All the coastal oceans receive far more fixed nitrogen from humans than they can process. (dotearth.blogs.nytimes.com)
The genes for fixing nitrogen have never been successfully transferred to plants — either naturally (over several hundred million years of evolution) or by humans. (dotearth.blogs.nytimes.com)
It can also affect the ratio of different species of trees by removing the competitive advantage of species that were better at fixing nitrogen. (treehugger.com)