Impacts of spent mushroom substrate amendment and season on microbial communities in a semiarid vineyard soil

Spent mushroom substrate (SMS) amendment provides multiple benefits to the soil and therefore can increase the sustainability of agroecosystems. However, very little is known on how SMS fertilization can affect microbial community diversity and composition. To bridge this gap, we collected soils in two seasons (Spring and Autumn) from replicated plots with two doses of SMS (25 and 100 Mg ha⁻¹) maintained at a vineyard in La Rioja, Spain. Using Illumina sequencing of both the 16S rRNA gene and the ITS, we found that the changes in soil chemistry, as a consequence of SMS amendment, did not influence microbial alpha-diversities, but shaped bacterial beta-diversity regardless of the season. This implies that bacterial beta-diversity patterns remain consistently stable across treatments over time. However, our research also underscores the significant role of seasonal dynamics in shaping the structure and composition of microbial communities, as we noted a noteworthy decrease in beta-diversity during Autumn (after the dry summer) compared to Spring. The resulting biotic homogenization of both fungal and bacterial communities led to reduced relative abundances of N-fixing bacteria, as well as fungal and bacterial pathogens in Autumn as opposed to Spring. Altogether, our findings indicate that vineyard soil microbial communities are influenced by both resource availability and the varying environmental conditions. This information is essential for steering soil microbial communities to enhance plant productivity. The results of this study may contribute to more effective management of Mediterranean vineyards in accordance with the principles of the circular economy.