Effects of nitrogen deposition on carbon sequestration in Chinese fir forests ecosystems

Abstract

Nitrogen deposition and its ecologic effects on forest ecosystems have received global attention. In this paper, the ecosystem model FORECAST was used to assess the effects of nitrogen deposition on carbon sequestration in Chinese fir plantation forests. This topic is important as China is intensifying its reforestation efforts to increase forest carbon sequestration for combating climate change impacts, and the Chinese fir is the most important plantation species in China. A series of scenarios including N deposition levels (1, 5, 10, 20, 30, 40 and 50 kg ha-1 y-1), management regime (rotation lengths of 15, 30 and 50 years) and site quality (poor and rich nutrient sites) were defined for the simulations. Our simulation results show that N deposition increased carbon sequestration in Chinese fir forests, with a higher increasing effect at lower N deposition levels and lower increasing effect at higher N deposition levels. When N deposition levels exceed 20-30 kg ha-1 y-1, the effects of N deposition on forest C pools were marginal; suggesting that N deposition levels of 20-30 kg ha-1 y-1 could lead to soil N saturation in Chinese fir forests. Any additional amounts of N input from deposition would likely be leached out. It is estimated that the contributions of N deposition to C sequestration in the whole Chinese fir forests, South-East China are 7.4 x 10 6 Mg C year-1 under the current N deposition levels (5 to 10 kg ha-1 y-1) and could reach up to 16 x 10 6 Mg C year-1 under hypothetic future N deposition conditions (7.5 to 15 kg ha-1 y-1).