COS 37-6
Does resource alteration alter the effects of biodiversity on ecosystem productivity?

Tuesday, August 12, 2014: 3:20 PM
302/303, Sacramento Convention Center
Dylan James Craven, Synthesis Centre for Biodiversity Sciences (sDiv), German Centre for Integrative Biodiversity Research (iDiv), Leipzig, Germany
Forest Isbell, Plant Biology, University of Georgia, Athens, GA
Anne Ebeling, Insitute of Ecology, University Jena, Jena, Germany
Pete Manning, Institute of Plant Sciences, University of Bern, Bern, Switzerland
Christiane Roscher, Department of Community Ecology, Helmholtz Centre for Environmental Research, Halle, Germany
Alexandra Weigelt, German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Leipzig, Germany
Brian J. Wilsey, Ecology, Evolution, and Organismal Biology, Iowa State University, Ames, IA
Nico Eisenhauer, Institute of Ecology, Friedrich-Schiller-University Jena, Jena, Germany
Background/Question/Methods  

Human activities are altering the availability of plant resources and reducing plant diversity globally, which also have strong effects on ecosystem productivity and services. The interaction between global change drivers and diversity has important implications for natural resource management, as it illustrates whether biodiversity buffers the response of ecosystems to disturbances. However, we lack a general framework for understanding this interaction and its underlying mechanisms. Here, we propose a hypothetical framework and test it using data from experimental grassland studies where diversity and resource alterations were manipulated.

We hypothesized that increased resource availability will increase community productivity and that this effect would be stronger in more diverse communities. Secondly, we hypothesized that reduced resource availability would reduce community productivity and that this reduction will be weaker in more diverse communities.

 To test these hypotheses, we identified 15 grassland diversity experiments that manipulated nutrient availability (N addition) or water availability (drought). We calculated the log response ratio (LRR) for each diversity level to resource alteration in each experiment. Using mixed-effects models, we analysed the extent to which diversity modified plant community responses to resource alteration and, subsequently, whether this relationship varied with the resource manipulation, here represented as the average LRR within an experiment.

Results/Conclusions

Along diversity gradients, plant communities exhibited contrasting responses to resource addition and reduction. Counter to expectations for both hypotheses, we found that the addition of resources significantly lowered diversity effects on productivity (-7.7 % ± 4.3), whereas resource reduction did not significantly alter diversity effects on productivity (- 1.7 % ± 9.0).  The lack of differences in diversity effects between droughted and control plant communities is likely attributable to temporal variation in precipitation.  Corroborating this, 18.7% of residual heterogeneity in resource reduction experiments was due to inter- and intra-annual variation, whereas only 8.5 % of residual heterogeneity in resource addition experiments could be attributed to inter- or intra-annual variation. In both instances of experimental resource alteration, we found that diversity effects on productivity are positive when resource availability is low and negative when resource availability is high, as indicated by the negative correlation between productivity responses to diversity and the strength of experimental resource manipulation. Our results suggest that more diverse plant communities varied less in response to resource alterations than less diverse communities, thus implying greater resilience to global change drivers.