模拟氮沉降对高硫沉降地区森林土壤酸化的贡献

以重庆铁山坪马尾松林下典型的酸化土壤为研究对象,按照40 kg·(hm²·a)^-1的N剂量分别喷洒NH₄NO₃和NaNO₃以模拟氮沉降翻倍的情景,对其影响下的土壤溶液pH值和主要阴阳离子浓度进行了为期1 a的野外观测.结果表明,与未经处理的对照相比,喷洒NH₄NO₃的土壤溶液的pH值有所下降,而NaNO₃则导致pH值略有上升.同时,喷洒NH₄NO₃和NaNO₃均导致盐基阳离子（Ca²⁺和Mg²⁺）和Al³⁺浓度的明显上升,其中Al³⁺与盐基阳离子（Ca²⁺、Mg²⁺和K⁺之和)的摩尔比值由对照的0.5左右升高到接近甚至超过1.0.盐基阳离子的加速淋溶和有毒Al³⁺的活化,表明氮沉降已加剧了土壤酸化.此外,氮输入的增加还引起了NO^-₃淋溶的大幅增加,土壤出现氮饱和现象.相对而言,NH⁺₄的酸化和富营养化效应均强于同当量的NO^-₃,表明中国氮沉降控制不应忽视NH₃的排放削减.

Contribution of Simulated Nitrogen Deposition to Forest Soil Acidification in Area with High Sulfur Deposition

The impacts of nitrogen deposition on a typical acidified soil under a masson pine (Pinus massoniana) forest at Tieshanping, Chongqing in Southwest China was studied through field experiments. The changes of soil water chemistry in different layers within one year after the spray of NH4NO3 and NaNO3 solution respectively with the same nitrogen dose of 40 kg x (hm2 x a)(-1)] indicated that although the pH value decreased a little (treated by NH4NO3) or even increased somewhat (treated by NaNO3), the concentration of base cations, i.e. Ca2+ and Mg2+, and Al3+ increased remarkably, with the Al3+ to base cation (sum of Ca2+, Mg2+ and K+) molar ratio increased from 0.5 of the reference to around or even higher than 1.0, which means Al3+ might do harm to the vegetation. The enhanced leaching of base cations and activation of toxic Al3+ both indicated the deterioration of soil acidification. In addition, the nitrogen saturation occurred with the increasing NO3- leaching. Since it was detected that NH4+ had more effect on soil acidification and eutrophication than NO3- with the same equivalence, ammonia (NH3) emission abatement should be possibly preferred to nitrogen oxides (NO(x)) for nitrogen deposition control in China.