Conclusions

The results illustrated in this chapter allow drawing some general conclusions. Enzymatic activities are usually correlated with soil quality, and, if not induced by disturbing agents (e.g., organic pollutants stimulating soil microflora activity), their increase is usually positive, as it indicates an efficient microbial recycling of essential plant nutrients.

A more complex issue is the relation between CO2 emission from soils (the main study of the MESCOSAGR project) and the biological parameters dealt with here. An increase in enzymatic activities related to total microbial activity (dehydroge-nase, FDA, catalase) will most probably result in larger CO2 emissions, although other factors such as organic carbon quantity and quality should be also considered. On the other hand, an increase in activities of enzymes involved in the biogeo-chemical cycles of phosphorus, sulfur and nitrogen do not necessary result in an increased CO2 emission. For example, in the case of phosphatase, it was found that this enzyme is more correlated with environmental availability of P than to decomposition rates, and that there is no relationship between CO2 efflux and its activity, at least in litter environments (Johnson et al. 2010). This was an important result and should be confirmed for other enzymatic activities, since it may derive that C sequestration methods can be applied to increase the biochemical quality of soils without affecting, or even reducing, CO2 emission. The relationship with other greenhouse gases should be also considered, especially in the case of N-related enzymatic activities which may affect N2O fluxes. However, our results within the MESCOSAGR project have shown that in four different Italian locations the adopted field methods for C sequestration did not significantly changed an important component of soil biochemical quality, such as soil enzymatic activities.

Upon a stimulation of soil microbial activities by carbon sequestration practices, the composition of microbial communities should also be affected. This was verified by our PLFA analyses, which also showed that microbial communities were shifted differently than for enzymatic activities. This discrepancy implied that values on enzymatic activities provide soil functional quality, while PLFAs (especially if analysed with a taxonomical approach) account for structural soil composition. Thus, it may be expected that a specific change in a soil function (e.g., an increase in phosphatase activity) can be related to a number of different changes at taxonomical level. This consideration highlights the importance of including both structural and functional measurements, when verifying the effects of soil treatments on soil microorganisms. Another conclusion of our approach is that changes in microbial communities should not be negatively considered, but they should be evaluated in the wider context of soil ecological functions.

Finally, it must be pointed out that the use of the biomimetic catalyst as a practice to sequester C in soil (the CAT treatment) through photo-polymerization of SOM, failed to bring about any change in the enzymatic activities in four different Italian field site under both maize and wheat cropping. As for PLFAs, the CAT treatment produced only a specific increase in fungal population of the Torino site.

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