雪岭云杉径向生长对饱和水汽压差响应的区域分异与个体异质性

Regional differentiation and individual heterogeneity in the response of radial growth to vapor pressure deficit in Picea schrenkiana

摘要

【目的】探究天山雪岭云杉径向生长对饱和水汽压差（VPD）响应的空间分异与个体异质性规律，解析 VPD 即时与滞后效应，以期为气候暖干化背景下山地森林动态预测提供理论依据。【方法】本研究基于天山雪岭云杉树轮宽度年表与气候数据，在区域尺度对比不同研究区样地平均年表，揭示 VPD 响应的空间分异；在单株尺度利用广义加性混合模型（GAMM）量化径向生长对当年及上一年 VPD 的响应强度，并运用随机森林模型评估树龄及环境因子的相对贡献。【结果】（1）1980—2023 年，4 个研究区均显著增温（ P < 0.01），夏季 VPD 均极显著上升（ P < 0.001），区域水热条件差异明显，其中哈密和板房沟相对暖干，乌苏和吉木萨尔相对湿润。（2）雪岭云杉径向生长及其气候响应呈区域分异：暖干区（哈密、板房沟）树轮宽度指数与夏季 VPD 显著负相关（ P < 0.01），而相对湿润区（乌苏、吉木萨尔）响应较弱或不显著。（3）区域尺度上，暖干区板房沟和哈密的当年 VPD 生长敏感度（ β_(VPDt)）均值分别为−0.041 和−0.055，表现为较强负向响应；相对湿润区乌苏和吉木萨尔 β_(VPDt)均值均接近 0。在上一年 VPD 响应方面，负向响应在暖干区进一步增强，负响应个体比例上升至 68% ~ 69%，表明暖干环境下 VPD 对径向生长的负向影响具有更强的滞后性。（4）单株尺度上，个体响应策略呈明显异质性。暖干区哈密、板房沟以双负型为主导（51.7% 和 47.1%），群体响应方向相对集中，而相对冷湿区乌苏、吉木萨尔各类策略比例均衡、正负响应并存，表明区域气候背景不仅影响总体响应强度，也调节个体响应策略。（5）随机森林分析表明，树龄的重要性最高（IncMSE = 0.005 79），海拔与气候因子次之，降水及坡向、坡度等地形因子贡献相对较小，表明树龄是影响 VPD 生长敏感度个体差异的主要因素。【结论】本研究从区域与单株两个尺度揭示了雪岭云杉 VPD 生长响应由区域水热梯度和个体属性共同调控的规律。树龄是决定 VPD 生长敏感度的内在基础，区域水热背景能够调节个体响应策略，VPD 即时效应与滞后效应的叠加进一步加剧了暖干区森林衰退风险。在气候暖干化背景下，将树龄结构与区域生境类型纳入森林动态预测模型，有助于提升山地森林生长响应与生态系统稳定性的评估能力。

Abstract

[Objective] This study aimed to investigate the spatial differentiation and individual heterogeneity in the radial growth response of Picea schrenkiana to vapor pressure deficit (VPD) in the Tianshan Mountains, and elucidate the immediate and lagged effects of VPD, thereby providing a theoretical basis for predicting mountain forest dynamics under climate warming and drying. [Method] Using tree-ring width chronologies and climate data from P. schrenkiana stands across the Tianshan Mountains, we compared site-level mean chronologies among different study areas to reveal spatial variation in VPD response. At the individual-tree scale, generalized additive mixed models (GAMMs) were employed to quantify the response intensity of radial growth to VPD in the current and previous years, and random forest models were used to evaluate the relative contributions of tree age and environmental factors. [Result] (1) From 1980 to 2023, all four study regions experienced significant warming ( P < 0.01), while summer VPD increased highly significantly ( P < 0.001). The regions showed marked differences in hydrothermal conditions, with Hami and Banfanggou being relatively warm and dry, whereas Wusu and Jimsar were relatively humid. (2) Radial growth of P. schrenkiana and its climatic responses showed clear regional differentiation. In the warm-dry zone (Hami and Banfanggou), the tree-ring width index (RWI) was significantly negatively correlated with summer VPD ( P < 0.01), whereas responses in the relatively humid zone (Wusu and Jimsar) were weaker or non-significant. (3) At the regional scale, the mean current-year VPD growth sensitivity ( β_(VPDt)) in the warm-dry zone were −0.041 and −0.055 in Banfanggou and Hami, respectively, indicating relatively strong negative responses, whereas the β_(VPDt) in the relatively humid zone (Wusu and Jimsar) were both close to zero. For previous-year VPD responses, negative responses were further strengthened in the warm-dry zone, with the proportion of individuals showing negative responses increasing to 68%–69%, indicating a stronger lagged negative effect of VPD on radial growth under warm-dry conditions. (4) At the individual-tree scale, response strategies showed marked heterogeneity. The warm-dry zone (Hami and Banfanggou) was dominated by the double-negative type (51.7% and 47.1%, respectively), with relatively concentrated response directions, whereas the relatively cold-humid zone (Wusu and Jimsar) showed a more balanced distribution of response types, with both positive and negative responses, indicating that regional climatic background not only affects overall response intensity but also regulates individual response strategies. (5) Random forest analysis showed that tree age had the highest importance (IncMSE = 0.005 79), followed by elevation and climatic factors, whereas precipitation and topographic factors such as aspect and slope contributed relatively little, indicating that tree age is the primary factor underlying individual differences in VPD growth sensitivity. [Conclusion] At both regional and individual-tree scales, the VPD growth response of P. schrenkiana is jointly regulated by regional hydrothermal gradients and individual attributes. Tree age constitutes the intrinsic basis determining VPD growth sensitivity, while regional hydrothermal background modulates the expression of individual response strategies. The combined effect of immediate and lagged VPD responses further exacerbates the risk of forest decline in warm-dry zones. Incorporating tree age structure and regional habitat type into forest dynamic prediction models can improve the assessment of mountain forest growth response and ecosystem stability under climate warming and drying.

关键词

雪岭云杉 / 饱和水汽压差 / 树轮宽度 / 个体异质性 / 树龄效应 / 空间分异

Key words

Picea schrenkiana / vapor pressure deficit / tree-ring width / individual heterogeneity / tree age effect / spatial differentiation

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基金资助

国家自然科学基金项目(31860149)

新疆维吾尔自治区自然科学基金项目(2022D01C398)