traits including seminal root (SR) angle, lateral root (LR) angle, LR density, elongation rates, and duration of primordium development were measured using dedicated image analysis software. Biomass and physiological traits were assessed at harvest. N limitation strongly reduced shoot and root biomass, with shoot dry weight decreasing by approximately 60% and root dry weight by 35%, resulting in a marked increase in the root-to-shoot ratio. In contrast, most root architectural traits showed limited plastic responses to N availability. LR density and elongation rate were reduced under severe N limitation, suggesting resource conservation rather than enhanced soil exploration. No consistent effect of N treatment was observed on SR elongation rate, possibly due to confounding effects of a water stress event during the second replicate. Multivariate analyses revealed coordinated plastic responses among biomass traits, and a negative association between LR density plasticity and root elongation plasticity, suggesting a resource allocation trade-off. Contrary to initial expectations, high- and low-NUE landraces could not be clearly distinguished based on early root traits, indicating that NUE differences may manifest at later developmental stages or depend on physiological mechanisms not captured here. Overall, the results suggest that adaptation to N limitation in young maize plants involves coordinated adjustments across multiple traits rather than strong modifications of individual architectural characteristics, and that genotypic variation in plasticity is more prominent within predefined NUE groups than between them.