Complex response of the forest nitrogen cycle to climate change
Complex response of the forest nitrogen cycle to climate change
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DOI：
10.1073/pnas.1121448109
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发表时间：
2012-02-28
影响因子：
11.1
通讯作者：
Buso, Don C.
中科院分区：
文献类型：
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作者：
Bernal, Susana;Hedin, Lars O.;Buso, Don C.
气候对生物过程有着重要的影响，但气候变化对生态系统养分通量和循环的影响还没有得到很好的解决。虽然罕见，但长期记录提供了一个独特的机会，可以将气候的影响与其他人为影响分开。在这里，我们研究了世界范围内最长和最完整的流域养分和气候动态记录，这些记录是在美国东北部的哈伯德布鲁克实验森林收集的。我们使用经验分析和模型计算来区分气候变化和过去的扰动对森林氮（N）循环的影响。我们发现，气候本身并不能解释在过去的46年中流域硝酸盐出口急剧下降>90%的发生，尽管生长季节较长，土壤温度较高。最强的气候影响是土壤温度的增加，伴随着流域内的土壤水流动路径的转变，但这种影响解释，充其量，只有类似于40%的硝酸盐下降。相比之下，至少50-60%的观察到的变化，在N输出可以解释的长期影响的森林砍伐在20世纪初的土壤和植被池的N循环。我们的分析表明，历史事件可以掩盖现代压力对N周期的影响，即使分析具有0.5个世纪长的数据集的优势。这些发现提出了关于长期趋势的解释的基本问题，作为理解气候变化如何影响复杂生态系统的基线。
Climate exerts a powerful influence on biological processes, but the effects of climate change on ecosystem nutrient flux and cycling are poorly resolved. Although rare, long-term records offer a unique opportunity to disentangle effects of climate from other anthropogenic influences. Here, we examine the longest and most complete record of watershed nutrient and climate dynamics available worldwide, which was collected at the Hubbard Brook Experimental Forest in the northeastern United States. We used empirical analyses and model calculations to distinguish between effects of climate change and past perturbations on the forest nitrogen (N) cycle. We find that climate alone cannot explain the occurrence of a dramatic >90% drop in watershed nitrate export over the past 46 y, despite longer growing seasons and higher soil temperatures. The strongest climate influence was an increase in soil temperature accompanied by a shift in paths of soil water flow within the watershed, but this effect explained, at best, only similar to 40% of the nitrate decline. In contrast, at least 50-60% of the observed change in the N export could be explained by the long-lasting effect of forest cutting in the early 1900s on the N cycle of the soil and vegetation pools. Our analysis shows that historic events can obscure the influence of modern day stresses on the N cycle, even when analyses have the advantage of being informed by 0.5-century-long datasets. These findings raise fundamental questions about interpretations of long-term trends as a baseline for understanding how climate change influences complex ecosystems.