O3 Flux-Related Responsiveness of Photosynthesis, Respiration, and Stomatal Conductance of Adult Fagus sylvatica to Experimentally Enhanced Free-Air O3 Exposure

• Published in: Plant biology (Stuttgart, Germany) Vol. 9; no. 2; pp. 197 - 206
• Main Authors: Löw, M., Häberle, K.-H., Warren, C. R., Matyssek, R.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01-03-2007
• Subjects: Carbon Dioxide - metabolism; Cell Respiration - drug effects; Cell Respiration - radiation effects; Disasters; dose response; drought; Electron Transport - drug effects; Electron Transport - radiation effects; Fagus - drug effects; Fagus - physiology; Fagus - radiation effects; Fagus sylvatica; free-air ozone exposure; Light; Ozone - pharmacology; Ozone flux; photosynthesis; Photosynthesis - drug effects; Photosynthesis - radiation effects; Plant Leaves - drug effects; Plant Leaves - radiation effects; Rain; Research Paper; stomatal conductance; Temperature; stomatal conductance; dose response; photosynthesis; drought; Ozone flux; Fagus sylvatica; free-air ozone exposure
• ISSN: 1435-8603; 1438-8677
• DOI: 10.1055/s-2006-924656

Abstract
Knowledge of responses of photosynthesis, respiration, and stomatal conductance to cumulative ozone uptake (COU) is still scarce, and this is particularly the case for adult trees. The effect of ozone (O
3
) exposure on trees was examined with 60-year-old beech trees (FAGUS SYLVATICA) at a forest site of southern Germany. Trees were exposed to the ambient O
3
regime (1 × O
3
) or an experimentally elevated twice-ambient O
3
regime (2 × O
3
). The elevated 2 × O
3
regime was provided by means of a free-air O
3
canopy exposure system. The hypotheses were tested that (1) gas exchange is negatively affected by O
3
and (2) the effects of O
3
are dose-dependent and thus the sizes of differences between treatments are positively related to COU. Gas exchange (light-saturated CO
2
uptake rate A
max
, stomatal conductance g
s
, maximum rate of carboxylation Vc
max
, ribulose-1,5-bisphosphate turnover limited rate of photosynthesis J
max
, CO
2
compensation point CP, apparent quantum yield of net CO
2
uptake AQ, carboxylation efficiency CE, day- and nighttime respiration) and chlorophyll fluorescence (electron transfer rate, ETR) were measured IN SITU on attached sun and shade leaves. Measurements were made periodically throughout the growing seasons of 2003 (an exceptionally dry year) and 2004 (a year with average rainfall). In 2004 Vc
max
, J
max
, and CE were lower in trees receiving 2 × O
3
compared with the ambient O
3
regime (1 × O
3
). Treatment differences in Vc
max
, J
max
, CE were rather small in 2004 (i.e., parameter levels were lower by 10 - 30 % in 2 × O
3
than 1 × O
3
) and not significant in 2003. In 2004 COU was positively correlated with the difference between treatments in A
max
, g
s
, and ETR (i.e., consistent with the dose-dependence of O
3
’s deleterious effects). However, in 2003, differences in A
max
, g
s
, and ETR between the two O
3
regimes were smaller at the end of the dry summer 2003 (i.e., when COU was greatest). The relationship of COU with effects on gas exchange can apparently be complex and, in fact, varied between years and within the growing season. In addition, high doses of O
3
did not always have significant effects on leaf gas exchange. In view of the key findings, both hypotheses were to be rejected.