Non-structural carbohydrates (NSCs) buffer the asynchrony of supply and demand on different temporal scales. At the long-term time scale, perennial plants might buffer yearly pattern of dormancy storing NSCs prior to winter to support early spring development. At the short-term time scale, plants may buffer diurnal cycle of photosynthetic activity. For example, it was shown that Arabidopsis thaliana regulates diurnal starch turnover rates in response to day/night length, in a pattern suggesting avoidance of starvation. Are similar pattern can be found in trees? There, the distributed starch storage is stretched over tens of meters and may operate under different micro-environmental conditions responding to local short- and long-term strategies. Local parenchyma cells provide the necessary capacity for NSCs storage that is needed not only for the long-term tree survival but also to meet short-term demand for growth, respiration and stress responses. Despite the importance of the topic it is not known to what degree wood NSCs content varies at diurnal time scale. To address this question we studied temporal and spatial variability of soluble and non-soluble NSCs content in Prunus tree over 24 hours diurnal cycle. In addition, we follow distribution of newly synthetized NSCs and their translocation within the tree using enriched 13CO2.
Here, we show first report describing NSCs diel variations in a perennial species to our knowledge. Analysis revealed that starch turnover in Prunus leaves follow similar trends as observed in the A. thaliana. However, we also show that NSCs storage is highly dynamic in all parts of woody tissue at the diurnal scale. In young branches, starch concentration may vary as much as 100%. Magnitude of the variation decreases with increasing total tissue storage capacity and is smallest for large limbs and trunk, while remains high in the roots. These findings are in line with recent paradigm shift on NSCs storage pool being dynamic and actively formed instead of a passive carbon overflow accumulation. Tracking newly assimilates with 13CO2 revealed that assimilates are exported and temporary stored in the xylem of branches and then diluted signal is observed in the trunk. The rate of bulk sugar translocation was smaller than expected from phloem models of carbon fluxes and might reflect high rates of exchange between wood and phloem of newly assimilated sugars