|An overlay of foliar N concentrations and nitrogen isotop ratios from the Konza flora (black) to a global dataset (gray).|
One of the key questions for understanding plant community assembly is to understand the environments that species inhabit--not just the dominant species, but the hundreds of species that are only occasionally or rarely seen to the casual observer. Do the rare species mirror the more abundant species in their traits? Or are they rare because they are built for different environments?
At Konza Prairie, there are over 500 herbaceous species. Over last 2 years we measured the leaves of over 400 species at Konza. One of the interesting patterns was examining the relationships between the leaf N concentrations and the foliar N isotopes. Together these two best reflect the N availability of the environment the plant inhabits. High N concentrations and high del15N generally mean that the plant is growing in an environment with high N availability.
Konza is considered a strongly N-limited ecosystem. The responses of aboveground productivity to N addition are some of the highest in North American grasslands--ANPP triples with N addition. Given this, at Konza, one thing that was surprising was how many species had really high N concentrations in their leaves. A fair number of species that didn't fix nitrogen had N concentrations over 40 mg g-1, or 4%. That's really high.
When you look at the flora as a whole, there were a lot of species that were found in high N availability sites. Edges of roads. Bison wallows. Places with high dung inputs. A lot of the diversity of Konza is likely maintained because of these high N availability sites.
When you look at Konza species by species the picture changes from one dominated by severe N limitation to one with a broad spectrum of N availability. In fact, we could compare Konza to the rest of the world with a global dataset on foliar N and N isotopes. Not only do many of the species occupy high N availability sites at Konza, but the typical species at Konza actually occupies areas of higher N availability than the "rest of the world".
The analysis of traits across a broad portion of a flora--the community's traitscape--is not novel, but definitely an undersubscribed approach. As we build more global datasets and measure more and more species, a lot more insight to how communities are constructed and florae assembled will come into new light.