title: Discontinuity in the responses of ecosystem processes and multifunctionality to altered soil community composition.
abstract: Ecosystem management policies increasingly emphasize provision of multiple, as opposed to single, ecosystem services. Management for such "multifunctionality" has stimulated research into the role that biodiversity plays in providing desired rates of multiple ecosystem processes. Positive effects of biodiversity on indices of multifunctionality are consistently found, primarily because species that are redundant for one ecosystem process under a given set of environmental conditions play a distinct role under different conditions or in the provision of another ecosystem process. Here we show that the positive effects of diversity (specifically community composition) on multifunctionality indices can also arise from a statistical fallacy analogous to Simpson's paradox (where aggregating data obscures causal relationships). We manipulated soil faunal community composition in combination with nitrogen fertilization of model grassland ecosystems and repeatedly measured five ecosystem processes related to plant productivity, carbon storage, and nutrient turnover. We calculated three common multifunctionality indices based on these processes and found that the functional complexity of the soil communities had a consistent positive effect on the indices. However, only two of the five ecosystem processes also responded positively to increasing complexity, whereas the other three responded neutrally or negatively. Furthermore, none of the individual processes responded to both the complexity and the nitrogen manipulations in a manner consistent with the indices. Our data show that multifunctionality indices can obscure relationships that exist between communities and key ecosystem processes, leading us to question their use in advancing theoretical understanding--and in management decisions--about how biodiversity is related to the provision of multiple ecosystem services.
authors.affiliation: School of Forestry and Environmental Studies, Yale University, New Haven, CT 06511; mark.bradford@yale.edu.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Bradford
authors.affiliation: Department of Ecology, Evolution, and Environmental Biology, Columbia University, New York, NY 10027;
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Wood
authors.affiliation: Faculty of Life Sciences, The University of Manchester, Manchester M13 9PT, United Kingdom;
authors.forename: Richard D
authors.initials: RD
authors.lastname: Bardgett
authors.affiliation: The James Hutton Institute, Aberdeen AB15 8QH, Scotland, United Kingdom;
authors.forename: Helaina I J
authors.initials: HI
authors.lastname: Black
authors.affiliation: Zoologisches Institut, University of Cologne, D-50674 Köln, Germany;
authors.forename: Michael
authors.initials: M
authors.lastname: Bonkowski
authors.affiliation: Centre for Population Biology, Department of Biological Sciences, Imperial College at Silwood Park, Berkshire SL5 7PY, United Kingdom;
authors.forename: Till
authors.initials: T
authors.lastname: Eggers
authors.affiliation: Department of Forest Sciences, University of British Columbia, Vancouver, BC, Canada V6T 1Z4;
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Grayston
authors.affiliation: Institute of Soil Science and Land Evaluation, University of Hohenheim, D-70593 Stuttgart, Germany;
authors.forename: Ellen
authors.initials: E
authors.lastname: Kandeler
authors.affiliation: Institute of Plant Sciences, University of Bern, CH-3013 Bern, Switzerland;
authors.forename: Peter
authors.initials: P
authors.lastname: Manning
authors.affiliation: Department of Environmental Sciences, University of Helsinki, Helsinki 00014, Finland; and.
authors.forename: Heikki
authors.initials: H
authors.lastname: Setälä
authors.affiliation: School of Biosciences, Cardiff University, Cardiff CF10 3AX, United Kingdom.
authors.forename: T Hefin
authors.initials: TH
authors.lastname: Jones
mesh_terms: D000818:Animals; D044822:Biodiversity; D018533:Biomass; D017753:Ecosystem; D065948:Grassland; D058458:Nitrogen Cycle; D010944:Plants / Q000145:classification / Q000378:metabolism*; D011157:Population Dynamics; D012987:Soil / Q000737:chemistry* / Q000469:parasitology; D012988:Soil Microbiology
chemical_list: D012987:Soil
keywords: aboveground–belowground interactions; ecosystem functioning; plant-soil feedbacks; soil biodiversity; soil fauna