Microbial taphonomy of Ginkgo leaves in fine‐grained substrates: how sediment type facilitates preservation

Ginkgophyte leaves similar to those of the ‘living fossil’ Ginkgo first appear in the Permian. Yet, little is known about the factors that have promoted the fossilization of Ginkgo leaf compressions through geological time. The formation of leaf compressions depends on geological factors such as sediment and burial depth, as well as biological factors like decomposition and biomineralization. Recent studies hypothesize that microbial biofilms on leaf surfaces in early decay stages enhance preservation by protecting from herbivory and facilitating mineralization. Here we investigate the microbial community composition of biofilms on floating and buried leaves of living Ginkgo in four substrates (pond mud, two types of clay, and quartz sand) to elucidate the role of biofilms in leaf decay and potential preservation in different sediments. Leaves in aquariums were either buried in a sediment or left floating with pond water for three months. Leaves, sediments and water were then evaluated with 16S rRNA and ITS rRNA sequencing to identify the bacterial and fungal communities. Through bioinformatics analysis, it was found the biofilms produced on the floating leaves differ in their basic microbial community composition from those buried. Leaves in both types of clay had most distinctive microbial communities, and contained several genera noted for biomineralization. Buried leaves contained more anaerobic microbes and biomineralizers, particularly in the clays. Thus, leaf biofilms forming in fine‐grained sediments with low organic content, such as clay, foster anaerobic environments which could lead to incorporating minerals that enhance biomineralization on leaf surfaces.