Stable layer of plant and species habitat

Roots are important nutrient organs of terrestrial plants, and the water and nutrients provided by the terrain must be absorbed and transported by roots before they can be used by plants. However, it should be pointed out that studies have proved that whether it is a deep-rooted plant or a shallow-rooted plant, or a straight-rooted or fibrous root plant, the real absorption function is not the old taproot and lateral roots, but the root tip of the fine root and the root on the root tip with pure hairs. They are the lowest branch level in the root system, large in number and updated quickly.

The distribution of the root system is uneven, often spindle-shaped in profile, the middle and upper part of the spindle is large, the root-soil ratio is high, the number of fine roots (roots with a root diameter of < 2 mm) is large, and the root hairs are the densest (Huang Jianhui et al., 1999; persson，1983;Cairns et al., 1997), also known as the root group (Xu et al., 2003, 2004). The root group is the main functional area of the root system to absorb water and nutrients, and the root group and the soil inside it are collectively called the root group circle, which is the most active place for microorganisms. Many microorganisms depend on the metabolites of the roots to survive, and at the same time, the microorganisms convert the inorganic salts in the soil into a bioavailable state for the roots to absorb.

As for those roots outside the root group, they only play an auxiliary role in plant growth.

Different species have different range of root circle depths. This is determined by the physiological habits and genetic characteristics of the species, as well as the status of climate, soil, water and fertilizer resources in the native place. In a sense, the depth of the root circle of a species is the result of the long-term optimization of the plant's vertical diversity of the habitat.

Different species of plants that grow in the same area can have different root group depths. Circles of plant roots of the same species are connected to form specific layers. Multiple species will have multiple layers, some of which are located in the shallow part and some of which are relatively deep, which is conducive to the sharing of water and fertilizer resources in different circles of various plants and avoids serious interspecific conflicts.

This structural characteristic of the landscape gives us important enlightenment: the growth of a plant has its specific underground environment ——— root circle, in which the physical and chemical properties of water and fertilizer conditions determine the growth status of the plant. The depth of the underground microenvironment of plants of different life forms is different.

Therefore, in the land reclamation work, the thickness of the covering soil must be determined according to the use of the land and the type of plants, and the design by using the concept of the maximum depth of the terrain often leads to the excessive increase of the amount of work and the cost, and it is difficult to generalize.

The distribution of vegetation species is regional, and the main compliance factor is the regional average temperature difference. Temperature directly restricts the activity of enzymes in plants and affects the metabolism of organisms, so temperature is the key factor, sunlight is just an additional measure, in places with low temperatures, the metabolism of vegetation is also very slow, the consumption of energy is also less, and the natural demand for light is reduced, but often, in high altitude and low temperature areas, the illumination will be better.