全球氮添加实验设计方法现状的定量分析

氮添加控制实验是研究全球氮沉降对陆地生态系统影响的最有效手段之一。目前数百个氮添加实验由于其实验设计和方法的差异给不同实验结果之间的比较以及全球数据整合分析带来很大的不确定性。我们搜集全球302个氮添加控制实验，并定量分析其实验设计方法和现状，发现全球氮添加控制实验中仅有8%的实验数量分布于苔原、湿地和荒漠；氮添加量低于2g·m^-2·a^-1的实验仅占到4.4%；单独使用NH⁺₄或NO^-₃态肥料的实验占17.5%；超过每年6次氮添加的实验数量仅占1.4%；氮添加实验持续时间基本小于5年，大于20年的实验占13.6%；全球84.9%的实验中氮添加水平数目在2个以内，4个以上的实验仅占5.1%。针对目前氮添加实验的设计方法和现状，我们对未来氮添加实验设计和方法提出了参考建议。

A Global Analysis of the Designs and Methods Among Nitrogen Addition Experiments

Nitrogen (N) addition experiment is one of the effective measures for assessing the effects of N deposition on terrestrial ecosystems. Though hundreds of N addition experiments have been conducted during the last decades,the differences of methods could cause large uncertainty for the comparison among the study results and global meta-analysis. Thus,we collected 302 N addition experiments in terrestrial ecosystems and performed a global analysis of their methods. Our results showed that only 8% of N addition experiments were conducted in tundra,wetland and desert ecosystems. Experiments implemented below the N rate of 2 g N·m^-2·a^-1 made up 4.4% and 17.5% for those solely using NH⁺₄ or NO^-₃ form fertilizer. 13.6% for experimental duration above 20 years,and 5.1% for those with more than 4 levels of N addition. Based on these results,we presented some suggestions for the design and the methodoly of future N addition experiments.