Greenhouse gas budget of fully vegetated peatland mesocosms

By Evelyn Hudson,2014-12-13 10:41
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Greenhouse gas budget of fully vegetated peatland mesocosms

CAPER 2008





    Felicity Hayes, Harry Harmens and Gina Mills

    Centre for Ecology and Hydrology, Environment Centre Wales, Deiniol Road,

    Bangor, Gwynedd, LL57 2UW. Contact:

    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

    on biodiversity.

    ; We are grateful to Defra and NERC for supporting this study




     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



    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.



    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.



    112 334 S. Benham, M. Broadmeadow , M. Schaub, V. Catalyud , M. Sanz, F. Busotti

    1 Environment and Human Sciences Division, Forest Research, Alice Holt Lodge,

    Farnham, Surrey, UK 2 WSL, Birmensdorf, Zurich, Switzerland 3 CEAM, Valencia, Spain 4 University of Tuscia, Italy

    This study investigated the extent of visible ozone injury in commercial tree nurseries across four countries in Europe, representing the north-west, central and Mediterranean areas. Visible assessments of injury were made from mid summer to the end of the growing season for all ozone sensitive species present. Commercial nurseries were chosen because nursery stocks are irrigated when necessary and therefore are not subject to the same levels of water stress as field species; these plants therefore represent the optimum conditions for assessment of potential risk; a wide range of ozone sensitive species can be assessed at each site; trees are generally smaller reducing the access problems associated with measuring ozone damage on mature forest trees.

    Ozone climate at each of the 13 sites was characterised using a combination of passive and active samplers to enable the estimate of accumulated ozone exposure over a threshold of 40 ppb. (AOT40). Meteorological and ozone monitoring data were used to calculate cumulative ozone flux using the DOSE model. 3

    Ozone injury was observed in all countries demonstrating that the impacts of ozone are not restricted to Central and southern Europe where higher ozone concentrations are experienced. In northern Europe, longer day-length and higher moisture availability compensate for lower concentrations with enhanced stomatal uptake. The most extensive damage was found in Switzerland. The UK showed the least injury with damage confined to the south east of England in late summer. Within the limitations of the project design, the extent of injury reflected ozone exposure expressed as both AOT40 and cumulative ozone stomatal flux. Injury was not -2 observed on sites with an AOT40 less than 12.7 ppm h, with 13.7 mmol mthe

    minimum cumulative ozone flux at which injury was observed.

    This work was part funded by the European Union under Forest Focus regulation (EC)2152/2003 with co-funding by CEAM (Spain), Forestry Commission (UK), Ministry for Forestry (Italy).




    Kerry Dinsmore, Ute Skiba, Mike Billett, Bob Rees

    CEH Edinburgh, Scottish Agricultural College Edinburgh

    Water table depth and temperature are widely cited as important drivers of greenhouse gas fluxes from peatlands. Much previous work has focussed on either CO, CH or 24

    NO though they are rarely considered together. In this study fully vegetated 2

    mesocosms were collected from an ombrotrophic Scottish peatland. The mesocosms were kept outside to mimic natural temperature and light conditions as far as possible. By covering with a clear plastic roof rain water was excluded and water table depth could be controlled. The study was set-up as a repeated measures factorial design. Replicate mesocosms were collected from different vegetation types and microtopographies, including Juncus dominated hummocks, grass dominated

    hummocks and moss dominated hollows, to compare the greenhouse gas budgets of each. The mesocosms were separated into 2 groups subjected to different water table levels (0-5 cm or 30-35 cm below to soil surface). The water table was held static for 3 months then switched for approximately 1 month. During the initial 3 month period CH and NO exchange was measured weekly using static chambers, soil atmosphere 42

    was measured weekly at 2 different depths to see if production within the soil mimicked surface fluxes, and soil water was sampled fortnightly. Soil water samples were then analysed for DOC, DIC, NO and NH. After switching water table levels, 34

    the frequency of measurements increased until surface emissions appeared to stabilise. Preliminary results from the study will be presented.



     11122Kerstin Wedlich, Mike Ashmore, Sylvia Toet, Simon Peacock, Jeremy Barnes

    1: Environment Department, University of York, Heslington, York, YO10 5DD 2: School of Biology and Psychology, University of Newcastle, Newcastle upon Tyne, NE1 7RU

    Few studies to date have considered the long-term effects of ozone on semi-natural plant communities, and especially on the ecosystem processes of communities such as grasslands and wetlands. It has been suggested that long-term ozone exposure may have an impact on carbon and nitrogen cycling, for instance through effects on carbon storage, litter quantity and microbial activity and through increased dark ecosystem respiration and methane emissions. However, there is little data available on such effects in wetland communities, and studies reported to date have been short-term.

    In this study we aimed to assess the effects of elevated ozone on mesocosms taken from a lowland raised bog (Roudsea Wood and Mosses, Cumbria), with vegetation dominated by the peat moss Sphagnum papillosum and Eriophorum vaginatum

    (cotton sedge). The mesocosms were exposed for 3 years to control and elevated levels of ozone in open-top chambers. The control treatment received non-filtered air, whereas the elevated ozone treatment consisted of non-filtered air plus 60 ppb during the growing season, and an increased level of 10 ppb in winter (enhanced levels only for 8 hours during the daytime). Methane emissions, ecosystem respiration, plant and soil responses and litter decomposition were examined. This presentation will focus on effects observed in a harvest carried out at the end of third and final summer of

    exposure, including results of a laboratory study to examine effects of ozone through litter quality and soil water on decomposition.



     1234Jennifer Williamson, Chris Freeman, Gina Mills, Niall McNamara.

     1rd2CEH Bangor & University of Bangor 3 year PhD student, University of Bangor, 34CEH Bangor, CEH Lancaster

    Tropospheric ozone has been known to be an important environmental pollutant since the 1950‟s but it is only recently that its impacts on semi-natural systems have been

    investigated. Wetlands have the potential to be particularly sensitive to the effects of ozone pollution as plants found in that environment are unlikely to be water limited and can keep their stomata open even during hot, sunny afternoons when ozone concentrations are highest. Adverse effects of tropospheric ozone on wetland plants could change the quantity of carbon stored in peat-forming wetlands with wider implications for climate change.

    Peat cores were taken from two contrasting North Wales wetlands and exposed to ozone in the solardomes at CEH Bangor for 20 weeks during the summer of 2007. Ozone concentrations were based on measurements taken in Snowdonia during summer 2006 and each dome followed the same ozone profile but with incremental starting points (see Hayes et al., for details). Exchange of carbon dioxide and

    methane from the peat cores was measured monthly throughout the ozone exposure. At the end of the ozone exposure peat from the cores was used to assess the potential of the cores to produce and consume methane.

    Ozone exposure did not appear to have a direct effect on methane emissions or carbon dioxide uptake from wetlands but both carbon gas fluxes were correlated with ozone-effects on plant physiological status and plant growth. For example, ozone induced reductions in canopy height and root cover occurred with increasing ozone exposure. At the same time, the net flux of methane from bog cores increased and the uptake of carbon dioxide decreased.

Policy implication:

    This study suggests that future ozone impacts on wetland plants could have a

    negative affect on the ability of northern peat-forming wetlands to act as a sink

    for carbon.

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