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Influence of ammonia and ozone on stress sensitivity of forest trees


The objective is to investigate the effects of the interaction of ammonia and ozone on physiological processes in forest trees.

The effects of ammonia and ozone, singly and in combination, will be determined on Fagus sylvatica and Pinus sylvestris seedlings. This will permit the identification of any interactions between the 2 pollutants with respect to the performance of these species. Performance will be assessed in terms of tree growth, gas exchange, root and mycorrhizal characteristics, and visible injury. The effects of the pollutants in changing the sensitivity of the plants to drought and frost injury will also be examined. Dose response data will be obtained for ammonia in at least one experiment using 6 concentrations of pollutants which will enable the identification of a threshold for adverse effects. 2 summer experiments will examine the effects of 2 levels of ammonium added to the soil in changing responses to ozone. 3 experiments will determine the impact of fumigation over winter with ammonia on subsequent exposure during the early summer to a high level of ozone. A further 2 experiments will examine the interaction b tween ozone and ammonia in the summer on plants which have been fumigated over winter with ammonia. One experiment will be performed under controlled environment conditions in which plants will be subjected to the following replicated treatments: ammonia; ozone; ammonia and ozone; and clean air. This will enable the clear identification of the nature and magnitude of any ammonia and ozone interactions in the absence of confounding influences induced by changing ambient environmental conditions. This gives a total of 8 major fumigation experiments to be carried out at Imperial College and IPO, Wageningen.

The physiological basis of the macroscale effects of ammonia, ozone and their mixture, and interactions with other environmental stresses will be determined by detailed studies of a range of key metabolites in the fumigated material. These will be aimed primarily at testing the hypothesis that there is an antagonistic ammonia and ozone interaction.

7 of the fumigation experiments will be performed in 2 sets of open top chambers, situated at Imperial College and IPO, with the single controlled environment fumigation at IPO. Full growth analyses will be performed at the end of periods of prolonged fumigation with ammonia, ozone or ammonia with ozone (concurrently or sequentially). Gas exchange will be measured as appropriate and related to growth measurements and possible alterations in drought sensitivity. At IPO, the influence of pollutant exposure on frost sensitivity will be determined, using controlled freezing treatments.

The controlled environment experiment will also incorporate a drought treatment to examine any interaction with the 2 pollutants, singly and in combination. All material from the fumigation experiments will be examined microscopically for effects on root characteristics, including mycorrhizal associations. Plants from Imperial College will be analysed for polyamines, lignin phenolics and peroxidases. Material from IPO will be analysed for key nitrogen metabolites including nitrate, nitrite, ammonium, organic nitrogen compounds, amino acids, polyamines and protein content. In addition pH and buffer capacity measurements will be made. Chlorophylls will be analysed by spectrophotometry.


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Campus at Silwood Park, Road A329 (Virginia Water
United Kingdom

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