Seasonal changes in carbohydrate reserves in mature northern<Emphasis Type="Italic"> Populus tremuloides</Emphasis> clones

To assess the changes in seasonal carbohydrate status of Populus tremuloides, sugar and starch concentrations were monitored in roots, stem xylem and phloem and branches of ten different clones. Time of root growth was assessed by extraction of roots from in-growth cores collected five times during the season. Overall the results showed that the main period of root growth in these northern clones was shifted from spring to late summer and fall likely due to the microclimatic conditions of the soil. This increase in root growth was associated with a decline in total non-structural carbohydrate content in the roots during this period. This study also found that the carbohydrate reserves in these clones were being stored as close as possible to the organs of annual growth (leaves and roots). At the time of leaf flush, the largest reduction in stored carbohydrates (3% of dry weight) was observed in the branches of the trees, compared to a slight decline in the stem and roots. Starch and sugar reserves in most tissues were very low in early summer. This suggests that reserves that might be used for the regrowth of foliage after insect defoliation or other disturbances, are relatively small compared to the portion that is needed for maintenance and typical growth developments such as leaf flush.