From the point of view of agricultural practice, plant growth occupies an absolute position in agricultural production. When plant growth is good, crop yields are high and farmers' income is high. When the income level of the people is high, the economy of the whole country goes up. Plant growth includes these aspects: the development of special organs, the development of the whole plant and so on. At present, scientists have identified 52 factors that affect plant growth. Such as soil organic matter, soil moisture, rhizosphere depth, temperature, humidity, light level, wind speed and so on. Here we will focus on analyzing the effect of temperature, humidity and lightness on plants.
The effect of temperature on plant growth Plants can only grow within a certain temperature range. The effect of temperature on growth is comprehensive, it can affect photosynthesis, respiration, transpiration and other metabolic processes, but also by affecting the synthesis and transport of organic matter and other metabolic processes to affect plant growth, but also directly affect the soil temperature, air temperature, by affecting the absorption of water and fertilizer transport to affect the growth of plants. Since the activities of enzymes involved in metabolic activities are different at different temperatures, the effect of temperature on plant growth also has three base points of minimum, optimum and maximum temperatures. Plants can only grow within the range of minimum and maximum temperatures. Although the optimum temperature for growth is the temperature at which the fastest growth occurs, it is not the temperature at which the plant grows most robustly. Because in the optimal temperature, the organic matter in the plant body is consumed too much, the plant grows thin and weak. Therefore, in production practice to cultivate robust plants, often require a temperature below the optimal temperature, this temperature is called the optimal temperature of coordination.
Different plants grow at different temperature triple base points. This is related to the climatic conditions of the plant's origin. Plants originating in the tropics or subtropics, the temperature three base points are high, respectively, 10 ℃, 30 ~ 35 ℃, 45 ℃; plants originating in the temperate zone, the temperature three base points are low, respectively, 5 ℃, 25 ~ 30 ℃, 35 ~ 40 ℃; originating in the frigid zone of the temperature of the growth of the plant three base points is even lower, the Arctic or alpine plants can be in 0 ℃ or 0 ℃ or the temperature below the growth of the optimal temperature is generally rarely more than 10 ℃. The optimum temperature generally rarely exceeds 10°C.
The temperature triple base point of the same plant also varies with organ and reproductive stage. Generally the temperature triple base point for root growth is lower than that for shoots. For example, the minimum temperature of apple root growth is 10 ℃, the optimal temperature is 13 ~ 26 ℃, the highest temperature is 28 ℃. And the above-ground part of all higher than this temperature. In the different reproductive stages of cotton growth, the optimal temperature is not the same, the optimal temperature of the primary roots and hypocotyl elongation in the seed germination is 33 ℃, but a few days later the roots fell to 27 ℃, while the hypocotyl elongation rose to 36 ℃. Most annual plants, from the early stages of growth through flowering to fruiting in the three stages, the optimal temperature of growth is gradually increasing, this requirement is exactly the same as the temperature change from spring to early fall. Sowing too late will cause the seedlings to grow too vigorously and weaken, and similarly if the summer temperature is not high enough, it will also affect the growth and delay the maturity.
The experimental data of artificial climate incubator proved that in the daytime temperature is higher, the night temperature is lower in the cycle of change, the plant's nutritional growth is the best. Such as tomato plants in the day temperature of 26 ℃, the night temperature of 20 ℃ day high and night low temperature difference, than day and night 25 ℃ constant temperature conditions grow faster. Under natural conditions, there is also a cyclical variation of higher day temperatures and lower night temperatures. The response of plants to this cyclical change in day and night temperatures is called the thermocyclic phenomenon of growth.
The reason that higher day temperatures and lower night temperatures can promote plant nutrient growth is mainly due to higher daytime temperatures, which are favorable to the photosynthetic rate under strong light and provide sufficient material for growth; lower night temperatures can reduce the consumption of organic matter by respiration. In addition, lower night temperatures favor root growth and cytokinin synthesis, thus also increasing the growth rate of the whole plant. In greenhouse or greenhouse cultivation, attention should be paid to changing the day and night temperatures, so that the plant is in natural conditions, moisture, mineral, light, temperature and other factors on plant growth is a cross, integrated impact. First of all, there is mutual influence between the environmental factors. For example, reactions such as rainy days, dim light, falling temperatures, increased soil moisture, and poor soil aeration can occur in a chain, affecting plant growth. Secondly, each environmental factor acts on the plant body, and life activities are closely related, they will also affect each other. For example, light to promote photosynthesis, photosynthesis will affect transpiration, transpiration will affect the water supply. They both promote and constrain each other. In agricultural production, we must pay attention to the various environmental conditions on the growth of individual physiological activities of the special role, but also to use the viewpoint of two, to seize the main contradictions, take reasonable measures to promote and inhibit the growth of plants to achieve the purpose of cultivation.
The effect of humidity on plant growth affects the absolute humidity of many factors, mainly depends on the source of water vapor, transport and the ability of the air to maintain water vapor. Thus, factors affecting the supply of water vapor such as precipitation, the presence of water bodies, the level of soil moisture and evaporation conditions, conditions affecting the transport of water vapor such as winds and vertical air currents, and conditions affecting the ability of the air to retain water vapor such as air temperature, may all affect absolute humidity. Generally tropical oceanic air masses have higher absolute humidity than polar oceanic air masses; at the same latitude, areas influenced by oceanic air masses have higher humidity than areas controlled by continental air masses. Absolute humidity during the year is higher in the rainy season than in the dry season. Changes in absolute humidity in a day, in coastal areas and fall and winter seasons is the largest in the afternoon, the smallest in the early morning, a single-peak type of change; for other areas, it is more bimodal, the two highs appeared in the 9 ~ 10 hours and before and after the sun didn't, and the two lows appeared in the sunrise before and after noon. The vertical distribution of absolute air humidity decreases with increasing height.
Relative humidity is determined by absolute humidity on the one hand and air temperature on the other. In cold regions and seasons, air humidity tends to be saturated, and relative humidity may be high when absolute humidity or water vapor pressure is not too high. Under the same condition of absolute humidity, the relative humidity in warm regions and seasons tends to be low. The general trend in the distribution of mean annual relative humidity in mainland China is that it decreases from southeast to northwest, and is higher in the mountains than in the plains. The annual variation of relative humidity is generally higher in dry inland areas in winter than in summer; it is lowest in northern and northeastern China in spring and higher in summer than in winter; and there is less annual variation in various parts of Jiangnan.
Air relative humidity or saturation difference is one of the important factors affecting plant water absorption and transpiration. When the relative humidity is small (saturation difference is large), if the soil moisture is sufficient, the plant transpiration is more vigorous and the plant grows better. If the air humidity is in saturated conditions for a longer period of time, plant growth will be inhibited, resulting in a reduction in the rate of irrigation of grain kernels, aggravation of cotton bud boll shedding, reduction in the vitality of cotton and affecting the quality of cotton harvest. Relative humidity is too small, will aggravate the soil drought or cause atmospheric drought, especially in the conditions of high temperature and lack of soil moisture, the plant's water balance is disrupted, the water is not enough to prevent the growth of yield reduction. The level of relative humidity and saturation difference can constrain the time of anther dehiscence, pollen dispersal and germination of certain plants, thus affecting the pollination and fertilization of plants. Humidity is also closely related to the occurrence of crop pests and diseases. Wheat sucker likes the environment with high humidity, while cotton aphid and red spider are suitable to live in the environment with low humidity. High humidity easily leads to the prevalence of many diseases such as wheat rust. For livestock, it is generally appropriate to have a relative humidity of 50 to 70%, too low humidity is easy to cause mucous membranes, skin, hoof and nail dryness and cracking and lead to germs and other infections, too high humidity, easy to cause germs and parasites breeding. Combination of high humidity and high temperature will inhibit evaporation and heat dissipation, easy to cause heat accumulation in livestock; high humidity and low temperature, increasing the thermal conductivity of the air, easy to aggravate heat loss in livestock and lead to disease.
Effect of light level on plant growth Effect of light level on growth and development of medicinal plants Light is the source of energy for photosynthesis in plants. Photosynthesis is mainly accomplished by the plant's organ, chlorophyll. In plant ecology, plants are usually categorized into three main groups, namely, positive plants, negative plants and shade-tolerant plants, based on their different requirements for light:
Masculine plants are those that can only grow robustly in a strong light environment and grow poorly under sheltered and low light conditions. Examples include licorice, atractylodes, paeoniae, dioscorea, cassia, and mint.
Shady plants are plants that grow better in weaker light conditions than in strong light conditions. However, this does not mean that the light requirement of yin plants is the weaker the better, because when the light is too weak to reach the compensation point of yin plants, it can not get the normal growth, so yin plants require weaker light is also only relative to the positive plants. Shade plants grow in damp, shady places or in dense forests, such as Lianqianzhu, ginseng, Tiannanxing, Huanglian, etc.
Shade-tolerant plants are those that fall between the two categories. These plants grow best in full sunlight, but can also tolerate moderate shade or require lighter shade during reproduction. Examples include Dangshen, Yellow Essence, Cinnamon, and Forsythia.
However, the same plant in different oh that stage of development of light requirements are not the same. Such as thick Park, Duchess and other woody plants, seedlings also need shade, afraid of strong light. When the ginseng seedlings like shade, adult plants like sun. Although Huanglian is a negative plant, different stages of growth, the degree of shade tolerance is different. Seedlings are the most shade-tolerant, but in the fourth year after planting, the shade can be removed and the plant can grow in bright light, which is conducive to root growth. In general, plants require more nutrients and have higher light requirements during the flowering and fruiting stages or during the formation of storage organs such as tubers. Understanding the ecological type of plants on light level is very important in the rational cultivation of medicinal plants, part-time do set seed, introduction and domestication.
