1.1 INTRODUCTION
Soil is a mixture of minerals, organic matter, gases, liquids, and countless organisms that together support life on Earth. Soil is a natural body called the pedosphere which has four important functions: it is a medium for plant growth; it is a means of water storage, supply and purification; it is a modifier of Earth’s atmosphere; it is a habitat for organisms; all of which, in turn, modify the soil.
Soil is called the Skin of the Earth (Miller and Austin, 1953) and interfaces with lithosphere, hydrosphere, atmosphere, and biosphere. The term pedolith, used commonly to refer to the soil, literally translates ‘ground stone’. Soil consists of a solid phase of minerals (the soil matrix) and organic matter, as well as a porous phase that holds gases (the soil atmosphere) and water (the soil solution) (Voroney et al., 2015). Accordingly, soils are often treated as a three-state system of solids, liquids, and gases (McCarthy and David, 2006).
Soil is a product of the influence of the climate, relief (elevation, orientation, and slope of terrain), organisms, and its parent materials (original minerals) interacting over time. Soil continually undergoes development by way of numerous physical, chemical and biological processes, which include weathering with associated erosion. Given its complexity and strong internal connectedness soil has been considered as an ecosystem by soil ecologists (Ponge and Jean-Francois, 2015).
Most soils have a dry bulk density (density of soil taking into account voids when dry) between 1.1 and 1.6 g/cm3
, while the soil particle density is much higher, in the range of 2.6 to 2.7 g/cm3
. Little of the soil of planet Earth is older than the Pleistocene and none is older than the Cenozoic (Buol et al., 1973), although fossilized soils are preserved from as far back as the Archean.Soil science has two basic branches of study: edaphology and pedology. Edaphology is concerned with the influence of soils on living things. Pedology is focused on the formation, description (morphology), and classification of soils in their natural environment. In engineering terms, soil is referred to as regolith, or loose rock material that lies above the ‘solid geology’. Soil is commonly referred to as “earth” or “dirt“; technically, the term “dirt” should be restricted to displaced soil.
Soil bacteria and fungi play pivotal roles in various biogeochemical cycles (BGC)(Wall and Virgins, 1999) and are responsible for the cycling of organic compounds. Soil microorganisms also influence above ground ecosystem by contributing to plant nutrition, plant health, soil structure, population. An estimated 1,500,000 species of fungi exist in the world (Giller, et al., 1997). But unlike bacteria, many fungi cannot be cultured by current standard laboratory methods. Although molecular methods have been used to study soil bacterial communities, very little research has been undertaken for soil fungi. All organisms in the biosphere depend on microbial activity (Pace, 1997).
The diversity of physical characteristics of soil associate with aggregation of small scales means that soil can contain a large diversity of microorganisms in close proximity, and the chemical composition of soil is also highly heterogeneous in both vertical and horizontal dimensions (Dighton, et al., 1997).
Potting soil, also known as potting mix or potting compost, is a medium in which to grow plants, herbs and vegetables in a pot or other durable container. The first recorded use of the term is from an 1861 issue of the American Agriculturis (Oxford English Dictionary). Some common ingredients used in potting soil are peat, composted bark, sand, perlite and recycled mushroom compost, although many others are used and the proportions vary hugely. Most commercially available brands have their pH fine-tuned with ground limestone; some contain small amounts of fertilizer and slow-release nutrients. Despite its name, little or no soil is used in potting soil because it is considered too heavy for growing houseplants (Brown, 2003).
Some plants require potting soil that is specific for their environment. For example, an African violet would grow better in potting soil containing extra peat moss, while a cactus requires sharp (i.e. plenty of) drainage, most commonly perlite or sand. But potting soil is not ideal for all contained gardening. Insectivorous plants, such as the Venus flytrap and the pitcher plant, prefer nutrient-poor soils common to bogs and fens, while water-based plants thrive in a heavier topsoil mix (The Christian Science Monitor).
1.2 AIM AND OBJECTIVES
Aim
The aim of the study is evaluate the diversity of fungi in potting soil with the following objectives.