Patterns of late-season photosynthate movement in sugar maple saplings

A more detailed understanding of seasonal dynamics of carbon allocation between roots and shoots of temperate zone trees is needed. We labeled sapling stands of sugar maple ( Acer saccharum Marsh) with 13 CO 2 in four 3 m diameter chambers during a 3 week interval in September 2006 and traced the movement of this 13 C pulse through trees and soil during autumn and spring. High enrichment of 13 C in foliage was achieved (δ 13 C = 387‰ ± 16‰). Late-season photosynthate was strongly mobilized during leaf senescence and stored in twigs, wood, and roots. Very high 13 C enrichment of soil CO 2 emissions at this time (δ 13 C = 766‰ ± 82‰) indicated the role of late-season photosynthesis in supplying root metabolism after the growing season. Rhizosphere soil was weakly enriched in 13 C during fall, and increased significantly over the winter. Earthworms were highly enriched in fall, indicating that they consumed roots. In spring, 13 C was strongly mobilized to growing shoots but not to growing fine roots; apparently, fine root growth in spring was not supplied by late-season stored photosynthate. These results provide insights into the seasonal dynamics of temperate tree carbon allocation with implications for disruption of these dynamics by global warming.