Data from: Dynamics of non-structural carbohydrates in terrestrial plants: a global synthesis

Plants store large amounts of non-structural carbohydrates (NSC). While multiple functions of NSC have long been recognized, the interpretation of NSC seasonal dynamics is often based on the idea that stored NSC is a reservoir of carbon that fluctuates depending on the balance between supply via photosynthesis and demand for growth and respiration (the source-sink dynamics concept). Consequently, relatively high NSC concentrations in some plants have been interpreted to reflect excess supply relative to demand. An alternative view, however, is that NSC accumulation reflects the relatively high NSC levels required for plant survival; an important issue that remains highly controversial. Here, we assembled a new global database to examine broad patterns of seasonal NSC variation across organs (leaves, stems and belowground), plant functional types (coniferous, drought deciduous angiosperms, winter deciduous angiosperms, evergreen angiosperms, and herbaceous) and biomes (boreal, temperate, Mediterranean and tropical). We compiled data from 123 studies, including seasonal measurements for 179 species under natural conditions. Our results showed that, on average, NSC account for ~10% of dry plant biomass and are highest in leaves and lowest in stems, whereas belowground organs show intermediate concentrations. Total NSC, starch and soluble sugars (SS) varied seasonally, with a strong depletion of starch during the growing season and a general increase during winter months, particularly in boreal and temperate biomes. Across functional types, NSC concentrations were highest and most variable in herbaceous species and in conifer needles. Conifers showed the lowest stem and belowground NSC concentrations. Minimum NSC values were relatively high (46% of seasonal maximums on average for total NSC) and, in contrast to average values, were similar among biomes and functional types. Overall, although starch depletion was relatively common, seasonal depletion of total NSC or SS was rare. These results are consistent with a dual view of NSC function: whereas starch acts mostly as a reservoir for future use, soluble sugars perform immediate functions (e.g., osmoregulation) and are kept above some critical threshold. If confirmed, this dual function of NSC will have important implications for the way we understand and model plant carbon allocation and survival under stress.植物会储存大量非结构性碳水化合物（non-structural carbohydrates, NSC）。尽管非结构性碳水化合物的多种功能早已得到学界认可，但针对其季节动态的解读通常基于源汇动态概念（source-sink dynamics concept）：即储存的非结构性碳水化合物作为一类碳储备库，其波动取决于光合作用的碳供给与生长、呼吸作用的碳需求之间的平衡。因此，部分植物中相对较高的非结构性碳水化合物浓度曾被解读为供给相对需求过剩的体现。然而，另一种观点则认为，非结构性碳水化合物的积累实则反映了植物生存所需的较高非结构性碳水化合物水平——这一关键议题至今仍存在极大争议。 本研究构建了一套全新的全球数据库，旨在探究不同器官（叶片、茎秆及地下器官）、植物功能型（plant functional types）和生物群区（biomes）中非结构性碳水化合物季节变化的整体格局。本次研究整合了来自123项研究的数据，涵盖179个物种在自然条件下的季节观测结果。 研究结果显示：平均而言，非结构性碳水化合物约占植物干生物量的10%，其中叶片中的浓度最高，茎秆最低，地下器官的浓度则处于中间水平。总非结构性碳水化合物、淀粉与可溶性糖（soluble sugars, SS）均存在季节波动：生长季期间淀粉会被大量消耗，而冬季月份则普遍出现回升，这一现象在北方与温带生物群区中尤为显著。 从植物功能型来看，草本植物与针叶植物针叶中的非结构性碳水化合物浓度最高且波动幅度最大；针叶植物的茎秆与地下器官非结构性碳水化合物浓度最低。最低非结构性碳水化合物值相对较高（总非结构性碳水化合物的最低值平均为季节峰值的46%），且与平均数值不同的是，不同生物群区与植物功能型之间的最低非结构性碳水化合物水平较为相近。 总体而言，尽管淀粉消耗现象较为普遍，但总非结构性碳水化合物或可溶性糖的季节消耗却极为罕见。上述结果与非结构性碳水化合物的双重功能观点相符：淀粉主要充当未来可用的储备库，而可溶性糖则执行即刻功能（例如渗透调节osmoregulation），且其浓度需维持在某一临界阈值之上。 若这一结论得到验证，非结构性碳水化合物的双重功能将对我们理解与模拟胁迫环境下植物的碳分配及生存策略产生重要意义。