Response of Soil Microbial Communities to Iron-Porphyrin Catalytic Amendments.

Intensive agricultural practices strongly increase CO2 emission from soil. Synthetic metal-porphyrins were shown to significantly decreased CO2 emission from soil due to an in-situ catalysis of oxidative polymerization of soil organic matter. This research aimed to assess the effects of iron-porphyrin (POR) amendments on soil microbial communities in three arable soils under wheat and maize cropping located in Naples, Turin and Piacenza, characterized by different pedological and climatic conditions. Bulk-soil and rhizo-soil were sampled during 4 years and the microbial groups directly involved in organic matter (OM) mineralization and in key processes of the nitrogen cycle were examined. Moreover some microbial indicators of soil quality, i.e. microbial and fungal biomass, basal respiration, metabolic quotient (qCO2), and coefficient of endogenous mineralization (CEM), were measured. Unexpectedly, POR treatment in bulk-soil caused a significant increase in microbial groups directly implicated in OM mineralization, in respect to NOPOR control. Consistently CEM was higher in POR treatment than in control. By contrast, the effect on rhizo-soil was different. In maize rhizosphere, POR treatment showed a significant decrease in microbial populations involved in the turn-over of OM as well as in fungal biomass, in respect to NOPOR. In wheat rhizosphere, there was no significant difference between POR and NOPOR treatments. However significantly higher CEM were found in POR rhizo-soil of Naples and Turin in the second and in the third experimental years, respectively. Finally, POR treatment did not significantly influence aerobic free-living N2-fixing, ammonia-oxidizing and denitrifying bacterial populations. The iron-porphyrin significantly reduced fungal biomass and the ratio fungal C/microbial C, suggesting a higher sensitivity of fungi to POR or to POR end-products. In conclusion, the effects of iron-porphyrin treatments on microbial communities are different in bulk- and rhizo-soil as well as in maize and wheat crop. This work was supported by FISR-MIUR Italy, (MESCOSAGR Project)