There is much evidence that external state factors influence ecosystem properties, including nitrogen fixation. But, I will here ask whether such a state-factor view may fail to offer the “whole story” of symbiotic nitrogen fixation, and how this process varies across biomes, time, and as a function of increasing atmospheric CO2. I will first review a few fundamental patterns of how nitrogen fixing plants and fixation vary across the land biosphere, and examine how these patterns compare against the traditional state-factor view. I will then use a new adaptive dynamics model that focuses on a very different class of ecosystem dynamics: the local-scale competitive interactions between plants, and the feedbacks that emerge from these interactions at the ecosystem scale.
I will offer evidence that local biotic interactions may be essential for understanding the distribution, the functional properties, and the emergent consequences of symbiotic nitrogen fixers within ecosystems. I will show that a world without these local interactions would both look and function very differently than today’s world. Finally, I will speculate about the interaction between atmospheric CO2 levels and the emergent ecosystem dynamics imposed by nitrogen fixation, with particular emphasis on the biome-specific distribution of nutrient cycles and net primary production.