长白山不同海拔岳桦非结构碳水化合物含量的变化

VARIATIONS OF NONSTRUCTURAL CARBOHYDRATE CONTENT IN BETULA ERMANII AT DIFFERENT ELEVATIONS OF CHANGBAI MOUNTAIN,CHINA

通常认为，随着林木不断接近其海拔分布极限，光合作用产量不断下降，导致碳水化合物供应不足（碳供应限制），或者低温限制了碳投资（生长限制）。植物组织内非结构性碳水化合物（Nonstructural carbohydrates，NSC）的含量反映了植物碳供应与碳吸收的平衡。为了检验“碳供应限制”和“生长抑制”假说，我们对长白山海拔1700～2050m的自然生境下生长的岳桦（Betula ermanii）的叶片和枝条组织的NSC含量进行了比较。结果表明：岳桦叶片的NSC含量随海拔升高变化不显著，枝条的NSC含量随海拔升高显著增加；叶片和枝条中淀粉含量与可溶性总糖含量的比值均随海拔的升高而减小；林线附近的岳桦林木不存在碳水化合物供应不足的问题，这在一定程度上表明生长限制导致长白山岳桦林线的形成。

Aims It is often assumed that trees near the high-elevation tree limit fall short in photosynthate （source limitation）. Alternatively, low temperature may restrict carbon investment （growth, sink limitation）. The content of mobile nonstructural carbohydrates （NSC） in tissues is considered as a measure of the carbon source-sink balance. Our objective was to test source vs. sink limitation. We compared late-season NSC concentrations in leaves and branches of Betula ermanii across elevational gradients from the subalpine forest interior to tree line on the north slope of Changbai Mountain, China. Methods We sampling the leaves and branches of B. ermanii on August 25, 2007. The NSC （including dissolubility total sugar, sucrose, and fructose） concentration was measured using a modified anthrone method; the perchloric acid method was used for starch concentration measure. Important findings The NSC （including starch） concentrations in branches increased significantly with elevation, while there were no significant trend in leaves. The ratio of starch to sugar decreased with elevation in branches and leaves. The overall elevational trends of the NSC revealed no depletion of carbon reserves near the tree limit, suggesting that sink limitation predominates across this treeline ecotone community.