Soil ciliates of the Indian Delhi Region: Their community characteristics with emphasis on their ecological implications as sensitive bio-indicators for soil quality

The present investigation aims to study the diversity of ciliates from different habitats in and around Delhi, India, and the correlation of this diversity with soil quality {agricultural lands (site 1 and 2), dump yards (site 3 and 4), sewage treatment plant (site 5), residential land (site 6), landfill (site 7) and barren land (site 8)}. Various physicochemical parameters of the different soil samples were studied and analysed for soil texture, interstitial water, pH, conductivity, total organic carbon, total organic matter, total nitrogen and phosphorous content, using standard protocols. Seventeen ciliate taxa belonging to four classes, seven orders, ten families, and 17 genera were recorded, with the maximum number of species (eleven) belonging to the class Spirotrichea. Ciliate diversity was highest at sites 5 and 6 and lowest at sites 1 and 2. Spathidium sp. was the dominant species in the conditioned land (site 8), while the ciliate Colpoda sp. was present in all the sites examined, showing the highest population density in the sewage treatment plant site (site 5). Statistical analysis showed that ciliate diversity was positively correlated to physicochemical parameters such as interstitial water, total organic matter and organic carbon, total nitrogen and total phosphorous content. Analyses of spirotrichs/colpodids (S/C) ratio and diversity indices implied that the habitat conditions of sites 1, 2, 3 and 8 are relatively unfavourable for soil ciliates to flourish; while sites 4, 5, 6 and 7 provided more favourable conditions. The ubiquity of ciliate distribution suggests their important role in the soil food webs and nutrient cycling, and their community structure and specific characteristics appear to be of major importance for soil formation. A full understanding of soil ciliate diversity and physicochemical parameters helps to inform best practice for improving soil quality as well as conservation practices for sustainable development and management of farms and cultivated lands. In conclusion, ciliate diversity serves as an important and sensitive bio-indicator for soil quality.