Volatile emissions and phenolic compound concentrations along a vertical profile of <Emphasis Type="Italic">Populus nigra</Emphasis> leaves exposed to realistic ozone concentrations |
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Authors: | Silvano Fares Elina Oksanen Mika Lännenpää Riitta Julkunen-Tiitto Francesco Loreto |
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Institution: | (1) Consiglio Nazionale delle Ricerche (CNR), Istituto di Biologia Agroambientale e Forestale (IBAF), 00016 Monterotondo Scalo (Rome), Italy;(2) Department of Biology, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland;(3) Consiglio Nazionale delle Ricerche (CNR), Istituto per la Protezione delle Piante (IPP), Florence, Italy |
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Abstract: | Plants are exposed to increasing levels of tropospheric ozone concentrations. This pollutant penetrates in leaves through
stomata and quickly reacts inside leaves, thus making plants valuable ozone sinks, but at the same time triggers oxidation
processes which lead to leaf injuries. To counteract these negative effects, plants produce an array of antioxidants which
react with ozone and reactive molecules which ozone generates in the leaf tissues. In this study, we measured the effect of
an ozone concentration which is likely to be attained in many areas of the world in the near future (80 ppb) on leaves of
the vertical profile of the widespread agroforestry species Populus nigra. Changes in (1) physiological parameters (photosynthesis and stomatal conductance), (2) ozone uptake, (3) emission of volatile
organic compounds (VOCs, i.e. isoprene, methanol and other oxygenated compounds), (4) concentration of antioxidant surface
compounds, and (5) concentration of phenolic compounds were assessed. The aim was to assess whether the defensive pathways
leading to isoprenoids and phenolics formation were induced when a moderate and chronic increment of ozone is not able to
damage photosynthesis. No visual injuries and minor changes in physiology and ozone uptake were observed. The emission of
isoprene and oxygenated six-carbon (C6) volatiles were inhibited by ozone, whereas methanol emission was increased, especially
in developing leaves. We interpret these results as suggesting an ontogenetic shift in ozone-treated leaves, leading to a
slower development and a faster senescence. Most surface and phenolic compounds showed a declining trend in concentration
from the youngest to the fully expanded leaves. Ozone reduced the concentrations of chlorogenic acid derivatives at the leaf
surface, whereas in total leaf extracts a metabolic shift towards few phenolics with higher antioxidant capacity was observed. |
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