Background and aims

Increased atmospheric nitrogen (N) deposition and climate warming can both exert strong, cumulative effects on N losses from ecosystems. However, given their potential interactions with interannual variability in environmental conditions or other factors, it is uncertain how effectively the comparison of short- vs. long-term results from N addition and warming field experiments can reveal these cumulative effects. Our aim was to compare the short-term versus long-term effects of N addition and warming on aboveground and belowground N retention while controlling for interannual variation in other factors.

Methods

We added ¹⁵N tracer to N addition and warming plots in a northern temperate grass-dominated old field in early spring, then assessed the amount of the added ¹⁵N recovered aboveground and belowground at the peak of the growing season. We controlled for interannual variation in background environmental conditions by comparing new N addition and warming plots (3 years old) to those of an existing field experiment (16 years old).

Results

Both N addition and warming significantly increased aboveground and belowground ¹⁵N tracer retention. However, there were no significant interactions between either of the treatments and plot age for ¹⁵N tracer retention, nor for plant production. The lack of interactions with plot age corresponded with the continued dominance of two non-native grass species in the plots.

Conclusion

Our results highlight the potentially important role of dominant species that resist replacement in buffering against the effects of global change on cumulative, long-term changes in ecosystem N retention.

中文翻译：

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氮添加和变暖对地上和地下氮保留的短期与长期影响

 背景和目标

大气氮（N）沉降的增加和气候变暖都会对生态系统的氮损失产生强烈的累积影响。然而，考虑到它们与环境条件或其他因素的年际变化之间的潜在相互作用，尚不确定氮添加和变暖现场实验的短期与长期结果的比较能否有效地揭示这些累积效应。我们的目的是比较氮添加和变暖对地上和地下氮保留的短期和长期影响，同时控制其他因素的年际变化。

 方法

我们在早春在北温带以草为主的老田中向氮添加和增温地块添加了¹⁵ N 示踪剂，然后评估了生长季节高峰期地上和地下恢复的添加¹⁵ N 量。我们通过将新的氮添加和变暖图（3 年）与现有现场实验（16 年）进行比较来控制背景环境条件的年际变化。

 结果

氮添加和变暖均显着增加了地上和地下¹⁵ N 示踪剂的保留。然而，两种处理和¹⁵ N 示踪剂保留的地龄之间没有显着的相互作用，植物生产也没有显着的相互作用。与地块年龄缺乏相互作用与地块中两种非本地草种的持续主导地位相对应。

 结论

我们的结果强调了抵抗替代的优势物种在缓冲全球变化对生态系统氮保留的累积长期变化的影响方面的潜在重要作用。