Input-output budgets for inorganic nitrogen under acid rain in a subtropical evergreen mixed forest in central-south China

Inorganic nitrogen deposition and leaching in stream water were monitored from January, 2001 to December, 2004 in a subtropical evergreen mixed forest in central-south China. The seasonal concentration and flux of inorganic nitrogen in bulk precipitation and stream water, seasonal mean net retention of nitrogen and net flux of H+ transformed by nitrogen were estimated and quantified in Shaoshan forest. The research results show that the correlation coefficient of fluxes between bulk precipitation and stream water is significant, with a coefficient 0.916 at the 0.01 level. Mean fluxes of inorganic nitrogen input are 2.62 g m(-2) a(-1) and 0.516 g m(-2) a(-1) in form of bulk precipitation and dry deposition respectively, and output in stream water is around 0.22 g m(-2) a(-1), which indicates that most of nitrogen input is reserved in the forest. Net retention of nitrogen reaches 2.916 g m(-2) a(-1), just higher than other study plots over the world. Along with the translating of nitrogen (NH4+ -N and NO3- -N), H+, is imported to the forest ecosystem at the same time. At our study plots, net flux of H+ transformed by nitrogen is about 73.57 mmol m(-2) a(-1). The positive value suggests that Shaoshan forest is still a finer buffering system to nitrogen deposition and it is far from nitrogen saturation in spite of the high nitrogen deposition.