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Comparative cultivation experiment was carried out in the greenhouse to verify the assumption that increased air CO2 concentration (up to 1000 ppm) stimulates the infection intensity and mortality rate of Scots pine and Norway spruce seedlings subjected to the artificial inoculation with Armillaria ostoyae (Romagn.) Herink. It was found that increased air CO2 concentration reduces the intensity of pine and spruce seedlings infection by A. ostoyae, what was expressed both by the greater number of healthy and lower number of died seedlings at the end of 16−months−long experiment. However, the statistical significance of the observed differences was confirmed in case of only one out of three A. ostoyae isolates used in the experiment. It was also found that during the first 12 months of the experiment growth of pine and spruce seedlings was significantly stimulated by 1000 ppm air CO2 concentration compared to the ambient air conditions (approximately 380 ppm CO2) with not statistically significant effect of A. ostoyae presence. It was manifested for both tree species with significantly higher values of diameter at the stem base in all variants subjected to increased air CO2 concentration. No such difference was observed for the height of seedlings. All the findings suggest that elevated air CO2 concentration may compensate negative impact of disease on growth at the early stages of pathogen attack.
A comparative experiment was carried out in growth chambers to determine the effects of elevated CO2 concentrations (either 760 ppm or 1140 ppm) versus ambient CO2 conditions on the growth of Armillaria ostoyae (Romagn.) Herink rhizomorphs, which is the infectious organ of a fungal pathogen affecting many forest trees. We found that one out of three isolates in the experiment differed significantly in rhizomorph production, which was measured as rhizomorph dry mass/100 days of growth. Rhizomorph production was also affected by the tree species used as a food source in the inoculum preparation, with beech wood being significantly different from oak and hazel. Under higher CO2 regimes the production of rhizomorphs was consistently lower for all three isolates compared to ambient CO2 concentrations. For one isolate (no. 11) the growth differences were significant between 380 ppm and both elevated CO2 concentrations (760 ppm and 1140 ppm), while for the other two (no. 30 and 32) significance was observed only between 380 ppm and 760 ppm. No statistically significant differences have been noted between 760 ppm and 1140 ppm CO2 for these two isolates. It was concluded that elevated concentrations of CO2 inhibited A. ostoyae rhizomorph growth and therefore have the potential to lessen the pathogenicity of the fungus.
An investigation carried out in the Western Carpathian Mountains (Ujsoły, Węgierska Górka, Ustroń and Wisła Forest Districts) demonstrated a strong relationship between dieback in Norway spruce stands and the intensity of occurrence of Armillaria ostoyae.For the most endangered site types – mountain deciduous forest (LG) and mountain mixed forest (LMG), analyses of losses of annual volume increment and of stand productivity were performed, and their financial dimensions determined. The greatest losses – of about 8 m 3 /ha/year for tree stands of the age of 100 years, and 400 m 3 /ha for the rotation period – were found for LG (Mountain broadleaved forest) site type.
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