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 13CO2 in four 3 m diameter chambers during a 3 week interval in September 2006 and traced the movement of this 13C pulse through trees and soil during autumn and spring. High enrichment of 13C in foliage was achieved (δ13C = 387‰ ± 16‰). Late-season photosynthate was strongly mobilized during leaf senescence and stored in twigs, wood, and roots. Very high 13C enrichment of soil CO2 emissions at this time (δ13C = 766‰ ± 82‰) indicated the role of late-season photosynthesis in supplying root metabolism after the growing season. Rhizosphere soil was weakly enriched in 13C during fall, and increased significantly over the winter. Earthworms were highly enriched in fall, indicating that they consumed roots. In spring, 13C 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.