{'fraction_non_alphanumeric': 0.02426470588235294, 'fraction_numerical': 0.016176470588235296, 'mean_word_length': 4.510121457489879, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Exposure of mature Norway spruce to ozone in twig-chambers: effects on gas exchange

Little is known about ozone (O 3 ) effects on adult trees in the field, where ecophysiological parameters control pollutant uptake. It was the goal of this study to examine how ambient and above ambient O 3 concentrations affect gas exchange of mature Norway spruce ( Picea abies (L.) Karst.). Therefore, twigs were enclosed in chambers and exposed to different O 3 concentrations for one and two seasons over three years. During winter periods twigs were maintained under ambient conditions. Data from the shade crown of spruce trees at 1000 m a.s.l. are presented. After one and two fumigation periods no clear treatment effects on gas exchange were observed in twigs fumigated with O 3 concentrations ranging from zero up to ambient (A) + 60 ppb. However, O 3 at 90 ppb reduced photosynthesis and conductance. CO 2 response curves indicated that in A + 90 twigs the efficiency of CO 2 uptake was diminished. Observed losses in P n of A + 90 twigs were greater than reductions in conductance indicating that stomatal closure alone did not limit CO 2 uptake. We conclude that ambient and slightly above ambient O 3 concentrations do not alter gas exchange of mature Norway spruce. Therefore, suppositions on O 3 damage on mature spruce trees should be critically questioned.