On the basis of relative proportion of these particles, soils are of following types:
Sandy soil: It is formed of 85% sand and 15% clay and silt. It is also called Light soil. It has high porosity percentage of pore-spaces in a given volume of soil) so has loose soil with low water holding capacity. It also has large Temperature fluctuations. It is characterized by the xerophytic plantations. This soil is not rich in nutrients and is less fertile.
Clayey soil: It is formed of 50 % clay and 50 % salt or sand or both. It is also Called cold or heavy soil. It has fine pore spaces so very high water holding Capacity. The temperature does not fluctuate much. It does not allow easy Penetration of soil and has less water logging capacity and presence of CO2.
Salt soil. It has 90% silt and 10 % sand. It has good soil porosity and water holding capacity but is poor in nutrient supply.
Loamy soil. It consists of 70% sand and 30% clay or silt or both. It is best soil For the plant growth because of its good water holding capacity, water Infiltration and adequate aeration. Root penetration is also good in loamy soil. Minerals, also called biogenic nutrients, are essential for the proper growth of Organisms so the type and distribution of plants and animals are determined By specific distribution of minerals. Deficiency or absence or excess of minerals results in abnormal growth or even death of organism. Snails occur in soils rich in calcium content.
Halophytes and some sea animals have salt secreting glands.
Soil, deficient in copper and cobalt, is unfit for raising cattle. High concentration of minerals greatly limits the distribution of animals e.g. Dead sea and great salt lake (areas with high salt contents) are devoid of much vegetation.
Soil nature and distribution of vegetation:
The type of soil (sandy, loamy or clayey) and its water retention, aeration and Mineral contents determine the nature of plants and animals. On the basis of These characters of soil, the plants are divided into following ecological categories.
Halophyets: The plants found on saline soil e.g. Rhizophora, Heritiera, etc.
Lithophytes: The plants found on rocky surface.
Chasmophytes. The plants found in rock crevices.
Oxylophytes (Calcifuges).The plants found on acidic soils e.g. maize, barley, Potato, Rumex and Rhododendron.
Calcipphytes. The plants growing on calcium-rich soils.
Soil water: soil water is more important than any other ecological factor in Distribution of plants because it is required for meeting the metabolic and Transportational needs of soil flora, soil fauna and the process of Humification Soil water is derived from rain. Rain water occurs in following forms:
Run-away water: It is drained away from the soil surface along the slope and is also called runoff. Gravitational water It is that amount of water which percolates downward Under the force of gravity and finally reaches the water table.
Capillary water: The water held up by capillary forces between the soil Particles in the micropores is called capillary water. This is the best form of Water available to the plants.
Soil air: Soil air is present in the pores of the. soil and is necessary for respiration of roots and soil flora and fauna. If the soil is not water-logged It pores partly contain water and partly air. The soil air is slightly rich in CO2 And poorer in O2 due to respiratory activities of underground parts of plants And micro-organisms. The oxygen of soil air is an important factor controlling
Soil fertility because it is required by humus forming micro organisms, nitrogen-fixing bacteria and other soil organisms like earthworms which increase the soil fertility.
Biotic community is an association of a number of interrelated populations Belonging to different species ,in a common environment which can survive In nature(Clarke, 1967).Biotic community was called biocoenosis(Mobius,1880).Clements(1916) stated the community as a sort Of super organism whose member species were tight bound together both Now and in their common evolutionary concept.
Some examples are:
Plant growth is reduced in deserts due to less availability of water. In deep lakes, due to low phosphorus contents, growth of phytoplanktons is retarded. Biotic community is an assemblage of a number of different but interacting Populations of different species. These populations can be divided into animal Community, plant community and microbial community. These three types of Communities in a biotic community are interdependent. The gradual physiological adjustment to slowly changing new environmental Conditions is called acclimatization. Osmoregulation involves regulation of osmotic concentration of the body fluids by regulating the water level in them. In all the vertebrates including Human beings, osmoregulatory organs are kidneys. The kidneys are flexible in Osmoregulation.