Achotegui-Castells A., Della Rocca G., Llusià J., Danti R., Barberini S., Bouneb M., Simoni S., Michelozzi M., Peñuelas J. (2016) Terpene arms race in the Seiridium cardinale - Cupressus sempervirens pathosystem. Scientific Reports. 6: 0-0.EnllaçDoi: 10.1038/srep18954
The canker-causing fungus Seiridium cardinale is the major threat to Cupressus sempervirens worldwide. We investigated the production of terpenes by canker-resistant and susceptible cypresses inoculated with S. cardinale, the effect of these terpenes on fungal growth, and the defensive biotransformation of the terpenes conducted by the fungus. All infected trees produced de novo terpenes and strongly induced terpenic responses, but the responses were stronger in the canker-resistant than the susceptible trees. In vitro tests for the inhibition of fungal growth indicated that the terpene concentrations of resistant trees were more inhibitory than those of susceptible trees. The highly induced and de novo terpenes exhibited substantial inhibition (more than a fungicide reference) and had a high concentration-dependent inhibition, whereas the most abundant terpenes had a low concentration-dependent inhibition. S. cardinale biotransformed three terpenes and was capable of detoxifying them even outside the fungal mycelium, in its immediate surrounding environment. Our results thus indicated that terpenes were key defences efficiently used by C. sempervirens, but also that S. cardinale is ready for the battle.
Balzarolo M., Vicca S., Nguy-Robertson A.L., Bonal D., Elbers J.A., Fu Y.H., Grünwald T., Horemans J.A., Papale D., Peñuelas J., Suyker A., Veroustraete F. (2016) Matching the phenology of Net Ecosystem Exchange and vegetation indices estimated with MODIS and FLUXNET in-situ observations. Remote Sensing of Environment. 174: 290-300.EnllaçDoi: 10.1016/j.rse.2015.12.017
Shifts in ecosystem phenology play an important role in the definition of inter-annual variability of net ecosystem carbon uptake. A good estimate at the global scale of ecosystem phenology, mainly that of photosynthesis or gross primary productivity (GPP), may be provided by vegetation indices derived from MODIS satellite image data.However, the relationship between the start date of a growing (or greening) season (SGS) when derived from different vegetation indices (VI's), and the starting day of carbon uptake is not well elucidated. Additionally, the validation of existing phenology data with in-situ measurements is largely missing. We have investigated the possibility to use different VI's to predict the starting day of the growing season for 28 FLUXNET sites as well as MODIS data. This analysis included main plant functional types (PFT's).Of all VI's taken into account in this paper, the NDVI (Normalized Difference Vegetation Index) shows the highest correlation coefficient for the relationship between the starting day of the growing season as observed with MODIS and in-situ observations. However, MODIS observations elicit a 20-21 days earlier SGS date compared to in-situ observations. The prediction for the NEE start of the growing season diverges when using different VI's, and seems to depend on the amplitude for carbon and VI and on PFT. The optimal VI for estimation of a SGS date was PFT-specific - for example the WRDVI for cropland, but the MODIS NDVI performed best when applied as an estimator for Net Ecosystem Exchange and when considering all PFT's pooled. © 2015 Elsevier Inc.
Bartrons M., Catalan J., Penuelas J. (2016) Spatial And Temporal Trends Of Organic Pollutants In Vegetation From Remote And Rural Areas. Scientific Reports. 6: 0-0.EnllaçDoi: 10.1038/srep25446
Persistent organic pollutants (POPs) and polycyclic aromatic hydrocarbons (PAHs) used in agricultural, industrial, and domestic applications are widely distributed and bioaccumulate in food webs, causing adverse effects to the biosphere. A review of published data for 1977-2015 for a wide range of vegetation around the globe indicates an extensive load of pollutants in vegetation. On a global perspective, the accumulation of POPs and PAHs in vegetation depends on the industrialization history across continents and distance to emission sources, beyond organism type and climatic variables. International regulations initially reduced the concentrations of POPs in vegetation in rural areas, but concentrations of HCB, HCHs, and DDTs at remote sites did not decrease or even increased over time, pointing to a remobilization of POPs from source areas to remote sites. The concentrations of compounds currently in use, PBDEs and PAHs, are still increasing in vegetation. Differential congener specific accumulation is mostly determined by continent - in accordance to the different regulations of HCHs, PCBs and PBDEs in different countries - and by plant type (PAHs). These results support a concerning general accumulation of toxic pollutants in most ecosystems of the globe that for some compounds is still far from being mitigated in the near future. © 2016, Nature Publishing Group. All rights reserved.
Bastos A., Janssens I.A., Gouveia C.M., Trigo R.M., Ciais P., Chevallier F., Peñuelas J., Rödenbeck C., Piao S., Friedlingstein P., Running S.W. (2016) European land CO2 sink influenced by NAO and East-Atlantic Pattern coupling. Nature Communications. 7: 0-0.EnllaçDoi: 10.1038/ncomms10315
Large-scale climate patterns control variability in the global carbon sink. In Europe, the North-Atlantic Oscillation (NAO) influences vegetation activity, however the East-Atlantic (EA) pattern is known to modulate NAO strength and location. Using observation-driven and modelled data sets, we show that multi-annual variability patterns of European Net Biome Productivity (NBP) are linked to anomalies in heat and water transport controlled by the NAO-EA interplay. Enhanced NBP occurs when NAO and EA are both in negative phase, associated with cool summers with wet soils which enhance photosynthesis. During anti-phase periods, NBP is reduced through distinct impacts of climate anomalies in photosynthesis and respiration. The predominance of anti-phase years in the early 2000s may explain the European-wide reduction of carbon uptake during this period, reported in previous studies. Results show that improving the capability of simulating atmospheric circulation patterns may better constrain regional carbon sink variability in coupled carbon-climate models. © 2016, Nature Publishing Group. All rights reserved.
Benavides R., Escudero A., Coll L., Ferrandis P., Ogaya R., Gouriveau F., Peñuelas J., Valladares F. (2016) Recruitment patterns of four tree species along elevation gradients in Mediterranean mountains: Not only climate matters. Forest Ecology and Management. 360: 287-296.EnllaçDoi: 10.1016/j.foreco.2015.10.043
Evidence of tree regeneration failure of some species in the Iberian Peninsula forests warns us about the impact that the global change may exert on the preservation of Mediterranean forests, such as we know them. Predictions agree about an exacerbation of the summer drought there, acknowledged as the main limiting factor for the recruits' survival. On the other hand, many studies have also proved the relevant role that local heterogeneity has over the spatial distribution of forest species recruitment by providing safe sites. Therefore, to unravel how climate interacts with local factors over juveniles' performance seems crucial for the design of successful management strategies that allow facing the global warming. Here, we surveyed the natural recruitment of four dominant tree species in seven mountainous regions in the Iberian Peninsula, along entire elevational ranges as surrogates of their climatic ranges. Two of them have alpine and temperate distributions with populations at their rear edge in the Spanish mountains: Fagus sylvatica and Pinus uncinata; and the other two have a genuine Mediterranean distribution: Quercus ilex and Pinus nigra. Our main goal was to analyze for each species the effect of climate, local factors (i.e. light availability, stand structure and ground cover) and the interactions among them to identify the main drivers leading the regeneration process, assessed in terms of presence, abundance and mean annual growth of juveniles. The results showed different environmental factors determining the recruitment patterns of each species. Nevertheless, they highlighted the pervasive role exerted by both climate and fine scale factors, particularly the co-occurring vegetation on recruits' abundance, and the light availability on their growth. Moreover, we found some interactions among annual mean temperature and local factors, suggesting that climate and local heterogeneity act hierarchically, i.e. the local conditions may mitigate or exacerbate the impact of climate on juveniles. These results advocate for further research to increase our knowledge on the complex net of interactions among factors involved in recruitment at different scales, which in turn should be taken into account and incorporated in forthcoming management strategies. © 2015 Elsevier B.V.
Camino-Serrano M., Graf Pannatier E., Vicca S., Luyssaert S., Jonard M., Ciais P., Guenet B., Gielen B., Peñuelas J., Sardans J., Waldner P., Etzold S., Cecchini G., Clarke N., Galić Z., Gandois L., Hansen K., Johnson J., Klinck U., Lachmanová Z., Lindroos A.J., Meesenburg H., Nieminen T.M., Sanders T.G.M., Sawicka K., Seidling W., Thimonier A., Vanguelova E., Verstraeten A., Vesterdal L., Janssens I.A. (2016) Trends in soil solution dissolved organic carbon (DOC) concentrations across European forests. Biogeosciences Discussions. 2016: 0-0.EnllaçDoi: 10.5194/bg-2015-632
Dissolved organic carbon (DOC) in soil solution is connected to DOC in surface waters through hydrological flows. Therefore, it is expected that long-term dynamics of DOC in surface waters reflect DOC trends in soil solution. However, a multitude of site-studies has failed so far to establish consistent trends in soil solution DOC, whereas increasing concentrations in European surface waters over the past decades appear to be the norm, possibly as a result from acidification recovery. The objectives of this study were therefore to understand the long-term trends of soil solution DOC from a large number of European forests (ICP Forests Level II plots) and determine their main physico-chemical and biological controls. We applied trend analys is at two levels: 1) to the entire European dataset and 2) to the individual time series and related trends with plot characteristics, i.e., soil and vegetation properties, soil solution chemistry and atmospheric deposition loads. Analyses of the entire dataset showed an overall increasing trend in DOC concentrations in the organic layers, but, at individual plots and depths, there was no clear overall trend in soil solution DOC across Europe with temporal slopes of soil solution DOC ranging between -16.8% yr-1 and +23% yr-1 (median= +0.4% yr-1). The non-significant trends (40%) outnumbered the increasing (35%) and decreasing trends (25%) across the 97 ICP Forests Level II sites. By means of multivariate statistics, we found increasing DOC concentrations with increasing mean nitrate (NO3 -) deposition and decreasing DOC concentrations with decreasing mean sulphate (SO4 2-) deposition, with the magnitude of these relationships depending on plot deposition history. While the attribution of increasing trends in DOC to the reduction of SO4 2- deposition could be confirmed in N-poorer forests, in agreement with observations in surface waters, this was not the case in N-richer forests. In conclusion, long-term trends of soil solution DOC reflected the interactions between controls acting at local (soil and vegetation properties) and regional (atmospheric deposition of SO4 2- and inorganic N) scales. © Author(s) 2016.
Diaz-de-Quijano M., Kefauver S., Ogaya R., Vollenweider P., Ribas À., Peñuelas J. (2016) Visible ozone-like injury, defoliation, and mortality in two Pinus uncinata stands in the Catalan Pyrenees (NE Spain). European Journal of Forest Research. 135: 687-696.EnllaçDoi: 10.1007/s10342-016-0964-9
Ozone concentrations in the Pyrenees have exceeded the thresholds for forest protection since 1994. We surveyed the severity of visible O3 injuries, crown defoliation, and tree mortality of Pinus uncinata, the dominant species in subalpine forests in this mountain range, along two altitudinal and O3 gradients in the central Catalan Pyrenees and analysed their relationships with the local environmental conditions. The severity of visible O3 injuries increased with increasing mean annual [O3] when summer water availability was high (summer precipitation/potential evapotranspiration above 0.96), whereas higher [O3] did not produce more visible injuries during drier conditions. Mean crown defoliation and tree mortality ranged between 20.4–66.4 and 0.6–29.6 %, respectively, depending on the site. Both were positively correlated with the accumulated O3 exposure during the last 5 years and with variables associated with soil–water availability, which favours greater O3 uptake by increasing stomatal conductance. The results indicate that O3 contributed to the crown defoliation and tree mortality, although further research is clearly warranted to determine the contributions of the multiple stress factors to crown defoliation and mortality in P. uncinata stands in the Catalan Pyrenees. © 2016, Springer-Verlag Berlin Heidelberg.
Estiarte M., Vicca S., Peñuelas J., Bahn M., Beier C., Emmett B.A., Fay P.A., Hanson P.J., Hasibeder R., Kigel J., Kröel-Dulay G., Larsen K.S., Lellei-Kovács E., Limousin J.-M., Ogaya R., Ourcival J.-M., Reinsch S., Sala O.E., Schmidt I.K., Sternberg M., Tielbörger K., Tietema A., Janssens I.A. (2016) Few multiyear precipitation-reduction experiments find a shift in the productivity-precipitation relationship. Global Change Biology. : 0-0.EnllaçDoi: 10.1111/gcb.13269
Well-defined productivity-precipitation relationships of ecosystems are needed as benchmarks for the validation of land models used for future projections. The productivity-precipitation relationship may be studied in two ways: the spatial approach relates differences in productivity to those in precipitation among sites along a precipitation gradient (the spatial fit, with a steeper slope); the temporal approach relates interannual productivity changes to variation in precipitation within sites (the temporal fits, with flatter slopes). Precipitation-reduction experiments in natural ecosystems represent a complement to the fits, because they can reduce precipitation below the natural range and are thus well suited to study potential effects of climate drying. Here, we analyse the effects of dry treatments in eleven multiyear precipitation-manipulation experiments, focusing on changes in the temporal fit. We expected that structural changes in the dry treatments would occur in some experiments, thereby reducing the intercept of the temporal fit and displacing the productivity-precipitation relationship downward the spatial fit. The majority of experiments (72%) showed that dry treatments did not alter the temporal fit. This implies that current temporal fits are to be preferred over the spatial fit to benchmark land-model projections of productivity under future climate within the precipitation ranges covered by the experiments. Moreover, in two experiments, the intercept of the temporal fit unexpectedly increased due to mechanisms that reduced either water loss or nutrient loss. The expected decrease of the intercept was observed in only one experiment, and only when distinguishing between the late and the early phases of the experiment. This implies that we currently do not know at which precipitation-reduction level or at which experimental duration structural changes will start to alter ecosystem productivity. Our study highlights the need for experiments with multiple, including more extreme, dry treatments, to identify the precipitation boundaries within which the current temporal fits remain valid. © 2016 John Wiley & Sons Ltd.
Fernández-Martínez M., Vicca S., Janssens I.A., Campioli M., Peñuelas J. (2016) Nutrient availability and climate as the main determinants of the ratio of biomass to NPP in woody and non-woody forest compartments. Trees - Structure and Function. 30: 775-783.EnllaçDoi: 10.1007/s00468-015-1319-8
Key message: Once the effect of stand age has been taken into account, nutrient availability and climate play a crucial role in determining the B:NPPs of woody and non-woody tissues. Abstract: Forest ecosystems accumulate large amounts of carbon in living tissues. The residence time of this carbon in the ecosystem depends largely on the turnover time of these tissues, which can be estimated as a surrogate of the ratio of biomass to net primary production (B:NPP). We used a global forest database of 310 sites containing data for biomass stocks and NPP to investigate the differences of B:NPPs among species and forest compartments and to determine B:NPPs main exogenous (mainly climate and nutrient availability) and endogenous (leaf habit and stand age) drivers. We used asymptotic exponential functions to adjust the B:NPPs of woody compartments to a theoretical stationary state to allow comparisons between forests of different ages. The B:NPPs of woody tissues (branches, stems, and coarse roots) were positively influenced by stand age, conversely to fine roots and leaves, which were weakly dependent on the age of the forest. The B:NPPs of woody tissues were positively correlated with nutrient availability, whereas fine-root B:NPPs decreased with increasing nutrient availability. The foliar B:NPP of evergreen forests was positively correlated with water deficit, and the fine-root B:NPP was correlated positively with the seasonality of precipitation and with annual thermal amplitude but negatively with water deficit. Our results support the influence of climate on the B:NPPs of non-woody compartments and identify nutrient availability as the main influence on the B:NPPs of woody tissues. © 2015, Springer-Verlag Berlin Heidelberg.
Fernández-Martínez M., Vicca S., Janssens I.A., Espelta J.M., Peñuelas J. (2016) The North Atlantic Oscillation synchronises fruit production in western European forests. Ecography. : 0-0.EnllaçDoi: 10.1111/ecog.02296
Weather and its lagged effects have been associated with interannual variability and synchrony of fruit production for several tree species. Such relationships are used often in hypotheses relating interannual variability in fruit production with tree resources or favourable pollinating conditions and with synchrony in fruit production among sites through the Moran effect (the synchronisation of biological processes among populations driven by meteorological variability) or the local availability of pollen. Climatic teleconnections, such as the North Atlantic Oscillation (NAO), representing weather packages, however, have rarely been correlated with fruit production, despite often being better predictors of ecological processes than is local weather. The aim of this study was to test the utility of seasonal NAO indices for predicting interannual variability and synchrony in fruit production using data from 76 forests of Abies alba, Fagus sylvatica, Picea abies, Pseudotsuga menziesii, Quercus petraea, and Q. robur distributed across central Europe. Interannual variability in fruit production for all species was significantly correlated with seasonal NAO indices, which were more prominently important predictors than local meteorological variables. The relationships identified by these analyses indicated that proximal causes were mostly responsible for the interannual variability in fruit production, supporting the premise that local tree resources and favourable pollinating conditions are needed to produce large fruit crops. Synchrony in fruit production between forests was mainly associated with weather and geographical distance among sites. Also, fruit production for a given year was less variable among sites during warm and dry springs (negative spring NAO phases). Our results identify the Moran effect as the most likely mechanism for synchronisation of fruit production at large geographical scales and the possibility that pollen availability plays a role in synchronising fruit production at local scales. Our results highlight the influence of the NAO on the patterns of fruit production across western Europe. © 2016 Nordic Society Oikos.
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