Soil Formation of Ecological Factors (complete information)

Communities cannot exist without a habitat, nor is a habitat likely to remain long without a community developing in it.

The functional interrelations between community and habitat are many and complex, constituting an ecosystem. Most important are soil formation nutrient cycling, and energy flow. Human interference in these processes often causes pollution, and exploitation, often bring exhaustion of natural resources.

We have already considered many of the reactions of plants upon the habitat, such as reduction of light and wind intensities, mitigation of temperature extremes, interception of rainfall and increase in relative humidity.

Plants also exert important effects on the formation, structure and characteristics of the soil or substratum produced by accumulation of dead plant remains: they further the weathering of rock through acid excretion and the mechanical action of roots: they offer obstruction to wind and water borne materials; they help stabilize moving sand and talus slopes and help prevent erosion generally: they variously increase or decrease the water content of the soil; they foster decomposition of raw humus into usable nutrients; and so forth.

Water plants form marl. It is by these reactions that plants exert dominance in terrestrial communities and establish the physical conditions of the habitat, which must be acceptable to all minor plants and animals that dwell there. Succession of plant stages eventually brings the interactions between habitat and community into equilibrium upon the establishment of the climax. In this chapter we will be primarily concerned with soils as dynamic components of ecosystems, including the cycling nutrients between the soil and the biota.

Soil Formation

Texture porosity, consistency arrangements of particles, chemical nature, and organic content of the soils are determined by three factors; parental rock material, the biota, and the climate. Differences in topography modify the relative effects of these three factors, and time is required before their full effects are realized.

Parental Rock

The basic rock from which the mineral portion of a soil is derived determines, to a large extent, not only its chemical composition but also its structure. For instance, soils derived from limestone are highly calcareous and more alkaline than soils derived from limestone are highly calcareous and more alkaline than soils derived from feldspar, sandy soils from quartite. Clay forms a finely textured compact, water-retaining soil.

Sand is coarse-textured and porous. Loan is a mixture of sand and clay and makes the best soil. The presence of iron oxides and silicates produces the red and yellow colours of some soils. Humus produces black soils. Soils from swamps or bogs and very rich in organic material is called muck.

Residual soils are formed in situ from underlying bedrock. Soils may however, be formed in one locality and moved considerable distances. Soils transported and deposited by wide are called losses, by water alluvium; by glaciers, till.

Plants and animals have a highly important role in the formation of soil, both of them affect its structure and they aid in the production of humus. Plants contribute to the mechanical and chemical weathering of rock. Plant roots, especially those of trees, can split large rocks. Lichens, mosses, and even bacteria and fungi excrete acids in the course of metabolism, which dissolve the substances that cement rock granules together. When plant roots die, fungi convert them to dry, soft spongy materials (punk) used as food by saprophytic micro-arthropods. Usually the bark of the ^root remains in fact the longest. Hollow tubes are thus formed than permit water and air to penetrate considerable depths into the soil. These channels gradually become filled with sit and animal excreta.

The addition of plant and animal organic matter to heavy compact soils or clay tends to open the soil, making it more porous. Addition of organic matter to sandy soils binds the particles closer and together, making the soil less porous.

Earthworms may be divided into deep and shallow-working species. Deep working species dig narrow tube-like channels which may reach 2-3 metre down through overlying soil to parent rock. Earthworms ingest soil while borrowing digest and absorb organic matter from it, and digest the residue in semi liquid form which is used to cement the walls of the burrow or else is deposited at the surface as castings.

Earthworms prefer easily digested succulent vegetation and dung for the purpose, but in the autumn may pull the freshly fallen leaves down into their burrows to use as food or nest linings. Ejected petioles may form madden piles around burrows. Earthworms are not, however, important soil builders in disturbed grassland; they may be absent altogether in and regions, the dry weight of casts brought to the surface annually by earthworms varied from 475g/m² (2.1 tons/acre) in a moderately hot dry climate, to 24,000 g/m² (10⁷ tons/acre). Earthworm casts compared with the surrounding soil show higher total nitrogen, organic carbon, exchangeable calcium, exchangeable magnesium, available phosphorous, exchangeable potassium, organic matter, base, capability, and pH and moisture equivalent. Only certain species make these surface castings; other species void the ingested soil into subterranean spaces.

The ant Lasius Niger Neoniger spends most of its time in its underground burrows and deposits excavated soil upon the ground surface around burrow entrances.

Humus in soil, organic matter that is partly or entirely decomposed is called humus. The amount of humus varies from less than 1 percent to as much as 20 percent of the soil: peat soil may be largely organic material, but much of it resists decomposition, and hence is not true humus. Decomposition breaks down compounds into similar ones that are washed back into the soil, thus becoming available again as nutrients.

Metric Tons/Hectare-year

The annual dry weight of leaves that fall to the ground in deciduous and coniferous forests varies from site to site and with the density of the trees, but is commonly in the range of 50 to 400 g/ms². In mature climax forests the rate of decomposition of the liter and re-absorption by plants of the nutrients thus yielded keeps pace with the annual accumulation so that an equilibrium is established. In several stages, decomposition, and utilization do not keep up with the annual accumulation so that the organic content of the forest floor increases with time. Litter production is lower in arctic than in tropical regions.

However, in the warm tropical regions the amount of humus that accumulates on the forest floor is low because of the high rate of decomposition, runoff and leaching.

The thick organic layer on the ground moderates extremes in the daily and seasonal rhythms of soil temperature, retards freezing of the ground in the autumn and thawing in the spring; and retains soil moisture.

Because of humus formation (involving oxidation) and the respiration of plant parts and animals undergrounds, soil air contains little oxygen but much carbon dioxide, and it possesses higher moisture content than does the general atmosphere above ground. This is especially marked the warm summer months when these processes go on more rapidly.

The decay of organic matter usually makes the top soil somewhat acid (most commonly pH 5 to 7), but in the mineral subsoil, the acid are often neutralized by the basic salts commonly present.

The mineral content of the leaf fall varies according to the species of tree.

Silcon, copper, manganese, carbon and zinc are also present in the leaves of hardwood trees. Carbon is relatively more abundant and nitrogen less abundant in coniferous than in deciduous leaves, but commonly the carbon nitrogen is 55:20.

Both plants and animals are important agents affecting the decomposition of organic matter and the formation of humus. An animal digests and mobilizes plants foods, much of which is returned to the soil, in parts as the excreta of the living animal, in part as the body of the dead animal, in part as gas. Fully formed human is in fact, derived mostly of fecal material.

The larger herbivorous and carnivorous animals pass urine and faces containing simple nitrogenous compounds and compounds of phosphorous, potassium, and traces of calcium, magnesium, sulphur and other elements. Humus is but one point in continuous cycles of decomposition of plant and animal organic matter, absorption of decomposition products by plants ingestion and metabolization of plant matter by animals, decomposition of plant and animal organic matter.

The most important soil organisms concerned in the decomposition of the little are the bacteria, both aerobic and anaerobic forms. They are commonly divided into two types. Heterotrophic bacteria obtain their energy from the oxidation of the carbohydrates and fatty substances as described above. They use this energy for the synthesis of cell substances and the production of enzymes that break down the complex compounds in the litter into simpler compounds, including proteins into ammonia compounds.

They then use part of the ammonia compounds in synthesizing the amino acids they need in building their own proteins. Autotrophic bacteria in turn, are of two types; chemosynthetic species, which obtain their energy from the oxidation of inorganic compounds (hydrogen, sulphur, hydrogen sulphide, iron and ammonia) and photosynthetic species which include purple and green sulphur bacteria, posses a form of chlorophyll, and utilize the energy of sunlight.

Chemosynthetic bacteria convert ammonia compounds into nitrites and nitrates, part of which they use in their own anabolism, the rest becoming available for plant to absorb. Photosynthetic bacteria use the ammonia compounds in their own anabolism and do not render them directly available to plants. Chemosynthetic bacteria are more abundant than photosynthetic bacteria in soil; photosynthetic bacteria are more abundant.

The decomposition products available to plants are reabsorbed by the roots and built up into plant tissue. Plants are eaten by animals and as plants and animals die the minerals are returned to the soil. All essential mineral cycles repeatedly through the ecosystem, the cycle of each mineral differing in various ways from the cycle of every other mineral.