Resilience of microbial communities in Mediterranean soil after induced drought and manipulated UV radiation

Enhanced UV radiation levels and decreased rainfall in Mediterranean terrestrial ecosystems due to climate change might impact soil bacterial communities, significantly altering their structure and affecting biogeochemical cycles. The aim of this study was to evaluate the effect of UV-B and UV-A radiation on soil bacterial richness, abundance and community composition in a Typic Dystroxerept of Mediterranean shrubland and to determine whether these effects depend on reduced rainfall and/or soil physicochemical properties. Soils were subjected to long-term UV conditions: UV-A + UV-B exclusion (UV0 plots), UV-B exclusion (UVA plots), or ambient UV-A + UV-B exposure (UVAB plots), and combined with two rainfall regimes, natural (NR) and reduced (RR) rainfall. Barcoded amplicon 16S rRNA gene sequencing was used to analyse changes in microbial diversity. UV radiation did not affect bacterial richness and diversity indexes and only minor differences in species composition were observed. Unidentified species of the Longimicrobiaceae appeared to be in greater abundance in the UV0 plots than in the UVA and UVAB, especially under natural rainfall, whereas members of the Pyrinomonadaceae and Ktedonobacteraceae were more abundant in UVAB. Rainfall reduction resulted in lower bacterial abundance but higher diversity (Shannon-Weiner and InvSimpson indexes) under UV exclusion. The results pointed to a combined response of soil bacterial communities to UV radiation and rainfall treatments. However, the small changes observed suggest a high resilience of the Mediterranean shrubland soil microbiome to the projected changes in UV and rainfall conditions. Highlights Microbial abundance and diversity were analysed in Mediterranean soils exposed to contrasted UV radiation and rainfall treatments Reduced rainfall exerted a greater effect on soil bacteria than UV radiation exposure. Limited effects of UV and rainfall changes support a high resilience of soil bacterial communities.

Automated summary

Enhanced UV radiation levels and reduced rainfall in Mediterranean terrestrial ecosystems can potentially impact soil bacterial communities, but this study found that UV radiation had minimal effects on bacterial richness and diversity. Species composition did show some variation under different UV and rainfall treatments. Reduced rainfall had a greater impact on bacterial abundance compared to UV radiation exposure. Overall, the results suggest that soil bacterial communities in Mediterranean shrublands have a high resilience to changes in UV and rainfall conditions.