Geoscience Reference
In-Depth Information
special hormones important for the growth of roots. Other species cooperate to
produce antibiotics important in the protection of plant roots against diseases. On
the other hand, some cause diseases and therefore belong into various groups of
plant pathogens. Still other species live symbiotically with plants roots - a relation-
ship known as mycorrhiza. The name is derived from two Greek words mykos
meaning fungus and riza meaning roots.
Mycorrhiza enables fungi the access to simple organic compounds like glucose
and sugar from the roots of plants. For fungi these gained compounds are simply
decomposed and the energy important for fungi is gained very quickly and effec-
tively. In return, the long and dense net of ultrafi ne hairlike mycorrhizal mycelia of
fungi enables the plants to gain nutrients and water from a substantially greater
volume of soil than that reachable by plant roots. It is not merely a simple physical
difference of soil volume. The more important aspect is that the permeability of
fungal cell membranes is much greater than the permeability of plant root mem-
branes. Hence, nutrients enter the plants simultaneously along two paths - one
directly from soil to the root and the other indirectly into the root after fi rst being
effi ciently absorbed by the dense net of ultrafi ne mycorrhizal mycelia surrounding
and in the immediate vicinity of the plant roots. Moreover, unique chemical reac-
tions occur within mycorrhizal domains that lead to more effi cient release of plant
nutrients from the original dead organic materials. Mycorrhizae are especially ben-
efi cial for the plant partner in nutrient-poor soils and when the soils are revitalized
after damaging technology, as, e.g., the mining of brown coal in the immediate
vicinity of a soil surface.
4.4
Soil Enzymes
Soil enzymes are powerful products of soil bacteria and fungi activities during
which bacteria usually play a leading role. Enzymes are proteins produced inside
the cell and exported out of the cell into the soil solution where they regulate the
breaking down of the complicated structure of the dead remnants of plants and ani-
mals that is commonly called a substrate. The processes lead either to the break-
down of organic matter only or to the release of plant-accessible forms of nutrients.
The latter process is commonly known as nutrient mineralization.
Because enzymes are energetically costly for the cells to make, they are tightly
regulated and made only when absolutely necessary. Regardless of substrate avail-
ability, the cell initially begins the production and expulsion of tiny amounts of
enzyme as a mechanism to detect the existence and nature of its substrate. If a sub-
strate is present, these constitutive enzymes generate signals that induce additional
enzyme synthesis. Although the synthesis of enzymes is sensitive to the presence or
absence of many other factors, the most important is the presence of suffi cient
amounts of organic substrate. Hence, we are obliged to keep the organic content of
substrate at or above threshold levels by green farming, introduction of cover crops,
and other steps leading to conservation of organic materials in soils. The quality and
