Soil fauna contribution to the soil system: multiscale approaches to address a complex interaction

The aim of this work was to evaluate the interaction of soil fauna and its habitat, with a multiscale approach, critically underlining their complex interaction. Due to considerable difficulties related to the taxonomic determination, it was necessary to utilize a reliable and easy-to-use index to be able to identify environmental stress states. In fact, simplistic systematic approach shows limitation when used as biological monitoring systems, in which it sustains the taxonomic side instead the ecological aspect. In this work, the adaptation of soil fauna into soil life was evaluated. This was verified by the use of Qbs-index "Biological Soil Quality" (Parisi, 2001). The adaptation makes different convergence phenomena to the morphological level. Soil fauna who lives in soil, shows shared morphological characters (e.g reduced size, depigmentation or reduction of jumping organ, i.e. caudal furca). The soil organisms are particularly sensitive to soil degradation and to the disturbances linked to the soil. Moreover here we attempted to investigate the relationship of soil fauna and different land uses. Through the use of the Qbs-ar index, it was observed an high level of soil quality for all the studied sites. Although it was possible to notice many differences between all the considered samples within the same land use, the soil quality classes used for their classification showed a very high value in each sample. This result underlines that all study sites exhibited a good level of biodiversity. Therefore, the soil fauna depend by soil quality and they depend each other. Overall, the data obtained from qualitative and quantitative analysis showed a good level of correlation, confirming a good soil quality for all study sites both by showing differences within a single sampling site with a specific land use and by correlating all sites with different land uses. In the successive research phase, we wondered in which way and in which amount the soil fauna can influence the soil structure, sampling some sites already analyzed in the previous experimental phase, in which the Qbs-index was applied. the soil samples were analyzed, and the different taxa of soil fauna where discerned. Moreover we applied imaging analysis of the collected soil samples, with aim to correlate the soil fauna with soil structure. More specifically, undisturbed soil samples, were impregnated with epoxy resin and investigated through the use of x-ray medical CAT. The x-ray medical CAT allows to discriminate the soil phase from the pore phase. The image processing was performed in order to obtain 3D reconstructions of the internal structure of the soil blocks. Pore size distribution was determined using the own-developed software Conmorph, through the iterative application of the "opening" algorithm, which classifies the porous phase according to the spacing from the walls. According to the results from investigations on the soil fauna, the samples having a high taxa was richness presented a good and different level of soil pore distribution. In the samples in which taxa differentiation was poor, soil pore size distribution resulted to be rather homogeneous. Although good results were obtained, it was difficult to characterize the porosity related only to the fauna activity in an undisturbed soil samples, since there are many factors influencing their porosity, like the own soil size distribution, the activity of plant roots and of soil fauna (e.g. burrow and casts). In order to better investigate the cause-effect relationships among different species of soil fauna and the soil pore system, a new experimental approach was developed considering the current knowledge. It consisted on the inoculation of different species in repackage soil mesocosms and it aimed to identify the different biological signatures of the soil fauna. Repacked soil mesocosms, after the burrows species activity, were impregnated with epoxy resin and undergo to x-ray medical CAT. Through the obtained images, it has been possible to obtain the pore size distribution for each studied samples, in order to discriminate the contribution of each species to soil pore structure. Additionally, eleven morphological parameters, such as total volume, tortuosity or individual burrowing ratio, were calculated for each burrow system, in order to better characterize the morphology of the bio-pore networks. The last experimental phase was conducted means by a laboratory test consisting in the inoculation of different soil fauna species under controlled conditions. Particular attention was given to the study of the CO2 and N2O fluxes and how the soil fauna may affect these fluxes. This was studied means by an Infrared gas analyzer after the accumulation of CO2 and N2O gas into repacked soil microcosms inoculated with different soil fauna types, individually or mixed each other. At the end of fluxes measurement, each microcosm was used for fauna extractions and for soil analysis (e.g. DOC, pH). The experiment showed the huge difficulty to control all the variables involved in complex processes due to living organisms, like the soil respiration and the soil emission of N2O and simultaneously allowed to state that an increase in the soil respiration and in the fluxes of N2O was essentially provided by the presence of the earthworms.