Supervisors: C.
N. Hewitt and G. Kerstiens
The neglect of emissions of volatile organic compounds (VOCs) from vegetation can lead to substantial underestimate of the ultimate release of carbon from tropical rainforests to the atmosphere (Critzen et al., 1999). VOC fluxes from northern European forests are also significant in the context of carbon cycling and tropospheric chemistry. It is therefore important to measure VOC emissions from typical UK tree species in controlled conditions representing present and future climate change scenarios.
In this project we wish to determine the effect of elevated CO2 concentrations on VOC emissions from typical UK woodland tree species growing in solar domes and to assess the overall contribution of VOC emissions to carbon cycling. The hypotheses to be tested are
(1) that elevated CO2 concentrations will effect the net emission of VOCs from emitting tree species and that VOC emission fluxes under future climate change scenarios can be predicted
(2) that this will affect the contribution of emitted VOC-carbon (VOC-C) to the tree species’ total carbon budget in present and future climate scenarios.
It is well known that VOCs have important roles to play in the tropospheric chemistry of ozone and aerosols and data obtained from this study could also be used as input to models to predict ozone and aerosol formation in climate change scenarios.
Many plant species emit VOCs and while the amount of carbon released by photosynthesising plants in the form of VOCs varies, it can account for 5% or more of assimilated CO2-C (e.g. Guenther et al., 1995). VOC emissions are known to depend on temperature and light in the short term, but there are also longer term environmental controls which are still not sufficiently researched to incorporate into predictive algorithms (Guenther, 1997). In particular, the long term effect of elevated CO2 on biogenic VOC emissions is still unknown. Isolated studies describe the effect of elevated CO2 concentrations on emissions of these compounds from North American and Mediterranean plant species, and unpublished data from this laboratory show an effect of elevated CO2 on VOC emissions from Sitka spruce. However, there is no published work to date on the effect of elevated CO2 concentrations on VOC emissions from north European tree species. In the work proposed here, base emission rates at ambient and elevated CO2 concentrations will be used to estimate the contribution of emitted VOC-C to UK tree species C budgets and to predict VOC emission fluxes in present and future climate scenarios. Added value will be obtained by using the VOC emission measurements in the solar dome experiments to extend the current UK biogenic VOCs emission inventory to future environmental conditions, with changes predicted for temperature, ambient CO2 concentrations and plant species distribution.
Samples will be taken and analysed using techniques that have been used routinely by this laboratory for many years (e.g. Owen et al., 1998). Four types of measurements are envisaged; (1) Tree species growing in various CO2 concentrations in the solar domes will be screened quantitatively for emissions of VOCs. Emission rates will be made at standard temperature and light conditions to give a direct estimate of “normalised” or “base” emission rates for each emitted compound; (2) Diurnal and seasonal courses of VOC emissions would be made in solar dome ambient conditions to complement the measurements made for the proposal described in form RG1; (3) Emissions of VOCs from the soil used for the solar dome experiments will be measured using a soil cuvette; (4) A short screening exercise will take place in field conditions at sites local to Lancaster University, where VOC emission samples will be taken from tree species used in the solar dome experiments. This will provide support data from mature specimens of the tree species studied in the solar domes, and will facilitate the extension of the UK biogenic emissions database.
The VOC emission measurements will be complemented by estimates of plant
lifetime C losses obtained from the ‘missing biomass’ determined by comparison
of average instantaneous, leaf level water use efficiency (from measurements
of plant tissue carbon isotope ratio) and actual transpiration efficiency
(deduced from lifetime water consumption and biomass at final harvest)
(Picon et al., 1996).
References:
Crutzen, P.J. et al., 1999, Nature, 399, 535.
Guenther, A., 1997, Ecological Applications, 7, 34-45.
Guenther, A.B., Hewitt, C.N. et al, 1995, Journal of
Geophysical Research, 100, 8873-8892.
Owen, S.M., Hewitt, C.N. et al., 1998, Journal of Geophysical
Research, 103, 25499 – 25511.
Picon, C., Guehl ,J.M., Aussenac, G., 1996, Annales des
Sciences Forestieres 53, 431-446.
Last update: 25/01/2002