Functional traits of a plant species fingerprint ecosystem productivity along broad elevational gradients in the Himalayas

Abstract

en

1. It is a challenge to scale-up from simplified proxies to ecosystem functioning since the inherent complexity of natural ecosystems hinders such an approach. One way to address this complexity is to track ecosystem processes through the lens of plant functional traits. Elevational gradients with diverse biotic and abiotic conditions offer ideal settings for inferring functional trait responses to environmental gradients globally. However, most studies have focused on differences in mean trait values among species, and little is known on how intraspecific traits vary along wide elevational gradients and how this variability reflects ecosystem productivity.
2. We measured functional traits of the sub-shrub Koenigia mollis (Basionym: Polygonum molle; a widespread species) in 11 populations along a wide elevational gradient (1515–4216 m) considering from subtropical forest to alpine treeline in the central Himalayas. After measuring different traits (plant height, specific leaf area, leaf area, length of flowering branches, leaf carbon isotope (δ¹³C), leaf carbon and leaf nitrogen concentrations), we investigated drivers on changes of these traits and also characterized their relationships with elevation, climate and ecosystem productivity.
3. All trait values decreased with increasing elevation, except for δ¹³C that increased upwards. Likewise, most traits showed strong positive relationships with potential evapotranspiration, while δ¹³C exhibited a negative relationship. In this context, elevation-dependent water–energy dynamics is the primary driver of trait variations. Furthermore, six key traits (plant height, length of flowering branch, specific leaf area, leaf carbon, leaf nitrogen and leaf δ¹³C) explained 90.45% of the variance in ecosystem productivity.
4. Our study evidences how elevation-dependent climate variations affect ecosystem processes and functions. Intraspecific variability in leaf functional traits is strongly driven by changes in water–energy dynamics, and reflects changes in ecosystem productivity over elevation. K. mollis, with one of the widest elevational gradients known to date, could be a model species to infer functional trait responses to environmental gradients globally. As inferred from K. mollis, the water–energy dynamics can be a hydrothermal variable to understand the formation of vegetation boundaries, such as alpine treeline. This study sheds new insight on how plants modify their basic ecological strategies to cope with changing environments.

Read the free Plain Language Summary for this article on the Journal blog.

摘要

zh

1. 由于生态系统固有的复杂性，如何利用简单易测的指标反映生态系统过程和功能变化一直是生态学研究的难点问题。植物功能性状是植物个体对环境变化响应的适应特征，为利用物种水平指标来指示生态系统功能提供了可能。随海拔的变化，生境条件发生了显著变化，而同时，不同尺度的生物因子如植物个体特征、群落结构和生态系统功能也随之变化。因此，海拔梯度为研究物种和生态系统功能对环境变化的响应提供了理想的平台。已有研究大部分集中在利用多个物种的功能性状来综合反映生态系统过程和功能，然而，单个物种的功能性状是否能用来指示生态系统功能的变化尚不明确。
2. 喜马拉雅山区拥有地球上最大海拔跨度，形成了从热带到寒带的陆地生态系统垂直景观。绢毛蓼(Koenigia mollis)是喜马拉雅山脉中部地区广泛分布的一种半灌木，其分布跨越了从亚热带常绿阔叶林到高寒树线约2700 m(1515–4216 m)的海拔跨度。我们沿海拔梯度选择了11个绢毛蓼种群，系统测定了与生长及养分利用密切相关的7个关键植物功能性状，即植株高度、叶面积(LA)、比叶面积(SLA)、花枝长度、叶碳稳定同位素比值(δ¹³C)，叶碳含量(C)和氮含量(N)。
3. 结果显示:植株高度、SLA、LA、C和N均随海拔的升高而降低，且这些性状均与表征生态系统水分动态的潜在蒸散量(PET)呈正相关关系；δ¹³C随海拔的升高而增大，并与PET呈负相关关系。这表明由海拔变化引起的水分-能量动态是驱动绢毛蓼功能性状变化的主要环境因子，绢毛蓼通过形成面积更小、建成成本更高和水分利用效率更高的叶片来适应高海拔地区的生境。同时，研究发现绢毛蓼的植株高度和SLA等6个主要功能性状能解释生态系统生产力90.45%的变化，表明单个物种的性状变化能有效指示生态系统水平的功能变化。
4. 本研究以海拔梯度带作为研究模板，阐明了环境变化对生态系统过程和功能的影响，指出水分-能量动态在调控物种特征和生态系统功能中的重要作用，强调了广布种的性状可以指示海拔梯度带上生态系统功能变化。绢毛蓼作为已知的全球最大海拔跨度物种之一，可以作为探究植物功能性状如何响应环境变化的模式植物。绢毛蓼的研究也暗示，水分-能量动态是理解植被边界(例如，高山树线)形成的重要指标。此研究针对植物如何改变生态策略适应环境变化方面提出了新见解。