Including the soil microbiota in the quality evaluation of soils vulnerable to desertification

The soil microbiota is recognized as key player in both diversity and productivity of terrestrial ecosystems and it is mandatory to include its role in soil quality evaluation. Drivers of below-ground diversity are still largely unknown and is still unclear if the main soil features (i.e. soil organic matter, nutrient and water availability) are potential drivers of microbial diversity or are regulated by it. Increasingly negative effects of climate change due to drought and extreme weather phenomena are causing Mediterranean soil degradation that rapidly degenerates to desertification. Within the LIFE Desert-Adapt project we investigated bacterial diversity in soils of southern Europe under high desertification risk and related it with the main soil physical-chemical indicators and land use. Soil Microbial Biomass (SMB) was estimated as total extracted dsDNA while soil bacterial diversity was analyzed by the Automated Ribosomal Intergenic Spacer Analysis (ARISA) metagenomics 16S gene sequencing. SMB significantly varied across countries and land uses, with positive correlation with soil organic carbon (SOC) and total nitrogen (N). Bacterial diversity resulted strongly related to pH and soil use but not to SOC. The abundances of soil bacterial phyla were affected by cation exchange capacity (CEC) followed by pH. Interestingly the phylum Firmicutes was related to all the edaphic variables considered, and Proteobacteria to none. The results of this research create the baseline for the monitoring of European soils facing climate change and desertification phenomena, and help to shed light on the complexity of interactions in the soil among biotic and abiotic factors and land management.