Bioscience Methods 2025, Vol.16, No.5, 246-253 http://bioscipublisher.com/index.php/bm 247 2 Physiological Responses of Kiwifruit to Water and Fertilizer 2.1 Root absorption and water stress adaptation Kiwifruit roots are mostly shallow fleshy roots, which are particularly sensitive to water and soil conditions. If the water is unstable or the soil is not good, the roots cannot absorb enough water and fertilizer, and the fruit yield and quality will decrease (Calabritto et al., 2024). Among them, lateral roots are particularly important for the absorption of water and fertilizer. Studies have found that genes such as AcEXPA23 can promote lateral root growth, allowing plants to better utilize water and fertilizer (Wu et al., 2022). When encountering drought or waterlogging, a signal called ABA is activated in the roots of kiwifruit. This signal can help plants adapt to environmental stress (Wurms et al., 2023). In addition, if some mycorrhizal fungi or melatonin are applied to the roots, the roots will grow more vigorously, and the ability to absorb fertilizer and water will also become stronger, thereby improving drought resistance (Xia et al., 2022). The study also found that kiwifruit roots mainly absorb water in the soil layer within 30 cm. Therefore, when irrigating, the amount of water and the water layer should be controlled to avoid the pressure caused by sudden changes in water. 2.2 Photosynthetic efficiency and nutrient transport Water and fertilizer directly affect the photosynthesis of kiwifruit leaves. If there is too little or too much water, the stomata of the plant will close and the photosynthesis efficiency will decrease. However, some drought-resistant rootstocks can maintain a certain gas exchange and photosynthesis even in drought (Li et al., 2020; Calabritto et al., 2025). Mycorrhizal fungi and melatonin are not only good for roots, but also increase chlorophyll content, thereby enhancing photosynthesis (Xia et al., 2022). Calcium is also important. It can stabilize cell structure, regulate signal transduction, and help various nutrients move in the plant body (Larocca et al., 2025). The smooth transportation of elements such as nitrogen, phosphorus and iron can maintain plant health and normal photosynthesis of leaves. 2.3 Regulation of fruit development and quality Water and fertilizer also affect the size and taste of kiwifruit. If there is a lack of water in the early stage of fruit growth, the fruit may become smaller; but if there is a lack of water when it is about to mature, it may increase the sugar content, taste sweeter, and the storage time may also be longer. Studies have shown that reasonable regulation of irrigation and fertilization at different growth stages, such as slight water shortage combined with fertilization, can make the fruit harder and sweeter, and increase the content of vitamin C and dry matter (Zha et al., 2023). During the development of the fruit, nutrients such as sugars, flavonoids and vitamins are accumulated. The changes in these components are controlled by the metabolic and gene regulatory systems in the plant, which are in turn affected by water and nutrients (Shu et al., 2023). At the same time, the distribution of calcium in the fruit is also critical, which is very helpful for the quality and storage performance of the fruit (Larocca et al., 2025). 3 Optimization of Irrigation Regimes 3.1 Trials on irrigation frequency and volume Many field tests and simulation studies have found that the reasonable arrangement of the number of irrigations and the amount of water each time are critical to saving water and increasing yields. There is now a technology called "variable irrigation (VRI)", which can adjust the watering frequency and water consumption of each plot of land according to the different soil and crop conditions of the plot. This not only saves water, but also does not reduce yields. It is particularly cost-effective to use in water-scarce areas (González Perea et al., 2018). However, conditions in different regions are different, so it is best to do some experiments locally to see how to make the most appropriate adjustments. 3.2 Stage-specific irrigation strategies Kiwifruit has different water requirements at different growth stages. If the right amount of water can be given at each stage, it is easier to grow good fruit. Now there are some "decision-making tools" and "prescription maps" that can help calculate when and how much water to apply, and they will be arranged according to the climate and plant needs (Neupane and Guo, 2019). Some methods also directly look at the state of the plant, such as whether
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