[Vegetation uptake of nitrogen and base cation in China and its role in soil acidification]

Vegetation uptake of nitrogen and base cation, as well as acid deposition, is an important source of soil acidity. Based on the net primary productivity and elemental composition, the uptake rate of nitrogen and base cation was estimated for each vegetation type in China. Result showed that the uptake rate of nitrogen was commonly low in southeast China and high in northwest China, and decreased gradually from southeast to northwest in northwest China. In addition, the uptake rate of base cation was very high (> 2.0 keq.(hm2.a)-1) for subtropical/tropical broadleaf evergreen forest, temperate limestone broadleaf deciduous forest, temperate deciduous shrub, and subtropical/tropical savanna in the northeast of Huabei Plain, the south of Yunan province, and the west of Hainan Island respectively, and low (< 0.5 keq.(hm2.a)-1) for subtropical evergreen coniferous forest in east China and deserts and steppes in arid region of west China. Although vegetation uptake caused no increase of soil acidity in almost all areas in China, the acidity input caused by vegetation uptake was quite high (> 0.5 keq.(hm2.a)-1) and even higher than the current acid deposition in some areas, where soil acidification might happen because the total acidity input exceeded the alkalinity produced by soil weathering.