Understanding the impact of climate change and elevated CO2 on tree microbial diversity

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Many trees, such as oak, are crucial to the British economy, environment, and culture. They support many species, providing a habitat that encourages rich woodland biodiversity across our natural environment. However, they are threatened by climate change. This causes alterations in the abundance and distribution of tree pathogens consequently increasing the likelihood of new disease breakouts. Acute Oak Decline (AOD) is caused by a multitude of factors including several bacterial species that become key members of the pathogenic oak microbiome. It is possible environmental change could increase trees' susceptibility to pathogens increasing AOD prevalence. A core component of climate change is a rise in carbon dioxide concentration, which affects tree growth and disease susceptibility. For instance, elevated levels of atmospheric CO2 (e[CO2]) cause changes in leaf composition and increase biomass through magnified levels of photosynthetic carbon fixation. There are well-established links between microbiome composition and the physiology of the host plant. Microbiomes typically extend an organism's functional capabilities, importantly increasing tolerance to stress and disease. However, the effect e[CO2] tree physiology has on tree microbiome community structure is somewhat unexplored. Utilising the Birmingham Institute of Forest Research (BIFoR) Free Air Carbon Dioxide (FACE) facility we can investigate e[CO2] effects on microbial community diversity (including bacteria, fungi, and bacteriophage) on different tree species (including Oak and Cherry), and how these microbes interact with tree pathogens. We hypothesise that as trees grow larger under e[CO2] there may be higher microbial abundance, but that leaf chemistry compositional changes will alter the diversity of the microbes, potentially with an overall negative impact in the microbiomes' ability to suppress pathogen establishment. We will examine how individuals and microbial consortia interact with key pathogens, for example, a polymicrobial consortium of Gram-negative Enterobacteriaceae (e.g. Brenneria sp., Gibbsiella sp., Rahnella sp.) that cause Acute Oak Decline (AOD). This approach is essential for making accurate predictions regarding future tree health and disease.