Diagnostic parameters for selecting against novel spruce (Picea abies) decline: II. Response of photosynthesis and transpiration to acute NOx exposures

The dose- and time-response effects of sequential 3 h+3 h NO→NO₂ day time exposures 0–9 μl l^?1 (ppm) NO, 0–7.5 μl l^?1 NO₂] followed by 3 h+3 h NO→NO₂ night-time exposures (0–9.5 μl l^?1 NO, 0–9 μl l^?1 NO₂) on photosynthesis, transpiration and dark respiration were examined for nine Carpatho-Ukrainian (‘Rachovo’) half-sib families and for two populations, one from the FRG (‘Westerhof’) and one from the GDR (‘Schmiedefeld’) of Norway spruce Picea abies (L.) Karst.], all in their 4th growing season. In a second exposure series the exposure sequence was reversed. None of the treatments induced needle scorching. The higher NO_x (NO or NO₂) concentrations reduced photosynthesis and transpiration within 1 h. The physiology of the different spruce types was affected significantly differently, the most sensitive spruce having its photosynthesis suppressed 6.6 times and its transpiration 5.5 times more than the most tolerant. ‘Westerhof’ was more sensitive to NO₂ than the average ‘Rachovo’ half-sibs. The gradients of different photosynthesis and transpiration sensitivities among the half-sibs (and ‘Westerhof’) demonstrated a significant, positive, mutual correlation, but significant negative correlations with the gradient of novel decline symptoms among their parents growing in Danish forests. The relative photosynthesis and transpiration sensitivies may thus serve as diagnostic parameters for laboratory selection of the most resistant trees to novel spruce decline. The average NO₂ flux density was three times larger than the average NO flux density. Only for NO₂ and in light was stomatal NO_x uptake larger than the total NO_x uptake. Both night transpiration and dark respiration were stimulated by high concentrations of night NO_x, preceded by day NO_x exposures.