Tree-ring stable isotopes provide insights into the drought-induced eco-physiological mechanisms of forests. We investigated the growth of poplar and Mongolian pine trees decline in the Three-North Shelter Forest, and analyzed the differences in tree-ring width (TW), δ¹³C, δ¹⁸O, and intrinsic water-use efficiency (iWUE) between dieback and healthy trees. An R package was used to quantify the relative contributions of climatic and physiological factors to growth. Both TW and basal area increment were lower for the dieback poplar and Mongolian pine than for the healthy trees.δ¹³C, δ¹⁸O, and iWUE were higher for the dieback poplar than for the healthy individuals; there were no significant differences in Mongolian pine. The measured iWUE for healthy poplar, healthy and dieback Mongolian pine were consistent with the modeled iWUE for C_i/ C_a scenario, indicating the stomata were open and C_i increased along with C_a. In contrast, the measured iWUE was higher for the dieback poplar than for the healthy individuals, which was consistent with the constant C_i scenario and partial stomatal closure. A significant decreasing C_i/C_a was detected only for the dieback poplar, reflecting the diversity in the leaf gas-exchange strategies of the two species. Pearson coefficients showed that on the annual timescale, tree growth was significantly negatively correlated with temperature, VPD, and iWUE, but positively correlated with SPEI. Moreover, the relationships between TW and stable isotopes and stomatal regulation, which differed in the two species, were affected by the dieback process. Furthermore, iWUE andδ¹⁸O had the highest and lowest relative contributions to TW, respectively. The relative contribution of meteorological factors (Tem, VPD and SPEI) to the growth was significantly lower than that of physiological factors (iWUE and δ¹⁸O). Compared with the healthy controls of both species, the dieback trees were less sensitive to climate conditions, but the effects of physiological activities on growth were greater. These results provide a better understanding of the climate sensitivity and physiological responses of trees under long-term drought conditions.

树轮稳定同位素提供了对干旱引起的森林生态生理机制的见解。我们调查了三北防护林中杨树和蒙古松树的生长情况，并分析了树轮宽度（TW）、δ ¹³ C、δ ¹⁸ O 和内在水分利用效率（iWUE）之间的差异。枯死和健康的树木。使用 R 包来量化气候和生理因素对生长的相对贡献。枯死白杨和蒙古松的 TW 和基面积增量均低于健康乔木。δ ¹³ C、δ ¹⁸枯萎杨树的 O 和 iWUE 高于健康个体；蒙古松无显着差异。测量的健康杨树、健康和枯死蒙古松的 iWUE 与模拟的 C _i / C _a情景的 iWUE 一致，表明气孔开放并且 C _i随 C _a增加。相比之下，枯萎杨树测量的 iWUE 高于健康个体，这与恒定 C _i情景和部分气孔关闭一致。_{C i} /C _a显着降低仅在枯萎杨树中检测到，反映了这两个物种叶片气体交换策略的多样性。Pearson 系数显示，在年度时间尺度上，树木生长与温度、VPD 和 iWUE 呈显着负相关，但与 SPEI 呈正相关。此外，TW与稳定同位素和气孔调节之间的关系在两个物种中不同，受到枯死过程的影响。此外，iWUE 和δ ¹⁸ O 对 TW 的相对贡献分别最高和最低。^{气象因素（Tem、VPD和SPEI}）对生长的相对贡献显着低于生理因素（iWUE和δ18 ）○）。与健康对照相比，枯死树对气候条件的敏感性较低，但生理活动对生长的影响更大。这些结果有助于更好地了解树木在长期干旱条件下的气候敏感性和生理反应。