S BINDSCHEDLER¹, V HERVE², T WUNDERLIN³, A LOHBERGER¹, I JAMIL¹, G CAILLEAU², LY WICK⁴, EP VERRECCHIA², P JUNEIR<sup>1

1</sup>Laboratory of Microbiology, University of Neuchâtel, Switzerland., ²Laboratory of Biogeosciences, IDYST, University of Lausanne, Switzerland., ³Molecular Ecology, Institute for Sustainability Science, Agroscope Zürich, Switzerland, ⁴Department of Microbiology, Hemholtz center for environmental research - UFZ, Leipzig, Germany.

Fungi and bacteria are both essential actors of organic matter turnover and nutrient cycling in soils, a crucial aspect of ecosystem functioning. While their individual roles are well described, the influence of bacterial-fungal interactions (BFI) in soil functioning is still poorly understood. Both organisms have shared the same environment for millions of years resulting in a myriad of interactions from mutualism to antagonism. Describing such interactions in complex systems such as soils is challenging, as their regulation depends on both biotic and abiotic factors. Consequently, both reductionist and systemic approaches are needed in order to get a comprehensive overview of BFI related to ecosystem functioning. First, by using model organisms in Petri dish experiments, we are starting to understand some basics regulatory elements of BFI in nature. In the systemic approach, our model is the oxalate-carbonate pathway (OCP), a natural process in which both fungi and bacteria play a crucial role. The OCP has a major impact on soil functioning by triggering alkalinisation in acidic soils, which positively impacts soil nutrient content. As a result, the OCP is a pertinent model to study the impact of microorganisms on soil functioning. Using soil microcosms studies we were able to highlight that BFI have a positive impact on OCP functioning. Traditional microbial ecology has usually focused more on bacteria than fungi. Therefore, in this presentation we will highlight the role of fungi in BFI. In the future we aim at understanding the complexity of BFI in soils and to decipher the instrumental role of BFI in soil nutrient bioavailability and plant health. Although there are still many aspects to disentangle, our studies highlight the overlooked role of BFI in biogeochemical processes. As a consequence, future studies aiming at unravelling the factors that drive soil functioning should definitely benefit from integrating BFI.