1,721,103 research outputs found
Leaf and stand-level carbon uptake of a Mediterranean forest estimated using the satellite-derived reflectance indices EVI and PRI
Full text linkVarious aspects of global environmental change affect plant photosynthesis, the primary carbon input in ecosystems. Thus, accurate methods of measuring plant photosynthesis are important. Remotely sensed spectral indices can monitor in detail the green biomass of ecosystems, which provides a measure of potential photosynthetic capacity. In evergreen vegetation types, however, such as Mediterranean forests, the amount of green biomass changes little during the growing season and, therefore, changes in green biomass are not responsible for changes in photosynthetic rates in those forests. This study examined the net photosynthetic rates and the diametric increment of stems in a Mediterranean forest dominated by Quercus ilex using three spectral indices (NDVI, EVI and PRI) derived from MODIS sensors. Average annual EVI accounted for 83% of the variability of the diametric increment of Q. ilex stems over a 10-yr period. NDVI was marginally correlated with the diametric increment of stems. This study was the first to identify a significant correlation between net photosynthetic rates and radiation use efficiency at the leaf level using PRI derived from satellite data analyzed at the ecosystem level. These results suggest that each spectral index provided different and complementary information about ecosystem carbon uptake in a Mediterranean Q. ilex forest.Fil: Garbulsky, Martín Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas A la Agricultura; Argentina. Consejo Superior de Investigaciones Cientificas. Centre de Recerca Ecologica I Aplicacions Forestals; España. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Produccion Animal. Cátedra de Forrajicultura; ArgentinaFil: Peñuelas, Josep. Consejo Superior de Investigaciones Cientificas. Centre de Recerca Ecologica I Aplicacions Forestals; EspañaFil: Ogaya, Roma. Consejo Superior de Investigaciones Cientificas. Centre de Recerca Ecologica I Aplicacions Forestals; EspañaFil: Filella, Iolanda. Consejo Superior de Investigaciones Cientificas. Centre de Recerca Ecologica I Aplicacions Forestals; Españ
Herbaria century record of increasing eutrophication in Spanish terrestrial ecosystems
No full textAdditional biological evidence is presented for the alteration of biogeochemical cycles by human activities. The leaf δ15N and the concentrations of nutrients in herbarium specimens of 24 species of vascular plants and 3 species of bryophytes collected in northern and eastern regions of Spain have substantially changed throughout the XX century. In the second half of the century, when anthropogenic nitrogen fixation and mobilization started to increase rapidly, leaf δ15N values started to decrease strongly, indicating that additional anthropogenic nitrogen is being retained in Spanish terrestrial ecosystems. The concentration of nutrients in vascular plants did not present any clear pattern, but there were increasing concentrations of N and other nutrients (P, K, and S) in the last decades in bryophytes, which are usually better biomonitors of airborne chemicals than vascular plants. Important consequences for ecosystem structure and functioning such as enhancement of the carbon sink or changes in community biodiversity and species distribution may be expected from this increase in eutrophication
Changed plant and animal life cycles from 1952 to 2000 in the Mediterranean region
No full textThe available data on climate over the past century indicate that the earth is warming. Important biological effects, including changes of plant and animal life cycle events, have already been reported. However, evidence of such effects is still scarce and has been mostly limited to northern latitudes. Here we provide the first long-term (1952-2000) evidence of altered life cycles for some of the most abundant Mediterranean plants and birds, and one butterfly species. Average annual temperatures in the study area (Cardedeu, NE Spain) have increased by 1.4 °C over the observation period while precipitation remained unchanged. A conservative linear treatment of the data shows that leaves unfold on average 16 days earlier, leaves fall on average 13 days later, and plants flower on average 6 days earlier than in 1952. Fruiting occurs on average 9 days earlier than in 1974. Butterflies appear 11 days earlier, but spring migratory birds arrive 15 days later than in 1952. The stronger changes both in temperature and in phenophases timing occurred in the last 25 years. There are no significant relationships among changes in phenophases and the average date for each phenophase and species. There are not either significant differences among species with different Raunkiaer life-forms or different origin (native, exotic or agricultural). However, there is a wide range of phenological alterations among the different species, which may alter their competitive ability, and thus, their ecology and conservation, and the structure and functioning of ecosystems. Moreover, the lengthening of plant growing season in this and other northern hemisphere regions may contribute to a global increase in biospheric activity
Changed plant and animal life cycles from 1952 to 2000 in the Mediterranean region
No full textThe available data on climate over the past century indicate that the earth is warming. Important biological effects, including changes of plant and animal life cycle events, have already been reported. However, evidence of such effects is still scarce and has been mostly limited to northern latitudes. Here we provide the first long-term (1952-2000) evidence of altered life cycles for some of the most abundant Mediterranean plants and birds, and one butterfly species. Average annual temperatures in the study area (Cardedeu, NE Spain) have increased by 1.4 °C over the observation period while precipitation remained unchanged. A conservative linear treatment of the data shows that leaves unfold on average 16 days earlier, leaves fall on average 13 days later, and plants flower on average 6 days earlier than in 1952. Fruiting occurs on average 9 days earlier than in 1974. Butterflies appear 11 days earlier, but spring migratory birds arrive 15 days later than in 1952. The stronger changes both in temperature and in phenophases timing occurred in the last 25 years. There are no significant relationships among changes in phenophases and the average date for each phenophase and species. There are not either significant differences among species with different Raunkiaer life-forms or different origin (native, exotic or agricultural). However, there is a wide range of phenological alterations among the different species, which may alter their competitive ability, and thus, their ecology and conservation, and the structure and functioning of ecosystems. Moreover, the lengthening of plant growing season in this and other northern hemisphere regions may contribute to a global increase in biospheric activity
Leaf mineral concentrations of Erica arborea, Juniperus communis and Myrtus communis growing in the proximity of a natural CO2 spring
No full textLeaf mineral concentrations of co-occurring Erica arborea, Juniperus communis and Myrtus communis were measured at bimonthly intervals throughout a year in a natural CO2 spring and in a nearby control site with similar soil chemistry in a Mediterranean environment. There were different responses to the elevated [CO2] (c. 700 μL L−1) of the spring site plants depending on the element and the species. In the CO2 spring site K, Ca, Mg, Mn, Al, Fe, and Ti leaf concentrations and the ratio C/N showed significant greater values in at least one or two of the three species. Leaf S concentration were greater in all three species. Leaf concentrations of N, Sr, Co, and B were lower in at least one or two species, and those of C and Ba were lower in all the three studied species near the CO2 spring. P, Na, Zn, Si, Cu, Ni, Cr, Pb, Mo, V and Cd leaf concentrations and the specific leaf area (SLA, measured in Myrtus communis) did not show any consistent or significant pattern in response to the elevated [CO2] of the spring site. There was a slight trend towards maximum concentrations of most of these elements during autumn-winter and minimum values during the spring season, especially in Myrtus communis. Multivariate principal component analyses based on the leaf elemental concentrations clearly differentiated the two sites and the three species. Lower concentrations at the spring site were not the result of a dilution effect by increased structural or nonstructural carbon. In contrast to most experimental studies of CO2 enrichment, mainly conducted for short periods, several of these elements had greater concentrations in the CO2 spring site. Nutrient acclimation and possible causes including decreased nutrient export, increased nutrient uptake capacity, photosynthetic down-regulation, Mediterranean water stress, and higher H2S concentration in the spring site are discusse
Herbaria century record of increasing eutrophication in Spanish terrestrial ecosystems
Full text linkAdditional biological evidence is presented for the alteration of biogeochemical cycles by human activities. The leaf δ15N and the concentrations of nutrients in herbarium specimens of 24 species of vascular plants and 3 species of bryophytes collected in northern and eastern regions of Spain have substantially changed throughout the XX century. In the second half of the century, when anthropogenic nitrogen fixation and mobilization started to increase rapidly, leaf δ15N values started to decrease strongly, indicating that additional anthropogenic nitrogen is being retained in Spanish terrestrial ecosystems. The concentration of nutrients in vascular plants did not present any clear pattern, but there were increasing concentrations of N and other nutrients (P, K, and S) in the last decades in bryophytes, which are usually better biomonitors of airborne chemicals than vascular plants. Important consequences for ecosystem structure and functioning such as enhancement of the carbon sink or changes in community biodiversity and species distribution may be expected from this increase in eutrophication
Leaf mineral concentrations of Erica arborea, Juniperus communis and Myrtus communis growing in the proximity of a natural CO2 spring
Full text linkLeaf mineral concentrations of co-occurring Erica arborea, Juniperus communis and Myrtus communis were measured at bimonthly intervals throughout a year in a natural CO2 spring and in a nearby control site with similar soil chemistry in a Mediterranean environment. There were different responses to the elevated [CO2] (c. 700 μL L-1) of the spring site plants depending on the element and the species. In the CO2 spring site K, Ca, Mg, Mn, Al, Fe, and Ti leaf concentrations and the ratio C/N showed significant greater values in at least one or two of the three species. Leaf S concentration were greater in all three species. Leaf concentrations of N, Sr, Co, and B were lower in at least one or two species, and those of C and Ba were lower in all the three studied species near the CO2 spring. P, Na, Zn, Si, Cu, Ni, Cr, Pb, Mo, V and Cd leaf concentrations and the specific leaf area (SLA, measured in Myrtus communis) did not show any consistent or significant pattern in response to the elevated [CO2] of the spring site. There was a slight trend towards maximum concentrations of most of these elements during autumn-winter and minimum values during the spring season, especially in Myrtus communis. Multivariate principal component analyses based on the leaf elemental concentrations clearly differentiated the two sites and the three species. Lower concentrations at the spring site were not the result of a dilution effect by increased structural or nonstructural carbon. In contrast to most experimental studies of CO2 enrichment, mainly conducted for short periods, several of these elements had greater concentrations in the CO2 spring site. Nutrient acclimation and possible causes including decreased nutrient export, increased nutrient uptake capacity, photosynthetic down-regulation, Mediterranean water stress, and higher H2S concentration in the spring site are discusse
The photochemical reflectance index (PRI) as an indicator of changes in photosynthetic dynamics and gross primary productivity in response to climate change
Full text linkBibliografia.Quantificar les dinàmiques fotosintètiques des de diferents escales espacio-temporals és molt important en la recerca de l'absorció de carboni, particularment en les condicions actuals de canvi climàtic. L'índex de reflectància fotoquímica (PRI) ha demostrat ser útil per estimar de forma remota el funcionament la vegetació i constitueix un mètode prometedor per estimar la productivitat primària bruta (GPP) a escala global. Als últims anys, diversos treballs han presentat possibles millores en la comprensió i formulació del PRI per tal de millorar la seva aplicabilitat a escales espacials i temporals més grans. El principal objectiu d'aquesta tesi va ser clarificar els mecanismes que causen la variabilitat del PRI i avaluar l'aplicabilitat de PRI per detectar les dinàmiques fotosintètiques i l'absorció de carboni sota diferents condicions d'estrès i a diferents escales espacio-temporals. En aquesta tesi es van plantejar tres objectius al llarg de sis capítols. El primer objectiu va ser resumir els principals factors que afecten la variació del PRI segons les publicacions més recents, també la relació entre PRI i RUE (eficiència en l'ús de la radiació)/GPP i altres variables al llarg de les escales diària i estacional i a nivell foliar de coberta i d'ecosistema, i també les millores en la implementació del PRI. El segon objectiu va ser avaluar la capacitat del PRI per seguir les dinàmiques de l'activitat fotosintètica estacional d'espècies perennifòlies i sota estressos hídrics i de temperatura. L'objectiu final va ser avaluar si el PRI obtingut amb MODIS (MODerate resolution Imaging Spectroradiometer) pot ser utilitzat per detectar els efectes de les sequeres severes en la GPP i l'emissió d'isoprè a nivell d'ecosistema. La principal conclusió d'aquesta tesi en el primer capítol va ser que el PRI és un bon estimador de la RUE i el GPP a diferents escales espacials i temporals i que a escala temporal curta està controlat principalment pels canvis facultatius en els pigments del cicle de les xantofil·les, mentre que a escala temporal llarga ho està pels canvis constitutius en el contingut de clorofil·les i carotenoides. Una altra conclusió és que es pot millorar la estimació de la RUE i el GPP corregint el PRI per disminuir els efectes dels factors físics i fisiològics que l'afecten, i també combinant PRI amb índexs de fluorescència induïda pel sol (SIF) o índexs convencionals de biomassa verda. El segon capítol mostra com l'espectre de fluorescència a nivell de fulla te un potencial similar a totes les longituds d'ona (de 670 a 800 nm) per seguir les dinàmiques estacional de la fotosíntesi durant el període de recuperació a la primavera en fules de pi roig, i que PRI i WI (índex d'aigua) també van ser bons indicadors de la recuperació de la fotosíntesi. El tercer capítol demostra que ambdós, el PRI i un índex de fluorescència basat en reflectància (R690/R630), no nomes van ser sensibles a un estrès hídric progressiu sinó que també van ser sensibles a la recuperació de la fotosíntesi en fulles d'una espècie perennifòlia mediterrània. El capítol quatre mostra que PRI i ΔPRI (PRI al matí menys PRI al migdia) van poder seguir l'estacionalitat i la depressió del migdia de la fotosíntesi en un matollar mediterrani en resposta a la sequera i escalfament experimentals. Al capítol cinquè la conclusió va ser que el PRI calculat amb MODIS normalitzat per la llum absorbida (APAR) (sPRIn) va detectar els efectes dels esdeveniments de sequera en la GPP de boscos mediterranis, però no en ecosistemes de prats. En el capítol final vaig concloure que el PRI és un índex prometedor per estimar les emissions d'isoprè, especialment quan es complementa amb informació sobre els potencials d'emissió.Quantifying photosynthetic dynamics from different spatiotemporal scales is highly important for carbon uptake research, particularly under ongoing climate changes. The photochemical reflectance index (PRI) has shown to be useful to remotely asses the physiological functioning of vegetation and it constitutes a promising method to estimate gross primary productivity (GPP) at global scale. In the last years, several works have presented possible improvements on PRI understanding and formulation to improve its applicability at larger temporal and spatial scales. The main objective of this dissertation was to clarify the mechanisms that elicit the variability in PRI and to evaluate the applicability of PRI in detecting photosynthetic dynamics and carbon uptake under various stress conditions at different spatiotemporal scales. Three special objectives were addressed in six chapters in this thesis. The first objective was to summarize the main factors that affect PRI variation according the most recent publications, also the relationships between PRI and RUE/GPP and other ecophysiological variables across diurnal and seasonal scales at foliar, canopy and ecosystemic levels, as well as the improvements in PRI implementation. The second objective was to evaluate the capacity of PRI in monitoring the dynamics of photosynthetic activity of evergreen species seasonally or under water or temperature stresses. The last objective was to assess whether the PRI retrieved from MODerate resolution Imaging Spectroradiometer (MODIS) can be utilized to detect the effects of extreme drought on GPP and isoprenoid emissions at ecosystem scale. The main conclusion of this thesis in the first chapter was that PRI is a good proxy of RUE and GPP at different spatial and temporal scales and was mainly constrained by facultative changes of xanthophyll-cycle pigments at short-term scales and by constitutive changes of chlorophyll and carotenoid pool sizes at long-term scales. Correcting PRI to decrease the effects of physical or physiological factors or combining PRI with solar-induced fluorescence (SIF) and conventional greenness biomass indices could greatly improve remote estimation of RUE and GPP. The second chapter showed that leaf-level fluorescence spectra from all wavelengths (670 to 800 nm) have similar potential to track the dynamics of photosynthetic seasonality during spring recovery period in Scots pine needles and that PRI and WI also acted as good indicators to track the recovery of photosynthesis. The third chapter demonstrated that both PRI and reflectance-ratio based fluorescence (R690/R630) were not only sensitive to progressively enhanced drought stress but also sensitive enough to the recovery of photosynthesis for Mediterranean evergreen leaves. The fourth chapter illustrated that PRI and ΔPRI (morning PRI subtracted from midday PRI) were able to monitor the seasonality and the midday depression of photosynthesis of Mediterranean evergreen shrub in response to experimental warming and drought. In the fifth chapter the conclusion was that the MODIS PRI normalized by absorbed light (APAR) (sPRIn) detected the effects of drought events on GPP for Mediterranean forest but not for grassland ecosystem. In the final chapter we concluded that PRI is a promising index to estimate isoprene emissions, especially when it is complemented by information on potential emission
Emissió de compostos orgànics volàtils en vegetació mediterrània : COVs oxigenats de cadena curta, interacció entre organismes i impacte atmosfèric
Full text linkDescripció del recurs: el 19 setembre 2011Els compostos orgànics volàtils (COVs) presents a l'atmosfera poden tenir fonts naturals o antròpiques. Els COVs estan implicats en reaccions químiques que afecten la química atmosfèrica i poden tenir impactes indirectes sobre el clima a través de la generació d'aerosols i compostos oxidants. Globalment, la vegetació és la font principal de COVs naturals, mentre que els COVs antropogènics són la majoria de vegades producte d'emissions industrials i de motors de vehicles. D'entre els COVs biogènics, els isoprenoids són els més coneguts i estudiats. La nostra recerca es va centrar en el grup de COVs de cadena curta oxigenats (oxCOVs), un grup poc conegut format per metanol, etanol, formaldehid, acetaldehid, acids fòrmic i acètic, i acetona. Els oxCOVs poden ser emesos directament tant per les plantes com per les activitats humanes, i també es poden formar per la degradació atmosfèrica d'altres COVs de major massa molecular. Entre d'altres raons, han estat menys estudiats degut a problemes analítics, que s'han resolt en part recentment amb l'aparició de noves tecnologies, especialment l'espectrometria de masses per transferència de protons. Els oxCOVs tenen diverses propietats que els diferencien d'altres COVs com els isoprenoids. Els oxCOVs són més solubles en aigua i això fa la seva emissió en plantes depenent dels estomes. També tenen una vida atmosfèrica relativament llarga i presenten concentracions considerables a l'atmosfera en el nivell de ppbv (1 part en 109 en volum). Les emissions d'oxCOVs en plantes mediterrànies són molt poc conegudes, per això vam estudiar-ne l'intercanvi en els arbres típicament mediterranis Quercus ilex i Pinus halepensis. Es va confirmar el control estomàtic i de la concentració atmosfèrica del seu intercanvi. Per exemple, es va observar un punt de compensació de 20 ppbv pel formaldehid en les dues espècies d'arbre, mentre que per l'acetaldehid va ser de 6 ppbv en P. halepensis. Un tractament de sequera i posterior reg va mostrar que la sequera afecta l'intercanvi d'oxCOVs perquè afecta la conductància estomàtica. A més, es va confirmar que Q. ilex emet isoprè, encara que amb taxes petites, i que l'emissió d'isoprenoids en Q. ilex va disminuir per la sequera. Els COVs poden tenir també un paper ecològic molt important: participar en les comunicacions entre organismes. En interaccions planta-planta la nostra hipòtesi era que el metanol podia jugar un paper senyalitzador, ja que el metanol s'emet en grans quantitats des de les fulles quan són atacades per un herbívor. Un experiment de fumigació amb metanol va mostrar que les respostes de Q. ilex al metanol arribat per l'aire eren similars a les respostes a l'herbivoria i també que l'emissió de monoterpens es va incrementar lleugerament. En la comunicació entre animals, vam identificar alguns components volàtils emesos pels capolls i els excrements d'una espècie d'abella solitària (Osmia cornuta), essent-ne l'àcid acètic un dels més abundants. Llavors vam provar l'atracció exercida per l'àcid acètic sobre femelles de Monodontomerus aeneus, una vespa parasitoide d'O. cornuta, que busquen capolls per ovipositar-hi. Encara que l'àcid acètic sol atreia M. aeneus, probablement un senyal volàtil complex intervé en el procés d'atracció, ja que la ràtio àcid acètic-acetaldehid característica dels excrements va resultar més atractiva que altres ràtios. L'objectiu final de la tesi va ser observar quin impacte tenen les emissions de COVs en l'atmosfera mediterrània, ja sigui pel nivell de concentració que atanyen els COVs a l'aire com també per la seva participació en la formació de compostos com l'ozó. Per això vam mesurar (hivern i estiu) les concentracions d'oxCOVs, isoprenoids i COVs aromàtics en una zona boscosa situada dins del parc natural del Montseny, a uns 60 km al NE de la ciutat de Barcelona. Mentre que els COVs aromàtics no varen presentar gairebé cap variació estacional, les concentracions dels oxCOVs van assolir nivells més alts a l'estiu degut a les majors emissions de la vegetació i a l'increment de les reaccions fotoquímiques resultants de les altes temperatures i radiació solar de l'estiu. Els COVs isoprenoids van mostrar el canvi entre estacions més gran: les concentracions van augmentar un ordre de magnitud a l'estiu, degut a l'increment de l'activitat fisiològica de la vegetació i de les seves taxes d'emissió. També les concentracions diürnes màximes d'ozó van augmentar a l'estiu, per la major activitat fotoquímica i la presència de més COVs a l'aire. La variació diària de concentracions de COVs seguia bàsicament el règim de vent de la muntanya. La brisa marina que es desenvolupa quan surt el sol transporta cap a la muntanya masses d'aire que prèviament han passat sobre la regió metropolitana de Barcelona, on han estat enriquides en NO2 i en COVs d'origen biòtic i abiòtic. A més, aquestes masses d'aire contaminades poden reaccionar amb els COVs biogènics emesos de forma local per la vegetació, tot afavorint la formació d'O3 en aquesta zona boscosa. L'únic tipus de COV que presentava un cicle diari diferent dels demés van ser els monoterpens, perquè tenien un origen biogènic local. L'isoprè també compartia parcialment el cicle diari dels monoterpens, però només a l'estiu quan les seves fonts biòtiques eren més fortes.Volatile organic compounds (VOCs) present in the atmosphere can have natural or anthropic sources. VOCs are involved in atmospheric chemistry reactions that can have indirect climatic impacts through the generation of aerosols and oxidant compounds. Globally, vegetation is the main source of natural VOC emission, while anthropogenic VOCs are in most cases product of vehicle exhaust and industry emissions. Within biogenic VOCs, isoprenoids are the most studied and known group. Our research was focused in a group of short-chain oxygenated VOCs (oxVOCs), a poorly known group composed by methanol, ethanol, formaldehyde, acetaldehyde, formic and acetic acids, and acetone. They can be emitted directly either by plants or by human activities, and they can also be formed through degradation in the air of other higher molecular mass VOCs. Among other reasons, they have been less studied due to analytical problems than have been partly solved in recent years with the advent of new technologies, specially proton transfer reaction mass spectrometry. OxVOCs have several properties that set them apart of other VOCs like isoprenoids. OxVOCs are more soluble in water and this fact makes their release from plants stomatal-dependent. In addition, these compounds have relatively long atmospheric halflives and reach considerable concentrations in the atmosphere in the range of parts per billion in volume (ppbv). Emissions of oxVOCs in Mediterranean plants are scarcely known, for this reason we studied oxVOCs exchange in the typically Mediterranean tree species Quercus ilex and Pinus halepensis. The stomatal and atmospheric mixing ratios control of their exchange was confirmed. For instance, a compensation point of 20 ppbv for formaldehyde was observed for both tree species, while for acetaldehyde it was of 6 ppbv in P. halepensis. A treatment of drought and posterior re-watering showed that drought affects oxVOC exchange because it affects stomatal conductance. In addition, it was confirmed that Q. ilex emits isoprene, although at small rates, and that isoprenoid emission in Q. ilex decreased due to drought. VOCs can also have an important ecological role: taking part in the communication between organisms. In plant-plant interaction our hypothesis was that methanol could have a signalling role, given that methanol is emitted in big amounts from leaves upon herbivore attack. An experiment of fumigation with methanol showed that Q. ilex responses to airborne methanol were similar to responses to herbivory and also that monoterpene emission was slightly increased. In communication between animals, we identified some volatile components emitted by the cocoons and frass of a solitary bee species (Osmia cornuta), being acetic acid an abundant one among them. We then tested acetic acid attractiveness for Monodontomerus aeneus female wasps, parasitoids of O. cornuta, that look for cocoons to oviposit. Although acetic acid alone attracted M. aeneus, a complex volatile signal is probably involved in the attraction process since the ratio acetic acid-acetaldehyde characteristic of the frass was more attractive than other ratios. The last objective of this thesis was to observe the impact that VOC emissions have on the Mediterranean atmosphere, either by the mixing ratios that VOC reach in the air or also by their participation in the formation of compounds like ozone. To achieve this, the mixing ratios of oxVOCs, isoprenoids, and aromatic VOCs were measured (winter and summer) in a forest site located within a densely forested natural park (Montseny) about 60 km NE of the city of Barcelona. While aromatic VOCs showed almost no seasonal variability, short-chain oxygenated VOCs presented higher mixing ratios in summer due to the increased emission by vegetation and the increased photochemistry, both enhanced by the high temperatures and solar radiation in summer. Isoprenoid VOCs showed the biggest seasonal change in mixing ratios:they increased by one order of magnitude in summer, as a result of the increased vegetation physiological activity and emission rates. Ozone highest diurnal concentrations increased in summer too, due to more photochemical activity and the presence of more VOCs in the air. The daily variation of the VOC mixing ratios was mainly governed by the wind regime of the mountain. Sea breeze that develops after sunrise advects to the mountain polluted air masses that previously had passed over the Barcelona metropolitan region, where they were enriched in NO2 and in VOCs of biotic and abiotic origin. Furthermore, these polluted air masses can react with biogenic VOCs emitted at the local valley by the vegetation, thus enhancing O3 formation in this forest site. The only VOC species that showed a different daily pattern were monoterpenes because of their local biogenic emission. Isoprene also shared partially the daily pattern of monoterpenes, but only in summer when its biotic sources were stronger
Biotic and abiotic factors that determine the emission of volatile organic compounds by flowers
Full text linkLes flors emeten compostos orgànics volàtils (VOCs) per tal d'atreure pol·linitzadors i estimular la fecundació creuada. Alguns volàtils florals però juguen altres funcions, com ara la defensa contra els herbívors. Aquesta dualitat de rols que tenen les olors florals les converteix en complexes mescles de compostos amb múltiples efectes sobre diferents organismes. La complexitat de comprendre i caracteritzar les emissions florals augmenta quan considerem que són variables en el temps i l'espai. A aquestes fonts de variabilitat cal afegir diversos factors ambientals biòtics i abiòtics que modifiquen les emissions de COVs florals de diverses maneres. L'objectiu principal d'aquesta tesi és esclarir quins són els factors que determinen les emissions florals de volàtils, i veure de quina manera les afecten a elles i a les seves funcions ecològiques. En el primer capítol de la tesi hem revisat el coneixement actual sobre les emissions florals de VOCs i hem identificat les qüestions que necessitaven ser investigades en aquest camp de recerca. Les emissions florals estan determinades en primer lloc per la diversitat de compostos que les espècies són capaces de produir, els seu potencial biosintètic i la seva capacitat d'emissió, que estan fortament lligades a la biologia de l'espècie. Hem testat i demostrat que les plantes pol·linitzades per insectes solen presentar major diversitat de volàtils florals i emeten una major quantitat d'aquests que les plantes pol·linitzades pel vent, que no necessiten volàtils florals per funcions d'atracció. Hem testat si els patrons estacionals de disminució de la competència que ocorren cada any entre plantes d'una mateixa comunitat vegetal han donat lloc a la selecció d'un patró de disminució de les emissions i les recompenses florals al llarg del període de floració de cada espècie. També hem observat que les plantes adapten la seva fisiologia per optimitzar les seves emissions florals sota les condicions climàtiques de la seva època de floració. Les emissions florals de COVs es veuen afectades per factors ambientals al nivell d'organisme o de teixit. Hi ha diversos estats fisiològics de la planta que poden modificar substancialment la composició i la quantitat de les emissions florals de COVs. Els nostres experiments han demostrat que la microbiota floral pot jugar un rol crucial sobre la quantitat i composició de les emissions florals de COVs. També hem mostrat que l'herbivoria de flors per part d'erugues de Pieris brassicae sobre plantes de Diplotaxis erucoides indueixen augments immediats de les emissions de compostos amb funcions defensives. A més, l'herbivoria de flors i fulles combinada va mostrar un efecte sinèrgic que augmenta la resposta defensiva. La recerca sobre els canvis que poden experimentar les emissions florals en resposta a diversos agents del Canvi Global són de gran interès degut als diversos efectes que aquests canvis poden tenir sobre les interaccions que s'estableixen mitjançant els COVs florals. Els nostres resultats revelen que els augments de temperatura previstos per al segle següent deguts a l'Escalfament Global poden conduir a augments significatius de les emissions totals de COVs i també a canvis importants en la composició relativa de les olors florals. També hem observat que l'ozó causa una degradació significativa dels compostos florals i provoca canvis en la composició relativa de les olors. Els testos de resposta indiquen que els canvis observats en les olors florals exposades a ozó resulten en la pèrdua de l'atracció de pol·linitzadors. Aquesta tesi proporciona una nova visió sobre els factors que determinen les emissions florals de volàtils i les seves repercussions sobre les interaccions planta-pol·linitzador, i garanteix una major consideració dels factors biòtics i abiòtics que afecten la química i l'ecologia de les olors florals en un ambient contínuament canviant.Flowers emit volatile organic compounds (VOCs) to attract pollinators and stimulate reproductive outcrossing. Some floral volatiles can play roles other than attraction, such as defense against herbivores. This duality of roles of flower emissions converts floral scents into complex mixtures of compounds with multiple effects on different organisms. The complexity of understanding and characterising floral emissions increases when considering that they are variable in time and space. To all these sources of variability we can add diverse biotic and abiotic environmental factors that modify floral VOC emissions in many different ways. The main objective of this thesis was to shed light on which are the factors that determine floral volatile emissions, and how do they affect these emissions and their ecological functions. In the first chapter of this thesis we reviewed the current knowledge on floral VOC emissions. We identified the open questions that still needed to be addressed or investigated in more detail in the research field of floral VOC emissions. Floral emissions are first determined by the array of compounds that the species are able to produce and their potential biosynthetic and emission capacities, which are strongly related to the species biology. We tested and demonstrated that flowering plants pollinated by insects usually present higher diversities of floral volatiles and emit higher amounts of them, than do plants pollinated by wind which do not need floral volatiles for attractive purposes. We tested whether well-known seasonal patterns of decreasing competition occurring every year in a community among co-flowering plants for pollinators led to the selection of a pattern of decreasing emission of floral volatiles and decreasing production of floral rewards along the flowering period of each species. We also observed that plants adapt their physiology to optimize their floral emissions under the climatic conditions of the flowering period. Floral VOC emissions of the species are affected by environmental factors at the individual (organism) or tissular level. There are diverse physiological states of the plant that can substantially modify the emission profiles and amounts of floral VOCs. Our experiments demonstrated that floral microbiota can play a crucial role in the quantity and quality of floral VOC emissions. We also showed that flower herbivory by Pieris brassicae caterpillars on Diplotaxis erucoides plants induced immediate increases in floral emission rates of few compounds with known defensive functions. Leaf herbivory caused no changes in the emissions of intact flowers, but the combination of leaf herbivory with flower herbivory showed a synergistic effect with enhanced defensive response. The research on the potential changes that floral emissions could experience in response to diverse drivers of Global Change are of critical interest because of the diverse effects that such changes can have on the interactions that floral VOCs mediate. Our results revealed that temperature increases as those predicted for the next century as a result of Global Warming can lead to significant total increases in floral VOC emissions and also to important changes in floral scent relative composition. We also detected that ozone caused significant degradation of floral compounds and changes in their relative composition. Behavioural tests indicated that all the changes observed in floral chemical cues when exposed to ozone resulted in the loss of attraction effect on pollinators. This thesis thus provides new insights on the factors that determine floral volatile emissions and their repercussions on plant-pollinator interactions and warrant deep consideration of both biotic and abiotic factors driving floral scent chemistry and floral scent ecology in a continuously changing environment
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