LB 7-61 - Large scale analysis of watershed nitrogen and carbon coupling across eco-regions

Background/Question/Methods:

Carbon and nitrogen cycles are often tightly coupled due to the limiting nature of nitrogen for carbon retention and assimilation by plants. Different environmental factors, like climate and plant composition affect cycling of both elements whereas environmental disturbances ranging from storm events to fires to seasonal changes can lead to the decoupling of both cycles. The strength of carbon and nitrogen coupling varies between eco-regions and environmental gradients, however the relative influence of different environmental variables of this coupling is not as well understood. Here we analyzed carbon and nitrogen pools and fluxes across a wide range of sites in the United States to determine how different environmental factors influence the coupling of these two nutrients.

Results/Conclusions:

We combined data on stream chemistry, stand composition, soil chemistry, and carbon exchange from over twenty co-located aquatic and terrestrial NEON sites to understand changes in C:N ratios from plants to soils to streams. Preliminary analyses focus on the relationship between annual average nitrogen and carbon exports compared to plant and soil C:N ratio, nitrogen mineralization rates, and mean annual precipitation and temperature. Plant C:N ratios varied from 16.1 to 55.0 g C/g N, whereas soil C:N ratios in the top 30 cm of soil ranged from 9.8 to 34.4 g C/g N, with significant correlations between both variables. Stream DOC:TDN ratios varied from 0.5 to 28.2 mg C/l / mg N/l, however these were not strongly correlated with soil or leaf chemistry. These results highlight nitrogen losses, relative to carbon, from the canopy to soils to streams. The large-scale nitrogen flux patterns shown in this work that should be mirrored by carbon fluxes at sites where the two nutrient cycles are tightly coupled. Further work aims to integrate eddy covariance and precipitation data to calculate a watershed level carbon and nitrogen mass balances and determine rates of change for both nutrients on an annual basis.