Abstract:

【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.

Key words: maize, ear leaves, senescence process, senescence indicator, accuracy