玉米穗位叶衰老进程及其适宜指示性指标研究

【目的】 探寻可精确指示玉米穗位叶衰老进程的优良方法及适宜性指标,明确玉米穗位叶衰老进程,为玉米精确高效栽培技术发展提供理论参考。【方法】 于2020年春、夏两季在江苏大丰（33°12′ N,120°28′ E）稻麦原种场开展田间试验,以苏玉29（SY29）为材料,基于不同施氮量（0、67.5、136.5、205.5、274.5、343.5 kg N·hm^-2）构建6个叶氮浓度差异群体（N1—N6）。采用Logistic模型对吐丝后12种与玉米穗位叶衰老相关的形态及生理指标的变化动态进行拟合,对比分析不同衰老相关指标指示衰老进程的精准性。【结果】 Logistic公式y=(a-d)/(1+(x/c)^b)+d对12种叶衰老相关指标变化动态的拟合趋势、拟合度R²整体优于前人所用Logistic公式y=a/(1+e^-b(x-c))。基于多指标分析,春、夏玉米穗位叶衰老启动分别发生在吐丝后18.8—29.1（$bar{x}$=25.8）d、17.5—28.2（$bar{x}$=23.9）d,快速衰老发生在吐丝后30.5—37.9（$bar{x}$=34.4）d、28.0—35.7（$bar{x}$=31.8）d,衰老终止发生在吐丝后40.6—54.1（$bar{x}$=45.9）d、38.3—47.0（$bar{x}$=42.1）d。春、夏玉米由吐丝至衰老启动的25.8 d、23.9 d内有效积温分别为392.9℃和477.6℃;春、夏玉米由衰老启动至衰老终止的20.1 d、18.2 d内有效积温分别为360.0℃和284.0℃。基于指标分类分析,相同衰老阶段内,生理指标所指示的衰老特征时间的正态分布σ值大于形态指标,春、夏玉米结果一致。丙二醛（MDA）、总叶绿素、叶绿素a、果糖、葡萄糖含量及蒸腾速率（T_r）所指示衰老特征时间的变异系数（CV）均小于5%;MDA、总叶绿素、果糖、葡萄糖含量及净光合速率（P_n）所指示衰老特征时间与各阶段时间均数的均方根误差（RMSE）均小于2。【结论】 Logistic公式y=(a-d)/(1+(x/c)^b)+d可作为准确拟合叶衰老指标动态变化的数学工具。春、夏玉米穗位叶分别在吐丝后26 d、24 d左右开始衰老,于34 d、32 d左右衰老速度达到峰值,于46 d、42 d左右进入功能性死亡的末端衰老阶段,有效积温是影响玉米穗位叶衰老进程重要因素。MDA、总叶绿素、果糖、葡萄糖含量是表征玉米穗位叶衰老进程的优良指标。

Research on Senescence Process and Suitable Indicators of Maize Ear Leaves

【Objective】The main objectives of this study were to find more optimized methods and suitable indicators to accurately indicate the senescence process of maize ear leaves, and to clarify the senescence process of maize ear leaves, so as to provide the theoretical reference for accurate and efficient cultivation measures of maize. 【Method】In the spring and summer of 2020, the field trial was carried out at Dafeng Research Station (33°12′ N, 120°28′ E) in Jiangsu province. By using hybrid cultivar Suyu 29 (SY29) as the testing material, six maize populations (N1-N6) with different leaf nitrogen concentration under different nitrogen application rates (0, 67.5, 136.5, 205.5, 274.5, and 343.5 kg N·hm^-2) were constructed. The dynamic changes of 12 morphological and physiological indicators after silking were fitted by the Logistic model and the accuracy of indicating the senescence process by these indicators were compared. 【Result】The fitting trend and degree of the Logistic formula y=(a-d)/(1+(x/c)^b)+d were better than the predecessor commonly used Logistic formula y=a/(1+e^-b(x-c)). It was showed by a multi-indicator analysis that the ear leaves of spring maize and summer maize initiated senescence process at 18.8-29.1 ($bar{x}$=25.8) days and 17.5-28.2 ($bar{x}$=23.9) days after silking, rapid senescence occurred at 30.5-37.9 ($bar{x}$=34.4) days and 28.0-35.7 ($bar{x}$=31.8) days after silking, and terminated senescence process at 40.6-54.1 ($bar{x}$=45.9) days and 38.3-47.0 ($bar{x}$=42.1) days after silking, respectively. The effective accumulated temperature of spring and summer maize at 25.8 days and 23.9 days from silking to the initiation of senescence process was 392.9 ºC and 477.6 ºC, respectively. The effective accumulated temperature of spring and summer maize at 20.1 days and 18.2 days from the initiation to termination of senescence process was 360.0 ºC and 284.0 ºC, respectively. It was showed by an indicator classification analysis that the σ-value under normal distribution of the senescence characteristic time indicated by physiological indicators was greater than that indicated by morphological indicators within the same senescence stage, which was the case in both spring maize and summer maize. The coefficient of variation (CV) of senescence characteristic time indicated by the content of malondialdehyde (MDA), total chlorophyll, chlorophyll a, fructose, glucose and transpiration rate (T_r) were all less than 5%. The root mean square error (RMSE) between the mean time of each stage and the senescence characteristic time indicated by the content of MDA, total chlorophyll, fructose, glucose and net photosynthetic rate (P_n) were all less than 2. 【Conclusion】The Logistic formula y=(a-d)/(1+(x/c)^b)+d could serve as a mathematical tool to accurately fit the dynamic changes of senescence related indicators of maize ear leaves. Based on this evaluation method, the ear leaves of spring maize and summer maize initiated senescence at 26 days and 24 days after silking, their senescence rate reached the maximum at 34 days and 32 days after silking, and substantially enter the functional death stage at 46 days and 42 days after silking, respectively. Effective accumulated temperature was an important factor to affect the senescence process of maize ear leaves. The content of MDA, total chlorophyll, fructose, and glucose were excellent indicators to characterize the senescence process of maize ear leaves.