A Review Study on Past 40 Years of Research on Effects of Tropospheric O3 on Belowground Structure, Functioning, and Processes of Trees: a Linkage with Potential Ecological Implications

Woody plants constitute a great sink of carbon storage, mitigating thus the greenhouse effect phenomenon. They are considered key players in ecosystems, and among others, they help in decreasing soil erosion and in maintaining soil moisture. Over the last decades, researches have shown negative effects of the ambient ozone (O-3) on many woody species, not only on canopy but also on belowground part of trees. Negative effects of elevated O-3 (eO(3)), which usually refers to any O-3 dosages above the current ambient levels, on belowground structure, function, and processes may have consequences to ecosystem sustainability. We reviewed reports of research published over the past 40 years and dealing with woodies belowground response to eO(3). eO(3) induces changes in C dynamics into plants and alterations in their metabolism accordingly, as a result of different strategies followed by the trees in order to compensate with eO(3) stress effects. In these strategies, phenolics seem to have a detrimental role in shoot/root allometry. Root and soil chemical composition can be also influenced, threatening thus the soil biodiversity, soil fertility, and nutrient cycling. Elevated O-3 impact is discussed with linkage to other potential ecological consequences.