The effects of vehicle emissions on Pinus sylvestris

Lawton, Katharine Frances (2005) The effects of vehicle emissions on Pinus sylvestris. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

The pollution climate in urban areas, which is now mainly derived from vehicle emissions, is highly complex and variable on a daily and annual basis. As a result, urban vegetation is exposed to a diverse mixture of pollutants, which are likely to affect their physiology, biochemistry and growth. This study looks at the responses to these pollutants of the Scots pine {Pimis sylvestris (L.)), which is commonly found in roadside shelterbelts. Three models were used to study the responses of the trees to vehicle emissions - two field experiments and a controlled environment study in hemispherical glasshouses (Solardomes) at CEH, Bangor. The field studies used trees at two sites along the M6 in Cheshire, one using mature trees from a motorway shelterbelt, and the other juvenile potted trees placed at roadside and non-roadside sites. The Solardome experiments used juvenile trees constantly fumigated with ambient air, or air of a similar pollutant concentration to that found at a busy urban roadside. The studies aimed to establish measures indicative of traffic pollution stress in the trees, to use these measures to determine injury to the trees, and to establish whether other non-pollution stress responses were influenced by prior exposure to pollution. Techniques used to measure atmospheric pollution stress in plants were adapted to pine trees exposed to vehicle pollution. The pollution caused reduced biomass accumulation and needle retention. Wax loss from needles was accelerated, leading to increased needle wettability, and water loss became more rapid. Pollution also caused increased needle asymmetry and membrane permeability. Nitrogen, carbohydrate and metal concentrations were raised, though generally non-significantly. Chlorophyll fluorescence parameters tended to be decreased following exposure to vehicle pollutants and gas exchange mechanisms were altered, with pollution tending to increase stomatal conductance - especially at night. Treatment of trees with additional stresses such as frost or drought caused further stress- specific responses, which often interacted with those caused by pollutants, although responses were highly dependent upon needle age and other environmental factors. Responses to frost, including a reduction in the Fv/Fm ratio and increased membrane permeability, were often greater in polluted needles than those grown in clean air, suggesting that pollution decreased frost tolerance. Drought responses in combination with pollutants appeared more variable, with some drought effects being exacerbated and others ameliorated by exposure to pollution. Many of the observed responses of trees exposed to pollutants alone were similar to those found in previous studies induced by other forms of stress, and indicate a peturbalion of tree metabolism and water retention mechanisms. Such measures could also potentially be used as indicators of traffic-pollution induced stress. However, when pollutants were present in combination with other environmental stresses, responses were altered, and often more severe than in trees exposed to pollutant stress alone. Therefore, Scots pine in urban areas may be more susceptible to damage from pollutants when other stresses are also present, or otherwise benign stresses including frost and drought may affect the reproductive or competitive success of polluted trees more severely than non-roadside individuals.