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Cite this article as:

 

Jadhav, KP., Sujatha H. T., Vishwanath and  Patil RS. (2021) Monitoring, Quantification and Evaluation of Soil Biodiversity. Food and Scientific Reports. 2 (9) 52-54.

ABSTRACT

One m² land surface may contain 10,000 species of soil organisms which indicates the soil biodiversity. Reduction in the level of biodiversity in global environment due to human activities will alter the ecosystem processes and change the resilience and resistance of ecosystems to environmental change. The need for action to protect biodiversity is unanimously acknowledged. Biodiversity conservation is essential both for ethical reasons and especially for the ecosystem services. Studies on soil biodiversity are often neglected and as such there is a paucity of knowledge on this subject. This article gives insight on major ecosystem functions, categories of ecosystem services, threats of soil biodiversity and soil biodiversity monitoring and evaluation.

Keywords: Earthworm, Ecosystem, Monitoring, Soil biodiversity, X-ray tomography

 

Soil biodiversity is the variation in soil life, from genes to communities and the variation in soil habitats and from micro-aggregates to entire landscapes. One square meter of land surface may contain some ten thousand species of soil organisms, whereas aboveground biodiversity is some orders of magnitude is lower. Humans have extensively altered the global environment and caused a reduction in the level of biodiversity. These changes in biodiversity alter ecosystem processes and change the resilience and resistance of ecosystems to environmental change. The recent Conference of the Parties of the Convention on Biological Diversity (May 2008, Bonn) demonstrated that, the need for action to protect biodiversity is unanimously acknowledged. Biodiversity conservation is essential both for ethical reasons and especially for the ecosystem services that the complex of living organisms provide for current and future generations. Studies on soil biodiversity are often neglected and as such there is a paucity of knowledge on this subject. The majority of soil organisms are still unknown and it has been estimated that, the currently described fauna of nematoda, acari and protozoa represents less than 5 per cent of the total number of species.

Ecosystem functions

Soil biodiversity may be better measured by considering the three major ecosystem functions. The first group comprises soil micro-organisms which act as follows. 

1. Chemical engineers or chemical decomposers: Bacteria and fungi are the main chemical decomposers are involved in the transformation and mineralization of complex organic compounds into nutrients available for plants. They are also involved in humification and in several other major biological processes such as nitrogen fixation, methanogenesis, nitrification and ammonification.

2. Biological regulators: it includes microfauna (<200 μm) to macrofauna (>2 mm) like phytophagous, rhizophagous and saprophagous which feed on decaying organic matter associated with bacteria and fungi. They are involved in the decomposition function directly by shredding and digestion and also through the facilitating/stimulating effect they have on the action of chemical decomposers.

3. Ecosystem engineers are termites, earthworms, ants, etc. These organisms can change the physical state of soil by producing biogenic structure. They modify the nature resources for other soil organisms, e.g. nutrient availability for plants, pores for non-burrowing invertebrates. This group has a major impact on soil functioning mainly by creating soil structures and regulating organic matter dynamics. 

Ecosystem services

These represent the benefits human populations derive directly or indirectly from ecosystem functions including both goods and services. Ecosystem Assessment was the first large scale ecosystem assessment report to evaluate the consequences of ecosystem change for human well-being and the scientific basis for action to enhance the conservation and sustainable use of those systems. MEA report identified four main categories of ecosystem services that as follow. 

1. Regulating Services: Regulating services provides climate regulation, water regulation and purification, disease and pest regulation and bioremediation of organic pollutants.

2. Supporting Services: Supporting services in which soil microbial communities are involved and mot directly used by humans includes soil formation, nutrient cycling, water cycling, primary production and habitat for biodiversity.

3. Provisioning Services: Provisioning services include products obtained from ecosystems, such as food, water, fibre, fuel, genetic resources, chemicals, medicines and pharmaceuticals. Rhizosphere microorganisms are an important bioresource for bioactive substances such as antibiotics, biosurfactants, enzymes and osmoprotective substances.

Threats of soil biodiversity

Soil management strongly influences soil biodiversity by agricultural ecosystems resulting in changes in abundance of individual species. Many processes carried out by soil organisms persist in native ecosystems as well as in intensively cultivated soil. There is only a limited insight to what extent these changes in management intensities are accompanied by changes in spectrum of soil microorganisms responsible for the processes involved. The most important factors affecting the soil biodiversity comprise (a) Habitat fragmentation, (b) Amount and quality of nutrients and energy sources, (c) Seasonal effects, (d) Spatial differences in the soil, (e) Climate variability and (f) Interactions within the biotic community. Reduction in biological diversity of soil macrofauna is one of the most profound ecological consequences of modern agriculture.  

Soil biodiversity monitoring

Soil biodiversity monitoring is the process of determining status and tracking changes in living organisms and the ecological complexes of which they are a part. It provides a basis for evaluating the integrity of ecosystems, their responses to disturbances and the success of actions taken to conserve or recover biodiversity. The inventory of soil biodiversity should consist of an estimation of taxonomic diversity at one site at a given time. A second possible step, the monitoring activity, is achieved by estimating diversity at the same site at more than one time to allow inferences regarding change to be drawn. Inventories should be based on the adoption of standardized, quantitative and repeatable protocols of sampling and estimation of soil biodiversity.

Any inventory protocol has to be designed to provide information on α and β-diversity. Replication in time of these protocols would then be the basis of monitoring activities. The selection of sites for inventory or monitoring programme can be based on a hierarchical design, or a grid based scheme. In the hierarchical design, factors that mainly affect soil biodiversity are the first level categories. The prediction of the possible distribution of living organisms in the environment can be achieved using the habitat suitability approach. In a wider perspective habitat suitability models are based on the application of linear and non-linear multivariate statistical analysis on a spatial base. Habitat suitability models are often used to predict the likelihood of occurrence and abundance of species, using habitat attributes considered important for their survival, growth and reproduction, application of these models to soil organisms is scarce.

Evaluation of earthworm and their ecosystem services

Some microfauna and mesofauna groups are highly abundant, their role in soil formation and transformation is well-recognized the area covered during their life cycle is representative of the site under examination, their life histories permit insights into soil ecological conditions, and several species have already been recognized as useful biological indicators of soil quality. Earth worm population and spices monitoring done according to International Standard Guidelines (ISO 23611-1) with species category as natural community (e.g. Lumbricidae, Glossocolecidae, etc.). Principle used for this monitoring is principle of combination of hand-sorting and formalin extraction and method followed is digging-out and hand-sorting of the soil within an area of 50 x 50 cm and a depth of 20 cm. Application of 5-10 litres of 0.5% aqueous formalin solution into the dugout hole followed by a period of 30 minutes until the worms appear at the soil surface. Further, storage is done by fixation in ethanol (70%) for 1–2 days, followed by 1–2 weeks in 4% formalin, then final storage in 70% ethanol. Parameters that can be measured are abundance, biomass and species composition.

The two circles represent the top and bottom of the core. Each letter labels the beginning of a digging event in alphabetical order. The type of line indicates the number of crossings per segment.

X-ray tomography unit used for determining burrow topography and earthworm movement, and tracking of earthworm movement using radio-labelled earthworms(c). It is being used increasingly to understand earthworm burrows and water movement although its application is still restricted to a few research groups. In addition, researchers have begun to use radio-labelling of earthworms to determine their movement in soil, in situ. Earthworm tagging is a technique that holds great potential for following earthworm movements inside the soil. Visual implant elastomer is injected into the muscle tissue of the earthworms, enabling identification of individual earthworms and raises the possibility of tracking migration rates of individual earthworms either in the field or laboratory experiments and of assessing survival rates. Studies to date have shown that the coloured tag can last in earthworms without any impact on earthworm mortality or reproduction for over 2 years, although after this time it becomes harder to identify the tag. Earthworms undoubtedly contribute significantly to many of the ecosystem services provided by the soil and whilst much is known about these processes. Further research along the lines discussed above will lead to a greater understanding of the role of earthworms in ecosystem services provision and, ultimately, an increased ability to manage such services through, amongst other things, manipulation of their abundances and diversity.

Conclusion

The role of soil microbial communities in soil health, plant growth and human benefits is widely acknowledged but ecosystem services related to this biotic portion of soil are often undervalued. Terrestrial services alone account for 60% of the value of total global ecosystem services, nevertheless a lack of understanding of the links between soil management, soil health and associated services and benefits, rarely leads to an establishment of soil management interventions for public benefits. Therefore, in order to reach an adequate protection goal of soil biodiversity, a reliable environmental risk assessment should take into account and also ecosystem services provided by microbial communities.

References

Archana Bhattarai., Bishwoyog Bhattarai and Sunil Pandey (2015). Variation of Soil Microbial Population in Different Soil Horizons. J Microbiol Exp; 2015, 2(2): 00044.

Baker, G. H., Chan, K. Y. & Munro, K. (2003). Influences of native (Megascolecidae) and exotic (Lumbricidae) earthworms on ryegrass production in acidic pasture soils from south-eastern Australia. Pedobiologia, 47: 830-834.

Daily, G. C. (1997). What are ecosystem services?. In: Nature’s Services: Societal Dependence on Natural Ecosystems (ed G.C. Daily), pp. 1-10.

Island Press, Washington, D. C., Dalby, P. R., Baker, G.H. & Smith, S.E. (1998). Potential impact of an introduced lumbricid on a native woodland in South Australia. Applied Soil Ecology, 9, 351-354.

Gardi, C. L., Montanarell, A., Arrouays, D., Bispo, A., Lemanceau, P. and  Jolivet, C.(2009). Soil biodiversity monitoring in Europe: ongoing activities and challenges. European Journal of Soil Science, 60: 807-819.

Wurst, S. (2010). Effects of earthworms on above- and belowground herbivores. Appl Soil Ecol., 45:123-130.

 

 

 

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