Linking drought legacy effects across scales: From leaves to tree rings to ecosystems
Linking drought legacy effects across scales: From leaves to tree rings to ecosystems
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DOI：
10.1111/gcb.14710
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发表时间：
2019-06-30
影响因子：
11.6
通讯作者：
Anderegg, William R. L.
中科院分区：
文献类型：
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作者：
Kannenberg, Steven A.;Novick, Kimberly A.;Anderegg, William R. L.
严重的干旱会对树木生理造成滞后影响，对森林功能产生多年的负面影响。这些“干旱遗留效应”在树木年轮记录中得到了广泛的记载，可能对我们理解更广泛的森林碳循环产生重要影响。然而，在树轮增量的遗产效应可能会脱钩生态系统通量由于（a）干旱后的碳分配模式的改变;（B）径向生长和碳吸收之间的时间间隔;（c）年轮采样偏差。为了将树木年轮的遗留效应与整个森林联系起来，我们利用了2012年受到干旱严重影响的美国中西部森林的丰富数据集。在这个网站上，我们编制了树木年轮记录，叶级气体交换，涡流通量测量，测树仪波段数据，以及2012年干旱之前，期间和之后的绿色和叶面积的卫星遥感估计。在考虑了林分中树种的相对丰富度后，我们估计，在严重干旱后的一年中，遗留效应导致年轮宽度增量减少了10%。尽管这种林分规模的径向生长减少，我们发现，叶片水平的光合作用，总初级生产力（GPP），植被绿度在2012年干旱后的一年没有受到抑制。径向生长和碳吸收之间的时间相关性和采样偏差都不能解释我们在树木年轮中观察到的遗留效应，但在GPP中则不然。相反，在2013年初，叶片水平光合作用升高与叶面积减少同时发生，表明资源可能已被分配远离径向生长与干旱后光合作用上调和冠层损伤修复。总的来说，我们的研究结果表明，在其他冠层过程中没有观察到树轮的遗产效应，干旱后冠层分配可能是一个重要的机制，从GPP的树轮信号。
Severe drought can cause lagged effects on tree physiology that negatively impact forest functioning for years. These "drought legacy effects" have been widely documented in tree-ring records and could have important implications for our understanding of broader scale forest carbon cycling. However, legacy effects in tree-ring increments may be decoupled from ecosystem fluxes due to (a) postdrought alterations in carbon allocation patterns; (b) temporal asynchrony between radial growth and carbon uptake; and (c) dendrochronological sampling biases. In order to link legacy effects from tree rings to whole forests, we leveraged a rich dataset from a Midwestern US forest that was severely impacted by a drought in 2012. At this site, we compiled tree-ring records, leaf-level gas exchange, eddy flux measurements, dendrometer band data, and satellite remote sensing estimates of greenness and leaf area before, during, and after the 2012 drought. After accounting for the relative abundance of tree species in the stand, we estimate that legacy effects led to similar to 10% reductions in tree-ring width increments in the year following the severe drought. Despite this stand-scale reduction in radial growth, we found that leaf-level photosynthesis, gross primary productivity (GPP), and vegetation greenness were not suppressed in the year following the 2012 drought. Neither temporal asynchrony between radial growth and carbon uptake nor sampling biases could explain our observations of legacy effects in tree rings but not in GPP. Instead, elevated leaf-level photosynthesis co-occurred with reduced leaf area in early 2013, indicating that resources may have been allocated away from radial growth in conjunction with postdrought upregulation of photosynthesis and repair of canopy damage. Collectively, our results indicate that tree-ring legacy effects were not observed in other canopy processes, and that postdrought canopy allocation could be an important mechanism that decouples tree-ring signals from GPP.