Hoogmoed Marianne, Sadras Victor O
South Australian Research and Development Institute, Adelaide, SA, Australia.
Front Plant Sci. 2018 Apr 6;9:406. doi: 10.3389/fpls.2018.00406. eCollection 2018.
Nitrogen dilution curves relate a crop's critical nitrogen concentration (%N) to biomass (W) according to the allometric model %N = W . This model has a strong theoretical foundation, and parameters and show little variation for well-watered crops. Here we explore the robustness of this model for water stressed crops. We established experiments to examine the combined effects of water stress, phenology, partitioning of biomass, and water-soluble carbohydrates (WSC), as driven by environment and variety, on the %N of wheat crops. We compared models where %N was plotted against biomass, growth stage and thermal time. The models were similarly scattered. Residuals of the %N - biomass model at anthesis were positively related to biomass, stem:biomass ratio, ΔC and water supply, and negatively related to ear:biomass ratio and concentration of WSC. These are physiologically meaningful associations explaining the scatter of biomass-based dilution curves. Residuals of the thermal time model showed less consistent associations with these variables. The biomass dilution model developed for well-watered crops overestimates nitrogen deficiency of water-stressed crops, and a biomass-based model is conceptually more justified than developmental models. This has implications for diagnostic and modeling. As theory is lagging, a greater degree of empiricism might be useful to capture environmental, chiefly water, and genotype-dependent traits in the determination of critical nitrogen for diagnostic purposes. Sensitivity analysis would help to decide if scaling nitrogen dilution curves for crop water status, and genotype-dependent parameters are needed.
氮稀释曲线根据异速生长模型%N = W 将作物的临界氮浓度（%N）与生物量（W）联系起来。该模型有坚实的理论基础，对于水分充足的作物，参数 和 变化很小。在此，我们探究该模型对水分胁迫作物的稳健性。我们开展实验，研究由环境和品种驱动的水分胁迫、物候、生物量分配以及水溶性碳水化合物（WSC）对小麦作物%N的综合影响。我们比较了将%N与生物量、生长阶段和热时间作图的模型。这些模型的离散程度相似。开花期%N - 生物量模型的残差与生物量、茎：生物量比、ΔC和水分供应呈正相关，与穗：生物量比和WSC浓度呈负相关。这些是具有生理意义的关联，解释了基于生物量的稀释曲线的离散情况。热时间模型的残差与这些变量的关联不太一致。为水分充足的作物开发的生物量稀释模型高估了水分胁迫作物的氮素缺乏情况，并且基于生物量的模型在概念上比发育模型更合理。这对诊断和建模有影响。由于理论滞后，在确定诊断用临界氮时，更大程度的经验主义可能有助于捕捉环境（主要是水分）和基因型依赖的性状。敏感性分析将有助于决定是否需要针对作物水分状况缩放氮稀释曲线以及是否需要基因型依赖参数。
