Microbial taxa and interactions can predict lignin mineralization in soil at continental scale

Abstract

Individual fungi and bacteria can decompose lignin, but little is known about how specific taxa and their interactions may be related to this critical carbon-cycling process across diverse environments. We characterized relationships between bacterial and fungal communities and mineralization of isotope-labeled lignin across 156 incubated mineral soil samples collected from 20 National Ecological Observatory Network sites spanning diverse ecosystems (tundra to tropics) across North America. Based on marker gene sequencing, bacteria were more closely related to lignin mineralization than fungi at the levels of overall community composition, individual taxa, and co-occurrence network. We identified 14 bacterial and fungal genera across sites and 26 taxa (mostly bacteria) within sites, including two genera (Occallatibacter and Terracidiphilus) that were significantly related to lignin mineralization within and across sites. Additionally, many microbial ‘modules’ from co-occurrence networks were related to lignin mineralization, and this was even more evident during the later stages of decomposition. This suggests the importance of microbial interactions for lignin decay and implies that microbes interacted in a way favoring lignin decomposition over the incubation. We identified 10 bacterial-fungal interactions (BFI) that could significantly strengthen and 10 BFI that could weaken microbial relationships with lignin mineralization, indicating that synergistic and antagonistic BFI were both important. Overall, our study illustrated the key importance of microbial interactions even more so than individual taxa for predicting lignin mineralization.