Running Head : Dynamics of NSC in terrestrial plants 1 2 Dynamics of non - structural carbohydrates in terrestrial plants : a global synthesis 3

24 25 Plants store large amounts of non-structural carbohydrates (NSC). While multiple functions of 26 NSC have long been recognized, the interpretation of NSC seasonal dynamics is often based on 27 the idea that stored NSC is a reservoir of carbon that fluctuates depending on the balance 28 between supply via photosynthesis and demand for growth and respiration (the source-sink 29 dynamics concept). Consequently, relatively high NSC concentrations in some plants have been 30 interpreted to reflect excess supply relative to demand. An alternative view, however, is that 31 NSC accumulation reflects the relatively high NSC levels required for plant survival; an 32 important issue that remains highly controversial. Here, we assembled a new global database to 33 examine broad patterns of seasonal NSC variation across organs (leaves, stems and 34 belowground), plant functional types (coniferous, drought deciduous angiosperms, winter 35 deciduous angiosperms, evergreen angiosperms, and herbaceous) and biomes (boreal, temperate, 36 Mediterranean and tropical). We compiled data from 123 studies, including seasonal 37 measurements for 179 species under natural conditions. Our results showed that, on average, 38 NSC account for ~10% of dry plant biomass and are highest in leaves and lowest in stems, 39 whereas belowground organs show intermediate concentrations. Total NSC, starch and soluble 40 sugars (SS) varied seasonally, with a strong depletion of starch during the growing season and a 41 general increase during winter months, particularly in boreal and temperate biomes. Across 42 functional types, NSC concentrations were highest and most variable in herbaceous species and 43 in conifer needles. Conifers showed the lowest stem and belowground NSC concentrations. 44 Minimum NSC values were relatively high (46% of seasonal maximums on average for total 45 NSC) and, in contrast to average values, were similar among biomes and functional types. 46 Page 2 of 73 Ecological Monographs