Why is the relative low temperature in winter and spring a necessary climatic condition for high yield of longan?

Temperature is one of the survival factors of longan, which determines its natural distribution, growth and development. From the production practice of longan, it is proved that moderate temperature and heat are the main signs to measure the economic cultivation effect of longan. If it exceeds the critical temperature line, it will lose its economic cultivation value. According to years of observation, the average annual temperature of 20 ~ 22℃ is the suitable condition for longan growth. Vegetative growth stopped at 4℃; The growth began to recover at 8 ~ 65438 00℃; 10 ~ 12℃ grows slowly; The growth rate increased between 13 ~ 18.5℃; It grows well above 2 1℃; It grows fastest at 23 ~ 25℃. Longan has certain requirements on temperature during flowering and fruiting period. It seldom blooms at 5 ~ 8℃, and starts to bloom above 10℃, and it blooms most at 18 ~ 24℃, and starts to decrease above 29℃. According to the study of pollen viability, the pollen germination rate is extremely low below 15℃, the temperature is 20 ~ 24℃, the air relative humidity is 70% ~ 80%, the temperature difference between day and night is large, there is no rain, and the breeze is the most favorable weather for pollination and fertilization. The high temperature above 30℃ not only weakens the physiological function of pollen and stigma, but also is very unfavorable to pollination. Moreover, the temperature has a great influence on the respiratory intensity of flowers. Every time the temperature rises 10℃, the respiratory intensity increases 1 times, which makes respiration worse, transpiration worse, destroys water balance, accelerates shedding, and ethylene release will also increase significantly, thus promoting flowering and fruiting, which is not conducive to the formation of yield. 22 ~ 27℃ longan secretes the most honey, which is the most suitable temperature for bee activity and has the best pollination effect. Late spring cold is extremely unfavorable to the flowering, pollination, fertilization and fruit setting of longan. After fertilization, the small fruit can grow and develop normally at the temperature above 15℃, but the low temperature below 15℃ can't make it bear fruit, and the normally fertilized female flower will also fall off. Low temperature below 16℃ in fruit-bearing period is also easy to induce abnormal fruit development. The average daily temperature is above 65438 05℃, and it can grow and mature normally. The higher the effective accumulated temperature above 15℃, the faster the fruit growth and development, and the better the quality.

Autumn shoot is the main fruiting mother branch of longan. Results The growth potential and nutrient accumulation of mother branches directly affected the quality of flower bud differentiation and fruit setting rate. High nutrient accumulation and strong fruiting mother branches can promote flower bud differentiation and fruit growth, and obtain higher yield. The fruiting branches of autumn shoots stop growing in winter when the relative low temperature is lower than 65438 05℃, and enter a pseudo-dormancy state. In warm and rainy weather, longan is easy to germinate and germinate winter buds. The germination of winter shoots can not meet the demand of physiological differentiation of longan flower buds to temporarily stop the vegetative growth of branches and leaves, and it consumes nutrients in the tree before wintering, reducing the storage of nutrients in the tree, resulting in less formation in the next year or poor flower quality on the ear, resulting in reduced production or poor harvest. During the flower bud differentiation of longan in spring, low temperature has a great influence on the morphological differentiation of longan flower buds. Due to different low temperatures, there will be pure spikes and flowers with leaves. When the flower bud differentiation temperature of longan in spring is in the range of 8 ~ 10℃, the flower bud differentiation lobules wither and fall off at the initial stage of development and slowly develop into pure spikes; At the temperature of 1 1 ~ 14℃, flowers and leaves can develop and still form pure panicles with economic value. The temperature above 14℃ is not conducive to the differentiation and development of flower buds, but it is beneficial to the development of lobules, which are easy to form spikelets with leaves, but rarely bear fruit; When the temperature is higher than 18℃, the leaflets will grow vigorously, and the small white spots (lateral inflorescence primordium) appearing in the axils will gradually disappear, and will no longer develop into flower spikes and become vegetative branches (spring shoots). Therefore, it is considered that 14℃ is the critical temperature for longan to become a pure flower ear. For example, the high temperature (the highest is 19.7℃) in Quanzhou12 ~ March 24, Fujian province for three consecutive days, resulting in serious spike rush and poor harvest. Because it is easy to bloom in cold winter years, such as 1990, 1992, 1993, 1994, 2002 and 2004, it shows that the relative low temperature in winter and spring has a great influence on the differentiation and quantity of longan flower buds under suitable lighting conditions.