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）的木质竹类在委内瑞拉安第斯山脉的广泛海拔梯度中均有分布，其生长型与种群密度沿云雾林-帕拉莫（páramo）生态梯度呈现规律性变化。本研究结合生理生态性状与种群遗传多样性数据，旨在阐释委内瑞拉梅里达安第斯山脉丘竹属植物生长型分布格局的形成机制。研究目的：本研究针对攀援型云雾林竹种与灌丛型帕拉莫竹种两类丘竹属植物，量化其生理生态响应与遗传多样性差异，并综合考量其开花模式、生长型与生境的区别。研究方法：本研究将丘竹属植物的低温抗性、水分生理特性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。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）标记检测。研究结果：无论在湿季还是干季，攀援型云雾林竹种与灌丛型帕拉莫竹种的各项生理生态指标响应均极为相似，且二者均可通过适度超冷作用耐受低温冻害。沿云雾林-帕拉莫生态梯度分布的竹种，可维持较低的气孔导度与蒸腾速率，从而保障较高的叶水势，且未对光合速率造成限制。生长于连续林线以上的灌丛型竹类，其净光合速率仅出现小幅下降，这与水分利用效率的提升密切相关。两类丘竹属植物均表现出极高的遗传多样性，水平与非克隆物种相当。研究结论：委内瑞拉安第斯山脉的丘竹属植物，在广泛的海拔梯度范围内生理特性相对均一。种群遗传多样性与其开花模式及生境条件的关联程度，显著高于其与生长型的关联。