Climate warming-induced changes in the hydrological habitat for the alpine treeline can significantly impact tree growth and community dynamics. However, composite indicators that capture typical alpine species' responses to temperature and precipitation are lacking. This study investigates the use of the H values of lignin methoxy groups (H) from the dominant deciduous conifer tree () and evergreen broadleaf shrub () in the upper treeline of the Qinling Mountains from 1960 to 2018 as potential hydroclimatic indicators. The H values of the shrubs were enriched by 23.3‰ in H compared with those of the trees. However, the multispecies H composite significantly reflected the temperature and precipitation during the growing season (May to September). Rapid warming and drying after the 1990s increased the interspecies consistency of H variability, accompanied by a decreasing enrichment trend. The weighted self-calibrated Palmer Drought Severity Index showed a similar variation tendency. Similar isotopic patterns were detected for the H values of precipitation (H) and the composite H values. The latest empirical relationship mode can effectively verify the reconstructed H values using the H composite from the alpine treeline. These results indicate that the cross-species composite tree-ring H can accurately indicate the alpine hydroclimatic conditions during the growing season, including the warming and drying periods.

中文翻译：

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变暖和干燥增加了高山林线树轮木质素甲氧基δ2H变异的种间一致性


气候变暖引起的高山林线水文栖息地的变化可以显着影响树木的生长和群落动态。然而，缺乏捕捉典型高山物种对温度和降水反应的综合指标。本研究调查了 1960 年至 2018 年秦岭山脉上部林线主要落叶针叶树 () 和常绿阔叶灌木 () 的木质素甲氧基 (H) 的 H 值作为潜在水文气候指标的用途。灌木H值较乔木富集23.3‰。然而，多物种H合成显着反映了生长季（5月至9月）的温度和降水量。 20世纪90年代后的快速变暖和干燥增加了H变异的种间一致性，同时伴随着富集趋势的下降。加权自校准帕尔默干旱强度指数也表现出类似的变化趋势。降水 H 值 (H) 和复合 H 值检测到类似的同位素模式。最新的经验关系模式可以有效地验证使用高山林线的 H 组合重建的 H 值。这些结果表明，跨物种复合树轮H可以准确地指示高山生长季的水文气候条件，包括变暖和干燥时期。