First of all, our results highlight the importance of combining different approaches to obtain complementary information on the microbiological status of agricultural soils.
Amendment with compost appears to have a promising environmental application, although its use depends on soil texture and clay content, as shown by our studied sites. In fact, compost was found to decrease cultivable microorganisms, microbial carbon, and coefficient of SOM mineralization in clayey soils, possibly due to an increased physical and chemical protection of organic matter from microbial attack. On the other hand, such an effect was not equally evident in soil with lower clay content. Van Elsas et al. (2007) denied direct correlation between abundance of microbial populations and their activities (e.g., N-fixation and cellulosolytic activities). The activities are sometimes enhanced by an improved nutrient availability caused by lower competition among microbial cells and by a large concentration of "microbivores" (microbial-feeding microfauna such as mites and nematodes), which keep bacterial abundance at a minimum. Thus, a poliphasic approach including microfauna analyses is necessary to fully understand the complex interactions within the soil food web.
The use of the biomimetic catalyst to fix and/or stabilize soil carbon by photo-polymerization caused contrasting responses of soil microbial community. It became evident from concomitant results of other MESCOSAGR groups that the different effects of the catalyst depend on whether the soil is either planted or bare, but also on plant species (maize or wheat), regardless of soil texture and climatic conditions. Such results are consistent with the results obtained by the biotechno-logical group of MESCOSAGR project (see Chap. 8).
It is thus hoped that further investigations will be conducted, to include analysis of microfauna-microflora interactions, in order to reach a deeper understanding of the long-term effects of compost and metal-porphyrin catalyst on carbon sequestration in soils cultivated with different plant species.
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