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Nitrogen oligotrophication in northern hardwood forests
- 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.
- Biogeochemistry 2018 v.141 no.3 pp. 523-539
- aquatic ecosystems, carbon, climate, forest ecosystems, global change, growing season, hardwood forests, mineralization, nitrogen, oligotrophication, plant litter, resorption, spring, temperate forests, trees, winter, New Hampshire
- 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.