Abstract:

Sicyos angulatus (commonly known as bur cucumber) is one of the most invasive and ecologically detrimental exotic species in North America. As a monoecious annual herbaceous vine in the Cucurbitaceae family, it produces unisexual flowers from July to October and fruit from August to November. Each plant can generate hundreds of fruit clusters, with each cluster containing 3-30 elongated oval fruits. The fruits are densely covered with slender yellowish-brown spines and short white pubescence, and each fruit contains a single seed inside. S. angulatus exhibits exceptional adaptability, thriving in diverse habitats, such as farmlands, roadsides, depressions, wastelands, low forests, and shrublands, which enables its aggressive colonization and ecological disruption. S. angulatus is a key-managed invasive weed in China. It exhibits a powerful invasive capacity and thrives abundantly and luxuriantly in diverse habitats, rapidly spreading outward or climbing to great heights. Within the areas it colonized, native herbaceous plants are nearly eradicated, while dense patches of shrubs and some trees become entangled and ultimately wither and die. This invasive behavior severely destroys ecological environments. Consequently, in August 2017, S. angulatus was added to China’s Fourth Batch of Invasive Alien Species List. By January 2023, it was further classified as a priority management target under the List of Key Managed Invasive Alien Species, jointly issued by the Ministry of Agriculture and Rural Affairs and five other ministries and commissions, highlighting its escalating ecological threat and the urgent need for coordinated control. The functional traits of leaves, stems, and inflorescences and their correlations were studied to explore habitat differentiation between trait characteristics and ecological adaptability of the species. We explored the regulation of plant functional traits on alien plant invasion and spatial variation patterns to understand the invasion mechanisms and provide insights into prevention, control, and governance. This study focused on S. angulatus during the blooming period in six habitats: forest edge (LY), riverbank (HB), vegetable field (CD), ditch (SG), wasteland (LH), and abandoned railways (FT). By measuring 21 functional traits of leaves, stems, and inflorescences, we employed one-way ANOVA, correlation analysis, and principal component analysis to examine variations and correlations among the morphological, physiological, and biomass traits of S. angulatus leaves, stems, and inflorescences. The results showed that 1) there were certain differences in the functional traits of the leaves, stems, and inflorescences of S. angulatus in different habitats. Specifically, leaf area, specific leaf area, stem node length, and female inflorescence axis length in the LY habitat were significantly greater than those in other habitats, whereas leaf thickness, chlorophyll content, leaf nitrogen content, and stem node biomass were lower. There were no significant habitat differences in the numbers of male and female flowers. The forest edge (LY) habitat tended to adopt a resource acquisition strategy, whereas the abandoned railway (FT) habitat leaned towards a resource conservation strategy. Populations in other habitats exhibited a neutral adaptation strategy. This reflects the differences in population resource utilization strategies and the high adaptability of S. angulatus to these heterogeneous habitats. 2) During long-term environmental adaptation, plants are consistently influenced by physiological constraints, phylogenetic history, and environmental fluctuations. Through continuous trade-offs and synergies, optimal combinations of functional traits adapted to specific environments have been developed. These traits exhibit intrinsic interconnections that reflect the distinct ecological strategies employed by plants in response to environmental pressures. The leaf length-to-width ratio of S. angulatus was significantly and negatively correlated with petiole length and diameter. The leaf area of S. angulatus was significantly and positively correlated with specific leaf area, petiole length, petiole diameter, and leaf biomass. The specific leaf area of S. angulatus was significantly and negatively correlated with leaf thickness, chlorophyll content, and leaf nitrogen content. Inflorescence axis length in S. angulatus was significantly positively correlated with inflorescence biomass, whereas there was no correlation between male and female inflorescence biomass. 3) The stability and variability of plant functional traits can be quantified using the coefficients of variation. Variations in plant growth and developmental processes across habitats are ultimately reflected in the differentiation of functional traits. The average coefficients of variation (CV) for leaf, stem, and inflorescence traits of S. angulatus were 19.48%, 21.30%, and 30.25%, respectively. Among the different habitats, the abandoned railway (FT) showed the highest leaf variation coefficient, whereas LY showed the lowest. The vegetable field (CD) exhibited the maximum stem variation coefficient, whereas the riverbank (HB) showed the minimum variation. The ditch (SG) displayed the greatest inflorescence variation coefficient, with the forest edge (LY) being the smallest. Notably, the biomass variation of male and female inflorescences in the abandoned railway (FT) demonstrated the highest plasticity and weakest genetic stability, whereas the rachis length of female inflorescences showed the opposite pattern. For leaf traits, biomass and petiole length exhibited the maximum variation coefficients with the strongest plasticity and poorest genetic stability, whereas leaf chlorophyll and leaf nitrogen content displayed contrasting characteristics. 4) Key indicators influencing the trait variation of S. angulatus include petiole length, petiole diameter, leaf area, specific leaf area, leaf thickness, stem internode biomass, leaf chlorophyll content, leaf nitrogen content, male inflorescence rachis length, number of male flowers and inflorescence biomass. In the lower reaches of the Yalu River, the functional traits of S. angulatus leaves, stems, and inflorescences across heterogeneous habitats showed significant variation and high levels of variability. These diverse functional traits collectively reflect their strong adaptability to heterogeneous environment. The research findings can contribute to understanding the invasion mechanisms of S. angulatus from the perspective of invasive plant functional traits, providing a scientific basis and reference for its prevention, control, and management in the future. In summary, the differential responses of functional traits in Sicyos angulatus leaves, stems, and inflorescences to environmental conditions reflect their distinct adaptive strategies in heterogenous habitats. These traits confer competitive advantages in resource acquisition, thereby promoting the stable invasion and establishment of the species. A limitation of this study is its exclusive focus on morphological and physiological traits of S. angulatus. Future efforts should emphasize strengthening foundational research, improving monitoring technologies, exploring sustainable utilization approaches, and developing targeted prevention and control measures to effectively mitigate its spread and ecological impacts. These strategies are critical for balancing invasive species management and conserving ecosystems.

Key words: invasive plants, functional traits, S. angulatus, lower reaches of the Yalu River, heterogeneous habitats

摘要：

探究刺果瓜（Sicyos angulatus）叶茎花序功能性状特征在不同生境下的差异及相互关系，可为揭示其入侵机制和防控治理提供参考。以林缘（LY）、河边（HB）、菜地（CD）、水沟（SG）、荒地（LH）和废弃铁路（FT）等6个生境盛花期刺果瓜为研究对象，采用单因素方差分析、相关分析和主成分分析研究了刺果瓜叶茎花序形态、生理和生物量等21个功能性状的生境差异及相关性。结果表明，1）不同生境刺果瓜叶茎花序功能性状存在一定的差异性，其中，LY生境叶面积、比叶面积、茎节长和雌花序轴长显著大于其他生境，叶厚、叶绿素量、叶氮素量及茎节生物量则相反，雌雄花数量无显著生境差异。LY生境倾向于资源获取型策略，FT生境偏向于资源保守型策略，其他生境种群为中性适应策略。2）叶长宽比和叶柄长、叶柄粗呈显著负相关；叶面积和比叶面积、叶柄长、叶柄粗、叶生物量呈显著正相关；比叶面积和叶厚、叶绿素含量、叶氮素含量呈显著负相关；花序轴长与花序生物量显著正相关，雌雄花序生物量不相关。3）叶茎花序性状平均变异系数分别为19.5%，21.3%和30.3%。各生境中FT叶变异系数最大，LY最小；CD茎变异系数最大，HB最小；SG花序变异系数最大，LY最小。其中，FT雌雄花序生物量变异程度最高，可塑性最强，遗传稳定性最差，雌花序轴长与之相反；叶生物量、叶柄长性状变异系数最大，可塑性最强，遗传稳定性最差，叶绿素、叶氮素含量与之相反。4）叶柄长、叶柄粗、叶面积、比叶面积、叶厚、茎节生物量、叶绿素含量、叶氮素量、雄花序轴长、雄花数量及花序生物量等是影响其性状变异程度的主要指标。刺果瓜叶茎花序功能性状存在较高差异和变异水平反映了其对异质生境的高度适应性。

关键词: 入侵植物, 功能性状, 刺果瓜, 鸭绿江下游, 异质生境