Abstract Nitrogen (N) accumulation in plant reproductive organs during the post-anthesis growth phase of maize and wheat plays a crucial role in the formation of grain yield and quality. However, little is known about the effect of crop pre-anthesis and post-anthesis N status on ear N accumulation (NAE). This study endeavored to extend the crop N dilution theory already developed for vegetative growth period to determine ear critical N concentration (%NcE) during post-anthesis period of crop growth for analyzing the difference of NAE under various N levels. The data including the weight of dry mass (W) and N concentration of entire plant and ear, post-anthesis plant N uptake (PANU) from soil, grain number (GN), and grain weight (GW) were collected on wheat (two cultivars) and maize (three cultivars) from eight N rates (0–300 kg N ha−1) field experiments. The results revealed that the process of %N dilution exists in ear and it is plausible to extend the concept of %NcE curve till crop post-anthesis period. The %NcE curves as function of ear dry mass (WE) of wheat (%NcE = 2.85WE-0.17) and maize (%NcE = 2.22WE-0.26) were lower than those developed in maize and wheat on whole plant basis. This study revealed that the ear has the potential to diagnose ear N status under different N conditions and the increases in ear N nutrition index (NNIE) during the post-anthesis period with increasing N rate were well synchronized with plant NNI (NNIp) at anthesis. GN and GW of maize and wheat showed significantly positive correlation with NNIp at anthesis and NNIE at maturity under N-limiting treatments, and GN and GW could keep relatively stable under non-N limiting treatments. NNIp and NNIE showed the potential capacity to predict GN and GW of maize and wheat under N limiting condition. Ear critical N accumulation (NAcE) was calculated using ear Nc curve to investigate the differences mechanism of NAE under different N conditions. The difference of NAcE under different N treatments was deduced from the pre-anthesis N status of maize and wheat by determining GN. The ear N deficiency (NDE) between NAcE and NAE was co-regulated by plant pre-anthesis and post-anthesis N status, which in turn have potential to explain the variance of GW at maturity in both crops. The significantly attenuated effect of pre-anthesis N deficiency on ear potential N demand in maize and wheat indicated that the post-anthesis N management must consider the pre-anthesis N status and the corresponding reduction of the post-anthesis N input to prevent N loss under N limiting treatment in both crops. Maize was more dependent on post-anthesis N status while wheat was more reliant on pre-anthesis N status for satisfying ear growth and producing optimum GN owing to the differential values of PANU/NAE in maize and wheat during post-anthesis period. This study provides a new viewpoint on post-anthesis N management of maize and wheat for enhancing N use efficiency and grain yield.

中文翻译：

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使用穗临界氮稀释曲线确定花后氮状态及其对玉米和小麦氮管理的影响

摘要 玉米和小麦花后生长阶段植物生殖器官中的氮（N）积累对粮食产量和品质的形成起着至关重要的作用。然而，关于作物开花前和开花后氮状态对穗氮积累（NAE）的影响知之甚少。本研究试图扩展已经为营养生长期开发的作物氮稀释理论，以确定作物生长后开花期的穗临界氮浓度（%NcE），以分析不同氮水平下 NAE 的差异。数据包括全株和穗的干重（W）和氮浓度，开花后植物从土壤中吸收的氮（PANU），粒数（GN），小麦（两个栽培品种）和玉米（三个栽培品种）从八种施氮量（0-300 kg N ha-1）田间试验中收集粒重（GW）。结果表明，在穗中存在％N稀释的过程，将％NcE曲线的概念扩展到作物开花后时期是合理的。作为小麦 (%NcE = 2.85WE-0.17) 和玉米 (%NcE = 2.22WE-0.26) 穗干质量 (WE) 函数的 %NcE 曲线低于在整株基础上在玉米和小麦中开发的曲线。本研究表明，穗具有诊断不同氮条件下穗氮状态的潜力，开花后穗氮营养指数（NNIE）随着施氮量的增加而增加，与开花时的植物NNI（NNIp）同步。 . 限氮处理下玉米和小麦的GN和GW与开花期NNIp和成熟期NNIE呈显着正相关，且GN和GW在非限N处理下可以保持相对稳定。NNIp 和 NNIE 显示了在 N 限制条件下预测玉米和小麦的 GN 和 GW 的潜在能力。利用穗Nc曲线计算穗临界氮积累量（NAcE），研究NAE在不同施氮条件下的差异机制。通过测定GN，从玉米和小麦开花前的N状态推断不同N处理下NAcE的差异。NAcE 和 NAE 之间的穗氮缺乏 (NDE) 受植物开花前和开花后 N 状态的共同调节，这反过来有可能解释两种作物成熟时 GW 的变化。花前缺氮对玉米和小麦穗位潜在氮需求的显着减弱表明花后氮管理必须考虑花前氮状况和相应减少花后氮输入以防止氮损失两种作物均在氮限制处理下。由于花后时期玉米和小麦的 PANU/NAE 值不同，玉米更依赖于花后氮状态，而小麦更依赖于花前 N 状态来满足穗生长和产生最佳 GN。本研究为玉米和小麦花后氮肥管理提高氮肥利用率和粮食产量提供了新的视角。