Drought impact on forest carbon dynamics and fluxes in Amazonia
Drought impact on forest carbon dynamics and fluxes in Amazonia
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DOI：
10.1038/nature14213
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发表时间：
2015-03-05
期刊：
影响因子：
64.8
通讯作者：
Malhi, Y.
中科院分区：
文献类型：
--
作者：
Doughty, Christopher E.;Metcalfe, D. B.;Malhi, Y.
2005年和2010年，亚马逊流域经历了两次强烈的干旱，“正如一些全球模式预测的那样，这是由热带水文状况的变化(2)驱动的，可能与全球气候变化(3)有关”。2005年干旱后树木死亡率增加(4)，区域大气反演模型显示，与2011年相比，2010年整个流域的二氧化碳吸收量减少（参考文献5）。但是，热带森林碳循环对这些干旱的响应尚未完全了解，也没有详细的多地点实地调查。为了更好地理解2010年干旱对亚马逊森林的影响，我们使用了分布在南美洲的13个1公顷森林样地的数年数据，分别测量了净初级生产（NPP）、自养呼吸和异养呼吸的每个组成部分。我们发现总NPP在整个干旱期间保持不变。然而，在干旱即将结束时，自养呼吸，特别是根和茎的自养呼吸，与2009年无干旱时的测量结果相比显著下降，三个最干旱的样地的自养呼吸下降幅度更大。干旱后1年，NPP总量保持不变，但碳的分配从细根NPP向冠层NPP转移。叶片水平和小区水平的测量都表明，严重干旱抑制了光合作用。根据降雨数据将这些测量结果扩展到整个亚马逊流域，我们估计2010年干旱使亚马逊流域的光合作用减少了0.38亿吨碳（0.23-0.53亿吨碳）。总的来说，我们发现在这次干旱期间，树木通过减少与生长无关的自养呼吸来优先生长，而不是减少总NPP。这表明树木减少了对组织维护和防御的投资，这与生态进化理论一致，即树木在缺乏生长的情况下处于竞争劣势(6)。我们认为，减少的维护和防御投资可能反过来导致在我们的样地观察到的干旱后树木死亡率增加。
In 2005 and 2010 the Amazon basin experienced two strong droughts', driven by shifts in the tropical hydrological regime(2) possibly associated with global climate change(3), as predicted by some global models'. Tree mortality increased after the 2005 drought(4), and regional atmospheric inversion modelling showed basin-wide decreases in CO2 uptake in 2010 compared with 2011 (ref. 5). But the response of tropical forest carbon cycling to these droughts is not fully understood and there has been no detailed multi-site investigation in situ. Here we use several years of data from a network of thirteen 1-ha forest plots spread throughout South America, where each component of net primary production (NPP), autotrophic respiration and heterotrophic respiration is measured separately, to develop a better mechanistic understanding of the impact of the 2010 drought on the Amazon forest. We find that total NPP remained constant throughout the drought. However, towards the end of the drought, autotrophic respiration, especially in roots and stems, declined significantly compared with measurements in 2009 made in the absence of drought, with extended decreases in autotrophic respiration in the three driest plots. In the year after the drought, total NPP remained constant but the allocation of carbon shifted towards canopy NPP and away from fine-root NPP. Both leaf-level and plot-level measurements indicate that severe drought suppresses photosynthesis. Scaling these measurements to the entire Amazon basin with rainfall data, we estimate that drought suppressed Amazon-wide photosynthesis in 2010 by 0.38 petagrams of carbon (0.23-0.53 petagrams of carbon). Overall, we find that during this drought, instead of reducing total NPP, trees prioritized growth by reducing autotrophic respiration that was unrelated to growth. This suggests that trees decrease investment in tissue maintenance and defence, in line with eco-evolutionary theories that trees are competitively disadvantaged in the absence of growth(6). We propose that weakened maintenance and defence investment may, in turn, cause the increase in post-drought tree mortality observed at our plots.