Oak seedling microbiome assembly under climate warming and drought

Despite that climate change is currently one of the most pervasive challenges, its effects on the plant-associated microbiomes is still poorly studied. The aim of this study was to evaluate the impact of climate warming and drought on the microbiome assembly of oak plants from seed to seedling. In a multifactorial experimental set up, acorns were subjected to different temperature (15 °C, 20 °C, 25 °C) and soil moisture levels (drought (15 %) and control (60 %)) from germination until the seedling stage, after which the bacterial and fungal communities associated with the rhizosphere and phyllosphere of the seedlings were characterized. The interaction of temperature and drought affected both the bacterial and the fungal communities, whereas the latter was more affected. Specifically, the interaction influenced bacterial and fungal community composition in rhizosphere and fungal diversity and abundance in phyllosphere; overall, the effects were contrasting depending on soil moisture level. Further, temperature and drought separately affected the oak microbiome, though temperature had a stronger effect. Temperature affected bacterial and fungal diversity and abundance and bacterial community composition in phyllosphere and bacterial and fungal community composition and abundance in rhizosphere. In contrast, drought separately only affected fungal abundance in phyllosphere and bacterial and fungal community composition and abundance in rhizosphere. Regardless of temperature, Actinobacteriota was significantly enriched in drought conditions. This study provides new insights into climate change related impacts on the plant-associated microbiota of a major forest tree species such as oak.