Key message

Radial growth of high-elevation shrubs shows the high sensitivity to climate in dry regions, providing new evidence for drought-mediated dynamics of alpine woody plants.

Abstract

In mountains, shrubs forming their uppermost distributional limits (shrubline) are highly sensitive to increasing cold limitations upwards. However, the constraints imposed by a shorter growing season due to lower temperatures upslope could interact with drought stress in mountainous regions. Here, we aim to investigate that question by comparing radial growth patterns of shrubs in wet (forest region of Nangqian County, BZ hereafter) vs. dry (forest region of Leiwuqi County, LWQ hereafter) regions located on the eastern Tibetan plateau. Considering the climate trend in this area towards warmer and drier conditions, we hypothesize that growth of high-elevation shrubs will be mainly limited by low summer temperatures under sufficient soil moisture. To test this hypothesis, we collected ring-width data from 123 alpine shrubs (Salix oritrepha Schneid.) along an altitudinal gradient from 4200 to 4600 m a.s.l. Dendroecological analyses showed that shrub growth was positively related to mean June or July temperature during the past decades in both wet (BZ) and dry (LWQ) regions regardless of site elevation. By contrast, correlations between shrub growth and seasonal precipitation were not significant. Shrub growth trends were positive before 2010 but turned negative afterwards. Overall, radial growth of shrubs along the altitudinal gradients up to the shrubline could shift from being temperature to moisture limited if warming-induced drought stress intensifies.

中文翻译：

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水分介导青藏高原高海拔灌木的温度-增长耦合

关键信息

高海拔灌木的径向生长显示出干旱地区对气候的高度敏感性，为干旱介导的高山木本植物动态提供了新的证据。

抽象的

在山区，形成其最高分布界限（灌木线）的灌木对向上增加的寒冷限制高度敏感。然而，由于上坡温度较低，生长季节较短所造成的限制可能与山区的干旱压力相互作用。在这里，我们旨在通过比较位于青藏高原东部的湿润（囊前县林区，以下简称 BZ）与干旱（雷乌旗县林区，以下简称 LWQ）地区灌木的径向生长模式来研究这个问题。考虑到该地区气候向更暖和更干燥的趋势发展，我们假设高海拔灌木的生长将主要受到土壤水分充足、夏季低温的限制。为了验证这一假设，我们从 123 种高山灌木中收集了环宽数据（Salix oritrepha Schneid 。) 沿着从 4200 米到 4600 米的海拔梯度，树木生态学分析表明，无论场地海拔如何，灌木生长都与过去几十年中潮湿 (BZ) 和干燥 (LWQ) 地区 6 月或 7 月的平均温度呈正相关。相比之下，灌木生长与季节性降水之间的相关性不显着。灌木生长趋势在 2010 年之前呈正增长，但之后转为负增长。总体而言，如果变暖引起的干旱胁迫加剧，灌木沿海拔梯度的径向生长直到灌木线可能会从温度限制转变为水分限制。