Fate and Distribution of Sulfur-35 in Yellow Poplar and Red Maple Trees

Archive description

Two deciduous tree species (yellow poplar and red maple) on walker branch watershed, near oak ridge, tennessee, were radiolabeled with sulfur-35 to study internal cycling, storage, and biogenic emission of sulfur. One tree of each species was girdled before radiolabeling to prevent phloem translocation to the roots, and the aboveground biomass was harvested prior to autumn leaf fall. Aboveground biomass, leaf fall, throughfall, and stemflow were sampled over 13 to 24 week period. Sulfur-35 concentrations in tree leaves reached nearly asymptotic levels within 1 to 2 weeks after radiolabeling. Foliar leaching of sulfur-35 and leaf fall represented relatively unimportant return pathways to the forest soil. The final distribution of sulfur- 35 in the nongirdled trees indicated little aboveground storage of sulfur in biomass and appreciable capacity to cycle sulfur either to the below-ground system by means of translocation or to the atmosphere by means of biogenic sulfur emissions. Losses of volatile sulfur-35 were estimated from the amount of isotope missing in final inventories of the girdled trees. Translocation to roots was a significant sink for sulfur-35 in the red maple tree. Research on forest biogeochemical sulfur cycles should further explore biogenic sulfur emissions from trees as a potential process of sulfur flux from forest ecosystems.