| Abstract
| - Trichloroacetic acid (TCA) has been implicated as anairborne pollutant responsible for adverse effects on foresthealth. There is considerable debate as to whether TCAobserved in trees and forest soils is derived from atmosphericdeposition or from in situ production. This experimentreports the results from treating 4-year-old Sitka spruce(Picea sitchensis (Bong.) Carr) plants in a greenhouse overa growing season with TCA supplied either to the soil orto the foliage at concentrations of 10 and 100 ng mL-1. Similaruptake of TCA by needles was observed for both modesof treatment, with significant accumulation of TCA (300 ngg-1 dry wt) at the higher concentration. Larger concentrationsin stem tissue were seen for the foliar-applied TCA (280 ngg-1) than for the soil-applied TCA (70 ng g-1), suggestingthat direct stem uptake may be important. Six months aftertreatments stopped, TCA concentrations in the needlesof plants exposed to 100 ng mL-1 TCA were still enhanced,showing that biological degradation of TCA in needleswas slow over the winter. By contrast, no significantenhancement of TCA in soil could be detected in the directlytreated soils even during the experiment. The proteincontent of needles treated with the higher concentrationof TCA by either route was significantly smaller than for thecontrols, but there was no effect of TCA on the conjugationof 1-chloro-2,4-dinitrobenzene in roots nor on theconjugation of 1,2-dichloro-4-nitrobenzene in needles.
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