Rapid increase in the distribution and abundance of non-native invasive plants is a major threat to the productivity and stability of natural forests. Ailanthus altissima, introduced in the United States in 1780s from China, is spreading widely throughout West Virginia and threatening the native forest. The same exotic tree species was also introduced to Japan in 1860s but is rarely found in natural forest. To understand key attributes associated to the successful establishment and invasion of Ailanthusspp., we examined its leaf structure (specific leaf area, relative water content and stomatal length and density) and physiological characteristics (stomatal conductance and chlorophyll fluorescence) in two sites that differed in climatic regions: cool temperate (Glenville, WV, USA) and warm temperate (Fukuoka, Japan).
Results/Conclusions
Leaf structure and physiological attributes varied significantly between Glenville and Fukuoka. Although mean leaf size was the same in both sites, specific leaf area, an indicator of photosynthetic capacity, was found larger in trees located in Glenville (297.2 ± 23.7 cm2 g-1) compared to those in Fukuoka (237.0 ± 33.5 cm2 g-1). Relative water content (RWC) was lower in Glenville (63.6 ± 2.6 %) than in Fukuoka (79.9 ± 2.0 %). Low RWC may indicate the ability of the plants to sustain excessive water loss without desiccation (RWC < 40%). There were also leaf structural differences between the two sites with those in Glenville exhibiting light-adapted leaf characteristics with shorter stomatal length (22.03 ± 0.46 mm) and higher stomatal density (232 ± 8 mm-2) than in Fukuoka (28.6 ± 0.87 mm; 196 ± 12 mm-2, respectively). Trees in Fukuoka sustained higher stomatal conductance (205.0 ± 14.7 mmol m-2 s-1) throughout the day compared to those trees in Glenville (135.6 ± 14.5 mmol m-2 s-1). Result of chlorophyll fluorescence analysis showed that Ailanthus trees in Glenville had a higher mean Fv/Fm of 0.80 than in Fukuoka (0.78). A lower value of Fv/Fm (< 0.80) may indicate photoinhibition which can result to a decline in photosynthetic capacity due to high light intensity. The leaf structure and ecophysiological parameters measured in this study revealed the key attributes of Ailanthus spp. that are associated with its invasiveness. Although Ailanthus spp. in Fukuoka may still be in its early stage of invasion, its successful establishment where it was originally planted and aggressive physiological characteristics showed its potential to continuously invade natural forest ecosystems of Japan.