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Strong Induction of Minor Terpenes in Italian Cypress, Cupressus sempervirens, in Response to Infection by the Fungus Seiridium cardinale

Achotegui-Castells A., Danti R., Llusia J., Rocca G.D., Barberini S., Penuelas J. (2015) Strong Induction of Minor Terpenes in Italian Cypress, Cupressus sempervirens, in Response to Infection by the Fungus Seiridium cardinale. Journal of Chemical Ecology. : 0-0.
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Doi: 10.1007/s10886-015-0554-1

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Seiridium cardinale, the main fungal pathogen responsible for cypress bark canker, is the largest threat to cypresses worldwide. The terpene response of canker-resistant clones of Italian cypress, Cupressus sempervirens, to two differently aggressive isolates of S. cardinale was studied. Phloem terpene concentrations, foliar terpene concentrations, as well as foliar terpene emission rates were analyzed 1, 10, 30, and 90 days after artificial inoculation with fungal isolates. The phloem surrounding the inoculation point exhibited de novo production of four oxygenated monoterpenes and two unidentified terpenes. The concentrations of several constitutive mono- and diterpenes increased strongly (especially α-thujene, sabinene, terpinolene, terpinen-4-ol, oxygenated monoterpenes, manool, and two unidentified diterpenes) as the infection progressed. The proportion of minor terpenes in the infected cypresses increased markedly from the first day after inoculation (from 10 % in the control to 30–50 % in the infected treatments). Foliar concentrations showed no clear trend, but emission rates peaked at day 10 in infected trees, with higher δ-3-carene (15-fold) and total monoterpene (10-fold) emissions than the control. No substantial differences were found among cypresses infected by the two fungal isolates. These results suggest that cypresses activate several direct and indirect chemical defense mechanisms after infection by S. cardinale. © 2015 Springer Science+Business Media New York

Llegeix més

Herbivory and seedling establishment in Pyrenean forests: Influence of micro- and meso-habitat factors on browsing pressure

Ameztegui A., Coll L. (2015) Herbivory and seedling establishment in Pyrenean forests: Influence of micro- and meso-habitat factors on browsing pressure. Forest Ecology and Management. 342: 103-111.
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Doi: 10.1016/j.foreco.2015.01.021

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Browsing damage is among the most determinant factors that limit the establishment of tree seedlings in forests. In some areas, this process leads to massive mortalities that can reduce or even completely prevent the regeneration of some tree species. Mediterranean mountain forests have undergone during the last decades important changes in land-uses that have significantly altered the type and abundance of herbivore populations. In this study we assessed the impact of current grazing conditions in forest regeneration using a set of experimental plantations established in the Eastern Pyrenees in areas visited by domestic livestock (cattle and horses) and wild ungulates (mainly roe deer and chamois). We analyzed during 4. years the role of seedling species and size, mesohabitat (elevation and type of forest cover) and microhabitat (herbaceous cover, distance to shrub, and light availability) on the browsing-induced mortality of more than 500 seedlings of Pinus sylvestris, Pinus uncinata, Betula pendula and Abies alba, the most common tree species in the study area. Browsing-induced mortality for the three conifer species was much lower (40%) and depended on both microhabitat - mainly on the distance to protective elements such as shrubs; and mesohabitat, with an interaction between the elevational belt (site) and the type of forest cover (gaps vs. understory). In the subalpine belt, browsing on A. alba and P. uncinata was higher during summer at plots located in the forest understory whereas, during winter, it was higher at plots located in gaps. The study shows that both mesohabitat and microhabitat can exert an effect on the patterns of plant damage by herbivores, providing useful information to adapt forest management in areas particularly exposed to them. © 2015 Elsevier B.V.

Llegeix més

Examining the role of landscape structure and dynamics in alien plant invasion from urban Mediterranean coastal habitats

Basnou C., Iguzquiza J., Pino J. (2015) Examining the role of landscape structure and dynamics in alien plant invasion from urban Mediterranean coastal habitats. Landscape and Urban Planning. 136: 156-164.
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Doi: 10.1016/j.landurbplan.2014.12.001

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This paper aims to disentangle the effects of both current landscape structure and recent land use-change on alien plant invasion in urban Mediterranean coastal habitats. Patches of four habitat types (rock outcrops, sand dunes, scrublands and forests) of different sizes and surrounding landscape compositions were selected along the coast of the Metropolitan Region of Barcelona (NE Spain). Attributes of habitat patches, historical (1956) and current landscape composition around them, land-cover changes (1956-2005) and other environmental and geographic factors within these patches were obtained. The association of these attributes with alien plant richness, abundance and composition was investigated using GLM and CCA. Alien species richness was mostly explained by patch size and shape and built-up area proportion from 1956 and 2005 in a 50. m buffer around patches. Alien species abundance was mostly related to patch shape, temperature, rainfall, land-cover changes within patches and cropland cover of 1956 in a 50. m buffer around patches. Alien species composition was primary related to habitat type, temperature, land-cover changes within patches and the composition of the surrounding landscape. Results suggest that landscape factors affect alien species richness and abundance differently, which are indicative of species colonization and spread, respectively. Landscape history positively affects both colonization and spread, with evidence for a colonization credit related with past urban cover, and the association between recent patch dynamics and present aliens spread. Results highlight the importance of including landscape structure and dynamics in the management of plant invasions in coastal Mediterranean habitats, especially in metropolitan regions. © 2014 Elsevier B.V.

Llegeix més

A minimal model of fire-vegetation feedbacks and disturbance stochasticity generates alternative stable states in grassland-shrubland-woodland systems

Batllori E., Ackerly D.D., Moritz M.A. (2015) A minimal model of fire-vegetation feedbacks and disturbance stochasticity generates alternative stable states in grassland-shrubland-woodland systems. Environmental Research Letters. 10: 0-0.
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Doi: 10.1088/1748-9326/10/3/034018

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Altered disturbance regimes in the context of global change are likely to have profound consequences for ecosystems. Interactions between fire and vegetation are of particular interest, as fire is a major driver of vegetation change, and vegetation properties (e.g., amount, flammability) alter fire regimes. Mediterranean-type ecosystems (MTEs) constitute a paradigmatic example of temperate fire-prone vegetation. Although these ecosystems may be heavily impacted by global change, disturbance regime shifts and the implications of fire-vegetation feedbacks in the dynamics of such biomes are still poorly characterized. We developed a minimal modeling framework incorporating key aspects of fire ecology and successional processes to evaluate the relative influence of extrinsic and intrinsic factors on disturbance and vegetation dynamics in systems composed of grassland, shrubland, and woodland mosaics, which characterize many MTEs. In this theoretical investigation, we performed extensive simulations representing different background rates of vegetation succession and disturbance regime (fire frequency and severity) processes that reflect a broad range of MTE environmental conditions. Varying fire-vegetation feedbacks can lead to different critical points in underlying processes of disturbance and sudden shifts in the vegetation state of grassland-shrubland-woodland systems, despite gradual changes in ecosystem drivers as defined by the environment. Vegetation flammability and disturbance stochasticity effectively modify system behavior, determining its heterogeneity and the existence of alternative stable states in MTEs. Small variations in system flammability and fire recurrence induced by climate or vegetation changes may trigger sudden shifts in the state of such ecosystems. The existence of threshold dynamics, alternative stable states, and contrasting system responses to environmental change has broad implications for MTE management. © 2015 IOP Publishing Ltd.

Llegeix més

Interactions between transplants of Phragmites australis and Juncus acutus in Mediterranean coastal marshes: The modulating role of environmental gradients

Batriu E., Ninot J.M., Pino J. (2015) Interactions between transplants of Phragmites australis and Juncus acutus in Mediterranean coastal marshes: The modulating role of environmental gradients. Aquatic Botany. 124: 29-38.
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Doi: 10.1016/j.aquabot.2015.03.003

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Interactions between two coastal marsh plants (Phragmites australis and Juncus acutus) were investigated along three natural gradients of salinity, water table and soil texture, variously combined in a microtidal Mediterranean coastal marsh. Our aim was to clarify to what extent plant interactions explain the occurrence of stands of both species, since they are not solely due to their tolerance to environmental conditions. We used a replacement series design of field transplants. Mortality and relative yield index of aerial biomass were analyzed to assess the outcome of interactions using Generalized Linear Mixed Models. Results show that mortality was entirely driven by natural gradients. Specifically, higher salinity and soil clay contents increased mortality in both species, whereas high water table increased survival only in P. australis. Growth was controlled by plant interactions and by natural gradients. According to these results P. australis can suppress J. acutus in waterlogged and non-saline conditions. Where water table is deeper, J. acutus can suppress P. australis along a wide range of saline conditions. In the driest situations both species exhibited mutual interference and, in some cases, P. australis can again suppress J. acutus. Facilitation occurred along the salinity gradient in situations that correspond to low, medium or high stress for the beneficiary species, pointing that exceptions to the stress gradient hypothesis may occur in systems including multiple stress gradients. Our results suggest that competitive interactions and environmental gradients are not fully responsible for plant distribution in microtidal coastal marshes. © 2015 Elsevier B.V.

Llegeix més

Filtering of plant functional traits is determined by environmental gradients and by past land use in a mediterranean coastal marsh

Batriu E., Ninot J.M., Pino J. (2015) Filtering of plant functional traits is determined by environmental gradients and by past land use in a mediterranean coastal marsh. Journal of Vegetation Science. 26: 492-500.
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Doi: 10.1111/jvs.12251

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Question: What is the effect of past land use and environmental gradients on plant functional traits within coastal marsh plant communities? Location: Mediterranean microtidal marshes in the Llobregat Delta, NE Spain. Methods: We used a data set collected previously comprising 45 vegetation plots with associated soil parameters, water table conditions and past land use. For each species we obtained the values or states for a set of plant functional traits: plant height, leaf dry matter content, specific leaf area, seed production, seed weight, life form and lateral expansion. To account for the effect of phylogeny, we evaluated trait diversity skewness by means of an ultrametric phylogenetic tree specifically constructed for the species studied. The association between both environmental gradients and past disturbance, and plant functional traits was tested by means of RLQ analysis. Results: Of all the traits, only seed weight showed a phylogenetic signal; consequently, phylogeny was not included in the RLQ analysis. Conductivity was negatively correlated with seed weight, whereas water table conditions and soil ionic balance were negatively correlated with specific leaf area. Past disturbance was negatively correlated with leaf dry matter content and with lateral expansion. Conclusions: Plant traits of Llobregat Delta coastal marsh communities are conditioned by environmental gradients and by past land use. Soil ionic balance and water table conditions determine key plant functional traits such as specific leaf area. This finding also corroborates the importance of soil ionic balance as a plant life driver in microtidal Mediterranean marshes. The effect of past land use on species traits might, however, be partially indirect and mediated by associated environmental changes. © 2014 International Association for Vegetation Science.

Llegeix més

Ecological impacts of small hydropower plants on headwater stream fish: From individual to community effects

Benejam L., Saura-Mas S., Bardina M., Sola C., Munne A., Garcia-Berthou E. (2015) Ecological impacts of small hydropower plants on headwater stream fish: From individual to community effects. Ecology of Freshwater Fish. : 0-0.
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Doi: 10.1111/eff.12210

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Hydroelectricity is increasingly used worldwide as a source of renewable energy, and many mountain ranges have dozens or hundreds of hydropower plants, with many more being under construction or planned. Although the ecological impacts of large dams are relatively well known, the effects of small hydropower plants and their weirs have been much less investigated. We studied the effects of water diversion of small hydropower plants on fish assemblages in the upper Ter river basin (Catalonia, NE Spain), which has headwater reaches with good water quality and no large dams but many of such plants. We studied fish populations and habitat features on control and impacted reaches for water diversion of 16 hydropower plants. In the impacted reaches, there was a significantly lower presence of refuges for fish, poorer habitat quality, more pools and less riffles and macrophytes, and shallower water levels. We also observed higher fish abundance, larger mean fish size and better fish condition in the control than in impacted reaches, although the results were species-specific. Accordingly, species composition was also affected, with lower relative abundance of brown trout (Salmo trutta) and Pyrenean minnow (Phoxinus bigerri) in the impacted reaches and higher presence of stone loach (Barbatula quignardi) and Mediterranean barbel (Barbus meridionalis). Our study highlights the effects of water diversion of small hydropower plants from the individual to the population and community levels but probably underestimates them, urging for further assessment and mitigation of these ecological impacts. © 2014 John Wiley & Sons A/S.

Llegeix més

Effects of enhanced UV radiation and water availability on performance, biomass production and photoprotective mechanisms of Laurus nobilis seedlings

Bernal M., Verdaguer D., Badosa J., Abadia A., Llusia J., Penuelas J., Nunez-Olivera E., Llorens L. (2015) Effects of enhanced UV radiation and water availability on performance, biomass production and photoprotective mechanisms of Laurus nobilis seedlings. Environmental and Experimental Botany. 109: 264-275.
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Doi: 10.1016/j.envexpbot.2014.06.016

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Climate models predict an increase in ultraviolet (UV) radiation and a reduction in precipitation in the Mediterranean region in the coming decades. High levels of UV radiation and water shortage can both cause photo-oxidative stress in plants. The aim of this study was to investigate the effects of enhanced UV radiation and its interaction with low water availability on seedling performance, biomass production, and photoprotective mechanisms of the sclerophyllous evergreen species Laurus nobilis L. (laurel). To achieve this goal, one-year-old seedlings of L. nobilis were grown outdoors under three UV conditions (ambient UV, enhanced UV-A, and enhanced UV-A. +. UV-B) and under two watering regimes (watered to field capacity and reduced water supply). The results show that plants produced more biomass when exposed to above ambient levels of UV-A or UV-A. +. UV-B radiation, especially under low water availability. This was probably related to a UV-induced increase in leaf relative water content and in leaf water use efficiency under water shortage. Even though our results suggest that UV-A supplementation may play an important role in the stimulation of biomass production, plants grown under enhanced UV-A plots showed higher levels of energy dissipation as heat (measured as NPQ) and a higher de-epoxidation state of the violaxanthin cycle. This suggests a greater excess of light energy under UV-A supplementation, in accordance with the observed reduction in the foliar content of light-absorbing pigments in these plants. Strikingly, the addition of UV-B radiation mitigated these effects. In conclusion, UV enhancement might benefit water status and growth of L. nobilis seedlings, especially under low water availability. The results also indicate the activation of different plant response mechanisms to UV-A and UV-B radiation, which would interact to produce the overall plant response. © 2014 Elsevier B.V.

Llegeix més

Ground-and satellite-based evidence of the biophysical mechanisms behind the greening Sahel

Brandt M., Mbow C., Diouf A.A., Verger A., Samimi C., Fensholt R. (2015) Ground-and satellite-based evidence of the biophysical mechanisms behind the greening Sahel. Global Change Biology. 21: 1610-1620.
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Doi: 10.1111/gcb.12807

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After a dry period with prolonged droughts in the 1970s and 1980s, recent scientific outcome suggests that the decades of abnormally dry conditions in the Sahel have been reversed by positive anomalies in rainfall. Various remote sensing studies observed a positive trend in vegetation greenness over the last decades which is known as the re-greening of the Sahel. However, little investment has been made in including long-term ground-based data collections to evaluate and better understand the biophysical mechanisms behind these findings. Thus, deductions on a possible increment in biomass remain speculative. Our aim is to bridge these gaps and give specifics on the biophysical background factors of the re-greening Sahel. Therefore, a trend analysis was applied on long time series (1987-2013) of satellite-based vegetation and rainfall data, as well as on ground-observations of leaf biomass of woody species, herb biomass, and woody species abundance in different ecosystems located in the Sahel zone of Senegal. We found that the positive trend observed in satellite vegetation time series (+36%) is caused by an increment of in situ measured biomass (+34%), which is highly controlled by precipitation (+40%). Whereas herb biomass shows large inter-annual fluctuations rather than a clear trend, leaf biomass of woody species has doubled within 27 years (+103%). This increase in woody biomass did not reflect on biodiversity with 11 of 16 woody species declining in abundance over the period. We conclude that the observed greening in the Senegalese Sahel is primarily related to an increasing tree cover that caused satellite-driven vegetation indices to increase with rainfall reversal. Copyright © 2015 John Wiley & Sons Ltd214 April 2015 10.1111/gcb.12807 Primary Research Article Primary Research Articles © 2014 John Wiley & Sons Ltd.

Llegeix més

Urban plant physiology: Adaptation-mitigation strategies under permanent stress

Calfapietra C., Penuelas J., Niinemets T. (2015) Urban plant physiology: Adaptation-mitigation strategies under permanent stress. Trends in Plant Science. 20: 72-75.
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Doi: 10.1016/j.tplants.2014.11.001

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Urban environments that are stressful for plant function and growth will become increasingly widespread in future. In this opinion article, we define the concept of 'urban plant physiology', which focuses on plant responses and long term adaptations to urban conditions and on the capacity of urban vegetation to mitigate environmental hazards in urbanized settings such as air and soil pollution. Use of appropriate control treatments would allow for studies in urban environments to be comparable to expensive manipulative experiments. In this opinion article, we propose to couple two approaches, based either on environmental gradients or manipulated gradients, to develop the concept of urban plant physiology for assessing how single or multiple environmental factors affect the key environmental services provided by urban forests. © 2014 Elsevier Ltd.

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