Unravelling changes in the Pinus radiata root and soil microbiomes as a function of aridity

Rising aridity is becoming a major consequence of climate change, impacting terrestrial ecosystems worldwide. Forest biomes are especially at risk due to their long lifespan and immobility, making them vulnerable to shifting environmental conditions. Over time, microbiomes have evolved alongside plants, fostering mutual benefits. However, rapid environmental changes and plant domestication may disrupt the ability of plants to recruit beneficial microbial partners that enhance stress tolerance. This study examines how aridity influences the symbiotic relationship between tree roots and microbes, focusing on the widely planted Pinus radiata. By analyzing samples across a broad geographic range and varying environmental conditions, we explore how aridity, soil properties, and climate factors shape microbial communities in P. radiata roots and surrounding soils. Our findings show that while aridity plays a major role in shaping microbial community assembly, factors like soil pH and organic carbon strongly influence bacterial diversity. Certain bacterial and fungal taxa were found to be conditionally associated with aridity, emphasising their potential role in Pinus radiata resilience under increasing environmental stress. As mesic ecosystems shift toward arid conditions due to climate change, the presence of these aridity-associated taxa varies in bulk soils expected to become drier. This raises concerns that these beneficial microbes may need to be recruited through alternative mechanisms to support tree adaptation.