Molecular Plant Breeding 2025, Vol.16, No.4, 221-230 http://genbreedpublisher.com/index.php/mpb 224 4.3 Effects on water-use efficiency and root physiology A reasonable frequency of irrigation not only ensures that tea plants have access to water but also promotes root development. Precision irrigation can maintain the concentration of leaf cell SAP within an appropriate range, prevent excessive water loss from leaves, and enhance photosynthesis and the assimilation capacity of leaves. Continuous and reasonable irrigation can also induce the root system to grow deeper and enhance the drought resistance capacity (Wang et al., 2021). When water management and fertilization are well combined, water and nutrients can work in synergy, enabling tea plants to grow better and have a higher yield. Figure 2 Models of possible mechanisms of tea plants responding to different water conditions. The red and blue arrows indicated that the levels of metabolites increased and decreased, respectively (Adopted from Shen et al., 2022) 5 Interaction Effects of Shading and Irrigation Frequency 5.1 Photosynthetic efficiency and water use synergy Shading can lower the temperature of the leaves and soil, which can improve the microenvironment around the tea plants and help enhance the efficiency of photosynthesis and water use. After being treated with multi-layer shading nets, the amino acids in the tea increased significantly and the soil moisture was also maintained more stably. This enables tea plants to maintain a relatively high photosynthetic rate and stomatal conductance during the hot summer days (Zhang et al., 2022; Ge et al., 2024). Shading can also enable tea plants to accumulate more chlorophyll and carotenoids, increase the content of photosynthetic pigments, and thereby enhance the photosynthetic capacity (Chen et al., 2021; Elango et al., 2023; Han et al., 2023). These changes work together to enhance the water use efficiency of tea plants. Especially in hot and dry weather, shading combined with a reasonable irrigation frequency can effectively alleviate the pressure of water shortage and help tea plants grow better. 5.2 Combined impacts on stress tolerance and bud viability Shading not only improves the physiological state of tea plants but also enhances their resistance to adverse environments such as high temperatures and drought. Studies have found that shading can regulate the activity of antioxidant enzymes and the levels of osmotic regulatory substances, enhancing the stress resistance of tea plants. Under shading conditions, the antioxidant system of tea plant leaves is activated, which can reduce the damage caused by strong light or high temperature and maintain the healthy growth and vitality of buds (Sano et al., 2020). In addition, shading can enhance the stability and stress resistance of cell membranes by regulating protein expression and metabolic pathways (Zaman et al., 2023). Reasonable arrangement of irrigation, combined with shading, can maintain the water and nutrient supply to the buds, further promoting the growth rate and quality improvement of the buds.
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