【摘要】 为了了解草原生态系统氨气挥发情况、历史放牧的影响及其影响机制,2005和2006年生长季期间,在长达17年放牧处理的样地上测定了5个放牧强度下的氨气挥发量。结果表明:氨气挥发随季节变化波动很大,春季和初秋高,晚秋和夏季低,变化范围为0.88-3.52 gN ha^-1d^-1。土壤pH值、NH₄⁺-N浓度、湿度以及容重对氨气挥发控制作用较强。但是容重的影响与其他3个因子的影响作用相反,而容重的大小直接受不同放牧强度影响。虽然不同的放牧强度对氨气释放的影响在统计学上来说并不显著,但是,相对不放牧的情况而言,氨气挥发量在放牧情况下更大。而土壤氮浓度、植物生物量却在放牧的情况下更低。这些都意味着放牧草地生态系统比不放牧草地生态系统恢复起来会更慢。这种关于草原生态系统氨气挥发的研究意义重大,因为它有助于加强了解氮素丢失对草原各进程的抑制作用,同时对制订适宜的放牧及施肥措施从而达到合理利用资源的目的也具有重要的参考价值。更多还原

【Abstract】 Gaseous N losses via ammonia（NH₃） volatilization were measured during the 2005 and 2006 growing seasons in a long-term（17 years） experiment with five grazing intensities(0.00,1.33,2.67,4.00 and 5.33 sheep ha^-1).We aim to understand the seasonal variations in ammonia production,the potential carry-over effects of previous grazing and the underlying regulating processes involved.It was found that rates of NH₃ volatilization varied seasonally,ranging from 0.88 to 3.52 g N ha^-1d^-1 during the measurement period,with higher values in spring and early summer and lower values in late summer and autumn.Soil pH value,NH₄⁺-N concentration,moisture and bulk density exerted controls on NH₃ volatilization over the two growing seasons.However,the constraining effect of bulk density on NH₃ flux,driven by grazing,muted the supporting effect of above other three environmental factors.Even though no statistically significant effects of different grazing intensities on rates of NH₃ volatilization were generally found,grazed treatments tended to result in relatively higher cumulative NH₃ volatilization,and relatively lower soil N content,plant growth and productivity.It indicates that restoration of the degraded grazed grassland may be slower in comparison with the ungrazed grassland.The study on NH₃ volatilization in grassland ecosystem is meaningful in terms of its contribution to advancing our understanding of the role of N loss in limiting grassland processes and to drawing up grazing guideline and fertilizing regime for utilizing the resources rationally.更多还原