Land use effects on bacterial diversity in Mediterranean 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. The bacterial communities in soils vulnerable to desertification can undergo perturbations by various human activities, such as unsustainable land use and management, and by climate change. Alteration in microbial diversity and composition are sentinels of the impact of environmental changes on soil quality. Within the LIFE Desert-Adapt project we analyze the soil bacterial diversity and composition across European Soils threatened by desertification in the southern Mediterranean regions (Italy, Spain and Portugal) and evaluate the influences on soil bacteria communities of five different land use type (Broad-leaved agroforestry, conifer forest, cropland, pasture-grassland, shurubland). Bacterial diversity was analyzed by the Automated Ribosomal Intergenic Spacer Analysis (ARISA), Microbial Biomass was estimated as total extracted dsDNA. The Illumina MiSeq sequencing technology was applied to determine the community composition. The bacterial diversity was related with land-use, Richness and Shannon index varied across land uses, although only croplands and shrublands significantly differed. The microbial biomass was also affected by land use and were highest in the conifer forests land and lowest in the cropland soils. Actinobacteria, Proteobacteria Acidobacteria, Firmicutes, Bacteroidetes, Chloroflexi and Verrucomicrobia phyla were detected in all countries with relative abundance variable across land use type. The firmicutes was abundant in cropland and grassland soil with low C and N content and neutral pH 7, the Chloroflexi was most abundant in shrubland soil with high C content and acid pH. Actinobacteria was abundant in conifer, shrubland and cropland with basic pH, and a high CEC and carbon content, while the Proteobacteria was abundant in all land use type. Within the same phyla, the genera abundance was influenced differently by soil chemical- physical variables. We analyze relationships between land use and the soil microbiota, and create the baseline for the monitoring of European soils facing climate change and desertification phenomena. The identification of soil management-sensitive bacterial taxa could have great potential as bioindicators for soil quality and loss of functionality associated with land use.