Impacts of enhanced nitrogen deposition and soil acidification on biomass production and nitrogen leaching in Chinese fir plantations

Abstract

Atmospheric pollution levels in China are increasing quickly. Experience from other polluted regions shows that tree growth could be affected, but long-term effects of N deposition and soil acidification on Chinese forests remain mostly unknown. Soil acidification and N deposition were simulated for Chinese fir plantations in Southeast China. A factorial experiment combined four levels of rain pHs (2.5, 4.0, 5.6 and 7.0), four N deposition rates (1, 7.5, 15 and 30 kg N ha-1 y-1) and two site qualities (poor and rich sites), managed for 3 consecutive 20-year rotations. Results indicate atmospheric pollution effects are not immediate, but after 1 to 2 rotations soil acidification effects could reduce ecosystem C pools significantly (-25% and -11% in poor and rich sites, respectively). N deposition rates above 15 kg N ha-1 y-1 could offset some of the negative effects of soil acidification and led to more ecosystem C (19 and 28 Mg C ha-1 more in poor and rich sites than in low N deposition). However, at high N deposition rates (>15 kg N ha-1 y-1), N leaching losses could greatly increase, reaching 75 kg N ha-1 y-1. Moderate N deposition could increase tree biomass production and soil organic mass, resulting in increased ecosystem C, but these gains could be associated to important N leaching. Atmospheric pollution could also result in the long-term in nutrient imbalances and additional ecological issues (i.e. biodiversity loss, eutrophication, etc.) not studied here.