In this paper, we present results indicating ozone effect on visible plants response as well as on other parameters, such as dry weight, chlorophyll concentration, cell membrane stability and salicylic acid content in bioindicator plants. Ozone-resistant and -sensitive clones of white clover (Trifolium repens L. cv. "Regal") were used in the investigations. The experiment was carried out in ambient air conditions of the Wielkopolska province (Poland) in 2005 growing season. The exposure led to changes in the level of plant response parameters that might be used as potential biomarkers of oxidative stress triggered by tropospheric ozone in ambient air conditions.
The major aim of the study was to identify the relationships of photosynthetic pigments with elemental contents of plants exposed to various ambient air conditions. Lolium multiflorum L. plants were exposed at five sites varying in environmental characteristics, including potential air pollution levels. The effect of air pollution by trace elements on plants was examined. Selected trace elements (Pb, Cd, As, Ni, Cr), some macro-elements as well as chlorophyll content were measured after each of four series. The graphical visualization revealed groups of sites with similar response of elements and chlorophyll contents. Sites located outside the city were grouped into one, and two urban sites were grouped into another. The trace element contents were relatively low and, excluding Ni and As, did not reach toxic levels in dry mass of leaves. However, some relations could be noted, which indicates the sensitivity of the photosynthetic process even at low levels of trace elements in ambient air. Chlorophyll b was found to be more sensitive to most of the analyzed trace elements than chlorophyll a. The results revealed chlorophylls, K and Na as indicators of plant stress caused by trace elements present in ambient air, even at relatively low levels.