氮素水平影响直播冬油菜群体消减的机制及环境胁迫对其叠加效应

Quality optimization of population is the foundation of high and stable yield of winter oilseed rape. Nitrogen (N) nutrition is the key factor impacted population density of winter oilseed rape. However, it is still unclear of the response of population decline dynamics on different N levels and the related mechanism of aggraviation of population reduction under N deficiency. To find out the yield reduction during different growth period caused by individual decline under unbalanced N supply and environment stress, our study would utilize field experiments, environment stress simulated experiments, and the verification-stress dissolution testing experiments. Our research contents would include the N nutrient dynamic of winter oilseed rape, population density decline dynamics, photosynthesis and plant physiology characters, rapeseed yield and yield composition characters. By using the inter-disciplinary approach of plant nutrition science, agronomic science, plant physiology science, data analysis and spectroscopy technology, we aim to (i) discuss the interaction among the above research contents, (ii) find out the character and dynamics of population density decline in winter oilseed rape, (iii) reveal the physiology mechanism and the impacts of N levels and its interaction with environment stress on the population density decline in winter oilseed rape, (iv) establish the critical threshold N value of individual death of oilseed rape. Our study would enrich nutrient management theory under environment stress for winter oilseed rape, and provide technology support of N controlling policy for direct-seeding winter oilseed rape with controllable population to against the environment stress.

群体质量优化是直播冬油菜高产稳产的基础，氮素营养是影响群体密度的关键因素，但不同氮素供应条件下油菜全生育过程的群体消减特征与缺氮增加群体衰亡的生理机制却不清楚。本研究拟从缺氮及阶段性逆境加剧直播冬油菜个体死亡导致收获群体消减过大而减产的生产问题出发，采用不同生态区田间试验、逆境模拟试验、结果验证与逆境解除田间反演试验相结合的方法，研究直播冬油菜氮素的营养动态、群体密度消减动态、光合和逆境生理、产量与构成因素等；综合利用植物营养学、农学、植物生理学、信息和光谱学多学科交叉的手段，深入探讨各研究内容间的相互作用关系，阐明直播冬油菜在不同生态环境条件下群体密度消减的过程和规律，重点揭示氮素及其与环境胁迫的交互作用对直播冬油菜群体消减的影响及其生理机制，并建立直播油菜个体死亡发生的临界氮素浓度阈值。研究结果将丰富逆境养分调控的基础理论，为直播冬油菜可控群体设计的抗逆减灾氮素调控提供理论和技术支撑。

我国直播油菜发展迅速，直播油菜适宜的收获密度是决定产量的重要因子之一，同时又是一个不确定因子。我国直播冬油菜收获密度往往不及播种密度的三分之一，造成这一现象的原因与氮素养分供应状况密切相关，同时受油菜生育过程中的环境胁迫影响。为了明确氮养分状况对直播冬油菜群体密度消减过程和规律的影响，揭示氮素与关键环境胁迫因素的交互作用对直播油菜群体消减影响生理机制，采用不同生态区田间试验和光合生理研究方法，研究了直播冬油菜的氮素营养动态、群体密度消减动态、光合和逆境生理、产量与构成因素，探讨了各研究内容间的相互作用关系，得到了如下主要研究结果。（1）氮养分的丰缺程度显著影响出苗数，在播种后2个月内，氮养分缺乏与养分充足处理均出现密度降低现象，降低的群体密度分别占各自全生育期内总消亡数的38.8%和50.3%；在播种后60-150天内，氮素缺乏和供应充足的群体密度降低分别占全生育期总消亡数的23.1%和31.4%；在进入盛花期后，氮素缺乏和供应充足的群体密度下降分别占全生育期内总消亡数的39.7%和16.7%。（2）冬油菜整个生育期内可能遭遇的主要环境胁迫为：播种后2个月内易遭遇干旱和/或渍害、播种后60-100天内易遭遇干旱和冷害（冻害）、进行抽苔期后（播种后130天）杂草及种内竞争、至盛花期后高温逼熟和早衰。与氮素充足供应相比，氮的缺乏会加剧逆境胁迫对成苗的负面影响。（3）氮素缺乏加剧冬油菜在全生育阶段的死亡与体内氮素浓度低及个体生物量小密切相关。氮素在光合器官（羧化系统、生物力能学组分和捕光系统）分配的差异是影响冬油菜苗期叶片光合氮利用效率及物质积累的重要原因。（4）油菜苗期和花期植株临界氮素浓度分别为3.97%和2.72%。（5）光谱诊断方法是快速精准诊断确定油菜植株氮素营养状况和群体密度的有效工具。研究结果为直播冬油菜可控群体设计的抗逆减灾氮素调控提供了理论和技术支撑，相关氮素营养调控与精量播种技术已经在油菜产业生产中应用。