Fungi in a Warmer World: evaluating fungal biodiversity and abundance during the Middle Miocene Climatic Optimum in the South China Sea

Fungi play a key role in ecosystems; most of them are cosmopolitan, but several species have distinctive geographical distributions due to climate and hosts availability. Although they are often overlooked in deep-time palynological preparations, their study in the fossil record is key to better understanding their role in past ecosystems under different climate conditions. Fungal remains are generally deposited close to the source, providing an accurate record of local environmental conditions at the time of deposition. Some fungi have very narrow environmental preferences, such as temperature, humidity, rainfall, and pH. The Middle Miocene Climatic Optimum (MMCO) is considered an excellent analogue for future global climate. Thus, the Fungi in a Warmer World (FiaWW) project is developing a global dataset of fungal diversity and distributions from different sites representative of the MMCO worldwide. One of the sections of this project, and the focus of this study is IODP site U1433 in the South China Sea. The research background of the South China Sea suggests the site was experiencing warm temperatures, significant precipitation, and a humid climate. Here we present the fossil fungal record within sediment from the MMCO of site U1433. Fossil fungal richness and ecological composition is based on 33 high-resolution samples. The fossils were identified using modern analogues when possible, to make ecological inferences. Identification of individual fossil fungal palynomorphs and the association of these assemblages with modern fungal taxa, and their ecological traits yield a framework to refine existing palaeoecologic and palaeoclimatic records, as well as to trace responses to climate change. Our preliminary results show that fossil fungi from the South China Sea location vary in biodiversity, opacity, abundance, and deterioration throughout the MMCO. Some of the genera found include Neomycoleptodiscus aff. pertusus, aff. Schiffnerula ziziphi, and aff. Canalisporium sp. The modern ecology of these genera primarily includes a tropical forest environment that is not only highly diverse, but also sometimes has a multistratified forest structure. Results from this work will aid in determining the impact an increase in global temperatures would have on modern fungi in tropical environments.