Plant Gene and Trait 2025, Vol.16, No.4, 162-172 http://genbreedpublisher.com/index.php/pgt 163 seedlings. The row type (60×90 cm) is suitable for close planting, while the double-row type (90+150×60 cm) is suitable for the middle and later stages or plots with different density requirements. On the vacant land beside the fields, people often grow some vegetables for intercropping, which makes the space utilization rate higher. In addition, new technologies such as hydroponics, aeroponics and aquaponics have also been used to grow mulberry in controlled environments, which can save water and increase yield (Baciu et al., 2023; Chanotra et al., 2024). 2.2 Typical crop combinations and ecosystem services Mulberry can also be grown in combination with many crops, such as alfalfa, turmeric, potatoes, garlic, onions and fennel. These intercropping patterns not only improve the land utilization rate, but also make the soil healthier, with more microorganisms and smoother nutrient cycling (Zhang et al., 2019; Chanotra et al., 2024). After planting vegetables, farmers can still harvest several crops a year, and their income becomes more stable. This combination can also reduce soil erosion, assist in carbon sequestration, and improve the microclimate (Kaushal et al., 2024). 2.3 Benefits and limitations of vertical agroforestry models Vertical agroforestry systems have many advantages. It can make full use of land and resources and increase the yield per unit area. The multi-layer structure can also make the soil looser and more nutrient-rich, which is conducive to improving the carbon sink function and regulating the climate (Kaushal et al., 2024). Meanwhile, when there are more types of crops, farmers’ income sources become more stable and their ability to withstand market fluctuations or natural disasters is stronger (Chanotra et al., 2024). From an ecological perspective, there are more types of microorganisms in the soil and the system is more stable (Zhang et al., 2019). But there are also some problems. For example, mulberry itself is relatively tall and have a high demand for water and space. If they are planted too densely, they may compete for resources with the crops below (Magadum et al., 2020). Different crops have different requirements for sunlight, water and nutrients. If not managed properly, some crops may not grow well. In addition, this type of system requires a considerable initial investment, is troublesome to manage after cultivation, and has relatively high technical requirements for farmers (Baciu et al., 2023). 3 Light Environment in Multilayer Planting Systems 3.1 Vertical light distribution and shading patterns In a multi-layer planting system, the distribution of light in the up and down directions is very uneven. The upper crops or trees will block the sunlight, greatly reducing the light that the lower crops receive. For instance, in the sloping forest where multiple plants are mixed, the relative photosynthetic photon flux density (rPPFD) at different heights varies significantly. The rPPFD under the forest is much lower than that on single-story slopes, and the light variation is significant whether in the up-down or left-right direction. In artificial cultivation factories, when planting in the traditional vertical I-shaped method, the lower down, the weaker the light becomes, and the photosynthesis of the lower layer crops will be affected. However, if S-shaped lateral layering planting is adopted and side supplementary lighting is added, the light distribution can be more uniform, and the crop quality and light utilization rate will also be higher. In addition, reasonable arrangement of planting structure and crop types can also reduce shadow coverage and enable the lower layer crops to grow better (Feng et al., 2019; Solanki et al., 2024). 3.2 Temporal and seasonal light dynamics The light in a multi-layer system is not only unevenly distributed but also varies greatly over time. The intensity of light under the forest or in multi-story structures fluctuates constantly with the position of the sun throughout the day and the change of seasons. Especially in places where there are gaps in the forest canopy, the changes in sunlight are even more obvious. Artificial light sources (such as leds) can adjust the duration and intensity of illumination, which can alleviate the influence of seasonal changes in natural light to a certain extent and maintain relatively stable illumination throughout the year (Gerovac et al., 2016). Nowadays, there are also lighting devices that can move along with the sun, which can guide natural light as much as possible to the lower layers of the structure. This not only enhances the lighting of the lower layers but also saves electricity.
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