What is the quantitative relation between nitrogen deposition and forest carbon sequestration?

摘要

There has been a lasting controversy over the quantitative effect of nitrogen deposition on forest growth and carbon sequestration (e.g., Townsend et al., 1996; Nadelhoffer et al., 1999; Ho¨gberg, 2007; Magnani et al., 2007; De Vries et al., 2008; Sutton et al., 2008; Dezi et al., 2010). It was first widely held that N deposition should increase tree growth in the northern hemisphere, in particular (e.g., Townsend et al., 1996); the Kyoto protocol even stated that this effect should be accounted for. However, based on the distribution of 15N tracer added experimentally to forests in Europe and N. America, Nadelhoffer et al. (1999) proposed that the effect of N additions on C sequestration should be minor as they found that most 15N ended up in the soil rather than in the above-ground parts of the trees. Their proposition was challenged by Magnani et al. (2007), who, based on estimates of net ecosystem production (NEP) derived from eddy-covariance studies, argued that the correlation between C sequestration and N deposition was very strong, with a slope indicating that many hundreds of kg of C were sequestered per kg of N deposited on the forest.