An overlay of foliar N concentrations and nitrogen isotop ratios from the Konza flora (black) to a global dataset (gray). |
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.
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