Abstract

Trees are long-lived organisms that integrate climate conditions across years or decades to produce secondary growth. This integration process is sometimes referred to as ‘climatic memory.’ While widely perceived, the physiological processes underlying this temporal integration, such as the storage and remobilization of non-structural carbohydrates (NSC), are rarely explicitly studied. This is perhaps most apparent when considering drought legacies (perturbed post-drought growth responses to climate), and the physiological mechanisms underlying these lagged responses to climatic extremes. Yet, drought legacies are likely to become more common if warming climate brings more frequent drought. To quantify the linkages between drought legacies, climate memory and NSC, we measured tree growth (via tree ring widths) and NSC concentrations in three dominant species across the southwestern USA. We analyzed these data with a hierarchical mixed effects model to evaluate the time-scales of influence of past climate (memory) on tree growth. We then evaluated the role of climate memory and the degree to which variation in NSC concentrations were related to forward-predicted growth during the hot 2011–2012 drought and subsequent 4-year recovery period. Populus tremuloides exhibited longer climatic memory compared to either Pinus edulis or Juniperus osteosperma, but following the 2011–2012 drought, P. tremuloides trees with relatively longer memory of temperature conditions showed larger (more negative) drought legacies. Conversely, Pinus edulis trees with longer temperature memory had smaller (less negative) drought legacies. For both species, higher NSC concentrations followed more negative (larger) drought legacies, though the relevant NSC fraction differed between P. tremuloides and P. edulis. Our results suggest that differences in tree NSC are also imprinted upon tree growth responses to climate across long time scales, which also underlie tree resilience to increasingly frequent drought events under climate change.

中文翻译：

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温度记忆和非结构性碳水化合物介导了美国西南部树木炎热干旱的遗留问题

摘要

树木是长寿的有机体，可以整合多年或数十年的气候条件以产生二次生长。这种整合过程有时被称为“气候记忆”。尽管人们普遍认为，这种时间整合背后的生理过程，例如非结构性碳水化合物 (NSC) 的储存和再动员，但很少被明确研究。在考虑干旱遗留问题（干旱后生长对气候的扰动反应）以及这些对气候极端事件的滞后反应背后的生理机制时，这可能最为明显。然而，如果气候变暖带来更频繁的干旱，干旱遗留问题可能会变得更加普遍。量化干旱遗产、气候记忆和 NSC 之间的联系，我们测量了美国西南部三个主要物种的树木生长（通过年轮宽度）和 NSC 浓度。我们使用分层混合效应模型分析了这些数据，以评估过去气候（记忆）对树木生长影响的时间尺度。然后，我们评估了气候记忆的作用以及 NSC 浓度变化与 2011-2012 年炎热干旱和随后的 4 年恢复期的前瞻预测增长相关的程度。与Pinus edulis或Juniperus bonesperma相比， Populus tremloides表现出更长的气候记忆，但在 2011-2012 年干旱之后，具有相对较长温度条件记忆的P. tremloides树表现出更大（更负面）的干旱遗产。相反，具有较长温度记忆的松树具有较小（较少负面）的干旱遗产。对于这两个物种，较高的 NSC 浓度伴随着更多的负面（较大）干旱遗产，尽管P. tremloides和P. edulis之间的相关 NSC 分数不同. 我们的研究结果表明，树木 NSC 的差异也印刻在树木生长对长期气候的反应上，这也是树木对气候变化下日益频繁的干旱事件的恢复能力的基础。