Trait-based drivers of nitrogen responsiveness in winter wheat: the role of phenotypic plasticity of yield, grain protein deviation, and maturity

Abstract

Wheat (Triticum aestivum L.) is a primary source of energy and protein in human nutrition, and improving both grain yield and quality remains a major challenge closely linked to nitrogen (N) supply. However, excessive N fertilization can lead to environmental concerns, including nitrate leaching and greenhouse gas emissions. Since cultivars differ in their response to N availability, a better understanding of how key agronomic traits influence these responses can help improve both yield and environmental outcomes. Among these traits, phenotypic plasticity of grain yield, grain protein deviation (GPD), and maturity have been suggested to influence wheat agronomic response to nitrogen. Phenotypic plasticity reflects the ability of a genotype to modify its performance across environments. We hypothesize that cultivars with greater yield plasticity will exhibit greater yield response to increasing N availability. Grain protein concentration is typically negatively related to yield, but some cultivars deviate from this trend, exhibiting positive or negative GPD. We hypothesize that cultivars with higher GPD will require greater N inputs to maximize grain yield due to increased protein accumulation per unit of grain yield. Finally, cultivar maturity influences the environmental conditions experienced during critical developmental stages. We hypothesize that early-maturing cultivars avoid high-temperature stress during grain filling and therefore show greater responsiveness to N. Our objectives were to validate whether the selected cultivars exhibit the expected levels of yield plasticity, GPD, and maturity, to test whether these trait differences are associated with variation in cultivar responsiveness to N availability, and to explain the physiological basis of cultivar-specific N response. Rainfed field experiments were conducted across 14 environments in Kansas during the 2023–2024 and 2024–2025 growing seasons. A split-plot design evaluated seven N rates (0, 33.6, 67, 101, 135, 168, and 202 kg N ha⁻¹) applied at green-up (Zadoks 30) as whole plots and eight winter wheat cultivars as subplots (SY Wolverine, LCS Julep, WB4401, WB4699, Bob Dole, LCS Chrome, WB4269, and SY Monument) contrasting in yield plasticity, GPD, and maturity. Phenotypic plasticity cultivar selection was validated using reaction norm slopes, GPD was validated as the residual from the relationship between grain protein concentration and grain yield, and maturity was validated through heading date scores. Linear mixed effects models were used to evaluate the effects of plasticity, GPD, maturity, and total N availability on grain yield across environments. A Bayesian quadratic-plateau model was applied to estimate agronomic optimum nitrogen availability (AONA) as a function of grain yield and total N availability, accounting for genotype-specific plasticity. Additionally, linear regressions were used to relate N-based yield response to mean grain filling temperature to assess differences among maturity groups. Cultivars classified as high-plasticity yielded more than their counterparts in five environments, without a yield trade-off (≈0.06 Mg ha⁻¹ more yield), and exhibited slightly higher AONA in ten environments compared to low-plasticity cultivars. High GPD cultivars had greater grain protein concentration in nine environments and did not present greater AONA across environments. Early and late-maturity cultivars did not differ in yield response to N, except for one environment. Overall, our results suggest that phenotypic plasticity of grain yield is the most promising cultivar trait for enhancing nitrogen-responsive yield across environments, when compared with grain protein deviation and maturity.