What kind of environmental conditions does Gastrodia elata need to grow?
I. The effect of temperature on the growth of Gastrodia elata
The effect of temperature on the growth of Gastrodia elata: temperature is the main factor affecting the growth of Gastrodia elata. Gastrodia elata prefers to grow in an environment that is relatively cool in summer and not too severely cold in winter. The longer the period of suitable temperature for its growth, the more favorable it is for the growth of Gastrodia elata.
(1) The effect of temperature on the asexual reproduction of Gastrodia elata
The underground tubers of Gastrodia elata begin to grow when the ground temperature is around 14°C, grow faster at 20-25°C, and are inhibited at 30°C. Within one year, the total accumulated temperature over the entire growing season is about 3800°C. At an altitude of about 1000 m, it is most suitable for the growth of Gastrodia elata and Armillaria mellea.
When introducing and cultivating Gastrodia elata in low-altitude or plain areas, the ground temperature should be kept below 25°C. In hot summers, when the soil temperature continuously exceeds 25°C, the growth of Armillaria mellea and Gastrodia elata is inhibited, affecting the yield of Gastrodia elata. At the same time, sustained high temperatures also accelerate the process of varietal degeneration of Gastrodia elata. Therefore, when cultivating Gastrodia elata in low-altitude areas, measures should be taken to prevent heat and lower the temperature during the hot summer season.
Although Gastrodia elata can tolerate cold, it has a certain limit and cannot withstand sudden drops in temperature or sustained extremely low temperatures. The degree of freeze damage suffered by Gastrodia elata varies depending on the season in which low temperatures occur. If the temperature drops suddenly in early winter, Gastrodia elata will suffer freeze damage. As the cold season arrives and the temperature gradually declines, the tissues of the newly grown tubers gradually age, the water content in the tuber cells decreases, the concentration of cell sap increases, the freezing point of the plant is lowered, and the shrinkage of protoplasm and coagulation of proteins are prevented. After cold-hardening, the cold resistance of Gastrodia elata increases. When Gastrodia elata is kept under low-temperature conditions below zero for a long period, no freeze damage has been observed after prolonged cold-hardening. Gastrodia elata growing in the severe cold regions of Northeast China has a certain resistance to low temperatures. For example, in Fusong County, Jilin Province, at an altitude of 774.2 m, the average temperature in January is -15.7 and the lowest temperature can reach -34.7°C, yet Gastrodia elata is still distributed there. However, under these freezing environmental conditions, there must be long-term thick snow cover, and the soil temperature in the layer where Gastrodia elata is distributed beneath the snow layer must not be lower than -5°C for Gastrodia elata to overwinter normally. If the snow cover is removed, Gastrodia elata will suffer freeze damage.
Because Gastrodia elata, during its phylogenetic development, overwinters for a long time under low-temperature conditions of around 0°C in winter, it has developed the characteristic of requiring low temperatures during the overwintering period. Low temperatures can break dormancy, so when the low-temperature conditions it receives cannot meet its requirements, the young buds after germination also grow weakly, and may even neither rot nor sprout after planting. Treatment at 0°C-2°C for 40 days is required to break dormancy and continue sprouting and growing. The experimental results of Shen Dongxia et al. showed that after the tubers of Gastrodia elata enter the dormant period, if a certain duration of low temperature is not met, they will not sprout or germinate even if germination conditions are suitable. Once the low-temperature requirement is met, if suitable temperature conditions are absent, the tubers still will not germinate; but when suitable germination conditions are encountered, they can germinate. This is the crux of why, under natural conditions, the winter dormancy of Gastrodia elata can last as long as several months. Wan Huilan's experimental results proved that white tubers and small tubers require 1-10°C for 30-60 days to pass through the dormant stage. However, the size of the seed tubers affects their requirements for low temperature and the duration under low temperature. Large and medium white tubers are about to enter the reproductive growth stage and are best treated at 1-5°C for 50-60 days, while small white tubers and small tubers are in the vegetative growth stage and can break dormancy with 6-10°C for 30-40 days.
(2) The effect of temperature on the growth of flower stems
In the Hanzhong area of Shaanxi, when the local ground temperature rises above 10°C in spring, the flower stems of arrow tubers begin to sprout; in late April to early May, when the 10 cm soil temperature is around 15°C, seedlings begin to emerge; from late May to early June, when the air temperature rises to 19.4°C-29.9°C, flowering occurs; the seed maturation period is from June 14 to the end of June, when the average temperature rises to 21.7°C-22.4°C. The temperature rose from 15°C to 22°C over nearly 70 days, and Gastrodia elata also needed nearly 70 days to complete the entire process from seedling emergence to seed maturation. In the northwestern suburbs of Beijing at an altitude of 50 m, when the 10 cm ground temperature was around 15°C in late April, the flower stem buds of arrow tubers emerged from the soil; in mid-to-late May, when the air temperature rose to 22.9°C, the seeds of Gastrodia elata matured, also taking nearly 50 days. The length of the flower stem growth cycle is somewhat correlated with the speed at which the temperature rises.
In autumn, the flower stems of arrow tubers differentiate and form and enter the reproductive growth period, and they must also go through a low-temperature stage to break dormancy. The dormant period of arrow tubers is longer than that of white tubers and small tubers. If their low-temperature requirements cannot be met, they will not bolt after planting, and even if seedlings occasionally emerge, the plants will grow abnormally. Arrow tubers should generally be stored at a low temperature of 3-5°C for 2.5 months in order to pass through the low-temperature dormant period and smoothly bolt, flower, and set seed.
(3) The effect of temperature on seed germination
Seeds of Gastrodia elata can germinate between 15-28°C, but the most suitable temperature for germination is 25-28°C. Above 30°C, seed germination is inhibited. After sowing in June and July, it is the hot summer season in the production areas, and a ground temperature of 20-25°C is just suitable for seed germination. Due to differences in geographical location and climatic conditions among regions, the seed maturation period of Gastrodia elata varies, the sowing period is earlier or later, and the growth rate of protocorms also differs. For example, at Fubao Mountain in Lichuan City, Hubei Province, at an altitude of 1550 m, seeds mature and are sown in mid-to-late July, germinate in late August, and by mid-October the ground temperature has dropped to 13.2°C, at which point the protocorms stop growing. The growing season is only 40-50 days. In the year of sowing
small tubers can be harvested, whereas at the experimental site of the Gastrodia elata Research Institute in Ningqiang County, Shaanxi Province, at an altitude of 1050 m, after seed germination the protocorm growing season reaches 70-90 days, and white tubers the size of a finger can be obtained in the same year of sowing. The white tubers and small tubers harvested in the same year at the two locations differed considerably in size. In the newly introduced cultivation areas of Gastrodia elata in southern Shaanxi, after seeds mature and are sown in June, late June to July is precisely the season for seed germination of Gastrodia elata, when the ground temperature exceeds 30°C and temperatures are generally high. Therefore, cooling measures should be taken to increase the seed germination rate and the growth rate of protocorms.