Enhanced ozone exposure of European beech (Fagus sylvatica) stimulates nitrogen mobilization from leaf litter and nitrogen accumulation in the soil

Abstract

In a lysimeter study with young beech trees, the effects of elevated ozone concentration on the decomposition and fate of nitrogen in ¹⁵N‐labeled leaf litter were analyzed after one growing season. Nitrogen in the litter was dominated by a relatively inert, residual fraction, but easily decomposable nitrogen was present in substantial amounts. Nitrogen loss was significantly higher at twice‐ambient ozone which was largely attributed to an enhanced mobilization of residual nitrogen. Enhanced mobilization of nitrogen from litter at twice‐ambient ozone exposure resulted in additional ¹⁵N incorporation into the soil down to 30 cm depth. Only 0.41–0.62% of the nitrogen in the litter was incorporated into plant material at both ozone concentrations. Twice‐ambient ozone exposure changed the distribution of the nitrogen taken up from litter inside the beech trees in favor of the shoot, where it may have been used in biosynthetic processes required for defense reactions.

Keywords:

• Free‐air ozone enrichment
• leaf litter
• lysimeter study
• nitrogen cycling
• nitrogen uptake
• nitrogen mobilization

Acknowledgements

Financial support of this study by the Helmholtz Association of German Research Centers within the frame of the Virtual Institute “Center for Stable Isotope Analysis in Ecosystem Research” under contract no. VH‐VI‐129 and by the Deutsche Forschungsgemeinschaft (DFG, FOR788) within the frame of the Beech Research Group (BRG) under contract no. RE 515/27‐1 as well as SFB607 Growth and Parasite defence is gratefully acknowledged. We thank Wolfgang Sternad, Chair of Tree Physiology, University of Freiburg, for his support during data analysis.