Nature2014-06-26 2:45 PM

水分供应情况在决定亚马逊流域碳平衡中所起作用 Drought sensitivity of Amazonian carbon balance revealed by atmospheric measurements

论文摘要 

本期封面所示为巴西Acre州Senador Guiomard市日出时的一棵坚果树。我们对陆地碳收支对气候异常的敏感性的认识在很大程度上是基于模拟及小规模生态系统研究,并且仍然是不确定的。这意味着,虽然以亚马逊雨林生物质形式存储的大量碳的命运对于未来气候趋势来说非常关键,但尚不清楚的是,亚马逊仍会是一个“碳汇”,还是会成为一个“碳源”,以及是否会成为气候变化的一个驱动因素。根据异常热和异常湿年份的二氧化碳和一氧化碳测量结果对季节和年度碳平衡所做的一项新的分析表明,水分供应情况在决定亚马逊流域碳平衡中起重要作用。在2010年,干旱降低了植物生产,限制了可以在植被中存储的碳的数量;与此同时,大量碳被林火释放。该地区在2011年(一个湿润的年份)是碳中性的,这是由于因林火所损失的碳减少了,被植被吸收的碳增加了。

Abstract 

Feedbacks between land carbon pools and climate provide one of the largest sources of uncertainty in our predictions of global climate. Estimates of the sensitivity of the terrestrial carbon budget to climate anomalies in the tropics and the identification of the mechanisms responsible for feedback effects remain uncertain. The Amazon basin stores a vast amount of carbon, and has experienced increasingly higher temperatures and more frequent floods and droughts over the past two decades. Here we report seasonal and annual carbon balances across the Amazon basin, based on carbon dioxide and carbon monoxide measurements for the anomalously dry and wet years 2010 and 2011, respectively. We find that the Amazon basin lost 0.48 ± 0.18 petagrams of carbon per year (Pg C yr−1) during the dry year but was carbon neutral (0.06 ± 0.1 Pg C yr−1) during the wet year. Taking into account carbon losses from fire by using carbon monoxide measurements, we derived the basin net biome exchange (that is, the carbon flux between the non-burned forest and the atmosphere) revealing that during the dry year, vegetation was carbon neutral. During the wet year, vegetation was a net carbon sink of 0.25 ± 0.14 Pg C yr−1, which is roughly consistent with the mean long-term intact-forest biomass sink of 0.39 ± 0.10 Pg C yr−1 previously estimated from forest censuses. Observations from Amazonian forest plots suggest the suppression of photosynthesis during drought as the primary cause for the 2010 sink neutralization. Overall, our results suggest that moisture has an important role in determining the Amazonian carbon balance. If the recent trend of increasing precipitation extremes persists6, the Amazon may become an increasing carbon source as a result of both emissions from fires and the suppression of net biome exchange by drought.

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