Taxodium plants are all ancient "relict plant". It flourished from the late Jurassic to the early Cretaceous. In the Miocene and Pliocene of Tertiary, it was still widely distributed in North America and northern Eurasia 20-30 million years ago. Fossils of leaves, cones and seeds of Taxodium ascendens in Mesozoic have been found in the United States, Siberia, Russia, Heilongjiang, Jilin, Songliao Plain and Yunnan. After the Quaternary Glacier, they all became extinct in Eurasia and only survived in parts of North America and Latin America.
Taxodium has strong adaptability and is cultivated as an ecological environment and timber afforestation tree species in Europe, Asia, Africa and Australia. China began to introduce plants around 1900, which was first planted in Yancheng saline-alkali land. At present, there are still several hundred-year-old trees in the campuses of the middle school affiliated to Nanjing Southeast University and Nanjing Normal University, as well as in the gardens of individual residents. The height of the tree is nearly 30m, DBH130cm, and the crown width16m. In Jigongshan Nature Reserve, Henan Province, there is still a 50-year-old budding forest of Taxodium ascendens (the original forest was cut down by the Japanese army in War of Resistance against Japanese Aggression, and then germinated and regenerated), with the maximum tree height of 32 meters and DBH of more than 70 centimeters. After 1970, Cunninghamia lanceolata, Taxodium ascendens and Taxodium ascendens were introduced in a large area as fast-growing and high-yield forest trees. Jiangsu, Shanghai, Zhejiang, Qiong and other provinces (cities) have afforested nearly 654.38 million hectares. Most of them have become forests and timber. It has brought good ecological, economic and social benefits into play. Chinese experts in forest genetics and breeding have been studying the genetic improvement of three species of Taxodium ascendens and cultivated some new cultivated varieties. 1960, Professor Ye Pei from Nanjing Forestry University crossed Taxodium mexicana ♀ and Cryptomeria fortunei ♂ and obtained a few hybrids. This hybrid is shaped like Taxodium ascendens in Mexico, planted in Jiangsu, Hubei and other places and has grown into a big tree. From 1973 to 1983, researcher Chen Yonghui of Institute of Botany, Nanjing Chinese Academy of Sciences crossed Taxodium ascendens ♀ with Taxodium ascendens ♂ to obtain excellent hybrid clone Zhongshan 302; Hybridization clone Shanshan 40 1 was obtained by crossing Taxodium ascendens ♀ and Taxodium mexicana ♂. Through appraisal, it has been popularized and applied in Jiangsu and surrounding provinces, and it is growing well. After 1990, researcher Wang Qiming of Jiangsu Academy of Forestry Science and others carried out the breeding of different geographical provenances and families of Taxodium ascendens, and selected the excellent provenance of Taxodium ascendens-Susong 1, which has been identified as a new tree species for popularization and application by the State Forestry Administration and Jiangsu Forestry Administration. Jiangsu, Shanghai and other provinces (cities) have begun to be excellent new varieties for ecological environment greening. According to the existing data, the modern natural distribution, tree morphology, biological characteristics and suitable application scope of Sushan 1, Zhongshan, Taxodium ascendens, Taxodium ascendens and Taxodium ascendens were compared and analyzed for reference in selecting and cultivating these tree species.
Since 2003, researchers from Institute of Botany, Jiangsu Academy of Sciences have made full use of the excellent characteristics of Taxodium distichum and Taxodium distichum (Taxodium distichum is a semi-evergreen tree with many branches on its trunk, wide crown, high ornamental value and strong saline-alkali tolerance (above 4‰); Taxodium ascendens has tall trunk, fast growth and high wood value. A new hybrid combination "Metasequoia glyptostroboides (♀) × Taxodium distichum (♂)" was studied in order to select new varieties with salt and alkali tolerance, fast growth and excellent wood quality. After 8 years' efforts, it was successful, and the "Taxodium ascendens (♀) × Taxodium ascendens (♂) hybrid breeding method" was granted the national invention patent on February 8, 20 10 (patent number: ZL2007 10025662.4). Four excellent clones of Metasequoia glyptostroboides, Zhongshan 405, 406, 407 and 502, were granted the national new forest variety right on February 28th, 1965. Among them, Zhongshan 405, 406 and 407 were granted the provincial forest variety recognition on 20 12 and 20 13 respectively. New clones such as "hybrid Taxodium ascendens" Zhongshan 405 not only have great advantages in volume growth and biomass growth, but also have outstanding adaptability to saline-alkali and arid habitats. They have broad application prospects in the future construction of timber forest, energy forest, carbon sink forest, leisure forest and water conservation forest in China, and can be widely used in wetland ecological restoration, coastal shelter forest construction, saline-alkali land greening and afforestation, urban and rural greening and farmland forest network in China.
Taxodium ascendens is a modern natural distribution. Taxodium ascendens and Taxodium ascendens are very similar in modern natural distribution, and both grow in the eastern and southern parts of the United States, in a wide range of 23 ~ 42 north latitude, from Virginia in the northeast to the southernmost tip of Florida. The climate zone belongs to temperate zone to subtropical zone, with annual extreme low temperature of 20 ~-35℃, annual precipitation of 760 ~ 1630mm and altitude of 0 ~ 150m. It grows in the permanent swamp all the year round, and the tree base is immersed in water for half a year. Therefore, there are few other tree species in the forest, only accompanied by some aquatic plants such as duckweed and purple duckweed. When the water recedes in autumn, only some herbs grow in the forest.
The modern natural distribution of Taxodium ascendens in Mexico is quite different from Taxodium ascendens and Taxodium ascendens. It is distributed in the tropical and subtropical areas from Texas in the southwest of the United States to eastern Mexico and Guatemala in the south, with a latitude of 25 ~ 16. The extremely low temperature plateau with annual temperature above 25℃, annual precipitation1200mm and altitude1400 ~ 2400m cannot grow in the swamp area. These trees are all tall trees. During the period from youth to middle age (under 50 years old), Sushan 1, Zhongshan, Taxodium ascendens and Taxodium mexicana all have oval crowns with cones or umbrellas, and some plants will gradually form irregular broad crowns over 50 years. Taxodium ascendens has a narrow crown, which is basically in the shape of a steeple under 50 years old.
Dry fir tree species are excellent in material and have the title of "eternal wood" in the United States. Taxodium ascendens, Susong 1 and Taxodium ascendens have obvious trunks, are completely straight, and do not branch from the base to the top of the trunk, so the yield is high. Irregular plate roots are formed on the dry foundation of low-lying areas and wetland areas. The trunks of Taxodium ascendens and Taxodium ascendens are obvious and completely straight, but they branch in the middle and upper part of the trunk to form a broom shape. The base will also form irregular plate roots.
The leaves and twigs of Taxodium ascendens, Susong 1, Taxodium mexicana and Cunninghamia lanceolata are all pinnately compound leaves. Leaves are strip-shaped, alternate and inserted on branchlets. The leaf length of Taxodium ascendens and Susong 1 is 1.0 ~ 1.8 cm, and they are arranged in two rows on the lateral branches. The leaves of Taxodium ascendens and Cunninghamia lanceolata are smaller, 0.6 ~ 1.0 cm long, and the spiral branchlets are scattered, not two rows. Taxodium ascendens leaves are drill-shaped, slightly inflected, extending spirally on the branchlets, with the lower part clinging to the branchlets and the base extending downward, with a length of 0.3 ~ 1.0 cm. Taxodium ascendens also has pinnate or pinnate, subulate and linear leaf shapes.
Both female cones and male cones are conidia cones, and female flowers and male flowers are the same plant. There are significant differences in morphology, biology and adaptability among different species, varieties and cultivated species of this genus, but the female cones and male cones are very similar in morphology. Female cones are attached to the top of new branches, single or 2-3 clusters, spherical when mature, and 3.5-5.0 mm long. When it is ripe, the scales of the pearl will open. Male cones are inserted on branchlets, which are oval when mature and 3.0 ~ 5.0 mm long. Many male cones form an inflorescence and spread a lot of pollen when they mature.
The mature cones of Taxodium ascendens, Taxodium ascendens and Susong 1 are spherical or oval, with a large volume of 8 ~ 10 cubic centimeter. Gray-green or brown. The cone of Taxodium ascendens is small, with a volume of only 0.7 ~ 1.0 cubic centimeter, showing a bluish gray color. The cone volume of Chinese fir is between Taxodium ascendens and Taxodium mexicana.
The seeds of Taxodium ascendens are irregular triangles or polygons, with obvious sharp ridges, thick skin, horny, hard, impermeable, nodules and flanges. The seeds of Taxodium ascendens, Susong 1 and Taxodium ascendens are relatively large, with the 1000-grain weight ranging from 40g(25000 grains/kg) to150g (6,666 grains/kg), and the maximum is 220g(4545 grains/kg). The seeds of Taxodium ascendens in Mexico are much smaller, and the 1000-grain weight is only 15g (66666 grains/kg) ~ 50g (20000 grains/kg). The seeds of Chinese fir are between Taxodium ascendens, Taxodium ascendens and Taxodium ascendens.
The root system and "root knee" root system are developed, which can penetrate into the soil layer for more than 3 meters. There are usually 1 ~ several main roots and a large number of fine roots. When Taxodium ascendens, Taxodium ascendens and Susong 1 grow in low-lying wetlands, rivers, lakes, beaches and shores, at the age of 6-8, their roots will grow "root knees" and protrude out of the soil. The height of the "root knee" varies from a few centimeters to 2.0 meters, and the thickness is more than 20 centimeters. General researchers believe that "root knee" is formed by long-term flooding in the original ecological area, which can play a certain role in breathing, ventilation, fixation and storage of nutrients. Taxodium ascendens in Mexico did not form a "root knee" because there was no flooded environment in the original ecological area. Zhongshan fir is an excellent fast-growing clone, which likes humidity and bears fertilizer. Therefore, good water and fertilizer management is one of the important measures to give full play to its excellent fast-growing characteristics. In addition to watering enough water when transplanting, water should be watered in time to fight drought during the whole growth period after survival. In addition, in addition to adequate base fertilizer, quick-acting organic fertilizer or chemical fertilizer should be applied in time according to the growth of seedlings during the growth period to promote the vigorous growth of seedlings.
After the transplanted seedlings survive and grow, weeding and loosening soil in time can promote the rapid growth of seedlings. However, in the early stage of survival, only the soil was hoed. Don't loosen the soil when weeding, so as not to affect the restoration of the original root system and the growth of new roots. When the root system resumes growth and the aboveground part begins to grow vigorously, weeding and loosening soil can be combined. Loosening soil after rain or irrigation can keep picking, which is beneficial to seedling growth. There are generally fewer pests and diseases in Chinese fir seedling stage, but under certain environmental conditions, different degrees of pests and diseases will also occur.
Prevention and treatment of verticillium wilt
Yellowing disease, also known as yellowing disease, is a biological disease. When Chinese fir is planted in alkaline soil and saline-alkali soil, its branches and leaves often lose their green and yellow colors. Because this kind of soil often lacks soluble iron ions that can be absorbed and utilized by plants, when the content in the soil is low to a certain extent, the branches and leaves of Chinese fir will lose their green due to iron deficiency, leading to physiological yellowing, affecting growth and even causing yellowing death. Its prevention and control methods: when choosing the transplanting place, choose the land with light alkali or saline-alkali soil for transplanting, or apply more calcium phosphate and organic base fertilizer during soil preparation to reduce the soil PH value. It can be irrigated with ferrous sulfate solution of 1: 80 at onset. When watering, prevent liquid medicine from being sprinkled on branches and leaves, otherwise it should be washed with clear water immediately to avoid phytotoxicity. You can also use 0. 5%— 1。 0% ferrous sulfate solution is sprayed on the leaves to promote the absorption of foreign elements, make the leaves turn green and resume normal growth. According to the secretary of the branch of Dianchi Water Resources Management Office in Kunming, the survival rate of planted Chinese fir is over 90% from the first phase of planting and maintenance, and it grows well without pests and diseases. When talking about the reasons for the death of some Chinese fir, Xu Jianzu thinks that there are roughly four factors: First, the quality problems of seedlings themselves will cause damage to seedlings during emergence and transportation, and long transportation time will lead to dehydration of some seedlings and even death after planting. Secondly, the first phase of planting Chinese fir was in March. At this time, the dormant period of Zhongshan fir has passed, and Zhongshan fir has begun to sprout. In addition, the weather in Kunming was hot at that time, and planting Chinese fir at this time would have a certain impact on its survival rate. In addition, the continuous drought in Kunming has led to a decline in survival rate. In some areas, Chinese fir was not planted according to the regulations, but directly planted in water, resulting in the death of Chinese fir seedlings because they could not breathe. As the follow-up work such as management and protection has been put in place, the growth of Chinese fir in the first phase is generally good. For the Chinese fir that has not survived after planting, the management and protection department has cleaned it up in time and will choose the right time to replant it.
In the second stage of planting, the seedlings of "Zhongshan fir 302" are used more. After planting Zhongshan 302 in a large area, the survival rate is the best system.
"The best time to plant Chinese fir is from June of that year 165438+ 10 to March of the following year, because this period belongs to the hibernation period of Chinese fir, and planting is conducive to improving the survival rate." Xu Jianzu said that the second phase of Chinese fir planting in Zhongshan will be fully launched. By then, another 470,000 Chinese fir trees with an area of 6,000 mu will take root in the lakeside and estuary of Dianchi Lake.
The Chinese fir seedlings planted in the second phase still need to be transported from Jingjiang City, Jiangsu Province, because although the Chinese fir seedling base has been built in Shilin County and other places in Kunming, it will take three years at the earliest to use the Chinese fir seedlings produced locally in Kunming. By summarizing the first-stage planting experience, they found that the seedling survival rate of "Zhongshan Shanshan 302" was higher than that of "Zhongshan Shanshan 1 18" and the growth rate was obviously faster than that of "Zhongshan Shanshan 1 18". Therefore, in the second stage of planting, we will choose as many seedlings as possible, and if possible, try to plant new varieties such as Zhongshan Shanshan 405. Cunninghamia lanceolata is the first fast-growing Chinese fir tree species in the world, which is resistant to wind disaster, water and humidity, salt and alkali, and landslides. High social value
The price of Chinese fir Zhongshan fir was first selected by the Institute of Botany of Jiangsu Academy of Sciences in the 1970s with the efforts of the older generation of experts such as researcher Chen Yonghui. After 30 years, it passed the national examination and approval in 2002 and became a national forest species [national S-SC-TDM-004-2002]. And it takes nearly 10 to 20 10 years to adapt to the growth of Chinese fir 302, 1 18. Expert evaluation: it is the best strain in salt and alkali resistance, wind resistance, water resistance, fast growth, landslide resistance and landscape effect. For other 10 varieties, such as 149, 69 and so on. Experts suggest careful promotion.