Nitrogen deposition and soil nitrogen dynamics in subtropical evergreen broad-leaved stands along an age-sequence

Abstract

In order to reveal the effects of nitrogen (N) deposition on forest ecosystems, we investigated the soil N dynamics across a chronosequence of subtropical evergreen broad-leaved forest stands in eastern China for two years. Current atmospheric N deposition was 18 kg ha-1 year-1. Nitrogen fluxes in throughfall varied from 17 to 23 kg ha-1 year-1 with an increasing trend with stand age. The total N fluxes ranged from 7.3 to 9.3 kg ha-1 year¹ under the forest floor and from 1.2 to 2.5 kg ha-1 year¹ at 30-cm soil depth with the high values in the older stand. The net mineralization potentials in the old stands ranged from 19 to 24 mg kg-1 month-1, and were 30-55% higher than those in the young stands. The inorganic N concentration and flux at 30-cm soil depth were significantly (p < 0.05) correlated with net mineralization potential. The potential N transformation rates were significantly (p < 0.05) correlated with soil C/N ratio and DON while not with forest floor C/N ratio. Input-output budget suggests that the forest at our site is a finer buffering system to N deposition and is far from N saturation.