随着气候变化的加剧, 全球高海拔和高纬度地区的灌木扩张现象日益显著。然而, 高山地区灌木扩张过程中植物防御性化学物质(如总酚和缩合单宁)含量的变化规律及其驱动机制尚不明确。该研究以青藏高原东缘的川西高山灌丛-草甸交错带为研究区域, 沿灌木扩张梯度选取对照(盖度0%)、轻度扩张(盖度<30%)、轻中度扩张(盖度30%–45%)、中重度扩张(盖度45%–60%)和重度扩张(盖度>60%)样地, 采用空间代替时间的方法, 分析了灌木扩张对植物防御性化学物质含量的影响及其与环境因子(如海拔、土壤pH、含水量等)的关系。结果表明: (1)灌木扩张显著增加了川西高山灌丛-草甸交错带的灌丛数量、高度、体积和加权密度; (2)与草本植物和红毛花楸(Sorbus rufopilosa)相比, 高山杜鹃(Rhododendron lapponicum)在灌木扩张过程中表现出较高的酚类物质含量; (3)群落水平物种组成的变化对植物酚类物质变异的影响显著高于物种内个体间表型可塑性的种内变异; (4)植物叶片与根系的酚类物质含量均与其碳氮比显著相关, 而土壤因子影响较小, 支持了碳-养分平衡假说。综上所述, 该研究揭示了灌木扩张对植物防御物质的正向影响, 并为全球变化背景下的生态系统管理和植物保护提供了重要的理论依据。

Aims With the intensification of climate change, shrub expansion or encroachment in high-altitudes and high-latitude has become increasingly significant. However, the patterns and driving mechanisms of changes in plant defensive chemicals such as total phenols and condensed tannins during such shrub expansion processes in alpine regions remain poorly understood. Methods Taking the alpine shrub-meadow transition zone or ecotone in western Sichuan on the eastern Qingzang Plateau as the study area, sample plots were established along a shrub expansion gradient including control (0% coverage), light expansion (<30% coverage), light-moderate expansion (30%–45% coverage), moderate-heavy expansion (45%–60% coverage), and heavy expansion (>60% coverage). The impact of shrub expansion on plant defensive chemical compounds and their relationships with environmental factors such as elevation, soil pH, and moisture content were analyzed by a space-for-time substitution approach. Important findings The results showed that: (1) Shrub expansion significantly increased the density, height, volume, and weighted density of shrubs in the alpine shrub-meadow transition zone of western Sichuan; (2) Compared to herbaceous plants and Sorbus rufopilosa, Rhododendron lapponicum exhibited higher levels of phenolic compounds during the shrub expansion process; (3) Changes in species composition at the community level had a significantly greater impact on the variation in plant phenolic compounds than intraspecific variation resulting from phenotypic plasticity among individuals; (4) Concentrations of phenolic compounds in both plant leaves and roots showed significant correlations with their carbon to nitrogen ratios, while soil factors had a relatively minimal effect, supporting the Carbon-nutrient Balance Hypothesis (CNBH). In summary, this study sheds light on the positive impact of shrub expansion on plant defense compounds and provides critically theoretical underpinnings for ecosystem management and plant conservation in the context of global change.