Dr. Laurent Philippot is Director of Research at the French Institute for Agricultural Research (INRA) and is leading a research group at the department of Agroecology in Dijon. He did a sabbatical at Georgia Tech in Atlanta and at the Swedish University of Agricultural Science (SLU) in Uppsala in 2000 and 2009, respectively. His research focuses on bridging microbial community ecology, microbial processes and ecosystem functioning using microbial guilds involved in nitrogen cycling and greenhouse gas. He is serving as Senior Editor of The ISME Journal and as editorial board member for FEMS Microbiology Ecology, Applied and Environmental Microbiology and Frontiers in Microbiology. He has over 120 peer-reviewed articles in ISI indexed international journals, including Nature Climate Change, Nature Reviews Microbiology, The ISME J, Trends in Plant Science, Global Change Biology, etc. with ISI citations of >6000 and H-index of 43. (Research ID: http://www.researcherid.com/rid/G-5598-2011). He participated in several European research projects such as EcoFinders, NORA and Metaexplore and his currently involved in the ERA-NET Biodiversa project “Digging Deeper”. Soil microorganisms form one of the largest biodiversity reservoirs on earth. They also play essential roles in ecosystem functions such as biogeochemical cycling. However, the importance of microbial diversity for ecosystem functioning is still debated. In this talk, I will give examples of how we addressed this knowledge gap using N-cycling microorganisms as model functional guilds. I will shows that microbial diversity loss can alter terrestrial ecosystem processes, which suggests that the importance of functional redundancy in soil microbial communities has been overstated[1]. We also examined the effectiveness of introducing microbial communities in altered communities, to recover soil biodiversity and functioning. We found consistent patterns within restoration treatments with minor idiosyncratic effects, which suggests the predominance of deterministic processes and the predictability of restoration trajectories. While the diversity of some alternative compositional states could be successfully increased, no significant restoration of soil N-cycle functioning was observed[2]. Finally I will discuss studies showing the importance of microbial community composition for emissions and consumption of N2O, a potent greenhouse gas [3-7].