Synopsis of the CASIROZ Case Study: Carbon Sink Strength of Fagus sylvatica L. in a Changing Environment ‐ Experimental Risk Assessment of Mitigation by Chronic Ozone Impact

Abstract

Databases are needed for the ozone (O(3)) risk assessment on adult forest trees under stand conditions, as mostly juvenile trees have been studied in chamber experiments. A synopsis is presented here from an integrated case study which was conducted on adult FAGUS SYLVATICA trees at a Central-European forest site. Employed was a novel free-air canopy O(3) fumigation methodology which ensured a whole-plant assessment of O(3) sensitivity of the about 30 m tall and 60 years old trees, comparing responses to an experimental 2 x ambient O(3) regime (2 x O(3), max. 150 nl O(3) l (-1)) with those to the unchanged 1 x ambient O(3) regime (1 x O(3)=control) prevailing at the site. Additional experimentation on individual branches and juvenile beech trees exposed within the forest canopy allowed for evaluating the representativeness of young-tree and branch-bag approaches relative to the O(3) sensitivity of the adult trees. The 2 x O(3) regime did not substantially weaken the carbon sink strength of the adult beech trees, given the absence of a statistically significant decline in annual stem growth; a 3 % reduction across five years was demonstrated, however, through modelling upon parameterization with the elaborated database. 2 x O(3) did induce a number of statistically significant tree responses at the cell and leaf level, although the O(3) responsiveness varied between years. Shade leaves displayed an O(3) sensitivity similar to that of sun leaves, while indirect belowground O(3) effects, apparently mediated through hormonal relationships, were reflected by stimulated fine-root and ectomycorrhizal development. Juvenile trees were not reliable surrogates of adult ones in view of O(3) risk assessment. Branch sections enclosed in (climatized) cuvettes, however, turned out to represent the O(3) sensitivity of entire tree crowns. Drought-induced stomatal closure decoupled O(3) intake from O(3) exposure, as in addition, also the "physiologically effective O(3) dose" was subject to change. No evidence emerged for a need to lower the "Critical Level for Ozone" in risk assessment of forest trees, although sensitive tree parameters did not necessarily reflect a linear relationship to O(3) stress. Exposure-based concepts tended to overestimate O(3) risk under drought, which is in support of current efforts to establish flux-related concepts of O(3) intake in risk assessment.

Interactions of forests with secondary air pollutants: Some challenges for future research

“…Whereas the observed effects on Ponderosa pine and other conifers in California were associated with peak ozone concentrations that exceeded 200 nl l -1 (ppbv) (Miller and McBride, 1998), more recent studies have emphasised the overall increase in ozone concentrations outside major 'episodes', and the potential for chronic injury (Coyle et al, 2003). There have been successful experiments that have moved from the study of young trees (seedlings or saplings) in the laboratory to the field-scale fumigation of adult trees with ozone, recognising that the responses of small, immature plants in a controlled chamber environment may not be a good predictor of effects on forest trees growing in situ (Karnosky et al, 2007b, Matyssek et al, 2007. This recognition of the importance of studying trees in the context of their normal environment is a step towards thinking about potential effects on the forest ecosystem as a whole and not just the major tree species that are the most obvious components.…”

Carbon flux to woody tissues in a beech/spruce forest during summer and in response to chronic O<sub>3</sub> exposure

“…The forest grew on luvisol derived from loess over tertiary sediments with high nutrition and water supply. Long-term mean (1970Long-term mean ( -2000 annual air temperature and rainfall were 7.8 • C and 786 mm, respectively (monitored by Deutscher Wetterdienst at climate station "Weihenstephan", at 4 km distance from the research site; DWD Offenbach, Germany; Matyssek et al, 2007). Scaffoldings and a canopy crane provided access to the tree canopies.…”

Impact of tropospheric ozone on the Euro-Mediterranean vegetation

“…Karnosky et al, 2001Karnosky et al, , 2007Nunn et al, 2002Nunn et al, , 2005Werner & Fabian 2002;Matyssek et al, 2007, 2010a, b andtherein reference). Free-air O 3 fumigation studies on field-grown trees have been conducted for several years at some locations in Europe and the US (Karnosky et al, 2001(Karnosky et al, , 2007Matyssek et al, 2007;Oksanen et al, 2007). All these studies have also shown that enhanced O 3 regimes have the capacity of counteracting the effects of elevated CO 2 and of substantial reduction of the carbon sink strength of woody-plant systems (Matyssek et al, 2010a, b).…”