IMPACTS OF INCREASING BACKGROUND OZONE CONCENTRATION
ON INTERSPECIES COMPETITION IN GRASSLANDS
Felicity Hayes, Harry Harmens and Gina Mills
Centre for Ecology and Hydrology, Environment Centre Wales, Deiniol Road,
Bangor, Gwynedd, LL57 2UW. Contact: firstname.lastname@example.org
Species from UK grasslands were exposed to ozone in the solardomes at CEH Bangor for 20 weeks to investigate the effects of increased background ozone concentration in the absence of „peaks‟ of ozone. This represents changes in ozone profile predicted for the UK due to projected increased background concentrations in the northern hemisphere following increased industrial development and car use in Asia. Two-species mixtures of Leontodon hispidus grown with Dactylis glomerata,
Anthoxanthum odoratum or Poa pratensis were used. Ozone exposure was based on
an upland profile from Snowdonia and the treatments used were ambient air (AA), AA-20 ppb ozone, AA+12, AA+24, AA+36, AA+48, AA+60 and AA+72.
Communities were cut back to 6cm mid-way through the exposure, but not at the end – plants were left to die back naturally.
Earlier and increased senescence occurred with increasing background ozone treatment for all species, with increases evident as the mean ozone concentration exceeded the current Snowdonia ambient concentration of 40 ppb. The magnitude of response of Leontodon hispidus was influenced by the competing species, with largest effects occurring when grown in competition with less vigorous P. pratensis,
intermediate effects with the intermediate competitior A. odoratum and least effects
when grown with the vigorous competitor Dactylis glomerata.
No differences in canopy height were found following ozone exposure, however, large reductions in root biomass of Leontodon hispidus plants grown individually
occurred after exposure to the ozone regime for 16 weeks. The cover of each species has also been non-destructively assessed at the end of the exposure period and will be re-assessed in 2008. It is likely that re-growth of the Leontodon plants will be
affected in 2008 and this may influence the competition with the grasses in the community.
Sampling of ozone within the plant canopy showed a diurnal profile of ozone concentration at the beginning of the exposure period, however this decreased and was eventually lost as the growing season progressed. This corresponded with increased senescence within the plant canopy, rather than changes in canopy density. This will be investigated further during exposure in 2008. Impacts of ozone on stomatal functioning and post-exposure carbon cycling are described by Mills et al. in
the following paper.
This study has relevance to Defra policy as:
; Significant effects on widespread species were found with only small
increases in current background ozone concentrations.
; Community composition may be affected which may ultimately have an effect
; We are grateful to Defra and NERC for supporting this study
OZONE IMPACTS ON STOMATAL CONTROL AND CARBON TURNOVER,
CARRY-OVER EFFECTS DURING THE WINTER
1*2*113Gina Mills, Kirsten Wyness, Felicity Hayes, Laurence Jones, Paul Hill, Davey 34445Jones, Sally Wilkinson, Russell Sharpe, Bill Davies, Simon Peacock and Jeremy 5 Barnes1 2stCEH Bangor,1 year PhD student (CEH, University of Newcastle, University of 345Bangor),Univeristy of Bangor, University of Lancaster,University of Newcastle.
This paper summarises recent progress with ongoing collaborative research into understanding the mechanisms behind the responses of grasslands to rising background ozone concentration presented in the previous paper (Hayes et al.).
During the last few weeks of the 20 week exposure, the emphasis of the mechanistic study was on quantifying the effects of ozone on stomatal functioning of leaves that had developed in the eight ozone profiles (representing pre-industrial to predicted post-2100 conditions). Clear evidence emerged that increasing background ozone increasingly impairs stomatal functioning. Under comparable climatic conditions, stomatal conductance increased with increasing ozone concentration for non-senesced inner canopy leaves of Dactylis glomerata and Leontodon hispidus, with the current
ambient treatment being an approximate threshold for this effect. Leaves exposed to rising background ozone were also less able to close their stomata when severe water stress was imposed. This may possibly be due to a lack of response to the plant hormone, abscisic acid (ABA). Unlike in the ambient – 20 ppb treatment and the
ambient + 24ppb treatment, Leontodon hispidus leaves from the ambient + 60 ppb
treatment failed to close their stomata in response to feeding with ABA.
The premature senescence of older foliage due to ozone damage and decreased carbon storage in below ground tissue observed during the summer (see Hayes et al.) may
have ongoing influence in the root-soil interface over winter, and during the next growing season, even after removal of the pollutant from the system. Therefore, ozone may have long-term and cumulative detrimental effects on microorganism communities, soil structure and the potential for carbon sequestration. Some of these effects are currently being studied for over-wintering plants; the results will be presented at CAPER. In addition, research at an open field release site at Keenley, Northumberland aims to address the long-term combined effects of ozone and nitrogen on carbon allocation below ground in the field situation, where plants are growing in natural soils in competition. This will be complimented by controlled environment and solardome studies at Bangor and Newcastle to further elucidate the mechanisms involved in ozone effects on C storage and turnover. The policy implications of this work are:
; Rising background ozone may impair the ability of plants to respond to
drought by closing their stomata
; Implications for ozone and CO fluxes require further study 2
* We are grateful to Defra and NERC for supporting this study
IMPACTS OF OZONE ON UPLAND GRASSLAND AND HEDGEROW
Simon Peacock and Jeremy Barnes
Institute for Research on Environment and Sustainability, Newcastle University,
Newcastle-upon-Tyne, NE1 7RU
We will present an update of ongoing DEFRA-funded work investigating impacts of present and future (2050) upland ozone climates on productivity and species composition of i) long-established upland mesotrophic (NVC MG3b) grassland mesocosms, representative of contrasting management regimes, and ii) a legume-rich, fixed-dune (NVC SD9) grassland community.
We will also report on interim results of an OTC experiment investigating a range of simulated present-day versus future UK spring ozone climates on several UK spring bulb species (Liliaceae) found in woodland, wood margins and hedgerows.
Finally, we will introduce a study to examine the impact of a range of ozone climates on the hemi-parasitic annual, Rhinanthus minor, and potential interactions with two
host plants (Lolium perenne and Phleum pratense) of contrasting ozone sensitivity.
IMPACTS OF OZONE ON NATURAL VEGETATION: ARE WE BARKING
UP THE WRONG TREE?
Chris Callaghan and Jeremy Barnes
Environmental and Molecular Plant Physiology, IRES: Biology Division, Newcastle
University. NE1 7RU.
Easily measurable surrogates are often used to determine the impacts of ozone on vegetation, but are the parameters we elect to measure (e.g. size, visible injury, senescence etc.) of any value whatsoever in the prediction of plant responses? In the present study we sought to screen a population of Arabidopsis (Nok-3 x Ga-0) for
„ozone sensitivity‟ in a bid to map regions of the genome determining ozone-related
traits. As a first step, it was necessary to screen candidate parents in order to elect for a cross likely to exhibit the greatest span of genetic variation in „ozone
responsiveness‟. As part of this exercise we explored the value of a variety of commonly-adopted measurements as a surrogate for effects on seed yield (the parameter of greatest relevance as a measurement of „ozone sensitivity‟ in this short-
lived species). It proved unreliable to use any surrogates to determine the effects of ozone on seed yield. Subsequent QTL studies identified several strong candidate genes determining ozone effects on growth and seed yield, the nature and function of these genes will be discussed.