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Foliar Leaching, Translocation, and Biogenic Emission of 35S in Radiolabelled Loblolly Pines

Garten, Charles T., Jr.
Ecology 1990 v.71 no.1 pp. 239-251
Pinus taeda, aboveground biomass, canopy, dry deposition, emissions, field experimentation, forest trees, leaching, radiolabeling, rain, roots, stemflow, sulfates, sulfur, sulfur dioxide, summer, throughfall
Foliar leaching, basipetal (downard) translocation, and biogenic emission of sulfur (S), as traced by ³ ⁵S, were examined in a field study of loblolly pines. Four trees were radiolabeled by injection with amounts of ³ ⁵S in the MBq range, and concentrations in needle fall, stemflow, throughfall, and aboveground biomass were measured over a period of 15—20 wk after injection. The contribution of dry deposition to sulfate—sulfur (SO₄ ² ——S) concentrations in net throughfall (throughfall SO₄ ² ——S concentration minus that in incident precipitation) beneath all four trees was >90%. Calculations indicated that about half of the summertime SO₂ dry deposition flux to the loblolly pines was fixes in the canopy and not subsequently leached by rainfall. Based on mass balance calculations, ³ ⁵S losses through biogenic emissions from girdled trees were inferred to be 25—28% of the amount injected. Estimates based on chamber methods and mass balance calculations indicated a range in daily biogenic S emission of 0.1—10 mg/g dry needles. Translocation of ³ ⁵ to roots in nongirdled trees was estimated to be between 14 and 25% of the injection. It is hypothesized that biogenic emission and basipetal translocation of S (and not foliar leaching) are important mechanisms by which forest trees physiologically adapt to excess S in the environment.