关键词: 丹桂, 多批次开花, 逐步趋近法, 低温指标, 负有效积温, 预报

Abstract: From 2016 to 2022, the flowering phenomenon of a orange Osmanthus tree in the courtyard Nanyang Meteorological Bureau had observed for 7 consecutive years. The observing was according to the "Agricultural Meteorological Observation Code and Natural Phenology Volume" woody plant flowering period observation standard, i.e. when "the petals of one or several flowers on the observation tree begin to fully open, it is the beginning of flowering", and when "the petals on the observation tree wither and fall off, leaving a very small number of flowers" is recorded as the end of flowering. The first flowering period of Osmanthus fragrans in autumn is recorded as the first batch of flowering. The phenomenon of a second flowering after the first batch of orange Osmanthus blossomed is recorded as the second batch of orange Osmanthus blossoming, just like the first flowering period. After the second flowering of orange Osmanthus, it was observed that in some years, one or several flowers on the observed orange Osmanthus tree had fully opened petals and withered and shed was recorded as the third batch of flowering. Seldomly, the fourth batch of flowering was observed and recorded until no further flowering occurred. From 2016 to 2022, the flowering number of batches of orange Osmanthus flowering in the autumn of Nanyang every year and the initial flowering period and attributes of each batch of flowering were totally different. First, from the aspects of number and attributes of flowering batches, only one batch of flowers was bloomed per year from 2016 to 2019, which was completed at one time, and the 1st batch was also the last batch. From 2020 to 2022, 2-4 batches was bloomed every year, of which the 2nd batch in 2020, the 4th batch in 2021, and the 3rd batch in 2022 are the last batch. The 1st batch in 2020, the 1st to 3rd batch in 2021, the 1st and 2nd batches in 2022 are not the last batch. From the beginning of each batch of flowering, the earliest is August 25 and the latest is October 19. According to previous studies, as a plant that blooms in autumn, the flowering of Osmanthus is caused by the gradual decrease in temperature to a certain limit. Then, each batch of Osmanthus flowers has at least 1 day of low-temperature process that temperature below this limit, Osmanthus blooming cannot be completed at one time must be the previous low-temperature process did not meet all the conditions that should be achieved, and there is at least 1 day of low-temperature process that temperature below this limit again, and it blooms again. As long as the temperature values of each batch before flowering are statistically analyzed in turn, we can gradually approach to finding this limit. With this boundary, the low-temperature process can be counted, so as to find out the conditions that should be met when all flowers bloom compared with the flowering situation of Osmanthus. Daily temperature values include daily average temperature, daily minimum temperature and daily maximum temperature, which respectively express the average situation and range of daily temperature fluctuation, and should be analyzed to identify their respective functions. This article is based on years of continuous observation records of the multiple batches flowering phenomenon of orange Osmanthus in Nanyang, the minimum temperature values with daily maximum temperature, daily average temperature, daily minimum temperature before the first batch of flowering each year be counted in sequence, the minimum temperature values with daily maximum temperature, daily average temperature, daily minimum temperature between the previous batch of flowering and the current batch of flowering be calculated in sequence when the second and subsequent batches of flowering each year. Their respective maximum values selected as that daily index of low-temperature in each expression form of temperature, statistics of natural low-temperature process according to daily index of low-temperature, merge the discontinuous natural low-temperature process with short intervals into one combined low-temperature process, after the start date and negative effective accumulated temperature of the combined low-temperature process are calculated, analyze the relationship between the beginning of flowering of orange Osmanthus and the start date of the combined low-temperature process, as well as the relationship between the attributes of each batch of flowering and the negative effective accumulated temperature during the combined low-temperature process, the index of low-temperature before flowering which can be used for forecasting the flowering period of each batch of orange Osmanthus to be determined. Tested by correlation coefficients and univariate linear regression methods, the results showed that:(1)the method of stepwise approach method is used to determine the index of low-temperature before flowering of orange Osmanthus in Nanyang, the best effect is to use the daily maximum temperature, which is better than using the daily average temperature and daily minimum temperature. (2) The daily index of low-temperature before flowering of orange Osmanthus is the daily maximum temperature <22.3℃. (3) The process index of low-temperature before flowering of orange Osmanthus is the daily maximum temperature <22.3℃ natural low-temperature process interval days ≤1d merged into one combined low-temperature process, when the negative effective accumulated temperature during the daily maximum temperature <22.3℃ combined low-temperature process >3.4℃·d, the orange Osmanthus flowering once completed, when the negative effective accumulated temperature during the daily maximum temperature <22.3℃ combined low-temperature process ≤3.4℃·d, the 1st batch of orange Osmanthus flowering is not the last batch, if the daily maximum temperature <22.3℃ again, orange Osmanthus will bloom again, until the negative effective accumulated temperature during the daily maximum temperature <22.3℃ combined low-temperature process >3.4℃·d, the orange Osmanthus flowering is the last batch. (4)The relationship between the beginning of flowering of orange Osmanthus and the low-temperature process is as follows: the sequence of daily maximum temperature <22.3℃ combined low-temperature process corresponds to the batch sequence of flowering of orange Osmanthus, the beginning of flowering of orange Osmanthus was 4-13d after the start date of the combined low-temperature process, the specific flowering date Y is predicted by the univariate regression equation that the factor X be the start date of each combined low-temperature process with daily maximum temperature <22.3℃, and Y=1.1255X+1.4683, which is a very significant positive correlation linear relationship.

Key words: Orange Osmanthus, Multiple batches of flowering, Stepwise approach method, Index of low-temperature, Negative effective accumulated temperature, Forecast