Microbial controls on seed germination

Germination onset is the first stage in the phenological plant cycle, influenced by abiotic and biotic factors. Both soil and seed microbiota are key drivers of germination, influencing seed storage, dormancy release, and germination rates. Interactions between plants and soil microbes contribute to plant adaptation to their environment. Therefore, plants could benefit more from interacting with soil microbes from the local ('home') environment than with those from other origins. As crucial germination drivers, plants may select for specific microbial taxa that provide them with a home-field advantage, regardless of microbial richness and diversity in their surroundings. Here, we looked at the role of seed-associated microorganisms on holm oak (Quercus ilex) germination, whether seed or soil microbes have a greater impact on this process, and how the interaction between seed and soil microbiotas influence holm oak germination. We found that microbes on Q. ilex seeds have a significant effect on germination, with non-sterilised seeds having higher germinated acorns than sterilised ones. Moreover, when co-occurring, soil microorganisms enhance the effect of seed-associated microbes on holm oak germination. Overall, our results evidence a home-field advantage where local soil communities, along with seed-associated microorganisms, enhance Q. ilex germination over that of different soil or plant species, evidencing the importance of local adaptation for plant fitness.