Lastra R A, Kenkel N C, Daayf F
Department of Biological Sciences, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada.
Department of Plant Science, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada.
J Chem Ecol. 2017 Oct;43(10):1023-1030. doi: 10.1007/s10886-017-0895-z. Epub 2017 Oct 24.
In the aspen-grassland ecotone of Riding Mountain, Manitoba, lightly browsed vigorous clones of trembling aspen (Populus tremuloides Michx.) occur in close proximity to heavily browsed dieback clones. This study examines whether intraspecific variation in the production of phenolic glycosides is correlated with this strong dichotomy in clonal vigor. Individual clones were sampled over four years at three sites located along a gradient of increasing soil moisture stress. At each site, eight aspen clones of similar size and age were sampled: four vigorous and four dieback clones (total of 24 individual clones). The severity of wapiti (elk) browsing was assessed as the ratio of browse-damaged to total branches per aspen ramet. Statistically significant differences in foliar concentrations of the phenolic glycosides salicortin and tremulacin were observed between vigorous and dieback clones: a mean of 14.8% dry mass for lightly browsed (vigorous) clones, versus just 7.0% for heavily browsed (dieback) clones. Mean concentrations of foliar phenolics were also significantly greater in more moisture-stressed sites. These results demonstrate that the strong dichotomy in clonal vigor (vigorous versus dieback clones) is associated with large differences in phenolic glycoside production. Vigorous clone ramets produce high amounts of phenolic glycosides and have low levels of herbivore browsing and low mortality rates, whereas dieback clone ramets have low amounts of phenolic glycosides and much higher herbivore browsing and mortality rates. This suggests that intraspecific variation in phenolic glycosides in trembling aspen is an important predisposing factor leading to ramet mortality, and by extension to the decline of aspen clones.
在曼尼托巴省骑马山的白杨-草原生态交错带，轻度啃食的活力旺盛的颤杨（Populus tremuloides Michx.）克隆体与重度啃食且出现枯死现象的克隆体相邻生长。本研究探讨了酚糖苷产生的种内变异是否与克隆体活力的这种强烈二分法相关。在沿着土壤水分胁迫增加梯度分布的三个地点，对单个克隆体进行了为期四年的采样。在每个地点，采集了八个大小和年龄相似的白杨克隆体样本：四个活力旺盛的克隆体和四个枯死的克隆体（共24个个体克隆体）。将马鹿（麋鹿）的啃食严重程度评估为每个白杨分株上被啃食损伤的枝条与总枝条的比例。在活力旺盛的克隆体和枯死的克隆体之间，观察到酚糖苷水杨苷和震颤素的叶片浓度存在统计学上的显著差异：轻度啃食（活力旺盛）的克隆体平均干重为14.8%，而重度啃食（枯死）的克隆体仅为7.0%。在水分胁迫更大的地点，叶片酚类物质的平均浓度也显著更高。这些结果表明，克隆体活力的强烈二分法（活力旺盛的克隆体与枯死的克隆体）与酚糖苷产生的巨大差异有关。活力旺盛的克隆体分株产生大量酚糖苷，食草动物啃食水平低且死亡率低，而枯死的克隆体分株酚糖苷含量低，食草动物啃食和死亡率则高得多。这表明颤杨中酚糖苷的种内变异是导致分株死亡进而导致白杨克隆体衰退的一个重要诱发因素。
