Chronic nitrate additions dramatically increase the export of carbon and nitrogen from northern hardwood ecosystems

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A long-term field experiment was initiated to simulate chronic atmospheric N deposition, a widespread phenomenon in industrial regions of the world. Eight years of experimental nitrate (NO3-) additions (3 g NO3--N m-2 per year) to four different northern hardwood forests located along a 500 km geographic gradient dramatically increased leaching losses of NO3--N, dissolved organic carbon (DOC), and dissolved organic nitrogen (DON). During the last two water years, the average increase in solution NO3--N and DON leaching from the NO3- -amended plots was 2.2 g N m -2, equivalent to 72% of the annual experimental N addition. Results indicate that atmospheric N deposition may rapidly saturate some northern hardwood ecosystems across an entire biome in the upper Great Lakes Region of the USA. Changes in soil C and N cycling induced by chronic N deposition have the potential in this landscape to significantly alter the flux of DOC and DON from upland to aquatic ecosystems. Michigan Gradient study site characteristics are similar to those of European forests most susceptible to N saturation.

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