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Title: A mechanistic study of the implications of ozone and drought effects on vegetation for global warming
Author: Wagg, Serena Keri
Awarding Body: Lancaster University
Current Institution: Lancaster University
Date of Award: 2012
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The effects of increasing background ozone on plant physiology, biochemistry and ecology is of growing concern as tropospheric ozone concentrations are predicted to continue to rise throughout this century in many regions in the Northern Hemisphere principally due to transboundary transport of precursor emissions from Asia and America. Alongside predicted ozone increases, climate models indicate more frequent global drought events. The aim of this study was to investigate the impacts of increasing background ozone in combination with reduced soil moisture availability on the mechanisms of ozone damage, principally with regard to impairment of stomatal response to closing stimuli. Mesotrophic grassland species, Dactylis glomerata, Ranunculus dcris, and Geranium sylvaticum, and ozone-sensitive and tolerant genotypes of a bioindicator species, Phaseolus vulgaris, commonly used in the International Cooperative Programme on the effects of air pollution on crops and (semi-) natural vegetation, were used to determine ozone effects in experiments using solardomes. A significant reduction in below-ground carbon allocation with increasing ozone was found for D. glomerata and R. Acris; this effect was the same and enhanced respectively, when in combination with reduced water availability, indicating loss of root sink strength, particularly in response to carbon fixation. Additional effects of elevated ozone included delayed flowering and seed-head production and reduced above-ground biomass for G. Sylvaticum and reduced pod yield for P. vulgaris. Furthermore, for some species studied (D. glomerata and R. acris) elevated ozone corresponded with an increase in stomatal conductance, in contrast to a decrease reported in several previous studies, and shown here for G. sylvaticum, indicating loss of stomatal control in these species. In addition to these effects, which can be directly related to species fitness, for D. glomerata (and to a lesser extent R. acris), a loss of stomatal sensitivity to soil drying and other environmental stimuli was observed in elevated ozone conditions. Further investigation of this, particularly of the reduced response to soil drying, and using the species, P. vulgaris indicated that this was due to a reduction in sensitivity to ABA in elevated ozone conditions, as there was a reduced response to exogenously applied ABA and reduced leaf ABA content in the ozone-sensitive but not ozone-resistant P. vulgaris. Implications for these reduced responses of stomatal conductance to environmental stimuli for the individual species concerned are varied and it is possible that this could be advantageous in the short term, but deleterious if the stress is maintained. Evidence of this was found for D. glomerata, where initially above ground biomass was stimulated with elevated ozone, but as the treatment continued, subsequently the above-ground biomass was substantially reduced. In a wider context, reduced response of stomatal conductance to environmental stimuli under elevated ozone conditions could influence predicted effects of Dynamic Vegetation Models and General Circulation Models, which assume reduced leaf gas exchange under elevated ozone and a 'normal' response to environmental stimuli, therefore these models may need to take account of this to improve accuracy when predicting effects in future ozone and CO2 scenarios. In addition, the findings here indicate that increased plant transpiration under elevated ozone concentrations could potentially influence catchment scale hydrology as soil moisture content would be reduced.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available