COMMUNITIES of species and their associated biological, chemical and physical processes, collectively known as ecosystems, drive the Earth’s biogeochemical processes(1,2). Currently most ecosystems are experiencing loss of biodiversity associated with the activities of human expansion(3-5), raising the issue of whether the biogeochemical functioning of ecosystems will be impaired by this loss of species(6-8). Current ecological knowledge supports a wide range of views on the subject(9-13), but empirical tests are few(9,14-16). Here we provide evidence from direct experimental manipulation of diversity by over an order of magnitude, using multi-trophic level communities and simultaneous measures of several ecosystem processes, that reduced biodiversity may indeed alter the performance of ecosystems.