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Determination of life form spectra in soil Collembola communities : a comparison of two methods

Karaban K., Karaban E., Uvarov A.

Polish Journal of Ecology

2012

Vol. 60, nr 1

201-206

Life form spectrum is an informative parameter in a comparative analysis of ecological structure of Collembola communities, and a valuable indicator of conditions of soil environment. This suggests a search of adequate methods of its determination. In the present study, two methods of evaluation of life form spectra in springtail communities are compared. A usual approach is a determination of the species composition and abundance, with a subsequent formal distribution of the species present among the life form categories of a chosen system, e.g. among epedaphic, hemiedaphic and euedaphic life forms considered as dwellers of litter surface and upper horizon, of litter depth and topsoil, and of soil horizon, respectively (Hopkin 1997). By this method (A) all the specimens of a given species are attributed to the same life form. However, species populations contain juveniles with smaller body size, thinner cuticle and weaker pigmentation, which tend to be more sensitive to environmental constraints and to dwell deeper in soil than adults. Therefore the attribution of juveniles and adults of a given species to the same life form may not be accurate. Another approach is a direct attribution of a life form category to each collembolan individual during the determination process, according to the visual assessment of its morphological characters (body size and development of pigmentation, number and pigmentation of ommatidia). In that case representatives of a given species might be attributed to more than one life form category, e.g. adults to epedaphic whereas juveniles to hemiedaphic life form, or to hemi- and euedaphic life form, respectively (method B). To compare both methods, mass collembolan material of a microcosm experiment carried out in a beech-oak forest at Mikolajki Research Station (NE Poland) and aimed at investigation of mesofauna/earthworm interactions, was used. The comparison showed a statistically significant bias between the spectra of Collembola life forms estimated by methods A and B: the latter spectrum was shifted to the favour of euedaphic forms. The range of the bias was larger in soil than in litter horizon. Method B is suggested to be closer to a real life form distribution in a collembolan community and may be used for corrections of the data obtained by the traditional taxonomic method A.

Combined effects of earthworms and diurnal temperature fluctuations on successional changes of litter nematode community

Uvarov A., Kolosova N., Kulinich O.

Polish Journal of Ecology

2009

Vol. 57, nr 4

685-696

Earthworm functioning and temperature regime are among the most important biotic and abiotic factors of soil environment; their combined action on soil nematode activities has not been studied. In a 4-month laboratory experiment, effects of the epigeic earthworm Dendrobaena octaedra on a succession of nematode community in litter of a mid-European birch/oak forest were tested in the gradient of an increase of diurnal temperature fluctuations from 0[degrees]C (constant 15[degrees]C; T[15]) to 10[degrees]C (daily range between 10[degrees] and 20[degrees]C; T[10-20]) and 20[degrees]C (daily range between 5[degrees] and 25[degrees]C; T[5-25]). Earthworm and temperature effects were measured as differences in nematode community respiration rates between the experimental treatments. Nematode respiration rates were calculated on the basis of body size/weight/O[2] consumption relationships for individual species. Nematode community was dominated by bacterial feeders and changed in a characteristic successional pattern which, however, was markedly modified by temperature regime and earthworm activities. Dominant nematode taxa revealed specific patterns of temporal dynamics in connection with their responses to temperature and earthworm presence. Thus, metabolic activity of Plectus acuminatus was strongly reduced by D. octaedra but did not react to variation of temperature regime. In contrast, activity of Panagrolaimus sp. significantly responded to temperature but not to earthworm presence, whereas Pl. thornei reacted to both factors separately and in combination. Ceratoplectus armatus was stronger affected by earthworm presence then by temperature; Tylocephalus auriculatus showed the opposite pattern. The variety of responses may explain the coexistence of several taxonomically related (Plectidae) and trophically similar species within the dominant group. Both earthworm presence and increase of the range of diurnal temperature fluctuations strongly affected the net of interspecific correlations within the nematode community. Earthworms strongly reduced total activities of nematode community at any temperature regime. T[15] regime showed markedly lower level of cumulative nematode respiration than both fluctuating regimes, irrespective of earthworm presence. In conclusion, combined effects of earthworms and temperature regime drastically changed patterns of relationships within the nematode litter community. The results of the experiments may have implications for the perspectives of global warming events at the study site: it is suggested that the ultimate vector of the changes in litter environment might be directed towards the conditions of the treatment [T[15] regime; earthworms present], with the corresponding trends in the development of the litter nematode community.