FEATURE
Figure 2 : Epigeic Collembola specimen as an example of adaptions to edaphic habitats on shallower surface horizons . Augmentation of appendage dimensions such as antennae , furca and legs , strong pigmentation , discernible body hairs and obvious ocelli can be noted ( Image source : Authors own 2019 ).
soil ( BQS ) indexing , using microarthropods and Collembola due to their high abundance in a wide range of soils as well as their sensitivity to land management practices , having been noted to correlate positively with beneficial soil functions ( Parisi and Menta 2008 ). Here , we discuss these methods of soil quality evaluation .
What is Collembola ?
Collembola are the most abundant arthropods in many agricultural and rangeland soils and can be found in a diverse range of habitats globally , often in great densities per cubic meter . These microarthropods are mostly known in their important role within the soil food web as fungal feeders , mineralising nutrients into plant-available forms . Soil invertebrates are generally classified according to their size , with Collembola being Mesofauna ( body size between 200 μm and 2 mm ).
Despite their six legs , Collembola ( Springtails ) are not classified as insects , but rather form a separate class within the phylum Arthropoda . Collembola are distinguished by their double furca , a spring mechanism utilised as a means of predator evasion , although the prominence of this appendage is dependent on the depth of soil it has evolved to inhabit .
Biotic and abiotic factors such as resource availability and physiochemical properties , in most habitats , create conditions for Collembola that would promote or impede persistence , with species demonstrating varying levels of specialisation suited to these environments .
Collembolan communities have been shown to vary according to open or closed vegetation types . Soils with low pH , high soil moisture as well as soils with high organic matter providing abundant resources favour overall Collembola abundance and diversity ( Heiniger et al 2015 ).
As the most abundant groups within terrestrial ecosystems , Collembola have been used alongside earthworms and nematodes in assessing soil quality ( An et al . 2013 ). Recent methods of evaluation by means of biological soil quality ( BSQ ) indices are based on the idea that high soil quality exhibits greater diversity in the assemblage of microarthropods such as Collembola ( Paz-Ferreiro and Fu 2016 ).
What can Collembola tell us ?
Collembola have been noted as being negatively impacted by the removal of organic matter observed as part of a temporal interaction and extremely sensitive to soil disturbances ( Eaton et al . 2004 ), therefore being considered useful as a bioindicator of soil condition and evaluation of soil quality .
It is understood that cultivated soils exhibit less diverse Collembola or exhibiting certain adapted morphological characteristics following soil disturbance . Because of their differences in response to contaminants , specific Collembola is frequently used as test organisms in soil toxicology tests , such as Folsomia candida , Onychiurus armatus , Orchesella , cincta , Isotoma notabilis and Tetrodontophora bielanensis in both sub-lethal and lethal testing ( Crouau et al 1999 ; Menta 2012 ; An et al 2013 ).
Morphological changes in Collembola composition characterise the soil stratum to which it has adapted ( Figure 2 ). Collembola adapted to deeper soil horizons , for instance , would exhibit characteristics suited to small dark soil spaces , such as reduced antenna , development of particular sensory hair , no discernible pigmentation , absent ocelli and a reduced or absent furca ( Figure 1e ) ( Conti 2015 ).
These morphological adaptions mean that they would be more sensitive and vulnerable to environmental changes , and so , regularly abundant in less disturbed soils such as permanent or semipermanent grasslands and vegetative cover ( Gregorich and Carter 2007 ). The degree to which they have adapted to varying hypogeal environments enables us to distinguish between biological forms of Collembola .
Soil Biological Quality Quantification
As most Collembola communities ’ compositions are highly dependent on their immediate environment , one could evaluate their role and function by using methodologies highlighting Col-
Figure 3 : Berlese Tullgren Funnels are typically used to extract arthropods from soil samples , via high-gradient dynamic extraction . Cores are placed top-end downward on a 5mm mesh disc within the extractor . Incandescent light is used as the repellent stimuli and specimens collected in modules below the funnel , typically containing 20ml 75 % ethyl alcohol . An extraction period of at least fifteen days is advised ( Image source : Authors own , 2019 ).
Grassroots Vol 20 No 4 December 2020 12