Authors: Bharat H. Gawade1, Zakaullah Khan1 and Sunanda Biswas2
1Division of Plant Quarantine, ICAR-National Bureau of Plant Genetic Resources, Pusa Campus, New Delhi-110012
2Division of Soil Science and Agril. Chemistry, ICAR-IARI, Pusa Campus, New Delhi-110012
The soil is the habitat for different types of soil organisms including bacteria, fungi, nematodes, annelids, arthropods etc. The population and proportion of these organisms can be correlated with soil health, however soil health assessment through complete analysis of such a diverse group of organisms may require several extraction techniques, which is technically daunting (Ferris and Bongers, 2006). Alternately, the biotic indicators (bioindicators) can be used to assess the soil health. In general, bioindicators are the organisms, such as lichens, birds, bacteria, microbes etc. that are monitored for assessment of health of the environment. These organisms are monitored for changes in their population, behavior, biology etc. which may indicate a problem within their ecosystem . Basically, the changes can be chemical, physiological, or behavioral. One basic and common criteria for organism to be used as a bioindicator is that, the indicator used should be able to reflect the structure and function of ecological processes and must respond to soil conditions. The nematodes are one of the most widely used indicators of soil health due to possession of large number of positive attributes required (Neher, 2001).
Nematodes, also called as roundworms are ubiquitous multicellular organisms that inhabit all the types of soils ranging from cultivated to grazing lands to forest soils. In general, soil nematodes are small organisms belonging to the phylum Nematoda. They are known to parasitize insects, plants as well as animals. The free-living nematode species inhabiting the soil graze on bacteria, fungi, and other nematodes. Several nematode genera are economically important as a pests of cultivated crops and belongs to the plant parasitic group while other soil dwellers contribute to nutrient mineralization while few are used for control of soil insects.
Uses of bioindicators:
Each organism within an ecosystem has the ability to report on the health of its environment. However, few of them can be used for practical purpose. The bioindicators are used to:
- detect changes in the natural environment;
- monitor for the presence of pollutants and their effect on the ecosystem;
- monitor the success of environmental cleanup drives and,
- test drinking water for the presence of contaminants etc.
Types of bioindicators:
- Plant indicators : Presence or absence of certain plant species can be related to environmental health like for example lichens, respond to environmental changes like air quality and climate and their disappearance can be related with environmental stresses.
- Animal indicators: The changes in the population of bioindicator animal species can be related to damage to the ecosystem due to external factors like pollution. Size and number of these animal species are observed.
- Microbial indicators: Microorganisms are used as indicators of ecosystem health. These microbes found everywhere and easy to sample than other organisms. Few microbes produce new proteins related to stress when exposed to contaminants and can be used as a bioindicators. The attributes like, microbial biomass, soil basal respiration, enzyme activities, and nutrient transformations also used as a indicators of soil health and soil fertility. Characters of nematodes, which make them good indicators: There are several characters of nematodes make them good indicators of soil health like:
- Nematodes are abundant multicellular and diverse invertebrates present in all the types of soil. They can readily be extracted and identified at genera level (Yeates, 1979).
- They are one of the important components of the soil biotic community and their assessment provides a unique insight into soil biological processes.
- They feed on all components of the soil food web and their population reflects the amount of food available and its diversity.
- Based on feeding habits, nematodes can be grouped into five major trophic groups; bacterivores, fungivores, plant parasites, predatory and omnivores. These organisms are functioning at various levels of food web.
- Nematode communities are sensitive to changes in soil environment caused by different agroecosystem management practices.
- Nematode faunal analysis based on the relative weighted abundance representation of the probable conditions of the soil food web. How nematodes acts as a bioindicators:
- Ferris, H. and Bongers, T. (2006). Nematode indicators of organic enrichment. Journal of Nematology, 38: 3-12.
- Ferris, H., Bongers, T., de Geode, R. G. M. (2001). A framework for soil food web diagnostics: extension of the nematode faunal analysis concept. Applied Soil Ecology, 18: 13-29.
- Neher, D. A. (2001) Role of nematodes in soil health and their use as indicators. Journal of Nematology, 33 (4):161–168.
- Yeates, G.W. (1979). Soil nematodes in terrestrial ecosystems. Journal of Nematology, 11: 213-229.
About Author / Additional Info: