Averill and co-workers compare two groups of mycorrhiza-forming fungi that are involved in decomposition of organic material. It was known already that access to nitrogen was the limiting factor for the growth of these organisms. One of the groups produces enzymes that can extract nitrogen from organic material, and it can therefore be predicted that this group is more efficient in sequestering carbon. This was confirmed by large scale measurements. Read the whole article in Nature. An editorial in the same issue of Nature further explains why the things we can't see are as least as important as the things we can when it comes to carbon sequestration.