Morphological and physiological characteristics of the Siberian elm (Ulmus pumila L.) along the precipitation and aridity gradient in northeast Asia
Siberian elm (Ulmus pumila L.) is one of the most commonly found species in arid region in northeast Asia. Recognizing the lack of study on the mature Siberian elm tree in the field, this research was conducted to understand the survival strategies of the Siberian elm tree at the leaf level under dry condition. To approach the answer of this question, Siberian elms under different annual precipitation and aridity index were investigated from seven regions of northeast Asia, Mongolia, Inner Mongolia in China, and Korea which cover a wide range of average annual precipitation from 232 mm yr-1 to 1,304 mm yr-1. The aridity index (AI) of each region was calculated by using the modified equation of Zhang et al. (2009) which considers both of annual precipitation (AP) and annual mean temperature (MAT) (AI = AP/(MAT+10)). From the investigated mature trees, leaf samples were collected and their morphological characteristics (tree size, leaf size, leaf mass per unit leaf area, leaf surface roughness, and stomatal area per unit leaf area) and physiological characteristics (foliar total N concentration and water use efficiency) were examined. Morphological and physiological variables were compared using ANOVA, and multiple comparisons were performed using Duncan’s multiple range test. An estimation of the derived parameters was performed and plotted using Sigma Plot 2011.
Siberian elms showed significant differences in morphological and physiological characteristics along the variation of the annual precipitation and the aridity index (p<0.05). In overall, tree size in arid regions was smaller than in humid region (p<0.0001). In addition, as annual precipitation and aridity index decreases, leaf mass per unit leaf area and water use efficiency of Siberian elm tree increased while leaf size and stomatal area per unit leaf area decreased (ps<0.05). The total N concentration in leaf, one of the representative nutrient statuses, also showed differences among each sites, however, did not show any noticeable trend with annual precipitation nor aridity index. On the other hand, water use efficiency estimated from carbon isotope composition, showed negative relationship with annual precipitation and aridity index (p=0.0131 and 0.0102, respectively). From this study it could be founded that the Siberian elm tree has responded to arid conditions by demonstrating high adaptability in foliar morphological and physiological characteristics.