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Effects of Ground Level Ozone on Vegetation

By J. Neil Cape

Abstract

All the experiments conducted in this project use ozone exposures that either are already currently\ud occurring or are expected to occur over UK uplands this century, if predictions of increasing „background‟\ud ozone exposure are correct. Uplands are particularly vulnerable to such increases, because they are\ud windy and wet – conditions which favour ozone uptake by vegetation. Consequently, the observations on\ud ozone effects on upland plant species are likely to occur in the foreseeable future, if they are not already\ud happening.\ud The novel field ozone exposure system at Keenley Fell (Northumberland) has been operating since spring\ud 2007. Seasonal average increases in ozone exposure at 10 m from the release point were very small in\ud 2007, increasing to around 5 ppb above ambient in 2008 and 2009. The effects of the ozone treatments\ud on this conservation-managed grassland should be seen in the context of this very modest increase in\ud annual mean exposure.\ud Average deposition velocity for ozone at Keenley Fell was between 1 mm/s (night) and 5 mm/s (mid-day),\ud varying with weather conditions. These flux data will assist with the modelling of ozone deposition to\ud upland grasslands. Limited flux measurements for CO2 showed uptake during the day and release at\ud night, as expected, and will contribute to modelling interactions between ozone and carbon fluxes under\ud these conditions.\ud The ozone treatments at Keenley Fell had no effect on total above-ground production in any of the three\ud years. However, there was a cumulative decrease in forb biomass, with an associated change in forb\ud species composition, over the three years. This was accompanied by an increase in grass biomass. These\ud effects of ozone are antagonistic to the objectives of the conservation management at this site.\ud The biomass and flowering of a small number of individual forb species were significantly reduced by\ud ozone exposure at Keenley Fell. Importantly, these species included the hemi-parasite Rhinanthus minor\ud which is frequently used to enhance species diversity in this type of conservation management. Hence,\ud the observed effects of ozone on species composition may partly have been caused through its adverse\ud effects on Rhinanthus .\ud Data compiled from several experiments show adverse effects of ozone on semi-natural plant species at\ud concentrations as low as 30 ppb, with 12 of the species studied showing effects at concentrations below\ud 50 ppbv. Effects on roots were greater than on shoots, with potentially significant implications for\ud overwintering, drought tolerance and carbon sequestration

Topics: Ecology and Environment
Publisher: NERC/Centre for Ecology & Hydrology
Year: 2010
OAI identifier: oai:nora.nerc.ac.uk:11623

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