Northern conditions enhance the susceptibility of birch (Betula pendula Roth) to oxidative stress caused by ozone

Summary

Impacts of increasing tropospheric ozone, together with the most important interactive stress factors (such as drought, soil N, and early frost) on European white birch (Betula pendula Roth) has been extensively investigated. In this paper, a summary of those studies, conducted both in chambers and realistic open-field conditions, is presented. Typical ozone responses in birch were found as impaired foliage, stem and root growth, altered shoot to root ratio, delayed bud burst, visible foliar injuries, enhanced leaf senescence, disturbed stomatal conductance, impaired net photosynthesis and water-use efficiency, reduced concentrations of Rubisco, pigments, starch, soluble protein and nitrogen, increased concentrations of phenolic compounds, increased transcription levels of genes encoding stress proteins PR-10 and PAL, increased stomatal density, reduced leaf thickness, ultrastructural injuries in chloroplasts and mitochondria, increased mesophyll cell wall thickness and reduced volume for intercellular space. Many of the negative responses were significantly promoted by simultaneous soil drought or early frost. Although elevated soil N counteracted ozone-caused growth reductions, delayed leaf senescence and increased shoot to root ratio may lead to disturbances in winter hardening processes and predispose the trees e.g. to soil drought due to a lower water uptake per higher water loss through transpiration.