Barbeta A., Peñuelas J., Ogaya R., Jump A.S. (2011) Reduced tree health and seedling production in fragmented Fagus sylvatica forest patches in the Montseny Mountains (NE Spain). Forest Ecology and Management. 261: 2029-2037.EnllaçDoi: 10.1016/j.foreco.2011.02.029
Habitat fragmentation results in smaller and more isolated populations that may be at higher risk of extirpation or further decline in comparison with their more continuously distributed progenitors. Risks to fragmented populations have frequently been considered from the perspective of population genetics, however, disruption of normal plant demography may be an equal or greater threat to population persistence. We compared demographic performance and tree health in continuous and fragmented forest plots with similar tree size structure and local climatic and physiographic conditions in order to determine if fragments are characterized by poor health and reproduction. We found that beech forest fragments showed lower seedling density, more tree crown damage and also higher percentage of dead trees. However, mortality of juveniles in the youngest age class was substantially lower in fragments such that long-term population structure remained similar between the two forest types. If reduced mortality compensates for reduced seedling establishment, as our data suggest, then fragmented populations should show greater long-term persistence than would be predicted based on comparison of young age cohorts alone. However, despite such demographic compensation, the decreased health of adult trees may pose an increasing future threat to the fragmented populations. Our results demonstrate the importance of integrating demographic patterns over long time periods and not relying on single year or cohort comparisons and may partly explain population genetic differences previously reported for the same populations. © 2011 Elsevier B.V.
Bernal M., Estiarte M., Peñuelas J. (2011) Drought advances spring growth phenology of the Mediterranean shrub Erica multiflora. Plant Biology. 13: 252-257.EnllaçDoi: 10.1111/j.1438-8677.2010.00358.x
Current climate projections predict drier and warmer conditions in the Mediterranean basin over the next century. While advanced spring growth due to warming has been described in the literature, few data are available on the effects of drought on phenology. Hence, the phenology and growth of two Mediterranean shrubs, Erica multiflora and Globularia alypum, was studied in a rainfall exclusion field experiment to simulate spring drought in a natural shrubland. We estimated the onset of growth in spring by monitoring the appearance of new stems, and the end of growth in summer by following the elongation of stems. Drought treatment caused earlier onset of the spring growing season in E. multiflora, whereas no advance was observed in G. alypum. However, growth cessation was not affected in E. multiflora. Drought reduced the growth of both shrubs, as reflected in less stem elongation. The results show that a drier climate might affect not only growth but also spring phenology of some Mediterranean species. We suggest that a reduction in the cooling effect of transpiration may have analogous effects to warming and might advance the start of growth in E. multiflora, a species whose phenology has been described as warming-sensitive. The lengthening of the growing season resulting from advanced growth did not imply higher productivity, as growth was restricted by drought. © 2010 German Botanical Society and The Royal Botanical Society of the Netherlands.
Díaz-De-Quijano M., Peñuelas J., Ribas A. (2011) Trends of AOT40 at three sites in the Catalan Pyrenees over the last 16 years. Journal of Atmospheric Chemistry. 68: 317-330.EnllaçDoi: 10.1007/s10874-012-9222-9
Ozone mixing ratios were monitored at three stations at different altitudes along the Catalan Pyrenees from 1994 to 2009. The AOT40 greatly exceeded the critical level for the protection of forest and semi-natural vegetation set by the UNECE's CLRTAP and the target value and long-term objective for the protection of vegetation set by the European Directive 2008/50/EC. The AOT40 showed an overall increasing trend over time with a slight decrease during the last 3 years, although longer-term records of ozone levels are required before affirming with certainty a declining or stabilising trend. These results indicate that plant life in the Pyrenean region can be at risk of ozone damage due to the high ozone mixing ratios detected. Nevertheless, more effort is warranted to determine the uptake of ozone by vegetation in this mountainous range. An ozone flux-based index that takes into account the local environmental conditions, plant phenology, and nocturnal uptake of ozone would provide a more accurate assessment of the risk from ozone for the particular vegetation in each area. © Springer Science+Business Media B.V. 2012.
Estiarte M., Puig G., Peñuelas J. (2011) Large delay in flowering in continental versus coastal populations of a Mediterranean shrub, Globularia alypum. International Journal of Biometeorology. 55: 855-865.EnllaçDoi: 10.1007/s00484-011-0422-9
Globularia alypum is a perennial shrub typical of western Mediterranean thermophilous shrublands. Nine populations of G. alypum located in different localities of Catalonia (NE Spain) were surveyed for flowering phenology. Flower-head buds were present in all the populations in July. Flowering time in the area spans from the late summer-early autumn to the next spring depending on the populations; there are two groups of populations, early and late flowering. Early populations grow mostly in coastal localities and flower from September to November, whereas late flowering populations grow in inland localities and flower from February to April. The flowering order of the populations correlated with minimum temperature of most months except the warmest ones, and correlated with maximum and mean temperatures of the coldest months. Correlations were similar when tested with annual climate. The flowering order also correlated with the thermic interval for most months except the coldest and with the index of continentality. Early populations alone did not present correlations with any variable, whereas late populations alone correlated similarly to all populations together. Flowering order did not correlate with precipitation. Late populations are proposed to be regulated by temperature according to our results whereas early populations could be regulated by timing in precipitation after summer drought, according to published results. We discuss the possibilities of the two flowering patterns, early and late, being due to phenotypic plasticity or to genetic adaptation to local climates. We also discuss the consequences at the plant and ecosystem level of climate warming causing shifts from late to early patterns, a possibility that is likely in the warmest of the late populations if flowering is modulated phenotypically. © 2011 ISB.
Filella I., Bosch J., Llusià J., Peñuelas A., Peñuelas J. (2011) Chemical cues involved in the attraction of the oligolectic bee Hoplitis adunca to its host plant Echium vulgare. Biochemical Systematics and Ecology. 39: 498-508.EnllaçDoi: 10.1016/j.bse.2011.07.008
Host recognition is a key process in oligolectic bees but the mechanisms through which they find and recognize appropriate pollen host plant are not entirely clear. Hoplitis adunca is a monolectic bee collecting pollen only from Echium spp. (Boraginaceae). We aimed to test whether Echium vulgare floral scent plays a major role in the attraction of H. adunca females, and to identify components of E. vulgare scent that may be involved in this specific attraction. We used a combination of behavioral and chemical (GC/GC-MS, PTR-MS) analyses. In order to identify the chemical cues likely to be involved in the specific attraction of H. adunca, we compared the scent of fresh flowers, nectar, pollen, and whole plants of E. vulgare and Anchusa officinalis, another Boraginaceae, which does not attract H. adunca. H. adunca females were attracted to the scent of E. vulgare flowers when offered against a blank or against the scent of A. officinalis flowers. However, H. adunca females were not attracted to the scent of A. officinalis flowers when offered against a blank. The emission spectra of the two plant species differed markedly, as did the emission spectra of various flower components (pollen, nectar and whole flowers) within a species. Pollen presented a low volatile release, but emitted significantly higher amounts of mass 55 (butanal, 1,3-butadiene, or other volatiles of molecular mass 54), and mass 83 (hexanal, hexenols, hexenyl acetate, or other volatiles of molecular mass 82) in E. vulgare than in A. officinalis. Nectar produced a particular emission spectrum with high emission rates of masses 109 and 123. Mass 109 may likely correspond to 1,4-benzoquinone, a volatile specifically measured in E. vulgare in parallel studies to this one. The flower emission spectrum was mainly a combination of the pollen and the nectar scents, although it also contained additional volatile compounds such as those of mass 63 or mass 81. As for terpenes, E. vulgare emitted limonene, longicyclene, junipene, trans-caryophyllene and α-humulene, that were not detected in A. officinalis, and the most emitted monoterpenes were α-pinene, junipene and limonene whereas the most emitted terpenoid by A. officinalis was α-pinene. After identifying these chemical cues, olfactory/behavioural assays with specific volatiles and combinations of volatiles are necessary to understand the chemical interactions of the H. adunca-E. vulgare system. © 2011 Elsevier Ltd.
Filella I., Bosch J., Llusiá J., Seco R., Peñuelas J. (2011) The role of frass and cocoon volatiles in host location by monodontomerus aeneus, a parasitoid of megachilid solitary bees. Environmental Entomology. 40: 126-131.EnllaçDoi: 10.1603/EN10165
Monodontomerus aeneus (Fonscolombe) is a parasitic wasp that oviposits on the prepupae and pupae of Osmia cornuta (Latreille) and other solitary bee species. A two-armed olfactometer was used to test the olfactory attractiveness of O. cornuta prepupae, cocoon, and larval frass to female M. aeneus. Both cocoon and frass attracted the female parasitoids, but frass alone was more attractive than the cocoon and the cocoon with frass was more attractive than frass alone. Female parasitoids were not attracted by the host prepupa. M33 (methanol) was the organic volatile most emitted by cocoons and m61 (acetic acid) was the compound most emitted by frass. However, cocoons showed higher emission for almost all compounds, including m61 (acetic acid). Although acetic acid alone attracted M. aeneus, a complex volatile signal is probably involved in the attraction process because the ratio of acetic acid and acetaldehyde characteristic of the frass was more attractive than other ratios. © 2011 Entomological Society of America.
Garbulsky M.F., Peñuelas J., Gamon J., Inoue Y., Filella I. (2011) The photochemical reflectance index (PRI) and the remote sensing of leaf, canopy and ecosystem radiation use efficiencies. A review and meta-analysis. Remote Sensing of Environment. 115: 281-297.EnllaçDoi: 10.1016/j.rse.2010.08.023
Traditional remote sensing techniques allow the assessment of green plant biomass, and therefore plant photosynthetic capacity. However, detecting how much of this capacity is actually realized is a more challenging goal. Is it possible to remotely assess actual carbon fluxes? Can this be done at leaf, canopy and ecosystem scales and at different temporal scales? Different approaches can be used to answer these questions. Among them, the Photochemical Reflectance Index (PRI) derived from narrow-band spectroradiometers is a spectral index increasingly being used as an indicator of photosynthetic efficiency. We examined and synthesized the scientific literature on the relationships between PRI and several ecophysiological variables across a range of plant functional types and ecosystems at the leaf, canopy and ecosystem levels and at the daily and seasonal time scales. Our analysis shows that although the strength of these relationships varied across vegetation types, levels of organization and temporal scales, in most reviewed articles PRI was a good predictor of photosynthetic efficiency or related variables with performances at least as good as the widely used NDVI as indicator of green biomass. There are possible confounding factors related to the intensity of the physiological processes linked to the PRI signals, to the structure of the canopies and to the illumination and viewing angles that warrant further studies, and it is expected that the utility of PRI will vary with the ecosystem in question due to contrasting environmental constraints, evolutionary strategies, and radiation use efficiency (RUE; the ratio between carbon uptake and light absorbed by vegetation) variability. Clearly, more research comparing ecosystem responses is warranted. Additionally, like any 2-band index that is affected by multiple factors, the interpretation of PRI can be readily confounded by multiple environmental variables, and further work is needed to understand and constrain these effects. Despite these limitations, this review shows an emerging consistency of the RUE-PRI relationship that suggests a surprising degree of functional convergence of biochemical, physiological and structural components affecting leaf, canopy and ecosystem carbon uptake efficiencies. PRI accounted for 42%, 59% and 62% of the variability of RUE at the leaf, canopy and ecosystem respective levels in unique exponential relationships for all the vegetation types studied. It seems thus that by complementing the estimations of the fraction of photosynthetically active radiation intercepted by the vegetation (FPAR), estimated with NDVI-like indices, PRI enables improved assessment of carbon fluxes in leaves, canopies and many of the ecosystems of the world from ground, airborne and satellite sensors. © 2010 Elsevier Inc.
Inclán R., Gimeno B.S., Peñuelas J., Gerant D., Quejido A. (2011) Carbon isotope composition, macronutrient concentrations, and carboxylating enzymes in relation to the growth of Pinus halepensis Mill. when subject to ozone stress. Water, Air, and Soil Pollution. 214: 587-598.EnllaçDoi: 10.1007/s11270-010-0448-3
We present here the effects of ambient ozone (O3)-induced decline in carbon availability, accelerated foliar senescence, and a decrease in aboveground biomass accumulation in the Aleppo pine (Pinus halepensis Mill.). Aleppo pine seedlings were continuously exposed in open-top chambers for 39 months to three different types of O3 treatments, which are as follows: charcoal-filtered air, nonfiltered air (NFA), and nonfiltered air supplemented with 40 ppb O3 (NFA+). Stable carbon isotope discrimination (Δ) and derived time-integrated c i/c a ratios were reduced after an accumulated ozone exposure over a threshold of 40 ppb (AOT40) value from April to September of around 20,000 ppb•h. An AOT40 of above 67,000 ppb•h induced reductions in ribulose-1,5-biphosphate carboxylase/oxygenase activity, aboveground C and needle N and K concentrations, the C/N ratio, Ca concentrations in twigs under 3 mm, and the aerial biomass, as well as increases in needle P concentrations and phosphoenolpyruvate carboxylase (PEPC) activity and the N and K concentrations in twigs under 3 mm. Macronutrients losses, the limitations placed on carbon uptake, and increases in catabolic processes may be the causes of carbon gain diminution in leaves which was reflected as a reduction in aboveground biomass at tree level. Stimulation of PEPC activity, the consequent decreased Δ, and compensation processes in nutrient distribution may increase O3 tolerance and might be interpreted as part of Aleppo pine acclimation response to O3. © 2010 Springer Science+Business Media B.V.
Llusià J, Peñuelas J, Llorens L (2011) Responses to low increase in UV radiation on Volatile terpene emission rates, photosynthetic rates and Stomatal conductance in four Mediterranean species. Acta Physiologiae Plantarum doi: 10.1007/s11738-011-0876-8.
Blanc JS, Llusià J, Niinemets Ü, Noe SM, Peñuelas J (2011) Instantaneous and historical temperature effects on a-pinene emissions in Pinus halepensis and Quercus ilex. Journal of Environmental Biology 32: 1-6.
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