模拟氮沉降对高硫沉降地区森林土壤酸化的贡献

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

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40kg.(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1a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NO3-淋溶的大幅增加,土壤出现氮饱和现象.相对而言,NH4+的酸化和富营养化效应均强于同当量的NO3-,表明中国氮沉降控制不应忽视NH3的排放削减.

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· （hm^2 · a） ^-l ] 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. Ca^2＋ and Mg^2＋ , and AI^3＋ increased remarkably, with the AI3^3＋ to base cation （sum of Ca^2＋, Mg^2＋ and K^＋ ） molar ratio increased from 0.5 of the reference to around or even higher than 1.0, which means Al^3 ＋ might do harm to the vegetation. The enhanced leaching of base cations and activation of toxic Al3^3＋ 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 he possibly preferred to nitrogen oxides （ NOx ） for nitrogen deposition control in China.