Alessio G.A., Peñuelas J., De Lillis M., Llusià J. (2008) Implications of foliar terpene content and hydration on leaf flammability of Quercus ilex and Pinus halepensis. Plant Biology. 10: 123-128.EnllaçDoi: 10.1111/j.1438-8677.2007.00011.x
We investigated the implications of foliar hydration and terpene content on leaf flammability in two widely distributed forest species of the Mediterranean basin, Quercus ilex, which does not store terpenes, and Pinus halepensis, a terpene-storing species. The experiments were carried out in plants grown under different water regimes that generated a wide range of foliar hydration and terpene contents. We monitored the temperatures and time elapsed to reach the smoke, pyrolysis and flame phases. Smoke appeared much earlier (37 versus 101 s) and at lower temperatures (96 versus 139 °C) in Quercus ilex than in Pinus halepensis. Quercus ilex reached pyrolysis earlier than Pinus halepensis (278 versus 338 s) but at the same temperature (365-371 °C). There were no significant differences in time elapsed nor in temperature for flammability (386-422 s; 505-487 °C in both species). Quercus ilex had lower water hydration than Pinus halepensis (41 versus 100%) and the leaf content of terpenes in Quercus was three orders of magnitude lower. The results of this study show no differences in the flame phase between the two species and the absence of a significant relationship between temperature and elapsed time of the different flammability phases in relation to monoterpene content; thus indicating that the role of monoterpenes in flammability phases is smaller than that of the water content. This, however, does not exclude the effects of terpene content on plant combustibility and fire propagation once fires start. © 2008 German Botanical Society and The Royal Botanical Society of the Netherlands.
Alessio G.A., Peñuelas J., Llusià J., Ogaya R., Estiarte M., De Lillis M. (2008) Influence of water and terpenes on flammability in some dominant Mediterranean species. International Journal of Wildland Fire. 17: 274-286.EnllaçDoi: 10.1071/WF07038
In the Mediterranean basin, fires are a major concern for forest and shrubland ecosystems. We studied flammability, its seasonality and its relationship with leaf moisture and volatile terpene content and emission in the dominant species of a Mediterranean shrubland and forest in Catalonia (NE Iberian Peninsula). We measured temperatures and time elapsed between the three flammability phases: smoke, pyrolysis and flame, for four seasons. We sampled twice in spring because of an occasional drought period during this season. Flammability had a significant relationship with leaf hydration, in the shrubland and in the forest. Few and only weak correlations were found between terpene content and flammability. In the future, arid conditions projected by climatic and ecophysiological models will increase fire risk through decreased hydration and subsequent increased flammability of the species. © IAWF 2008.
Asensio D., Owen S.M., Llusià J., Peñuelas J. (2008) The distribution of volatile isoprenoids in the soil horizons around Pinus halepensis trees. Soil Biology and Biochemistry. 40: 2937-2947.EnllaçDoi: 10.1016/j.soilbio.2008.08.008
We measured the terpene concentration in pentane and water extracts from soil horizons (litter, organic, top and low mineral) and from roots growing in top and low mineral horizons on a distance gradient from Pinus halepensis L. trees growing alone on a grassland. Terpene concentrations in pentane were higher than in water extracts, although β-caryophyllene showed relatively high solubility in water. The litter and roots were important sources of terpenes in soil. Alpha-pinene dominated in roots growing in both "top" (A1) and "low" (B) mineral horizons (123 ± 36 μg g-1 or 14 ± 5 mg m-2) and roots in low mineral horizon (270 ± 91 μg g-1 or 7 ± 2 mg m-2). Beta-caryophyllene dominated in litter (1469 ± 331 μg g-1 or 2004 ± 481 mg m-2). Terpene concentration in soil decreased with increasing distance to the trunk. This is likely to be related to changes in litter and roots type on the distance gradient from pine to grass and herbs. The relative contributions of all compounds, except α-pinene, were similar in the mineral soils and litter. This suggests that litter of P. halepensis is probably the main source of major terpene compounds. However, long-term emissions of α-pinene from P. halepensis roots might also contribute to α-pinene concentrations in rhizosphere soils. © 2008 Elsevier Ltd. All rights reserved.
Asensio D., Peñuelas J., Prieto P., Estiarte M., Filella I., Llusià J. (2008) Interannual and seasonal changes in the soil exchange rates of monoterpenes and other VOCs in a Mediterranean shrubland. European Journal of Soil Science. 59: 878-891.EnllaçDoi: 10.1111/j.1365-2389.2008.01057.x
Information about soil VOC inventories and exchange rates in different soils is very scarce. Seasonality of soil VOC exchange rates is also largely unknown, despite the increasing interest in some soil volatile compounds, such as monoterpenes, because of their important role in soil ecology. We aimed to explore and quantify soil VOC exchange rates in a Mediterranean shrubland and their seasonality. Measurements of soil VOC exchange were taken using GC-MS and PTR-MS techniques, together with soil temperature, soil moisture and soil CO2 efflux measurements, during two annual campaigns with contrasting precipitation. Methanol, acetic acid, ethyl acetate, acetaldehyde, acetone, C3 and C4 carbonyls (such as methyl ethyl ketone), α-pinene and limonene, showed the highest emission rates. Maximum soil monoterpene emission rates were very low (0.003 nmol m-2 s -1) compared with foliar monoterpene emission rates. The emission rates of the other VOCs were also low (maximum 0.8 nmol m-2 s -1) except for methanol (1.2 nmol m-2 s-1). Maximum soil uptake rates for some VOCs, such as methanol and acetonitrile (ranging from -0.1 to -0.5 nmol m-2 s-1) were, however, comparable with foliar uptake rates. Further studies are needed to corroborate these results and the possible importance of the soil VOC sink in regional chemistry-climate models. Long-term severe drought increased soil monoterpene emission rates in this Mediterranean shrubland. The increases seem to be linked to changes in the soil's physical properties induced by low soil moisture. Unlike monoterpenes, other soil VOC emission rates decreased when soil moisture was low. The results suggest a seasonal control of soil temperature on the emission rates of monoterpenes and other VOCs. The emission rates increase with soil temperature. Positive correlations between the VOC exchange rates and the soil CO2 fluxes suggest that phenology of roots and microorganisms also controls seasonal changes in soil VOCs in this Mediterranean shrubland. © 2008 The Authors.
Kleist E, Dalmaso M, Kiendler-Scharra A, Llusià J, Mentel T, Peñuelas J, Seco R, Tillmann R, Hohaus T, Uerlings R, Wildt J (2008) SOA formation from stress induced emissions . II EGU meeting, Vienna, 2008.
Wildt J, Llusià J, Peñuelas J, Seco R, (et al) (2008) SOA formation from stress induced BVOC emissions I. EGU2008-A-03145 BG2.9-1FR1O-005. EGU 2008 Meeting Vienna, Biogeosciences.
Llusià J, Peñuelas J, Alessio GA, Estiarte M (2008) Contrasting species-specific, compound-specific, seasonal, and inter-annual responses of foliar isoprenoid emissions to experimental drought in a Mediterranean shrubland. International Journal of Plant Sciences. 169: 637–645.
Peñuelas J, Filella I, Estiarte M, Ogaya R, Llusià J, Sardans J, Jump A, Garbulsky M, Carrillo B, Stefanescu C, Lloret F, Terradas J (2008) El canvi climàtic altera i alterarà la vida als ecosistemes terrestres Catalans. L'Atzavara 16: 13-28.
Peñuelas J, Jump A, Sardans J, Filella I, Estiarte M, Ogaya R, Llusià J, Owen S, Lloret F (2008) From Phosphorous and VOCs to Biodiversity: some studies on the effects of global change inspired by Margalef’s legacy. (2008).. In: F. Valladares, A. Camacho, A. Elosegi, C. Gracia, M. Estrada, J.C. Senar, J.M. Gili (eds.), Unity in Diversity. Reflection s on Ecology after the legacy of Ramon Margalef, pp. 83-94. Fundación BBVA, Bilbao.
Rapparini F., Llusià J., Peñuelas J. (2008) Effect of arbuscular mycorrhizal (AM) colonization on terpene emission and content of Artemisia annua L.. Plant Biology. 10: 108-122.EnllaçDoi: 10.1055/s-2007-964963
Plant roots interact with a wide variety of rhizospheric microorganisms, including bacteria and the symbiontic arbuscular mycorrhizal (AM) fungi. The mycorrhizal symbiosis represents a series of complex feedbacks between plant and fungus regulated by their physiology and nutrition. Despite the widespread distribution and ecological significance of AM symbiosis, little is known about the potential of AM fungi to affect plant VOC metabolism. The purpose of this study was to investigate whether colonization of plant roots by AM fungi and associated soil microorganisms affects VOC emission and content of Artemisia annua L. plants (Asteraceae). Two inoculum types were evaluated: one consisted of only an arbuscular mycorrhizal (AM) fungus species (Glomus spp.), and the other was a mixture of different Glomus species and associated soil bacteria. Inoculated plants were compared with non-inoculated plants and with plants supplemented with extra phosphorus (P) to obtain plants of the same size as mycorrhizal plants, thus excluding potentially-confounding mycorrhizal effects on shoot growth. VOC emissions of Artemisia annua plants were analyzed by leaf cuvette sampling followed by off-line measurements with pre-concentration and gas chromatography mass spectrometry (GC-MS). Measurements of CO2 and H2O exchanges were conducted simultaneously. Several volatile monoterpenes were identified and characterized from leaf emissions of Artemisia annua L. by GC-MS analysis. The main components identified belong to different monoterpene structures: α-pinene, β-pinene, camphor, 1,8-cineole, limonene, and artemisia ketone. A good correlation between monoterpene leaf concentration and leaf emission was found. Leaf extracts included also several sesquiterpenes. Total terpene content and emission was not affected by AM inoculation with or without bacteria, while emission of limonene and artemisia ketone was stimulated by this treatment. No differences were found among treatments for single monoterpene content, while accumulation of specific sesquiterpenes in leaves was altered in mycorrhizal plants compared to control plants. Growth conditions seemed to have mainly contributed to the outcome of the symbiosis and influenced the magnitude of the plant response. These results highlight the importance of considering the below-ground interaction between plant and soil for estimating VOC emission rates and their ecological role at multitrophic levels. © 2007 German Botanical Society and The Royal Botanical Society of the Netherlands.
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