The root system of the tree performs physiological functions, by taking water from the soil with mineral salts dissolved in it, and mechanical, by fixing the tree in the ground. Besides, tree roots can fulfill a number of other tasks, such as the storage of spare materials, impact on soil, etc.. The root system of the tree, densely overgrowing the soil, contributes to its strengthening and prevents erosion. According to these tasks, the root system is properly developed. Its horizontal extent is generally greater than the horizontal extent of the crown. The total root length of large deciduous trees exceeds significantly 100 km. The root mass is up to 25% the mass of the whole tree (in spruce 15-25%, in fir 14-22, u sosny 10-20, on the oak 14-20, in noise 5—15%). The study of root systems is associated with great technical difficulties, and therefore they are a less well-known part of the tree.
The primary root anatomy differs from the above-ground shoot. The young root is covered with an epidermis called rhizoderma. It consists of one layer of thin-walled cells not covered by a cuticle, there is also no stomata in it. So-called trichomes are formed at the end zone of the root (hair zone), which, together with rhizoderma, take part in the absorption of substances needed by the plant. So the final part of the root is the zone where water and nutrients are most strongly absorbed from the soil.
Root growth occurs due to the apex meristem, which is covered with a so-called cap (kalyptra), facilitating root growth into the substrate. Trees produce root systems characteristic of a given species. However, depending on the soil conditions, and above all water relations, the type of root system can vary considerably. Tree root systems can be broadly classified into three types: palowy, oblique (cardiac) and flat (disc).
Drawing. Tree root systems: on the left - pile; in the middle of the heart; on the right - disc; (according to Kostler).
The characteristic pile system is formed by Scots pine, silver fir, Weymouth pine, often larch, and at a younger age also Douglas fir. Many deciduous trees with different root systems also initially develop a tap root.
Most types of oaks and some elms retain their tap root type for many decades. The development of the pile-type root system often depends on the possibility of free root growth, e.g.. on deep sands. Under different conditions, the type of root system characteristic for a given species may undergo various modifications.
System ukośny (cardiac) characterized by the presence of several highly developed roots, which form a uniform hemisphere and relatively numerous branches. Larchs produce typical heart root systems, daily reading, linden trees, birches and hornbeams. Disc system (flat) consists of several highly developed horizontal roots (shallow) and deviating from them, often vertically, roots of the second order. A typical example of a tree with such a root system is Norway spruce among conifers. Often such a root system is produced by white thread, ash, aspen.
Drawing. Root systems of some conifers and deciduous trees (according to Kostler): successively from left to right pine, fir, spruce, grab, lipa.
Apart from fundamental differences in the arrangement of the main roots, there may be significant differences in the overgrowth of the soil by the roots of further rows. The roots of deciduous trees grow into the soil much more intensively than those of conifers. Among the conifers, the roots of larch and Douglas fir grow the most strongly. Among our deciduous trees, oaks and elm are the least overgrowing. It exceeds the ash tree much more, aspen and rapids, beech is the strongest, grab, olsze, sycamore, Norway maple and linden trees. It can be stated, that trees with a heart-shaped root system outgrow the soil most intensively.
The characteristic features of the root system also include the ability to adapt to changing conditions, mainly to change the groundwater level. Deciduous trees are superior to conifers in this respect. The distribution of nutrients in the soil may cause various modifications of the type of the root system. Overall it can be said, that rich soils are less well overgrown by roots than less rich soils. If the plants mainly use rainwater, so when the groundwater level is low (sands), trees produce flat, shallow, but widely branched root system (e.g.. scots pine). A similar phenomenon is observed in the city, for example if after
the top is covered with boards around the tree. The roots then gather in a compact mass at the points where water enters the soil. Sometimes the roots, in search of water and air, overgrow the soil under the entire width of the impermeable surface. Such roots do not have a mechanical function, they are relatively thin and highly conductive to water. It needs to be highlighted that, that in the city under the paved surface, soil air is a factor that modifies the root system as no less important than water. Roots of Norway spruce, Weymouth, Sitka spruce and beech are particularly sensitive to the lack of sufficient oxygen in the soil air. The phenomenon of root aerotropism can often be observed in trees growing at impermeable surfaces (negative geotropism), just caused by the lack of oxygen.
The mechanical properties of root wood are different from that of the trunk wood. For example, the crushing strength of a root in the radial direction, important when bending the root, it is three times lower than the tensile strength. The shapes and dimensions of the roots depend on various loads on individual roots. For example, the roots are most likely to be crushed, as the main lateral roots in the disc or heart system, they are thick, whereas, in the meantime, the second-order roots in the disc system are "predominantly stretched" relatively thin. Roots have great potential to overcome mechanical obstacles in the soil or to adapt to them. The development of the root system is also influenced by meteorological factors, mostly wind. Thick roots are found on the leeward side, more resistant to crushing and bending, on the windward side, however, longer roots develop, with higher tensile strength. Thus, there is also the same asymmetry within the root system, as in the area of the crown and trunk.
Most forest trees have a symbiosis between roots and fungi - the so-called mycorrhiza. Such symbiosis is especially important for trees in dry and nutrient-poor habitats. The hyphae of the fungus are like additional organs for collecting mineral salt solutions. In urban conditions, the development of mycorrhiza is very limited. Adding soil to the pits from natural forest sites when planting trees in cities has this added benefit, that, at least for a while, it enables the development of mycorrhiza. Most fungi that coexist with tree roots grow in slightly acidic soils.