Plant and Soil

, Volume 203, Issue 2, pp 301-311

Long-term effects of experimental nitrogen additions on foliar litter decay and humus formation in forest ecosystems

  • Alison H. MagillAffiliated withComplex Systems Research Center, University of New Hampshire
  • , John D. AberAffiliated withComplex Systems Research Center, University of New Hampshire

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Decomposition rates and N dynamics of foliar litter from 4 tree species were measured over a 72 month period on the Chronic Nitrogen Addition plots at the Harvard Forest, Petersham MA, beginning in November 1988. Plots received nitrogen additions of 0, 5 and 15 g N m-2yr-1 in two different stand types: red pine and mixed hardwood. Bags were collected in August and November of each year and litter analysed for mass remaining, nitrogen, cellulose and lignin content. Mass remaining was significantly greater for litter in nitrogen treated plots than in control plots after 48 months. Lignin content of litter was significantly higher with nitrogen treatments but there was little effect of treatment on cellulose content. N concentration was similar between treatments, but greater mass remaining in treated plots resulted in a higher total amount of N in humus produced in the high N plot. This mechanism could be a sink for up to 1.5 g N·m-2yr-1 of the 1.5 g N·m-2yr-1 added annually to the high N plots. Reduced decomposition rates in conjunction with increased lignin accumulation could impact global carbon sequestration as well.

ammonium nitrate additions humus formation litter decay rate litter decomposition N deposition