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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.