What is the collection and preservation of ornamental trees?

Before collecting seeds, we must first identify the maturity of the seeds. There are two indexes of seed maturity, namely physiological maturity and morphological maturity. Physiological maturity of seeds means that the embryo of seeds has matured, the accumulation of nutrients in seeds has been basically completed, and seeds have the ability to germinate. Physiologically mature seeds still have high water content, the nutrients in the seeds are still in a soluble state, the seed coat has not been able to protect the seeds, and the seeds are easy to shrink, difficult to store, small and light in size and low in germination rate. The seeds that have reached physiological maturity have no obvious external morphological markers. However, when the seed matures, the biochemical changes in the seed basically end, the accumulation of nutrients has stopped, and it has been transformed into water-insoluble starch, fat and protein. The water content of the seed is reduced, the enzyme activity is weakened, the embryo is in a dormant state, the seed coat is hard, the resistance is enhanced, and the seed is storable. Mature seeds often have certain appearance characteristics, such as discoloration, fruit softening, fragrance, shedding and so on. In production, morphological maturity is often used as a sign of seed maturity to determine the seed collection time.

Generally, the physiological maturity of seeds is completed before the morphological maturity, but there are also some fruits of Ginkgo biloba, Fraxinus mandshurica and other tree species, although the morphological maturity. But it is not fully developed, and it will take some time. During storage, the embryo develops gradually and has the ability to germinate, which is called post-ripening.

The fruits and seeds of different tree species have their own characteristics when they mature, which can be roughly divided into three categories:

(1) The pericarp of dried fruit changes from green to yellow, brown and purple-black. The pericarp is dry, compact, hardened or naturally cracked, and some seeds are scattered due to maturity and cracking. It mainly includes pods (such as Robinia pseudoacacia, Bauhinia, Albizia Albizia and Wisteria), capsules (such as clove, crape myrtle, hibiscus and Hypericum), samara (such as Acer, elm, Fraxinus mandshurica and Eucommia ulmoides) and nuts (such as hickory and horse chestnut).

(2) The skin of fleshy fruits is discolored, and some fruits appear hoarfrost, and the flesh becomes soft, and the colors are yellow (such as Ginkgo biloba), red (such as Pyracantha fortunei, Holly, Nandina domestica) and blue-black (such as Ligustrum lucidum and Cinnamomum camphora).

(3) After the cone conifer fruit matures, the seed scales are dry, hard and slightly cracked, and the cone changes from green to yellow-brown. Because the seeds are easy to fall off after the seed scales crack, they should be harvested in time.

Besides harvesting seeds in time after maturity, we should also pay attention to other matters. If you want to choose a good seed-collecting mother tree first, the mother tree should be robust, well-developed, old and free from pests and diseases, which can reflect the excellent characteristics of the species or varieties. For cross-pollinated tree species, pollinated trees should be planted or supplemented by artificial pollination. In addition, it is best to collect some dried fruit seeds in the morning, because the air humidity is high in the morning, and the fruit will not crack when touched, which will affect the harvest.

(2) seed treatment

After seed collection, it is often difficult to store because of its wings, cones, peels, pulp and other reasons. Only after drying, threshing, seed cleaning, grading and other steps can pure seeds and fruits suitable for transportation, storage and use be obtained.

1. Threshing

(1) Dry threshing method can be used for seeds such as pods, capsules, samara and cones. Dry threshing can be divided into natural dry threshing and manual dry threshing Natural drying and threshing is to spread the fruit into a thin layer with a thickness of no more than 20 cm. After proper sun exposure or air drying, the scales or shells of the fruits are cracked, and the seeds are scattered by themselves or crushed by manual striking, and then the seeds are collected. Artificial drying and threshing uses artificial ventilation and heating to promote fruit drying. The drying temperature should not be too high, generally not exceeding 43℃. If the seed is wet and the temperature is lower, 32℃ is better.

(2) Water-washing seed-taking method The seeds of succulent fruits are often washed with water, and the fruits are soaked in water. After the succulent fruits become soft, they are washed and beaten with a wooden stick to separate them. After cleaning, take out the seeds and dry them.

2. Clean seeds and graded seeds should be cleaned in time after threshing, and empty and shriveled seeds and sundries should be removed to improve seed purity. Commonly used methods in production are:

(1) Wind is natural or artificial, which blows away hollow seeds and inclusions with different weights from full seeds. Wind separation can also roughly grade seeds. Wind separation is often used for small and medium-sized seeds.

(2) Screening and utilizing sieves with different apertures to screen out sundries and hollow seeds with different volumes from full seeds.

(3) Water separation uses the different densities of seeds and inclusions to soak seeds in water or other solutions such as salt water and copper sulfate solution, so that full seeds sink and empty particles and impurities floating on the water surface are removed. The soaking time of water-selected seeds should not be too long. Seeds should be dried in the shade in time after washing.

After cleaning, seeds should be classified according to size or weight, which can be generally divided into three grades: large, medium and small, and the classification is generally screened by sieves with different apertures. For the same batch of seeds, the bigger the seeds, the higher the emergence rate, the stronger the seedlings, the neater the seedlings and the easier to manage.

(3) Storage and life of seeds

1. Seed longevity and its influencing factors

Seed life refers to the period of maintaining vitality under certain environmental conditions. As far as the population is concerned, the life span of the seed group is the time from harvest to half of the seeds are still alive.

Seed life mainly depends on its genetic factors, but also has a great relationship with seed maturity, seed integrity, seed water content, storage conditions and other factors.

(1) Genetic factors Because of their own genetic characteristics, the life span of different kinds of tree seeds is quite different. Under suitable conditions, seeds with a life span of less than 1 year are called short-lived seeds, seeds with a life span of 2 ~ 15 years are called medium-lived seeds, and seeds with a life span of more than 15 years are called long-lived seeds. Generally speaking, many temperate broad-leaved tree species, tropical tree species and seeds with a large number of fleshy cotyledons have a short life span. For example, Ulmus pumila died after a month and a half of high temperature in summer. The viability of poplar seeds decreased sharply at room temperature for one month; Others such as aesculus, loquat, citrus, litchi, pecan and chestnut are short-lived seeds. Most conifer species are middle-aged seeds. In addition, seed inclusions are also related to seed life. For example, the water content of starch seeds is higher than that of fat seeds, and starch is easy to absorb moisture, decompose and consume, which makes starch seeds (such as chestnut and ginkgo) less storable than fat seeds (such as pine and cypress seeds). Longevity seeds that can be stored are often dense and hard, with poor permeability, thick cuticle and waxy coating. This kind of seed coat is almost impermeable to water and has strong resistance to external adverse conditions, such as locust and Gleditsia sinensis.

(2) The seed maturity is not fully mature, and the seed coat is not tight, so it does not have normal protective effect. The storage substances in seeds are still in a soluble state, and the seeds have high water content, strong respiration, easy consumption of nutrients, easy infection with pests and diseases, and difficult storage.

(3) Water content of seeds The water content of seeds is low, the respiration of seeds is weak, the enzymes in seeds are adsorbed, the physiological activity is low, the seeds are dormant, the seeds with low water content can keep vitality for a long time, and the seeds with low water content can effectively resist the influence of high temperature and low temperature on seeds. Of course, the water content of seeds is not as low as possible, but has a certain limit, which is called "safe water content". Safe water content is the allowable water content for seeds to pass the storage period safely. According to the level of safe water content, seeds can be divided into two categories: one is seeds that can tolerate drying, and the safe water content is about 10%, such as pine, fir and cypress; The other kind is seeds that can't stand drying, and the safe water content is 30% or more, such as citrus, horse chestnut and ginkgo. Safe water content is related to storage time and storage temperature. If the storage time is long, the lower limit of safe water content should be taken; The time is short, and the upper limit of safe water content can be taken. But when the storage temperature is high, the water content should be low, and vice versa.

(4) Seed integrity is often damaged in the modulation process such as threshing and screening, and this damage is easy to spread and cause rot under poor storage conditions, thus affecting seed germination.

(5) The environmental conditions for seed storage are to maintain seed vitality and prolong its life. The most fundamental thing is to slow down the metabolic activities such as seed respiration and not damage the embryo. Therefore, it is very important to adjust the humidity, temperature and ventilation conditions of the environment. The change of environmental humidity often directly affects the change of seed water content, especially when the air relative humidity is too high, it is easy to increase seed water content, accelerate metabolism and even make seeds germinate. For most seeds, the relative humidity should be kept at 30% ~ 60% during storage. Temperature is also an important factor. When the temperature is high, the respiration of seeds is enhanced, while when the temperature is low, it will inhibit the respiration of seeds. Temperature also affects the change of air humidity, and the two affect each other. Seeds can maintain viability for a long time under dry and low temperature conditions, but it is easy to lose viability under high temperature and high humidity conditions. Most seeds should be stored at 65438 0 ~ 5℃ after drying. Reasonable use of ventilation can effectively reduce the relative humidity of storage environment, reduce the fluctuation range of seed water content, and also reduce the temperature of seeds and take away the local heat generated by breathing; It can also reduce the concentration of carbon dioxide produced by respiration in the seed pile, which is much higher than the surrounding environment, and avoid the harm of anaerobic respiration to seeds. Of course, under artificially controllable conditions, seeds can be preserved in a closed environment by combining low temperature, drying and other measures. Moreover, different kinds of seeds can often prolong their life if they are placed in nitrogen, hydrogen and carbon monoxide gas during closed storage.

2. Storage of seeds

(1) Dry storage method is suitable for seeds with low water content. There are ordinary dry storage method and sealed dry storage method.

Ordinary dry storage method: suitable for most trees and shrubs, especially conifer seeds and common capsules and pods. Storage should be fully dry, then put into seed bags or barrels and put in a cool, ventilated and dry room. According to the storage time and storage conditions, proper use of ventilation and moisture absorption equipment or desiccant. Generally, the indoor relative humidity should be kept below 50%.

Sealed dry storage method: ordinary dry storage is not suitable for long-term preservation of seeds, especially some seeds that are easy to lose germination ability, such as willow, elm and eucalyptus. That is, put the dried seeds in a closed container, add a proper amount of desiccant in the container, and check and replace the desiccant regularly. The sealed dry storage method can effectively prolong the life of seeds, and the effect is better if given low temperature.

(2) Wet storage method Wet storage method is suitable for seeds with high water content. Most of them are limited to overwintering storage and often combined with germination. Common tree species such as ginkgo, oak, privet, pyracantha, begonia, peach, plum, papaya and so on. Generally, seeds are mixed with wet sand or other substrates 2 ~ 3 times the capacity of seeds, buried in well-drained underground or stacked indoors to maintain a certain humidity. There are also layered storage of seeds and sand, which is called layered storage. This method can effectively maintain the vitality of seeds, accelerate germination and improve the germination rate and uniformity of seeds.