Nitrogen oligotrophication in northern hardwood forests
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While much research over the past 30 years has focused on the deleterious effects of excess N on forests and associated aquatic ecosystems, recent declines in atmospheric N deposition and unexplained declines in N export from these ecosystems have raised new concerns about N oligotrophication, limitations of forest productivity, and the capacity for forests to respond dynamically to disturbance and environmental change. Here we show multiple data streams from long-term ecological research at the Hubbard Brook Experimental Forest in New Hampshire, USA suggesting that N oligotrophication in forest soils is driven by increased carbon flow from the atmosphere through soils that stimulates microbial immobilization of N and decreases available N for plants. Decreased available N in soils can result in increased N resorption by trees, which reduces litterfall N input to soils, further limiting available N supply and leading to further declines in soil N availability. Moreover, N oligotrophication has been likely exacerbated by changes in climate that increase the length of the growing season and decrease production of available N by mineralization during both winter and spring. These results suggest a need to re-evaluate the nature and extent of N cycling in temperate forests and assess how changing conditions will influence forest ecosystem response to multiple, dynamic stresses of global environmental change.
KeywordsClimate change; Carbon; Dissolved organic carbon; Hubbard Brook Experimental Forest; Nitrogen
Groffman, Peter M.; Driscoll, Charles T.; Durán, Jorge; Campbell, John L.; Christenson, Lynn M.; Fahey, Timothy J.; Fisk, Melany C.; Fuss, Colin; Likens, Gene E.; Lovett, Gary; Rustad, Lindsey; Templer, Pamela H. 2018. Nitrogen oligotrophication in northern hardwood forests. Biogeochemistry. 141(3): 523-539. https://doi.org/10.1007/s10533-018-0445-y.