Weese Dylan J, Heath Katy D, Dentinger Bryn T M, Lau Jennifer A
Department of Biology, St. Ambrose University, 518 West Locust St, Davenport, Iowa, 52803; Kellogg Biological Station and Department of Plant Biology, Michigan State University, 3700 E. Gull Lake Drive, Hickory Corners, Michigan, 49060.
Evolution. 2015 Mar;69(3):631-42. doi: 10.1111/evo.12594. Epub 2015 Feb 5.
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.
人类活动已经改变了全球氮循环，结果是，氮输入增加正在给各种生态系统带来深刻的生态变化。尽管预计氮输入增加会导致共生关系破裂以及资源共生者之间合作减少的进化，但这种全球变化的进化后果在很大程度上被忽视了。通过一项长期（22年）的氮添加实验，我们发现氮输入增加改变了豆科植物-根瘤菌共生关系（根瘤菌通过交换氮以换取豆科植物的光合产物），导致共生性较低的根瘤菌进化。与接种未施肥对照地块菌株的植物相比，接种从施氮处理中分离出的根瘤菌菌株长成的植物生物量减少了17%-30%，叶绿素含量也降低了。由于豆科植物-根瘤菌共生关系是陆地生态系统中自然固氮的主要贡献者，共生性较低的根瘤菌的进化可能会产生重要的环境后果。
