Microbial communities have a central role in ecosystem processes by driving the Earth’s biogeochemical cycles. However, the importance of microbial diversity for ecosystem functioning is still debated. While functional trait-based approaches are commonly used for at least two decades in microbiology, most microbial diversity studies are still carried out with the rRNA genes. This talk will show how metagenomic approaches targeting microbial guilds involved in nitrogen cycling can help bridging microbial community ecology and ecosystem processes in terrestrial environments.