School of Ecosystem and Forest Sciences, The University of Melbourne, 500 Yarra Boulevard, Richmond, Victoria 3121, Australia.
School of Ecosystem and Forest Sciences, The University of Melbourne, 4 Water Street, Creswick, Victoria 3363, Australia.
Tree Physiol. 2018 Apr 1;38(4):570-581. doi: 10.1093/treephys/tpx141.
Non-structural carbohydrates (NSCs) form a fundamental yet poorly quantified carbon pool in trees. Studies of NSC seasonality in forest trees have seldom measured whole-tree NSC stocks and allocation among organs, and are not representative of all tree functional types. Non-structural carbohydrate research has primarily focussed on broadleaf deciduous and coniferous evergreen trees with distinct growing seasons, while broadleaf evergreen trees remain under-studied despite their different growth phenology. We measured whole-tree NSC allocation and temporal variation in Eucalyptus obliqua L'Hér., a broadleaf evergreen tree species typically occurring in mixed-age temperate forests, which has year-round growth and the capacity to resprout after fire. Our overarching objective was to improve the empirical basis for understanding the functional importance of NSC allocation and stock changes at the tree- and organ-level in this tree functional type. Starch was the principal storage carbohydrate and was primarily stored in the stem and roots of young (14-year-old) trees rather than the lignotuber, which did not appear to be a specialized starch storage organ. Whole-tree NSC stocks were depleted during spring and summer due to significant decreases in starch mass in the roots and stem, seemingly to support root and crown growth but potentially exacerbated by water stress in summer. Seasonality of stem NSCs differed between young and mature trees, and was not synchronized with stem basal area increments in mature trees. Our results suggest that the relative magnitude of seasonal NSC stock changes could vary with tree growth stage, and that the main drivers of NSC fluctuations in broadleaf evergreen trees in temperate biomes could be periodic disturbances such as summer drought and fire, rather than growth phenology. These results have implications for understanding post-fire tree recovery via resprouting, and for incorporating NSC pools into carbon models of mixed-age forests.
非结构性碳水化合物（NSCs）是树木中基本但量化程度较低的碳库。森林树木中 NSC 季节性的研究很少测量整树 NSC 存量及其在器官间的分配，而且不能代表所有树木的功能类型。非结构性碳水化合物的研究主要集中在具有明显生长季节的阔叶落叶和针叶常绿树种上，而阔叶常绿树种尽管具有不同的生长物候，但仍研究不足。我们测量了广泛分布于混合年龄温带森林中的一种常绿阔叶树种桉树（Eucalyptus obliqua L'Hér.）的整树 NSC 分配及其时间变化，该树种具有全年生长和火灾后重新萌发的能力。我们的总体目标是提高对该功能类型树木和器官水平上 NSC 分配和存量变化的功能重要性的理解的经验基础。淀粉是主要的储存碳水化合物，主要储存在年轻（14 岁）树木的茎和根中，而不是木质块茎中，木质块茎似乎不是专门的淀粉储存器官。由于根和茎中淀粉质量显著减少，整个树木的 NSC 存量在春季和夏季消耗殆尽，这似乎是为了支持根和冠层的生长，但可能因夏季的水分胁迫而加剧。年轻和成熟树木的茎 NSCs 季节性不同，并且与成熟树木的茎基部面积增量不同步。我们的研究结果表明，季节性 NSC 存量变化的相对幅度可能随树木生长阶段而变化，而温带生物群落中阔叶常绿树木 NSC 波动的主要驱动因素可能是周期性干扰，如夏季干旱和火灾，而不是生长物候。这些结果对于通过重新萌发来理解火灾后树木的恢复，以及将 NSC 池纳入混合年龄森林的碳模型具有重要意义。
