Valutazione delle interazioni tra composti organici volatili (VOC) ed ozono in foreste sottoposte ad eventi climatici estremi

Responsabili di progetto

Carlo Calfapietra, Otmar Urban

Accordo

REPUBBLICA CECA - CAS (ex AVCR) - Czech Academy of Sciences

Bando

CNR/AVCR 2013-2015

Dipartimento

Terra e Ambiente

Area tematica

Scienze del sistema Terra e tecnologie per l'ambiente

Stato del progetto

Nuovo

Proposta di ricerca

Biogenic volatile organic compounds (BVOC) emitted by plants are mainly isoprenoids, i.e. isoprene, monoterpenes, and sesquiterpenes. The isoprenoids are synthesized from photosynthetic carbon. Trees may emit 2-10% of photosynthetic carbon as isoprene (Monson and Fall, 1989), while but especially under extreme stress conditions this percentage can increase up to 40%. Biosynthesis and emission are strongly influenced by the environment: in particular they increase with increasing light and temperature (Niinemets et al., 2004; Guenther et al., 1995), thus producing higher emissions during spring–summer seasons (Holzinger et al., 2006) when temperatures and ozone concentrations are highest. In contrast, because of their photosynthetic origin, the emission of isoprenoids is inhibited when carbon assimilation is limited by biotic or abiotic stressors such as ozone or drought. Ozone (O3) is an important agent of climate change as it is the third most powerful greenhouse gas after CO2 and CH4. Ozone is also the main pollutant of forest concern because: 1. it is a strong phytotoxic gas, affecting plant physiology, biochemistry and growth; 2. ozone concentrations have doubled since the pre-industrial age and are still increasing at 1-2% annual rate; 3. concentrations are higher at remote (forest) sites than in the cities (Paoletti, 2007). The latter phenomenon is due to a different nitrogen oxides (NOx) composition in urban environments and higher BVOC availability at forest sites. The quick reactivity of isoprenoids, in fact, may stimulate the formation of tropospheric ozone, in addition to two other dangerous pollutants, peroxy and methylperoxy acetyl nitrate (Fehsenfeld et al., 1992), while nitric oxide (NO) contributes to ozone degradation. Ecosystems remove ozone from the atmosphere through both stomatal and non-stomatal deposition. Non-stomatal processes include ozone deposition to any external surface (e.g. soil, stems, cuticles) and gas-phase chemical losses involving reactions between ozone and BVOCs or NO emitted by the ecosystem (Kurpius and Goldstein, 2003). Although we now know a great deal about ozone impacts on forest, a comprehensive assessment of the effects of ozone uptake on carbon exchange and sequestration by forests is still missing. Significant uncertainties are due to parameterisation based on a small number of long-term experiments and neglecting the combined effects of O3, CO2, N deposition, and climate (Royal Society, 2008). Another significant gap of knowledge is ozone impact on canopy water losses. Decline in stomatal conductance is a commonly observed effect of atmospheric ozone, so that the ability of plants to exchange water and CO2 is negatively affected by ozone pollution (Wittig et al., 2007). In contrast, several authors observed that ozone exposure increased transpiration in excised twigs/leaves (e.g. Barnes et al. 1990; Grulke 1990). Paoletti (2005) focused on the dynamics of stomatal responses to ozone exposure and noted that stomatal responses to fluctuating light and abrupt water stress were slowed by ozone. Biotic and abiotic stresses may also elicit qualitative and quantitative changes in the emitted volatiles (Dicke and Baldwin, 2010). Plants communicate by complex bouquets of volatile chemicals that convey information about the plant’s physiological conditions (Niinemets, 2010). Air pollutants can react rapidly with many of the emitted chemicals (Calogirou et al.,1999; Atkinson and Arey, 2003; Pinto et al., 2007, 2010). Reactions between monoterpene and sesquiterpene emissions and ozone have been shown to result in aerosol formation (Virtanen et al., 2010). In particular, ozone reduces the distance over which plant-to-plant communication by volatiles occurs (Blande et al., 2010). Field observations of plant-to-plant communication, however, have only been made over short distances (60cm as a maximum) (Karban et al., 2006). A combination of isoprene and NO is emitted in response to ozone stress and reactions between these emissions and ozone can alleviate oxidative stress (Velikova et al., 2008). There is clearly a need to increase our understanding of the effects ozone has on volatile-mediated ecological processes. The project includes a field experiment where long-term monitoring of carbon, ozone and BVOC fluxes will be carried out and short-term experiments under controlled conditions. The long-term monitoring will be carried out at the Bily Kriz experimental research site (Moravian-Silesian Beskydy Mountains, 49° 33' N, 18° 32' E, NE of Czech Republic, 908 m a.s.l.), where eddy-correlation measurements of carbon and ozone fluxes are in progress inside the CzechGlobe programme (described in details e.g. by Urban et al., 2012) and field laboratory, meteorological station and air quality control station are available (including the measurements of concentrations O3 and NOx). The forest is a monoculture of Picea abies (L.) Karst (Norway spruce); this plant species is known to emit both isoprene and monoterpenes (Kesselmeier and Staudt, 1999). Fluxes of isoprene, monoterpenes and oxidation products will be measured by a gas chromatograph connected with mass-spectrometer (TSQ Quantum XLS-Triple Quadrupole GC-MS/MS, ThermoFisher Scientific, USA) and by a real-time proton-transfer-reaction mass-spectrometer (PTR-MS) during 2-week periods in the growing seasons of Year 2 and of Year 3 of the project using early tested protocols (Karl et al. 2002; Fares et al. in preparation). The timing of the campaigns will be chosen to possibly meet the most extreme conditions in terms of highest temperatures, drought and ozone concentrations (July – August). The PTR-MS will be provided by the National Research Council of Italy (CNR) and the costs covered by this project. In case a PTR-MS can be purchased by CzechGlobe, continuous measurements will be carried out throughout the growing season of year 2 and 3. Two short-term experiments will be carried out: 1. Short-term ozone exposure to be carried out in branch chambers at Bily Kriz. BVOC emissions will be collected by traps and consequently analysed in the laboratory. 2. Campaign for measuring leaf-level stomatal conductance and responses to fluctuating stimuli before and after the ozone exposure carried out in exp.1. A portable gas exchange analyser LICOR-6400 (Li-Cor, USA) and a portable fluorometer PAM-2000 (H.Walz, Germany) will be used for the physiological measurements. Data from different sources will be collated and cross-compared by using sophisticated statistical approaches such as multiple regression models. References Atkinson, R. & Arey, J. (2003). Atmos. Environ. 37, S197–S219. Barnes, J.D., Eamus, D., Davison, A.W., Ro-Poulsen, H., Mortensen, L., (1990). Environmental Pollution 63, 345–363. Blande, J.D., Holopainen, J.K. & Li, T. (2010) Ecol. Lett. 13, 1172-1181. Calogirou, A., Larsen, B.R. & Kotzias, D. (1999). Atmos. Environ. 33, 1423–1439. Dicke, M. & Baldwin, I.T. (2010). Trends Plant Sci. 15, 167-175. Fehsenfeld F., Calvert, J., Fall, R., Goldan, P., Guenther, A. B., Hewitt, C. N., Lamb, B., Liu, S., Trainer, M.,Westberg, H., and Zimmerman, P.: (1992). Global Biogeochemical Cycles, 6, 389–430. Grulke, N.E., (1999). In: Miller, P.R., McBride, J.R. (Eds.), Oxidant Air Pollution Impacts in the Montane Forests of Southern California. Springer-Verlag, New York. Guenther, A., Hewitt, C.N., Erickson, D., Fall, R., Geron, C., Graedel, T., Harley, P., Klinger, L., et al., (1995). Journal of Geophysical Research 100, 8873–8892. Holzinger, R., Lee, A., McKay, M., Goldstein, A.H., (2006). Atmospheric Chemistry and Physics 6, 1267–1274. Karban, R., Shiojiri, K., Huntzinger, M. & McCall, A.C. (2006). Ecology 87, 922–930. Karl, T.G., Spirig, C., Rinne, J., Stroud, C., Prevost, P., Greenberg, J., Fall, R., and Guenther, A.: (2002) Atmospheric Chemistry and Physics, 2, 279–291, 2002, Kesselmeier J and Staudt M, (1999) Journal of Atmospheric Chemistry 33: 23–88. Kurpius, M.R.; Goldstein, A.H. (2003). Geophysical Research Letters 30: 1371. Monson R.K., Fall, R. (1989) Plant Physiol. 90, 267-274. Niinemets, U. (2010) Trends Plant Sci. 15, 145-153. Niinemets, U., Loreto, F., Reichstein, M., (2004). Trends in Plant Science 9, 180–186. Paoletti E.: (2005), Environmental Pollution, 134: 439-445. Paoletti E.: (2007) CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources, 2 (No. 68): 13 pp. Pinto, D.M., Blande, J.D., Nykänen, R.,et al. (2007). J. Chem. Ecol. 33, 683–684. Pinto, D.M., Blande, J.D., Souza, S.R., et al. (2010). J. Chem. Ecol. 36, 22–34. Royal Society (2008). Report 15/8 The Royal Society, London, pp. 132. Urban, O., Klem, K., Ac, A., et al. (2012). Functional Ecology 26, 46–55. Velikova, V., Fares, S. & Loreto, F. (2008). Plant Cell Environ. 31, 1882-1894. Virtanen, A., Joutsensaari, J., Koop, T. et al. (2010). Nature 467, 824-827. Wittig, V. E., Ainsworth, E. A. & Long, S. P. (2007). Plant, Cell and Environment, 30: 1150-1162.

Obiettivi della ricerca

The main aim of this project is to determine the impact of BVOC emissions on the carbon balance of a Norway spruce forest under extreme conditions as those determined by the combination of high temperature, dry conditions and high ozone levels. Short-term experiments will be planned to answer specific cause-effect questions. Specific aims are: 1. to compare the total carbon losses due to BVOC emissions under different stress conditions with a particular focus on the extreme events; 2. to investigate the role of BVOC in the gas-phase reactions of ozone; 3. to determine the impacts of ozone uptake on canopy-level carbon exchange and sequestration; 4. to study canopy water losses due to extreme climatic events; 5. to improve the understanding of BVOC-mediated resistance to abiotic stresses induced by extreme climatic conditions; 6. to provide data for the validation of models about carbon sequestration, trace gas exchange and gas phase chemistry.

Ultimo aggiornamento: 09/05/2025