Analysis of decadal time series in wet N concentrations at five rural sites in NE Spain

Avila A., Molowny-Horas R., Gimeno B.S., Peñuelas J. (2010) Analysis of decadal time series in wet N concentrations at five rural sites in NE Spain. Water, Air, and Soil Pollution. 207: 123-138.
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Doi: 10.1007/s11270-009-0124-7

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Nitrogen emissions have grown in Spain during the last 15 years. As precipitation scavenges gases and aerosols from the atmosphere, an effect on rainwater concentrations can be expected. However, time-series studies on wet N concentrations in the Iberian Peninsula are very scarce. This paper aims to fill this gap by analysing weekly rainfall N concentrations at a set of rural sites in Catalonia (NE Spain) from 1995/1996 to 2007 and a forest site monitored from 1983 to 2007. The sites encompass a range of rural environments and climate conditions, from the inland pre-Pyrenees (Sort) to the Mediterranean coast (Begur) and from north (Sort and Begur) to central (Palautordera and La Castanya) and south Catalonia (La Senia). We found a 1-year cycle for concentrations of NH 4 + and NO 3 - whereby higher values were reached at the end of spring-early summer, except at the easternmost coastal site of Begur. Weekly NH 4 + concentrations decreased with time at all sites (except at La Senia) whilst NO 3 - concentrations increased at all sites during the same period. Rainfall SO 4 2- concentrations decreased with time at all sites. The opposite trends in NO 3 - and SO 4 2- concentrations determined a shift in the relative acid contribution of those anions during the 12-13-year period. To interpret the increasing trend, mean annual NO 3 - concentrations were regressed against NO 2 Spanish emissions and to some indicators of local anthropogenic activity. The increase at Sort and Palautordera showed good correlation with local anthropogenic indicators. Wet inorganic N deposition ranged between 4.2 and 6.7 kg ha -1 year -1. When including estimates of dry deposition, total annual deposition rose up to 10-20 kg ha -1 year -1, values that have been found to initiate adverse effects on Mediterranean-type forest ecosystems. © 2009 Springer Science+Business Media B.V.

Llegeix més

Patterns and controls of the variability of radiation use efficiency and primary productivity across terrestrial ecosystems

Garbulsky M.F., Peñuelas J., Papale D., Ardö J., Goulden M.L., Kiely G., Richardson A.D., Rotenberg E., Veenendaal E.M., Filella I. (2010) Patterns and controls of the variability of radiation use efficiency and primary productivity across terrestrial ecosystems. Global Ecology and Biogeography. 19: 253-267.
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Doi: 10.1111/j.1466-8238.2009.00504.x

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Aim: The controls of gross radiation use efficiency (RUE), the ratio between gross primary productivity (GPP) and the radiation intercepted by terrestrial vegetation, and its spatial and temporal variation are not yet fully understood. Our objectives were to analyse and synthesize the spatial variability of GPP and the spatial and temporal variability of RUE and its climatic controls for a wide range of vegetation types. Location: A global range of sites from tundra to rain forest. Methods: We analysed a global dataset on photosynthetic uptake and climatic variables from 35 eddy covariance (EC) flux sites spanning between 100 and 2200 mm mean annual rainfall and between -13 and 26°C mean annual temperature. RUE was calculated from the data provided by EC flux sites and remote sensing (MODIS). Results: Rainfall and actual evapotranspiration (AET) positively influenced the spatial variation of annual GPP, whereas temperature only influenced the GPP of forests. Annual and maximum RUE were also positively controlled primarily by annual rainfall. The main control parameters of the growth season variation of gross RUE varied for each ecosystem type. Overall, the ratio between actual and potential evapotranspiration and a surrogate for the energy balance explained a greater proportion of the seasonal variation of RUE than the vapour pressure deficit (VPD), AET and precipitation. Temperature was important for determining the intra-annual variability of the RUE at the coldest energy-limited sites. Main conclusions: Our analysis supports the idea that the annual functioning of vegetation that is adapted to its local environment is more constrained by water availability than by temperature. The spatial variability of annual and maximum RUE can be largely explained by annual precipitation, more than by vegetation type. The intra-annual variation of RUE was mainly linked to the energy balance and water availability along the climatic gradient. Furthermore, we showed that intra-annual variation of gross RUE is only weakly influenced by VPD and temperature, contrary to what is frequently assumed. Our results provide a better understanding of the spatial and temporal controls of the RUE and thus could lead to a better estimation of ecosystem carbon fixation and better modelling. © 2009 Blackwell Publishing Ltd.

Llegeix més

Annual and seasonal changes in foliar terpene content and emission rates in cistus albidus L. submitted to soil drought in Prades Forest (Catalonia, NE Spain)

Llusià J., Peñuelas J., Ogaya R., Alessio G. (2010) Annual and seasonal changes in foliar terpene content and emission rates in cistus albidus L. submitted to soil drought in Prades Forest (Catalonia, NE Spain). Acta Physiologiae Plantarum. 32: 387-394.
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Doi: 10.1007/s11738-009-0416-y

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We measured the gas exchange and foliar terpene concentrations and terpene emission rates of Cistus albidus throughout the seasons of two annual periods (2003 and 2005) of contrasting precipitations (900 vs. 500 mm) and in response to experimental drought in a Mediterranean forest of southern Catalonia. C. albidus showed a typical seasonal oscillation of photosynthetic rates and stomatal conductance. Maximum photosynthetic activity appeared in the spring of the first year of the study and minimum ones in both summers. Net photosynthetic rates and stomatal conductance tended to decrease with drought treatment. In the first year, Cistus albidus presented maximum values of stored terpenes in autumn and winter and minimum values in spring and summer. Average concentrations in the first year were 154 and 96 μg g-1 dry matter (d.m.) for control and drought, respectively. Average concentrations in the second year were higher, 339 and 263 μg g-1 (d.m.) for control and drought, respectively. The most abundant terpene was zingiberene, followed by aromadendrene, germacrene, (-)-α-cedrene, and sesquiphel-landrene. The drought treatment tended to decrease terpene content, but not significantly. Considering all the treatments together, total terpene emissions ranged between practically 0 (spring 2003) to 9 μg g-1 (d.m.) h-1 (winter 2003). In the second year, total terpene emission rates decreased 39% in control plants, and 29% in drought plants. Significant seasonal differences in emission rates were found. Total emission rates tended to be higher in the drought treatment, especially in spring and autumn. These results help for a better understanding of the behavior of plant volatiles in Mediterranean conditions interannualy and seasonally, an issue of great interest for forest flammability and atmospheric chemistry. © Franciszek Górski Institute of Plant Physiology.

Llegeix més

Measurement of volatile terpene emissions in 70 dominant vascular plant species in Hawaii: Aliens emit more than natives

Llusià J., Peñuelas J., Sardans J., Owen S.M., Niinemets Ü. (2010) Measurement of volatile terpene emissions in 70 dominant vascular plant species in Hawaii: Aliens emit more than natives. Global Ecology and Biogeography. 19: 863-874.
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Doi: 10.1111/j.1466-8238.2010.00557.x

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Aim Alien plant invasion is prominent in the Hawaiian Islands. There are many factors involved in invader success. To date, there is a general lack of information about one of them, which we aim to study here: the terpene emission capacity of both Hawaiian native and alien plants.Location Oahu (Hawaii).Methods We screened 35 alien and 35 native dominant plant species on Oahu Island for monoterpene emissions. The emission rates were measured from field-grown plants under standardized conditions of temperature and quantum flux density in the laboratory.Results The emission rates of total terpenes ranged from 0 μg g-1 h-1 to 55 μg g-1 h-1, and altogether 15 different terpenes were emitted in detectable amounts by the overall set of species. A phylogenetic signal was observed for total terpene emissions. Total terpene emission rates were higher in aliens than in native species (12.8 ± 2.0 vs. 7.6 ± 1.9 μg g-1 h-1, respectively).Main conclusions The greater terpene emission capacity may confer protection against multiple stresses and may partly account for the success of the invasive species, and may make invasive species more competitive in response to new global change-driven combined stresses. These results are consistent with aliens coming from very diverse ecosystems with generally higher biotic and abiotic stress pressures, and having higher nutrient concentrations. On the contrary, these results are not consistent with the 'excess carbon' hypotheses. These results indicate changes in vegetation terpene emissions brought about by alien plant invasions. © 2010 Blackwell Publishing Ltd.

Llegeix més

Genome size unaffected by moderate changes in climate and phosphorus availability in Mediterranean plants.

Pellicer J, Estiarte M, Garcia S, Garnatje T, Peñuelas J, Sardans J, Valles J (2010) Genome size unaffected by moderate changes in climate and phosphorus availability in Mediterranean plants. African Journal of Biotechnology 9: 6070-6077.

Responses of the reflectance indices PRI and NDVI to experimental warming and drought in European shrublands along a north-south climatic gradient

Mänd P., Hallik L., Peñuelas J., Nilson T., Duce P., Emmett B.A., Beier C., Estiarte M., Garadnai J., Kalapos T., Schmidt I.K., Kovács-Láng E., Prieto P., Tietema A., Westerveld J.W., Kull O. (2010) Responses of the reflectance indices PRI and NDVI to experimental warming and drought in European shrublands along a north-south climatic gradient. Remote Sensing of Environment. 114: 626-636.
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Doi: 10.1016/j.rse.2009.11.003

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The aim of this study was to evaluate the use of ground-based canopy reflectance measurements to detect changes in physiology and structure of vegetation in response to experimental warming and drought treatment at six European shrublands located along a North-South climatic gradient. We measured canopy reflectance, effective green leaf area index (green LAIe) and chlorophyll fluorescence of dominant species. The treatment effects on green LAIe varied among sites. We calculated three reflectance indices: photochemical reflectance index PRI [531 nm; 570 nm], normalized difference vegetation index NDVI680 [780 nm; 680 nm] using red spectral region, and NDVI570 [780 nm; 570 nm] using the same green spectral region as PRI. All three reflectance indices were significantly related to green LAIe and were able to detect changes in shrubland vegetation among treatments. In general warming treatment increased PRI and drought treatment reduced NDVI values. The significant treatment effect on photochemical efficiency of plants detected with PRI could not be detected by fluorescence measurements. However, we found canopy level measured PRI to be very sensitive to soil reflectance properties especially in vegetation areas with low green LAIe. As both soil reflectance and LAI varied between northern and southern sites it is problematic to draw universal conclusions of climate-derived changes in all vegetation types based merely on PRI measurements. We propose that canopy level PRI measurements can be more useful in areas of dense vegetation and dark soils. © 2009.

Llegeix més

The emission factor of volatile isoprenoids: Stress, acclimation, and developmental responses

Niinemets Ü., Arneth A., Kuhn U., Monson R.K., Peñuelas J., Staudt M. (2010) The emission factor of volatile isoprenoids: Stress, acclimation, and developmental responses. Biogeosciences. 7: 2203-2223.
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Doi: 10.5194/bg-7-2203-2010

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The rate of constitutive isoprenoid emissions from plants is driven by plant emission capacity under specified environmental conditions (Es, the emission factor) and by responsiveness of the emissions to instantaneous variations in environment. In models of isoprenoid emission, Es has been often considered as intrinsic species-specific constant invariable in time and space. Here we analyze the variations in species-specific values of E s under field conditions focusing on abiotic stresses, past environmental conditions and developmental processes. The reviewed studies highlight strong stress-driven, adaptive (previous temperature and light environment and growth CO2 concentration) and developmental (leaf age) variations in Es values operating at medium to long time scales. These biological factors can alter species-specific Es values by more than an order of magnitude. While the majority of models based on early concepts still ignore these important sources of variation, recent models are including some of the medium- to long-term controls. However, conceptually different strategies are being used for incorporation of these longer-term controls with important practical implications for parameterization and application of these models. This analysis emphasizes the need to include more biological realism in the isoprenoid emission models and also highlights the gaps in knowledge that require further experimental work to reduce the model uncertainties associated with biological sources of variation. © Author(s) 2010.

Llegeix més

The leaf-level emission factor of volatile isoprenoids: Caveats, model algorithms, response shapes and scaling

Niinemets Ü., Monson R.K., Arneth A., Ciccioli P., Kesselmeier J., Kuhn U., Noe S.M., Peñuelas J., Staudt M. (2010) The leaf-level emission factor of volatile isoprenoids: Caveats, model algorithms, response shapes and scaling. Biogeosciences. 7: 1809-1832.
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Doi: 10.5194/bg-7-1809-2010

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In models of plant volatile isoprenoid emissions, the instantaneous compound emission rate typically scales with the plant's emission potential under specified environmental conditions, also called as the emission factor, ES. In the most widely employed plant isoprenoid emission models, the algorithms developed by Guenther and colleagues (1991, 1993), instantaneous variation of the steady-state emission rate is described as the product of ES and light and temperature response functions. When these models are employed in the atmospheric chemistry modeling community, species-specific ES values and parameter values defining the instantaneous response curves are often taken as initially defined. In the current review, we argue that ES as a characteristic used in the models importantly depends on our understanding of which environmental factors affect isoprenoid emissions, and consequently need standardization during experimental ES determinations. In particular, there is now increasing consensus that in addition to variations in light and temperature, alterations in atmospheric and/or within-leaf CO2 concentrations may need to be included in the emission models. Furthermore, we demonstrate that for less volatile isoprenoids, mono- and sesquiterpenes, the emissions are often jointly controlled by the compound synthesis and volatility. Because of these combined biochemical and physico-chemical drivers, specification of ES as a constant value is incapable of describing instantaneous emissions within the sole assumptions of fluctuating light and temperature as used in the standard algorithms. The definition of ES also varies depending on the degree of aggregation of ES values in different parameterization schemes (leaf- vs. canopy- or region-scale, species vs. plant functional type levels) and various aggregated ES schemes are not compatible for different integration models. The summarized information collectively emphasizes the need to update model algorithms by including missing environmental and physico-chemical controls, and always to define ES within the proper context of model structure and spatial and temporal resolution. © Author(s) 2010.

Llegeix més

Changes in monoterpene emission rates of quercus ilex infested by aphids tended by native or invasive lasius ant species

Paris C.I., Llusia J., Peñuelas J. (2010) Changes in monoterpene emission rates of quercus ilex infested by aphids tended by native or invasive lasius ant species. Journal of Chemical Ecology. 36: 689-698.
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Doi: 10.1007/s10886-010-9815-1

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The emission of volatile organic compounds (VOCs) depends on temperature and light. Other factors such as insect herbivory also may modify VOC emission. In particular, aphid feeding promotes the release of new compounds and changes the composition of plant volatile blends. Given that some aphids are tended by ants, we investigated whether ants change the emission of VOCs indirectly through attendance on aphids. The effect of Lachnus roboris aphids and two different tending ant species on terpene emission rates of 4-year-old holm oak (Quercus ilex) saplings was investigated during a field experiment. There were five treatments: saplings alone (T1), saplings infested with L. roboris aphids (T2), saplings infested with aphids tended by the local ant Lasius grandis (T3), those tended by small colonies of the invasive ant Lasius neglectus (T4), and those tended by large colonies of the same invasive ant species (T5). The infestation by L. roboris elicited the emission of Δ3-carene and increased the emission of myrcene and γ-terpinene. Terpene emissions were modified depending on the tending ant species. Attendance by the local ant L. grandis increased α and β-pinene and sabinene. Attendance by the invasive ant L. neglectus only decreased significantly the emission of myrcene, one of the major compounds of the Q. ilex blend. Aphid abundance decreased with time for all treatments, but there was no difference in aphid abundance among treatments. Total terpene emission rates were not correlated with aphid abundance. These results highlight that aphids and tending ants may change terpene emission rates, depending on the ant species. © 2010 Springer Science+Business Media, LLC.

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Faster returns on 'leaf economics' and different biogeochemical niche in invasive compared with native plant species

Penuelas J., Sardans J., Llusià J., Owen S.M., Carnicer J., Giambelluca T.W., Rezende E.L., Waite M., Niinemets Ü. (2010) Faster returns on 'leaf economics' and different biogeochemical niche in invasive compared with native plant species. Global Change Biology. 16: 2171-2185.
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Doi: 10.1111/j.1365-2486.2009.02054.x

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Plant-invasive success is one of the most important current global changes in the biosphere. To understand which factors explain such success, we compared the foliar traits of 41 native and 47 alien-invasive plant species in Oahu Island (Hawaii), a location with a highly endemic flora that has evolved in isolation and is currently vulnerable to invasions by exotic plant species. Foliar traits, which in most cases presented significant phylogenetic signal, i.e. closely related species tended to resemble each other due to shared ancestry, separated invasive from native species. Invasive species had lower leaf mass per area and enhanced capacities in terms of productivity (photosynthetic capacity) and nutrient capture both of macro- (N, P, K) and microelements (Fe, Ni, Cu and Zn). All these differences remain highly significant after removing the effects of phylogenetic history. Alien-invasive species did not show higher efficiency at using limiting nutrient resources, but they got faster leaf economics returns and occupied a different biogeochemical niche, which helps to explain the success of invasive plants and suggests that potential increases in soil nutrient availability might favor further invasive plant success. © 2009 Blackwell Publishing Ltd.

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