Dry matter partitioning and canopy traits in wheat and barley under varying N supply

• DM partitioning between leaves and stems in wheat and barley follow a common allometric function.
• The more rapid spring growth of barley compared to wheat may be attributed to the higher leaf DM at a given stem DM than wheat.
• In wheat, N supply decreased the stem DM proportion of the total above-ground biomass.
• During stem elongation, SLA positively correlated with GAI in both crops presumably due to mutual shading.

The prediction of the allocation of carbon and nitrogen into the different organs, e.g., leaves, stems, roots of a growing plant is a pivotal part of mechanistic growth models. Based on 2 year (winter wheat) and 3 year (winter barley) field trials with different N treatments (0–240 kg N ha−1), the objectives of this study were to verify currently used parameters for (i) specific leaf area, and (ii) allometric relationships between leaf and stem dry matter (DM).Green area index (GAI) differed between years and increased with N supply rate. The course of the specific leaf area (SLA) within the growth period after winter showed a large variation between the years as well as between the N treatments. During stem elongation, SLA positively correlated with GAI in both crops, indicating that leaves became thinner when the canopy was denser. The allometric relationships between stem and leaf dry DM clearly varied with the growth stages. Stem DM of wheat showed a higher proportion of the total above-ground biomass compared to barley. The effect of N fertilization on allometry remained small during early growth stages in barley, whereas in wheat, an increased N supply significantly decreased the proportion of stem DM.Our results suggest similar GAI and SLA patterns for wheat and barley, albeit depending on the N supply. Especially, using a constant SLA in plant growth models seems to be not suitable.