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.
Bartomeus I., Bosch J., Vilà M. (2008) High invasive pollen transfer, yet low deposition on native stigmas in a Carpobrotus-invaded community. Annals of Botany. 102: 417-424.EnllaçDoi: 10.1093/aob/mcn109
• Background and Aims: Invasive plants are potential agents of disruption in plant-pollinator interactions. They may affect pollinator visitation rates to native plants and modify the plant-pollinator interaction network. However, there is little information about the extent to which invasive pollen is incorporated into the pollination network and about the rates of invasive pollen deposition on the stigmas of native plants. • Methods: The degree of pollinator sharing between the invasive plant Carpobrotus affine acinaciformis and the main co-flowering native plants was tested in a Mediterranean coastal shrubland. Pollen loads were identified from the bodies of the ten most common pollinator species and stigmatic pollen deposition in the five most common native plant species. • Key Results: It was found that pollinators visited Carpobrotus extensively. Seventy-three per cent of pollinator specimens collected on native plants carried Carpobrotus pollen. On average 23% of the pollen on the bodies of pollinators visiting native plants was Carpobrotus. However, most of the pollen found on the body of pollinators belonged to the species on which they were collected. Similarly, most pollen on native plant stigmas was conspecific. Invasive pollen was present on native plant stigmas, but in low quantity. • Conclusions: Carpobrotusis highly integrated in the pollen transport network. However, the plant-pollination network in the invaded community seems to be sufficiently robust to withstand the impacts of the presence of alien pollen on native plant pollination, as shown by the low levels of heterospecific pollen deposition on native stigmas. Several mechanisms are discussed for the low invasive pollen deposition on native stigmas. © The Author 2008. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved.
Bartomeus I., Vilà M., Santamaría L. (2008) Contrasting effects of invasive plants in plant-pollinator networks. Oecologia. 155: 761-770.EnllaçDoi: 10.1007/s00442-007-0946-1
The structural organization of mutualism networks, typified by interspecific positive interactions, is important to maintain community diversity. However, there is little information available about the effect of introduced species on the structure of such networks. We compared uninvaded and invaded ecological communities, to examine how two species of invasive plants with large and showy flowers (Carpobrotus affine acinaciformis and Opuntia stricta) affect the structure of Mediterranean plant-pollinator networks. To attribute differences in pollination to the direct presence of the invasive species, areas were surveyed that contained similar native plant species cover, diversity and floral composition, with or without the invaders. Both invasive plant species received significantly more pollinator visits than any native species and invaders interacted strongly with pollinators. Overall, the pollinator community richness was similar in invaded and uninvaded plots, and only a few generalist pollinators visited invasive species exclusively. Invasive plants acted as pollination super generalists. The two species studied were visited by 43% and 31% of the total insect taxa in the community, respectively, suggesting they play a central role in the plant-pollinator networks. Carpobrotus and Opuntia had contrasting effects on pollinator visitation rates to native plants: Carpobrotus facilitated the visit of pollinators to native species, whereas Opuntia competed for pollinators with native species, increasing the nestedness of the plant-pollinator network. These results indicate that the introduction of a new species to a community can have important consequences for the structure of the plant-pollinator network. © 2007 Springer-Verlag.
Beier C., Emmett B.A., Peñuelas J., Schmidt I.K., Tietema A., Estiarte M., Gundersen P., Llorens L., Riis-Nielsen T., Sowerby A., Gorissen A. (2008) Carbon and nitrogen cycles in European ecosystems respond differently to global warming. Science of the Total Environment. 407: 692-697.EnllaçDoi: 10.1016/j.scitotenv.2008.10.001
The global climate is predicted to become significantly warmer over the next century. This will affect ecosystem processes and the functioning of semi natural and natural ecosystems in many parts of the world. However, as various ecosystem processes may be affected to a different extent, balances between different ecosystem processes as well as between different ecosystems may shift and lead to major unpredicted changes. In this study four European shrubland ecosystems along a north-south temperature gradient were experimentally warmed by a novel nighttime warming technique. Biogeochemical cycling of both carbon and nitrogen was affected at the colder sites with increased carbon uptake for plant growth as well as increased carbon loss through soil respiration. Carbon uptake by plant growth was more sensitive to warming than expected from the temperature response across the sites while carbon loss through soil respiration reacted to warming in agreement with the overall Q10 and response functions to temperature across the sites. Opposite to carbon, the nitrogen mineralization was relatively insensitive to the temperature increase and was mainly affected by changes in soil moisture. The results suggest that C and N cycles respond asymmetrically to warming, which may lead to progressive nitrogen limitation and thereby acclimation in plant production. This further suggests that in many temperate zones nitrogen deposition has to be accounted for, not only with respect to the impact on water quality through increased nitrogen leaching where N deposition is high, but also in predictions of carbon sequestration in terrestrial ecosystems under future climatic conditions. Finally the results indicate that on the short term the above-ground processes are more sensitive to temperature changes than the below ground processes. © 2008 Elsevier B.V. All rights reserved.
Belmonte J., Alarcón M., Avila A., Scialabba E., Pino D. (2008) Long-range transport of beech (Fagus sylvatica L.) pollen to Catalonia (north-eastern Spain). International Journal of Biometeorology. 52: 675-687.EnllaçDoi: 10.1007/s00484-008-0160-9
Local and long-range transport of beech (Fagus sylvatica) pollen was analysed by using 23-year data (1983-2007) at six stations in Catalonia, Spain, and numerical simulations. Back trajectories and synoptic meteorology indicated a consistent north European provenance during beech pollen peak days. Specifically, the area from northern Italy to central Germany was the most probable source, as indicated by a source-receptor model based on back trajectories. For the event with the highest pollen levels (17 May 2004), back trajectories indicated a source in the Vosges (NE France) and the Schwarzwald (SW Germany) regions. By applying a mesoscale model (MM5) to this event, pollen transport could be further refined, allowing its entrance to Catalonia through the lower easternmost pass of the Pyrenees (the Alberes pass, 500 m a.s.l.) to be described. Hourly counts of Fagus pollen allowed the timing of pollen arrival during this episode to be matched with the model results regarding the above-mentioned passage. This study may help to interpret some results of modern beech genetic diversity and contribute to the understanding of paleopalynological records by taking long-range transport into consideration. © 2008 ISB.
Blanes I., Zabala A., Moré G., Pons X., Serra-Sagristà J. (2008) Classification of hyperspectral images compressed through 3D-JPEG2000. Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics). 5179 LNAI: 416-423.EnllaçDoi: 10.1007/978-3-540-85567-5-52
Classification of hyperspectral images is paramount to an increasing number of user applications. With the advent of more powerful technology, sensed images demand for larger requirements in computational and memory capabilities, which has led to devise compression techniques to alleviate the transmission and storage necessities. Classification of compressed images is addressed in this paper. Compression takes into account the spectral correlation of hyperspectral images together with more simple approaches. Experiments have been performed on a large hyperspectral CASI image with 72 bands. Both coding and classification results indicate that the performance of 3d-DWT is superior to the other two lossy coding approaches, providing consistent improvements of more than 10 dB for the coding process, and maintaining both the global accuracy and the percentage of classified area for the classification process. © 2008 Springer-Verlag Berlin Heidelberg.
Bosch J. (2008) Production of undersized offspring in a solitary bee. Animal Behaviour. 75: 809-816.EnllaçDoi: 10.1016/j.anbehav.2007.06.018
As predicted by Conditional Sex Allocation Theory, females of the solitary bee Osmia cornuta exposed to scarce floral resources biased their progeny sex ratio towards males, the least costly sex, and produced smaller-than-average females. Surprisingly, nesting females also produced a number of 'tiny' offspring, which contrasted with regular-sized offspring within the same nest. Developmental and wintering mortality are strongly size dependent in O. cornuta, and a high proportion of tiny offspring did not survive. This result is in disagreement with Optimal Allocation Theory, according to which resources should be allocated in portions that maximize fitness returns. I ask why did O. cornuta females build tiny provisions and why did they lay female eggs (with lower survival probability than male eggs) on these provisions. I argue that egg maturation rates and selective pressure to avoid kleptoparasitism and provision desiccation in cells left unsealed for long periods may impose a limit to the time available for cell provisioning. Under low food availability, this limit will be reached before provision sizes resulting in maximum fitness returns are attained. I also argue that the decision to fertilize an egg (and thus produce a female) is made at the beginning of the cell-provisioning process, so that females cannot adjust offspring sex to provision size. At the same time, altering the female-male cell sequence within a nest would result in fratricide because of protandric emergence. I provide evidence supporting these ecological and physiological constraints on resource allocation decisions in O. cornuta. © 2007 The Association for the Study of Animal Behaviour.
Bosch J., Sgolastra F., Kemp W.P. (2008) Life Cycle Ecophysiology of Osmia Mason Bees Used as Crop Pollinators. Bee Pollination in Agricultural Ecosystems. : 0-0.EnllaçDoi: 10.1093/acprof:oso/9780195316957.003.0006
Several solitary bee species in the genus Osmia have been studied as potential pollinators of fruit trees and other early-blooming crops. Methods to manage large populations in agro-ecosystems have been developed for at least three species. This chapter reviews current knowledge on the life cycle of Osmia and emphasizes the need to establish a solid ecophysiological basis to develop adequate rearing methods for these species. Two phenological events - the timing of adult diapause in the autumn, and the timing of emergence in the spring - require particular attention when managing Osmia populations. The timing of adult diapause is critical because prewintering temperatures have a profound effect on fat body depletion, winter survival, and vigor at emergence. Timing of emergence and its synchronization with bloom of the target crop is important to maximize pollination and production of bee progeny. Both events can be adjusted with proper temperature management. © 2008 by Oxford University Press, Inc. All rights reserved.
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