Carbohydrates and secondary compounds of alpine tundra shrubs in relation to experimental warming

BACKGROUND: It is critical to understand the sensitivity, response direction and magnitude of carbohydrates and secondary compounds to warming for predicting the structure and function of the tundra ecosystem towards future climate change. RESULTS: Open-top chambers (OTCs) were used to passively increase air and soil temperatures on Changbai Mountain alpine tundra. After seven years’ continuous warming (+ 1.5 °C), the vegetation coverage, nonstructural carbohydrates (soluble sugars and starch) and secondary compounds (total phenols, flavonoids and triterpenes) of leaves and roots in three dominant dwarf shrubs, Dryas octopetala var. asiatica, Rhododendron confertissimum and Vaccinium uliginosum, were investigated during the growing season. Warming did not significantly affect the concentrations of carbohydrates but decreased total phenols for the three species. Carbohydrates and secondary compounds showed significantly seasonal pattern and species-specific variation. No significant trade-off or negative relationship between carbohydrates and secondary compounds was observed. Compared to Dr. octopetala var. asiatica, V. uliginosum allocated more carbon on secondary compounds. Warming significantly increased the coverage of Dr. octopetala var. asiatica, did not change it for V. uliginosum and decreased it for Rh. confertissimum. Rh. confertissimum had significantly lower carbohydrates and invested more carbon on secondary compounds than the other two species. CONCLUSIONS: Enhanced dominance and competitiveness of Dr. octopetala var. asiatica was companied by increased trend in carbohydrate concentrations and decreased ratio of secondary compounds to total carbon in the warming OTCs. We, therefore, predict that Dr. octopetala var. asiatica will continue to maintain dominant status, but the competition ability of V. uliginosum could gradually decrease with warming, leading to changes in species composition and community structure of the Changbai tundra ecosystem under future climate warming.