Ecological theories in soil biology

Soil life or soil biota is a collective term for all the organisms living within the soil. Soil biology is the study of microbial and faunal activity and ecology in soil. These organisms include earthworms, nematodes, protozoa, fungi and bacteria. Soil biology plays a vital role in determining many soil characteristics yet, being a relatively new science, much remains unknown about soil biology and about how the nature of soil is affected. Overview The soil is home to a large proportion of the world's genetic diversity. The linkages between soil organisms and soil functions are observed to be incredibly complex. The interconnectedness and complexity of this soil 'food web' means any appraisal of soil function must necessarily take into account interactions with the living communities that exist within the soil. We know that soil organisms break down organic matter, making nutrients available for uptake by plants and other organisms. The nutrients stored in the bodies of soil organisms prevent nutrient loss by leaching. Microbial exudates act to maintain soil structure, and earthworms are important in bioturbation. However, we find that we don't understand critical aspects about how these populations function and interact. The discovery of glomalin in 1995 indicates that we lack the knowledge to correctly answer some of the most basic questions about the biogeochemical cycle in soils. We have much work ahead to gain a better understanding of how soil biological components affect us and the planet they share with us. In a balanced soil, plants grow in an active and vibrant environment. The mineral content of the soil and its physical structure are important for their well-being, but it is the life in the earth that powers its cycles and provides its fertility. Without the activities of soil organisms, organic materials would accumulate and litter the soil surface, and there would be no food for plants. The soil biota includes: Megafauna: size range 20 mm upwards, e.g. moles, rabbits, and rodents. Mesofauna: size range 100 micrometre-2 mm, e.g. tardigrades, mites and springtails.

Oryx, 2006

European Journal of Soil Science, 2006

1997

Going underground: ecological studies in forest soils, Publisher: Research Signpost, Trivandrum, India, Editors: Nayerah Rastin, Jürgen Bauhus, 1999

Interactions between soil animals and their environment can be described in terms of positive and negative feed-back loops taking place in the build-up and steady-state of soil ecosystems, respectively. The size of animals determines the scale at which they interact with their physical and biotic environment. Nevertheless varying scales at which animals intervene in functional processes is not relevant to any hierarchical position within the ecosystem, due to symmetrical patterns in the relationships between microbes, animals, humus forms and vegetation types. The present knowledge has been reviewed and discussed to the light of an integrated view of the soil ecosystem, with a particular accent put on soil acidity.

This paper will provide information with critical logic about relation between soil and organisms

The biological activity of the soil is highest in the upper layer, predominantly the rooting layer, where energy is present. This upper layer is extremely biotic and is, therefore, called a living system. This living system is surprisingly diverse. The basis for this diversity is provided by this spatial and temporal heterogeneity. Mineralization of organic matter or recycling of elements is the collective responsibility of soil fauna and soil microflora. Soil fauna fragments organic structures and influences primary decomposers such as the soil microflora. They also play a role in the synthesis of organic matter and any kind of formation of soil material. Quantification of the role of single species or size groups is extremely difficult since many feeding interactions are still not well understood. In principle, this dynamic system of mineralization of organic matter is sustainable, because of the equilibrium and stability of the soil system. The three key functions related to soil quality are (i) dynamics and mineralization of organic matter, (ii) soil structure formation and maintenance, and (iii) support and control of plant production and species diversity. Although these functions can be carried out by alternative systems, and via alternative pathways, as routes in food webs, it is the author's opinion that some functions are irreplaceable. Therefore, there is concern that repeated stress will lead to impoverishment of the soil community. Disturbance by contaminants, such as heavy metals, can best be measured by fauna, looking at species diversity. In the majority of soils, microorganism diversity is probably never reduced to such a level that it affects the functioning of the decomposer system. It is likely, that only those processes carried out by a few microbial species, such as nitrification and nitrogen fixation, have the potential to show clear responses. Defining the cause of disturbance, such as changes in land use, including desiccation, acidification or fragmentation, determines the direction of monitoring. Using the Dutch Soil Quality Indicator System may be the safest way to monitor soil quality. Indicators of soil quality should be physical chemical biological and visible. This selection should be based on land use, the relationship between soil function and the indicator, spatial and temporal patterns of variation and the importance of this variation, the sensitivity of the measurement to changes in soil management, and comparability with routine sampling and monitoring programmes.

Soil biodiversity has become a major area of research over the last decade, and the literature on the topic has expanded tremendously in recent years, so much so that a huge number of publications now deal with soil biodiversity every year. This article does not attempt the formidable task of drawing a general picture of where the field is at the moment, but it zeroes in instead on two perspectives that seem to have gathered momentum over time and raise concern about future progress. The first perspective involves the implicit assumption that to make sense of either the species-, genetic-, or functional biodiversity of soils, it is not necessary to consider in detail the features of (micro)habitats provided by soils to organisms, and that analysis of the information provided by extracted DNA or RNA suffices. The second perspective is associated with research on the effect of the physical and chemical characteristics of microhabitats on the activity of microorganisms. It basically hypothesizes that all microorganisms behave similarly, and therefore that observations made mostly with bacteria can be extended readily to all organisms, ignoring taxonomic biodiversity. To illustrate both perspectives, we provide a number of illustrative examples from the relevant literature and analyze them briefly. We argue that these two perspectives, if they spread, will hinder progress in our understanding of soil biodiversity at any level, and especially of its impact on soil processes. In order to return to a more fruitful middle ground, where both a variety of organisms and the characteristics of the microhabitats where they reside are carefully considered, several routes can be envisaged, but our experience suggests that an emphasis on genuinely interdisciplinary research is crucial.