Phytotoxic effects of trichloroacetic acid on Scots pine and birch determined by chl a fluorescence and the JlP-test

Abstract

Trichloroacetic acid (TCA) is a phytotoxic substance that, until the 1980s was used in the form of sodium trichloroacetate (TCA-Na) as a herbicide in agriculture and forestry. Since then it has been banned almost everywhere in Europe and in many other countries in the world. Although much has been learned about the natural and anthropogenic sources of TCA over the past few years, at present little is known about the harmful effects of TCA and its atmospheric precursors (such as tetrachloroethylene, PER) on wild and forest plant species. Therefore experiments lasting a number of years were carried out on pine trees (Pinus sylvestris L.) and birch trees (Betula pendula Roth) with respect to the chronic uptake of airborne PER via the air/leaf pathway, the aim being to study the fate of PER and its metabolisation into TCA. This work was augmented by outdoor model experiments on pines about 10 years old regarding the uptake of TCA-Na via the soil/root pathway. Chlorophyll a fluorescence measurements on needles and leaf material affected by TCA-Na and PER indicated that the extent to which TCA influences photochemical and biochemical mesophyll processes varies depending on the entry pathway, the particular part of the plant directly affected by TCA, and weather-related factors. It was proven that TCA-Na applied via the soil/root pathway moderately raises the vitality of pine trees depending on the concentration involved, despite high levels of TCA in the needles (up to 1 800μg TCA kg–1 dry weight needles). By contrast, fumigating pine trees and birch trees with PER led to the accumulation of up to 70μg TCA kg–1 dw in the assimilation organs and exacerbated the trees’ sensitivity to stressors. Although physiological activity was initially stimulated, the effect of additional stress in the form of an artificially induced drought caused PER-affected birch trees, in particular, to sometimes undergo sharp losses of vitality of as much as 58% compared to the controls. One may thus expect that, future climate changes accompanied by long periods of drought are likely to exacerbate the ecotoxicological risk in regions with high PER pollution, possibly resulting in the vegetation in the terrestrial ecosystems of the areas concerned being destabilised.