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Title: Physiological responses and susceptibility of plants to atmospheric ammonia pollution
Author: Soares, Adrian
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 1996
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A range of physiological responses of higher plants and mosses to atmospheric ammonia (NH3) and ammonium (NH4+) (collectively NHx), were investigated. Foliar uptake of NHx caused an induction of glutamine synthetase and NADP malic enzyme, whereas nitrate reductase activity was inhibited. The concentration of organic acids also declined, particularly malate and citrate. Net photosynthesis and stomatal conductance were also stimulated following uptake of NHx. Physiological responses were the same for both NH3 and NH4+ applications for a number of species. The ability of plants to store nitrogen (N), coupled with NHx assimilation leading to the production of acidity, suggests that pH is an important factor that plants have to control, in the presence of excess NHx. Multivariate assessment of physiological characteristics of higher plants and mosses, provided a means of assessing plant susceptibility to atmospheric NHx and acidity. Plants that are capable of foliar nitrate (NO3-) assimilation have higher buffering capacities against acidity. Plants which assimilate most of their NO3- in the leaf, tend to have high base cation contents, which may also contribute towards overall buffering ability. The total N content of mosses increased after exposure to N containing pollution. In addition, δ15N values varied consistently between mosses collected in rural and urban areas, with being more negative and more positive respectively. δ15N values reflected the predominant N compound present in each area, as well as the level of N pollution. The results suggest that N compounds in the atmosphere, particularly NHx and NOx, have individual 15N signatures, that can be traced in biological material.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available