Correlating the above- and belowground genotype of Pinus pinaster trees and rhizosphere bacterial communities under drought conditions

Increasing temperatures along with severe droughts are factors that may jeopardize the survival of the forests in the Mediterranean basin. In this region, Pinus pinaster is a common conifer species, that has been used as a model species in evolutionary studies due to its adaptive response to changing environments. Although its drought tolerance mech-anisms are already known, knowledge about the dynamics of its root microbiota is still scarce. We aimed to decipher the structural (bacterial abundance), compositional, functional and associative changes of the P. pinaster rhizosphere bacterial communities in spring and summer, at DNA and RNA level (environmental DNA, live and dead cells, and those synthesizing proteins). A fundamental aspect of root microbiome-based approaches is to guarantee the correct origin of the samples. Thus, we assessed the genotype of host needles and roots from which rhizosphere samples were obtained. For more than 50% of the selected trees, genotype discrepancies were found and in three cases the plant species could not be determined. Rhizosphere bacterial communities were homogeneous with respect to diver-sity and structural levels regardless of the host genotype in both seasons. Nonetheless, significant changes were seen in the taxonomic profiles depending on the season. Seasonal changes were also evident in the bacterial co-occurrence pat-terns, both in DNA and RNA libraries. While spring communities switched to more complex networks, summer popu-lations resulted in more compartmentalized networks, suggesting that these communities were facing a disturbance. These results may mirror the future status of bacterial communities in a context of climate change. A keystone hub

Automated summary

The structure, composition, and functional changes of the P. pinaster rhizosphere bacterial communities vary with seasons, without being influenced by the host genotype. Seasonal changes are reflected in the patterns of bacterial co-occurrence, suggesting potential disturbances for bacterial communities in the context of climate change.