Dynamics of non‐structural carbohydrates in terrestrial plants: a global synthesis

Abstract

AbstractPlants store large amounts of non‐structural carbohydrates (NSC). While multiple functions ofNSChave long been recognized, the interpretation ofNSCseasonal dynamics is often based on the idea that storedNSCis 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 highNSCconcentrations in some plants have been interpreted to reflect excess supply relative to demand. An alternative view, however, is thatNSCaccumulation reflects the relatively highNSClevels required for plant survival; an important issue that remains highly controversial. Here, we assembled a new global database to examine broad patterns of seasonalNSCvariation 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 121 studies, including seasonal measurements for 177 species under natural conditions. Our results showed that, on average,NSCaccount for ~10% of dry plant biomass and are highest in leaves and lowest in stems, whereas belowground organs show intermediate concentrations. TotalNSC, 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,NSCconcentrations were highest and most variable in herbaceous species and in conifer needles. Conifers showed the lowest stem and belowgroundNSCconcentrations. MinimumNSCvalues were relatively high (46% of seasonal maximums on average for totalNSC) and, in contrast to average values, were similar among biomes and functional types. Overall, although starch depletion was relatively common, seasonal depletion of totalNSCorSSwas rare. These results are consistent with a dual view ofNSCfunction: 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 ofNSCwill have important implications for the way we understand and model plant carbon allocation and survival under stress.