Long‐term nitrogen addition causes the evolution of less‐cooperative mutualists |
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Authors: | Dylan J. Weese Katy D. Heath Bryn T. M. Dentinger Jennifer A. Lau |
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Affiliation: | 1. Department of Biology, St. Ambrose University, Davenport, Iowa;2. Kellogg Biological Station and Department of Plant Biology, Michigan State University, Michigan;3. Department of Plant Biology, University of Illinois, Urbana, Illinois;4. Jodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey, United Kingdom |
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Abstract: | Human activities have altered the global nitrogen (N) cycle, and as a result, elevated N inputs are causing profound ecological changes in diverse ecosystems. The evolutionary consequences of this global change have been largely ignored even though elevated N inputs are predicted to cause mutualism breakdown and the evolution of decreased cooperation between resource mutualists. Using a long‐term (22 years) N‐addition experiment, we find that elevated N inputs have altered the legume–rhizobium mutualism (where rhizobial bacteria trade N in exchange for photosynthates from legumes), causing the evolution of less‐mutualistic rhizobia. Plants inoculated with rhizobium strains isolated from N‐fertilized treatments produced 17–30% less biomass and had reduced chlorophyll content compared to plants inoculated with strains from unfertilized control plots. Because the legume–rhizobium mutualism is the major contributor of naturally fixed N to terrestrial ecosystems, the evolution of less‐cooperative rhizobia may have important environmental consequences. |
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Keywords: | Adaptation coevolution nitrogen deposition resource mutualism symbiosis |
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