Foliage type specific susceptibility to ozone in Picea abies, Pinus cembra and Larix decidua at treeline: A synthesis

Cumulative ozone uptake (COU, mmol m−2) and O3 flux (FO3, nmol m−2 s−1) were related to physiological, morphological and biochemical characteristics of field-grown mature evergreen Norway spruce [Picea abies (L.) Karst.], Cembran pine [Pinus cembra L.], and deciduous European larch [Larix decidua Mill.] trees at treeline. The threshold COU causing a statistically significant decline in photosynthetic capacity (Amax) ranged between 19.6 mmol m−2 in current-year needles of evergreen conifers and 22.0 6 mmol m−2 in short-shoot needles of deciduous L. decidua subjected to exposure periods of ≥84 and ≥43 days, respectively. The higher O3 sensitivity of deciduous L. decidua than of evergreen P abies and P. cembra was associated with differences in FO3 and specific leaf area (SLA), both being significantly higher in L. decidua. FO3 was 5.9 nmol m−2 s−1 in L. decidua and 2.7 nmol m−2 s−1 in evergreen conifers. Species-dependent differences were also related to detoxification capacity expressed through total surface area based concentrations of reduced ascorbate and α-tocopherol that both increased with SLA. Findings suggest that differences in O3 sensitivity between evergreen and deciduous conifers can be attributed to foliage type specific differences in SLA, the latter determining physiological and biochemical characteristics of the treeline conifers.

► Ozone injury results from an imbalance between ozone uptake and detoxification.
► Ozone sensitivity of treeline associated conifers appears to depend on foliage type.
► Deciduous larch is more susceptible to ozone than evergreen spruce and pine.
► This is due to differences in ozone uptake and surface area based defense capacity.
► Specific leaf area can explain differences in ozone sensitivity between species.