Nonstructural Carbohydrates in Forest Trees at Harvard Forest 2007-2010

Forest trees accumulate and store surplus nonstructural carbohydrates (NSC) as resources to be used to support future growth. This can be viewed as a conservative investment strategy, providing reserves that the tree can utilize in times of stress. NSC reserves are thus important in the context of forest responses to climate change, and forest ecosystem carbon cycling. At quarterly intervals over a three year period, we have monitored stemwood nonstructural carbohydrate (NSC) reserves of the dominant tree species of New England at three sites along a forest composition gradient: an oak-dominated transition hardwood forest (Harvard Forest), a maple-beech-birch northern hardwood forest (Bartlett Experimental Forest), and a spruce-fir boreal transition forest (Howland Forest). Adding to recent evidence indicating that in mature forest trees the nonstructural carbohydrate pool is surprisingly large, our results suggest that this pool is also highly dynamic, and unexpectedly old. In most species, seasonal dynamics in starch (2-4x higher in the growing season, lower in the dormant season) mirrored those of sugars. This data set contains 3 y of quarterly NSC concentration measurements (stemwood starch and sugars - sucrose, glucose, fructose, raffinose, stachyose - in mg per g OD wood tissue) for red maple, eastern hemlock, and red oak at the Harvard Forest.

林木可积累并储存过剩的非结构性碳水化合物（nonstructural carbohydrates, NSC），作为支撑未来生长的储备资源。这可被视作一种保守的投资策略，可为树木在逆境胁迫时期提供可调用的储备。因此，非结构性碳水化合物储备在森林应对气候变化以及森林生态系统碳循环研究中具有关键意义。本研究在三年周期内按季度对新英格兰地区沿森林组成梯度分布的三个样地的优势树种进行了树干非结构性碳水化合物储备监测：三个样地分别为以橡树为主的过渡性阔叶林（哈佛大学森林保护区，Harvard Forest）、以枫木-山毛榉-桦木为主的北方阔叶林（巴特利特实验林，Bartlett Experimental Forest），以及云杉-冷杉寒带过渡林（豪兰森林，Howland Forest）。本研究进一步佐证了近期的研究结论：成熟林木体内的非结构性碳水化合物库规模惊人庞大；同时我们的结果显示，该库不仅动态性极强，其周转周期也长得出人意料。多数树种中，淀粉的季节动态变化（生长季含量为休眠季的2-4倍，休眠季含量更低）与糖类的变化趋势完全一致。本数据集涵盖了哈佛大学森林保护区内红枫、东部铁杉与红栎三种优势树种为期三年的季度性非结构性碳水化合物浓度检测数据，检测指标包括树干组织中的淀粉与糖类（蔗糖、葡萄糖、果糖、棉子糖、水苏糖），单位为毫克每克烘干干重木材组织（mg/g OD wood tissue）。