Diagnostic parameters for selecting against novel spruce (Picea abies) decline: IV. Response of photosynthesis and transpiration to SO2+NO2 exposures

Abstract

The dose‐ and time‐response effects of 3 days of 6 h day‐time sequential exposures to NO2, SO2 and SO2+NO2 of 0.45–1.81 μl l−1 (ppm) SO2 and 1.50–7.65 μl l−1 NO2 on photosynthesis, transpiration and dark respiration were examined for nine Carpatho‐Ukrainian half‐sib families and a population from the GFR (‘Westerhof’) of Norway spruce [Piecea abies (L.) Karst.], all in their 5th growing season.SO2+NO2 inhibited photosynthesis and transpiration and stimulated dark respiration more than SO2 alone. SO2 and SO2+NO2 at the lowest concentrations inhibited night transpiration, but increased it at the highest concentration, the strongest effects being obtained with combined exposures. Photosynthesis of the different half‐sib families was affected significantly differently by SO2+NO2 exposures. NO2 alone had no effects.Sensitivity to transpiration decline correlated negatively with branch density. Height of trees correlated postitively with decline sensitivity in the seed orchard. The distribution of photosynthesis and transpiration sensitivities over all tested half‐sib families correlated negatively with the distribution of decline sensitivity of their parents in a rural Danish seed orchard. The relative photosynthesis and transpiration sensitivities may thus serve as diagnostic parameters for selecting against novel spruce decline.