What is the relationship between ecological environment and tea quality

The formation of tea quality is greatly influenced by the ecological environment conditions and technical measures of cultivation, in addition to variety factors. The same variety of tea trees can exhibit significant differences under different ecological conditions and technological measures.

 

1. Soil

The soil has a significant impact on the growth and development of tea trees. Different soil types, soil nutrients, soil acidity and alkalinity, soil texture and structure, soil layer thickness, and soil moisture conditions can all have varying degrees of impact on tea trees.

(1 ) Soil type and texture

Tea trees can grow well on sandy loam, loam, and clay loam soils. However, in terms of tea quality, it is generally believed that tea trees grown on sandy loam soil (especially white sand soil and black sand soil) that contains a lot of humus and is formed by parent rocks such as quartz sandstone, granite, and gneiss, have a loose soil texture, good aeration, and contain a large amount of potassium, magnesium, and other trace elements. Therefore, the amino acid content in fresh leaves is high, the taste is fresh and mellow, and the tea quality is the best; Tea trees grown on sticky loess or stiff loess often have higher levels of tea polyphenols in their fresh leaves due to poor soil aeration, resulting in a bitter taste; Tea trees grown on red clay formed from limestone and Quaternary red clay have the worst quality of fresh leaves.

(2) PH value of soil

Tea trees are acid loving plants, and soil acidity has a significant impact on their growth. It is generally believed that tea trees can grow normally when the soil pH is between 4.5 and 6.5; The best growth rate is between 5 and 5.5; If it is lower than 4 or higher than 6.5, it affects the formation of chlorophyll in tea trees, and the leaf color often turns yellow or even withered, resulting in poor growth. Moreover, soil conditions that are excessively acidic or alkaline can weaken the physiological functions of tea plants, hinder substance metabolism, and therefore reduce the synthesis of quality related components.
The results of tea seedling hydroponic experiments using culture media with different pH values showed that the content of tea polyphenols, catechins, and amino acids was highest when the pH value was between 5-5.5, while the content was lower when the pH value was below 5 or above 6.5. From this perspective, only under suitable pH conditions can the carbon and nitrogen metabolism of tea trees proceed smoothly, and more tea polyphenols, amino acids, etc. can be synthesized.

(3) Soil nutrients and fertilization

During the growth and development process of tea trees, they need to absorb more than 40 essential nutrients such as nitrogen, phosphorus, potassium, sulfur, iron, aluminum, calcium, magnesium, manganese, zinc, copper, molybdenum, etc. from the soil. Among them, nitrogen, phosphorus, and potassium absorb the most, so they are also known as the three elements of fertilizer. For tea trees, nitrogen, phosphorus, and potassium are the most basic nutrients, and none of them are indispensable. But as a leaf crop, nitrogen is particularly important for tea trees. To increase tea yield, increasing the amount of nitrogen fertilizer applied appropriately is the most reliable measure. The use of phosphorus and potassium fertilizers is beneficial for the formation of tea tree skeleton. In the early stage of tea trees, more phosphorus and potassium fertilizers should be applied.

The effects of nitrogen, phosphorus, and potassium fertilizers on the chemical composition of tea are very significant. Experiments have shown that applying nitrogen fertilizer is beneficial for increasing the total nitrogen and amino acid content in tea leaves, but single application of nitrogen fertilizer tends to reduce the content of tea polyphenols, while phosphorus and potassium fertilizers can increase the content of tea polyphenols. When nitrogen, phosphorus, and potassium are applied in combination, the content of tea polyphenols and amino acids can be balanced. It can be seen that only when the three elements are applied in combination can the tea quality be comprehensively improved and the tea yield steadily increase.

Applying nitrogen fertilizer can increase the content of nitrogen-containing substances such as protein and chlorophyll, as well as amino acids in tea. Therefore, more nitrogen fertilizer is often applied in green tea production, which is beneficial for the quality of green tea; However, excessive application of nitrogen fertilizer can lead to a decrease in tea polyphenol content, which should be given special attention in black tea producing areas. Red tea regions should apply more phosphorus and potassium fertilizers, which are beneficial for carbon metabolism and the quality of black tea.

(4) Fertilization in tea gardens

In addition to using chemical fertilizers, it is more important to apply more organic fertilizers. Organic fertilizers (such as cake fertilizers, manure, soil manure, green manure, etc.) have comprehensive nutrition. In addition to nutrients such as nitrogen, phosphorus, and potassium, there are also many trace elements (boron, zinc, magnesium, iron, copper, molybdenum, etc.) that play a crucial role in the quality of tea. After rotting, organic fertilizers produce various humic acids, which can improve soil particle structure, increase soil aeration and water retention, improve soil environment, and make tea leaves plump and durable.

Research has shown that tea gardens with excessive application of organic fertilizers can significantly increase the content of water extracts in tea soup, which is extremely beneficial for increasing the concentration of tea soup flavor. The quality of Hangzhou West Lake Longjing tea is outstanding among green teas. The tea farmers in the Longjing tea area of West Lake apply a large amount of organic fertilizers such as rapeseed cake as base fertilizers in the tea gardens every autumn and winter, which is closely related to the unique quality of West Lake Longjing tea, such as its high aroma, rich taste and mellow flavor.

2. temperature

The starting temperature for the growth of tea trees is about 8 ℃ for early growing varieties and about 10 ℃ for medium growing varieties; Tea trees can grow normally at temperatures between 10 ℃ and 35 ℃, but the optimal temperature for tea trees is between 18 ℃ and 25 ℃. During the optimal temperature period, tea buds grow vigorously and have good quality.
The substance metabolism in tea plants is controlled by various enzymes, and the direction and speed of substance metabolism of the same tea plant variety are different under different temperature conditions. Within the temperature range of 10 ℃ to 35 ℃, as the temperature increases, the synthesis, transportation, and transformation of sugars in tea plants accelerate, and the metabolism of tea polyphenols formed from sugar conversion accelerates. Therefore, the synthesis of tea polyphenols in high temperature summer and autumn is much higher than in low temperature spring, with a higher phenol ammonia ratio, making it suitable for making black tea; On the contrary, when the temperature is low in spring, it is conducive to the transportation and accumulation of amino acids, and the phenol ammonia ratio is small, making it suitable for making green tea.

When the temperature is too high, many amino acids will accelerate their decomposition, so the content of amino acids in summer tea will significantly decrease. So the significant difference in quality between spring tea and summer tea is mainly caused by changes in the metabolism of substances in tea plants due to different temperatures. When the temperature exceeds 35 ℃, the physiological activities of tea trees are inhibited, and the decomposition and transformation of their contents result in poor quality of both black and green tea.

During the summer tea season, due to the increase in temperature, it is also beneficial for the formation of green tea, which is unfavorable for both black and green tea. Many tropical tea gardens in Guangdong, Yunnan, Hainan and other regions of China often plant shade trees or use sprinkler irrigation to cool down, which is an effective measure to improve tea quality. High temperature is often associated with sunlight. With a large amount of sunlight and radiation, it is often a high temperature season. Under these conditions, ammonia metabolism cannot proceed smoothly, and the amino acid content in tea leaves will significantly decrease.

3. Illumination

The influence of light on tea quality mainly lies in the intensity and quality of light.

(1) Light intensity

Tea trees originated in the forest areas of southwestern China and have adapted to growing under diffuse light conditions during long-term phylogenetic processes. Therefore, primitive large leaf varieties in Yunnan, Guangdong, Guangxi, and other regions have lower requirements for light intensity; On the contrary, small and medium-sized leaf varieties have higher requirements for light intensity due to their environment being different from forest conditions.

In view of this situation, some tea regions in southern China often use shade (such as Yunnan’s rubber, tea intercropping, etc.) to increase tea production and improve quality. According to experiments, appropriate shading (when the shading degree reaches 30% to 40%) is not only beneficial for the accumulation of tea dry matter and the increase of tea yield, but also has an impact on the material metabolism of tea trees themselves.

After shading, carbon metabolism is significantly inhibited, and the content of sugars and polyphenols decreases. However, nitrogen metabolism is significantly enhanced, and the content of total nitrogen, caffeine, and amino acids increases. Therefore, shading treatment is beneficial for improving the quality of green tea. The experiment also showed that too weak or too strong light is detrimental to the synthesis and accumulation of amino acids in tea leaves. When the daily light exposure is 12552-16736 kilojoules per meter, the amino acid content in tea tree shoots is the highest. Under weaker lighting conditions, the content of tea polyphenols decreases.

Overall, such lighting is beneficial for the quality of green tea. The production of Yuru tea in Japan is carried out under shading conditions, which can reduce the formation of coarse fibers and improve the quality of tea.

(2) Light quality

The quality of light is also related to the quality of tea. The shading experiment of tea trees using different colored coverings showed that after covering with yellow shading nets and removing blue and purple light from natural light, tea buds grew vigorously and their tenderness was enhanced. The content of chlorophyll, amino acids, and water in tea leaves increased significantly, while tea polyphenols decreased. This is beneficial for improving the color and taste of green tea. During the high temperature season of summer tea, using a yellow shading net to eliminate some blue purple light can significantly improve the quality of green tea. In mountainous areas with frequent clouds and mist, the refraction of light by clouds and mist reduces the exposure of blue and purple light, thereby improving the quality of green tea.

4. Water content

Water is an essential factor in all life activities, including photosynthesis, respiration, and the formation and transformation of nutrient absorbing substances. So, without water, there is no life.

During the growth and development of tea trees, the roots absorb a large amount of water from the soil. Although a portion of the absorbed water is used for photosynthesis and a portion accumulates in the tea plant, most of it is lost through transpiration from the stomata of the leaves. The result of transpiration in tea trees can regulate body temperature and also facilitate the absorption of more nutrients by tea roots. Tea gardens consume approximately 1300 millimeters of water per year. Among them, water consumption is relatively high from April to September, about 900 millimeters; And the daily water consumption ranges from 1 to 6 millimeters.

In the case of poor water supply in tea gardens, the growth and development of tea trees will be severely affected. Manifesting as slow growth, stagnation, and even withering and death. At the same time, the metabolism of substances in tea plants tends to hydrolyze, with an increase in monosaccharides and disaccharides, a decrease in starch content, and inhibition of protein and tea polyphenol biosynthesis, resulting in a sharp decline in content.

Experimental analysis shows that under drought conditions, when the moisture content in the new shoots of tea plants is less than 70% due to drought and water shortage, the moisture content drops sharply as the degree of leaf withering and coking increases. Due to the decrease in moisture content and abnormal substance metabolism, the chlorophyll content significantly decreased. Therefore, photosynthesis is hindered and material synthesis metabolism is affected. From the content of catechins and amino acids, it can be seen that as the degree of leaf wilting increases, the synthesis rate and accumulation significantly decrease. This indicates that tea plants lack water, which not only reduces yield but also greatly lowers quality. Therefore, irrigation during drought is an important technical measure for tea gardens to achieve high yield and high quality.