Abstract
The Siberian elm (Ulmus pumila L.) is one of the most commonly found tree species in arid areas of northeast Asia. To understand the morphological and physiological characteristics of Siberian elms in arid regions, we analyzed leaves from seven study sites (five arid or semi-arid and two mesic) in China, Mongolia and the Republic of Korea, which covered a wide range of average annual precipitation (232 mm·year−1 to 1304 mm·year−1) under various aridity indexes (AI) and four different microenvironments: sand dune, steppe, riverside and forest. The traits of Siberian elms varied widely along different annual precipitation (P) and AI gradients. Tree height (H), leaf size (LS) and stomatal area per unit leaf area (AS/AL) decreased with increasing AI, whereas leaf mass per unit leaf area (LMA) and water-use efficiency (WUE) increased significantly. In addition, trees at the five arid sites showed significant differences in LS, LMA and AS/AL but not in H and WUE. Thus, our study indicated that indigenous Siberian elm trees in arid areas have substantially altered their morphological and physiological characteristics to avoid heat stress and increase water conservation in comparison to mesic areas. However, their changes differed depending on the surrounding microenvironment even in arid areas. Trees in sand dunes had a smaller LS, higher LMA, thicker leaf cuticle layer and higher stomatal density and AS than those in steppes and near a riverside.
Highlights
Drylands cover more than 41% of the global terrestrial area, larger than that of forests [1].10%–20% of these drylands face severe degradation, which is accelerated by climate change and population growth
We proposed two major hypotheses with respect to two aspects: (1) Physiological and morphological characteristics of Siberian elm will be differentiated along a variation in annual precipitation; (2) Even under a similar range of annual precipitation, the above characteristics will vary according to micro-environmental conditions
Mean annual temperature and minimum monthly temperature increased mean and maximum monthly temperatures than QY, a temperate forest site located at lower latitude as the(6.6 latitude of 5.1 the±experimental decreased
Summary
Drylands cover more than 41% of the global terrestrial area, larger than that of forests [1].10%–20% of these drylands face severe degradation, which is accelerated by climate change and population growth. In countries including China and Mongolia where more than 250 million people are directly affected by desertification, the efforts to prevent this expansion and to rehabilitate degraded areas by restoring vegetation are increasing [2,3,4,5]. To avoid failure and side effects caused by planting trees in these areas, it is necessary to select appropriate species which have already survived and adapted to the drought and harsh conditions [5,7,8]. The survival of indigenous species in arid and semi-arid areas is directly attributed to their ability to adapt to surrounding environmental conditions including water availability and heat stress [9,10,11,12,13,14]
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