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

Cumulative ozone uptake (COU, mmolm^-2) and O₃ flux (FO₃, nmolm^-2s^-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 (A_max) ranged between 19.6mmolm^-2 in current-year needles of evergreen conifers and 22.0 6mmolm^-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 5.9nmolm^-2s^-1 in L. decidua and 2.7nmolm^-2s^-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.