Light intensity plays an important role in plant growth and morphology. Light has direct and indirect effects on plant growth. Direct impact refers to the effect of light on plant morphogenesis. As far as the plant growth process itself is concerned, it does not require light. As long as there are enough nutrients, plants can grow in the dark. However, plants growing in the dark have abnormal morphology. For example, plants that grow out of light are yellow seedlings. Indirect effects mainly refer to photosynthesis, which synthesizes organic matter by fixing carbon dioxide in the air, which is the material basis for plant growth.
Light intensity can have an indirect effect on the growth of tree roots. Sufficient light conditions are conducive to the growth of seedling roots, forming a larger rhizome ratio, which is beneficial to the later growth of seedlings. When the light is insufficient, there is a significant inhibition on root growth. Effect, the amount of root elongation is reduced, the number of new roots is small, and even the growth is stopped. Although the root system grows in the soil without light, most of its material source comes from the assimilated material in the aerial part. When the amount of assimilation decreases and the amount of assimilation decreases due to insufficient sunlight, according to the principle of organic matter transportation and nearest distribution, the assimilated material is first used for the ground part and then sent to the root system. Tree species form low light compensation points to suit their environmental conditions. The tree body appears excessively long or yellow due to lack of light, and the root system grows poorly, which will inevitably lead to the failure of the upper branches to mature well, fail to dormantly overwinter, and have a shallow root system and low resistance to drought and cold. In addition, light can inhibit germ activity to a certain extent, such as trees growing on sites with better sunlight conditions, and their disease is significantly reduced.
If the light intensity distribution is not uniform, the branches and leaves of the tree will grow luxuriantly in the direction of strong light, and will grow poorly in the direction of weak light, forming a significant phenomenon of partial crown. This phenomenon is very obvious in urban garden tree species. Due to the high-rise buildings and narrow streets in modern cities, the distribution of light intensity has changed. On the same street and on both sides of the building, the light intensity will vary greatly. If the east-west direction goes to the street, the north side receives far more light than the south side, so that the trees will be crowned due to the growth of branches. Trees and buildings too close together can also cause trees to grow asymmetrically towards the center of the street.