Ecophysiology and genetic diversity in species of the bamboo Chusquea in the high Andes, Venezuela

Background: Woody bamboos of the genus Chusquea grow along a broad range of elevations in the Venezuelan Andes. Their growth-form and density vary along the cloud forest – páramo gradient. In this article, we related ecophysiological traits and population genetic diversity information to explain the distribution of growth-form patterns of Chusquea in the Merida Andes, Venezuela. Aims: We quantified differences in the ecophysiological response and genetic diversity of scandent cloud forest and shrub-like páramo bamboos of the genus Chusquea, taking in account the differences in their flowering patterns, growth-form and habitat. Methods: We related low temperature resistance, water relations and leaf gas exchange variables to the growth-form, habitat, flowering patterns and genetic diversity in species of Chusquea. The genetic diversity study was based on Inter Sequence Simple Repeats and Random Amplified Polymorphic DNA markers analysis of cloud forest and páramo populations. Results: Scandent cloud forest and shrub-like páramo species of Chusquea had a very similar ecophysiological response for all the variables analysed during wet and dry seasons and were capable of enduring freezing temperatures through moderate supercooling. Species associated with the cloud forest – páramo gradient maintained low stomatal conductance and transpiration rates that favoured high leaf water potentials, without limiting photosynthetic rates. Shrub-like bamboos growing above the continuous forest line had a small decline in net photosynthesis rates, associated with an increase in water use efficiency. Both scandent and shrub-like bamboos had a remarkably high genetic diversity, comparable to non-clonal species. Conclusions: Species of Chusquea in the Venezuelan Andes are a physiologically relatively homogeneous group across a broad elevation gradient. Population genetic diversity appears to be more related with their flowering pattern and habitat conditions than with their growth form.

背景：丘竹属（Chusquea）的木本竹类广泛分布于委内瑞拉安第斯山脉的不同海拔区域，其生长型与种群密度随云雾林（cloud forest）-帕拉莫（páramo）生境梯度呈现规律性变化。本文结合生态生理性状与种群遗传多样性信息，旨在阐明丘竹属植物在委内瑞拉梅里达安第斯山脉的生长型分布格局。
研究目的：量化丘竹属中攀援型云雾林竹类与灌木型帕拉莫竹类的生态生理响应及遗传多样性差异，并综合考量其开花模式、生长型与生境的差异。
研究方法：本研究将丘竹属物种的低温抗性、水分关系与叶片气体交换参数，与其生长型、生境、开花模式及遗传多样性进行关联分析。其中，遗传多样性分析基于对云雾林与帕拉莫种群的简单序列重复区间（Inter Sequence Simple Repeats，ISSR）及随机扩增多态性DNA（Random Amplified Polymorphic DNA，RAPD）分子标记检测。
研究结果：攀援型云雾林竹类与灌木型帕拉莫竹类在干湿季的所有分析参数上均表现出高度相似的生态生理响应，且可通过适度过冷作用耐受低温冻害。分布于云雾林-帕拉莫梯度的丘竹属物种维持较低的气孔导度与蒸腾速率，这有助于维持较高的叶片水势，且未对光合速率造成限制。生长在连续林线以上的灌木型竹类净光合速率仅出现小幅下降，该现象与水分利用效率的提升相关。攀援型与灌木型竹类均表现出极高的遗传多样性，其水平与非克隆繁殖物种相当。
结论：委内瑞拉安第斯山脉的丘竹属物种在广泛的海拔梯度上属于生理特性相对均一的类群。种群遗传多样性与开花模式及生境条件的关联程度更高，而非其生长型。