Articles | Volume 8, issue 11
Research article
03 Nov 2011
Research article |  | 03 Nov 2011

Carbon flux to woody tissues in a beech/spruce forest during summer and in response to chronic O3 exposure

W. Ritter, C. P. Andersen, R. Matyssek, and T. E. E. Grams

Abstract. The present study compares the dynamics in carbon (C) allocation of adult deciduous beech (Fagus sylvatica) and evergreen spruce (Picea abies) during summer and in response to seven-year-long exposure with twice-ambient ozone (O3) concentrations (2 × O3). Focus was on the respiratory turn-over and translocation of recent photosynthates at various positions along the stems, coarse roots and soils. The hypotheses tested were that (1) 2 × O3 decreases the allocation of recent photosynthates to CO2 efflux of stems and coarse roots of adult trees, and that (2) according to their different O3 sensitivities this effect is stronger in beech than in spruce.

Labeling of whole tree canopies was applied by releasing 13C depleted CO213C of −46.9‰) using a free-air stable carbon isotope approach. Canopy air δ13C was reduced for about 2.5 weeks by ca. 8‰ in beech and 6‰ in spruce while the increase in CO2 concentration was limited to about 110 μl l−1 and 80 μl l−1, respectively. At the end of the labeling period, δ13C of stem CO2 efflux and phloem sugars was reduced to a similar extend by ca. 3–4‰ (beech) and ca. 2–3‰ (spruce). The fraction of labeled C (fE,new) in stem CO2 efflux amounted to 0.3 to 0.4, indicating slow C turnover of the respiratory supply system in both species.

Elevated O3 slightly stimulated the allocation of recently fixed photosynthates to stem and coarse root respiration in spruce (rejection of hypothesis I for spruce), but resulted in a significant reduction in C flux in beech (acceptance of hypotheses I and II). The distinct decrease in C allocation to beech stems indicates the potential of chronic O3 stress to substantially mitigate the C sink strength of trees on the long-term scale.

Final-revised paper