Mikheyev A.S., McBride C.S., Mueller U.G., Parmesan C., Smee M.R., Stefanescu C., Wee B., Singer M.C. (2013) Host-associated genomic differentiation in congeneric butterflies: Now you see it, now you do not. Molecular Ecology. 22: 4753-4766.EnllaçDoi: 10.1111/mec.12423
Ecotypic variation among populations may become associated with widespread genomic differentiation, but theory predicts that this should happen only under particular conditions of gene flow, selection and population size. In closely related species, we might expect the strength of host-associated genomic differentiation (HAD) to be correlated with the degree of phenotypic differentiation in host-adaptive traits. Using microsatellite and Amplified Fragment Length Polymorphism (AFLP) markers, and controlling for isolation by distance between populations, we sought HAD in two congeneric species of butterflies with different degrees of host plant specialization. Prior work on Euphydryas editha had shown strong interpopulation differentiation in host-adapted traits, resulting in incipient reproductive isolation among host-associated ecotypes. We show here that Euphydryas aurinia had much weaker host-associated phenotypic differentiation. Contrary to our expectations, we detected HAD in Euphydryas aurinia, but not in E. editha. Even within an E. aurinia population that fed on both hosts, we found weak but significant sympatric HAD that persisted in samples taken 9 years apart. The finding of significantly stronger HAD in the system with less phenotypic differentiation may seem paradoxical. Our findings can be explained by multiple factors, ranging from differences in dispersal or effective population size, to spatial variation in genomic or phenotypic traits and to structure induced by past histories of host-adapted populations. Other infrequently measured factors, such as differences in recombination rates, may also play a role. Our result adds to recent work as a further caution against assumptions of simple relationships between genomic and adaptive phenotypic differentiation. © 2013 John Wiley & Sons Ltd.
Mizunuma T., Wilkinson M., L. Eaton E., Mencuccini M., I. L. Morison J., Grace J. (2013) The relationship between carbon dioxide uptake and canopy colour from two camera systems in a deciduous forest in southern England. Functional Ecology. 27: 196-207.EnllaçDoi: 10.1111/1365-2435.12026
Carbon dioxide flux measurements using the eddy covariance (EC) methodology have helped researchers to develop models of ecosystem carbon balance. However, making reliable predictions of carbon fluxes is not straightforward due to phenological changes and possible abiotic/biotic stresses that profoundly influence tree functioning. To assess the influence of canopy phenological state on CO2 flux, we installed two different digital camera systems at different viewing angles (an outdoor webcam with a near-horizontal view and a commercial 'fisheye' digital camera with a downward view) on a flux measurement tower in southern England and tracked the visual change of the canopy in this oak-dominated (Quercus robur L.) forest over two growing seasons. Changes in the setting of the camera's white balance substantially affected the quality of the webcam images. However, the timing of the onset of greening and senescence was, nevertheless, detectable for the individual trees as well as the overall canopy for both years. The greening-up date assessed from the downward images from a hemispherical lens was ~5 days earlier than from the horizontal-view images, because of ground vegetation development (not visible in the horizontal view). The effects of a late air frost in 2010 were evident in the canopy greenness, and these led to reductions in daily gross primary productivity (GPP). The cameras recorded differences between individual tree crowns, showing their different responses to the late frost. A major new finding from this work is the strong relationship between GPP and Hue, which was stronger than the relationship between GPP and NDVI. © 2012 The Authors. Functional Ecology © 2012 British Ecological Society.
Morfopoulosl C., Prentice I.C., Keenan T.F., Friedlingstein P., Medlyn B.E., Penuelas J., Possell M. (2013) A unifying conceptual model for the environmental responses of isoprene emissions from plants. Annals of Botany. 112: 1223-1238.EnllaçDoi: 10.1093/aob/mct206
Background and Aims Isoprene is the most important volatile organic compound emitted by land plants in terms of abundance and environmental effects. Controls on isoprene emission rates include light, temperature, water supply and CO2 concentration. A need to quantify these controls has long been recognized. There are already models that give realistic results, but they are complex, highly empirical and require separate responses to different drivers. This study sets out to find a simpler, unifying principle. Methods A simple model is presented based on the idea of balancing demands for reducing power (derived from photosynthetic electron transport) in primary metabolism versus the secondary pathway that leads to the synthesis of isoprene. This model's ability to account for key features in a variety of experimental data sets is assessed. Key results The model simultaneously predicts the fundamental responses observed in short-term experiments, namely: (1) the decoupling between carbon assimilation and isoprene emission; (2) a continued increase in isoprene emission with photosynthetically active radiation (PAR) at high PAR, after carbon assimilation has saturated; (3) a maximum of isoprene emission at low internal CO2 concentration (ci) and an asymptotic decline thereafter with increasing ci; (4) maintenance of high isoprene emissions when carbon assimilation is restricted by drought; and (5) a temperature optimum higher than that of photosynthesis, but lower than that of isoprene synthase activity. ConclusionsAsimple modelwas used to test the hypothesis that reducing power available to the synthesis pathway for isoprene varies according to the extent to which the needs of carbon assimilation are satisfied. Despite its simplicity the model explains much in terms of the observed response of isoprene to external drivers aswell as the observed decoupling between carbon assimilation and isoprene emission. The concept has the potential to improve globalscale modelling of vegetation isoprene emission. © The Author 2013.
Mulder C., Ahrestani F.S., Bahn M., Bohan D.A., Bonkowski M., Griffiths B.S., Guicharnaud R.A., Kattge J., Krogh P.H., Lavorel S., Lewis O.T., Mancinelli G., Naeem S., Penuelas J., Poorter H., Reich P.B., Rossi L., Rusch G.M., Sardans J., Wright I.J. (2013) Connecting the Green and Brown Worlds. Allometric and Stoichiometric Predictability of Above- and Below-Ground Networks. Advances in Ecological Research. 49: 69-175.EnllaçDoi: 10.1016/B978-0-12-420002-9.00002-0
We examine the potential of trait-based parameters of taxa for linking above- and below-ground ecological networks (hereafter 'green' and 'brown' worlds) to understand and predict community dynamics. This synthesis considers carbon, nitrogen and phosphorus-related traits, the abundance of component species and their size distribution across trophic levels under different forms of management. We have analysed existing and novel databases on plants, microbes and invertebrates that combine physico-chemical and biological information from (agro)ecosystems spanning the globe. We found (1) evidence that traits from above- and below-ground systems may be integrated in the same model and (2) a much greater than expected stoichiometric plasticity of plants and microbes which has implications for the entire food-web mass-abundance scaling. Nitrogen and phosphorus are primary basal resources (hence, drivers) and more retranslocation of P than of N from leaves will lead to higher N:P in the litter and soil organic matter. Thus, under nutrient-rich conditions, higher foliar concentrations of N and P are reflected by lower N:P in the brown litter, suggesting less P retranslocated than N. This apparent stoichiometric dichotomy between green and brown could result in shifts in threshold elemental ratios critical for ecosystem functioning. It has important implications for a general food-web model, given that resource C:N:P ratios are generally assumed to reflect environmental C:N:P ratios. We also provide the first evidence for large-scale allometric changes according to the stoichiometry of agroecosystems. Finally, we discuss insights that can be gained from integrating carbon and nitrogen isotope data into trait-based approaches, and address the origin of changes in δ13C and δ15N fractionation values in relation to consumer-resource body-mass ratios. © 2013 Elsevier Ltd.
Mänd P., Hallik L., Peñuelas J., Kull O. (2013) Electron transport efficiency at opposite leaf sides: Effect of vertical distribution of leaf angle, structure, chlorophyll content and species in a forest canopy. Tree Physiology. 33: 202-210.EnllaçDoi: 10.1093/treephys/tps112
We investigated changes in chlorophyll a fluorescence from alternate leaf surfaces to assess the intraleaf light acclimation patterns in combination with natural variations in radiation, leaf angles, leaf mass per area (LMA), chlorophyll content (Chl) and leaf optical parameters. Measurements were conducted on bottom- and top-layer leaves of Tilia cordata Mill. (a shadetolerant sub-canopy species, sampled at heights of 11 and 16 m) and Populus tremula L. (a light-demanding upper canopy species, sampled at canopy heights of 19 and 26 m). The upper canopy species P. tremula had a six times higher PSII quantum yield (ΦII) and ratio of open reaction centres (qP), and a two times higher LMA than T. cordata. These species-specific differences were also present when the leaves of both species were in similar light conditions. Leaf adaxial/abaxial fluorescence ratio was significantly larger in the case of more horizontal leaves. Populus tremula (more vertical leaves), had smaller differences in fluorescence parameters between alternate leaf sides compared with T. cordata (more horizontal leaves). However, optical properties on alternate leaf sides showed a larger difference for P. tremula. Intraspecifically, the measured optical parameters were better correlated with LMA than with leaf Chl. Species-specific differences in leaf anatomy appear to enhance the photosynthetic potential of leaf biochemistry by decreasing the interception of excess light in P. tremula and increasing the light absorptance in T. cordata. Our results indicate that intraleaf light absorption gradient, described here as leaf adaxial/abaxial side ratio of chlorophyll a fluorescence, varies significantly with changes in leaf light environment in a multi-layer multi-species tree canopy. However, this variation cannot be described merely as a simple function of radiation, leaf angle, Chl or LMA, and species-specific differences in light acclimation strategies should also be considered. © The Author 2013. Published by Oxford University Press. All rights reserved.
Obersteiner M., Penuelas J., Ciais P., Van Der Velde M., Janssens I.A. (2013) The phosphorus trilemma. Nature Geoscience. 6: 897-898.EnllaçDoi: 10.1038/ngeo1990
[No abstract available]
Ojeda G., Patrício J., Navajas H., Comellas L., Alcañiz J.M., Ortiz O., Marks E., Natal-da-Luz T., Sousa J.P. (2013) Effects of nonylphenols on soil microbial activity and water retention. Applied Soil Ecology. 64: 77-83.EnllaçDoi: 10.1016/j.apsoil.2012.10.012
The main aim of this study is to analyze the influence of 4-nonylphenol (NP) on soil water retention and biological activity. Two doses of 4-nonylphenol (25 and 50mgkg-1) were tested in a loam soil with and without peat amendment. In general, one week after the start of the experiment, the soil water content retained at -0.75MPa of soil suction was 18% higher in the soil amended and its basal respiration (BR) was 15% higher than soil without peat. In contrast, the microbial activity indices (CM: coefficient of mineralization or BR:total organic carbon (TOC) ratio; Cmic:Corg: microbial biomass carbon (MBC):TOC ratio; qCO2: metabolic quotient or BR:MBC ratio) were higher in the soil without peat, compared to the soil amended with peat. On the other hand, the addition of NP to soil was able to modify soil biological but not physical (water retention, desorption) properties. When soil was amended with peat, MBC was reduced one week after applying NP. In contrast, no effects of NP on MBC were observed in the soil without peat. BR was reduced by 16% one week after applying 50mgkg-1 of NP to soil with peat, and was increased by 46% one week after applying 25mgkg-1 of NP to soil without peat. The effects of NP on MBC and BR could be associated more with the adsorption of NP by soil organic matter, while changes in CM or Cmic:Corg ratio were more closely related to changes in soil water retention. The potential toxic effects of NP (high qCO2 values) were only observed in the absence of peat amendments. Peat addition reduced NP toxic effects on microorganisms. © 2012 Elsevier B.V.
Owen S.M., Penuelas J. (2013) Volatile isoprenoid emission potentials are correlated with essential isoprenoid concentrations in five plant species. Acta Physiologiae Plantarum. 35: 3109-3125.EnllaçDoi: 10.1007/s11738-013-1344-4
This study offers new insight and data in support of the "opportunist hypothesis", which suggests that there might be a relationship between carotenoid and volatile isoprenoid production. Five species of volatile isoprenoid-emitting plants (Eucalyptus globulus, Eucalyptus gunnii, Mucuna pruriens, Lycopersicon esculentum and Quercus ilex) were exposed to a range of imposed and natural stress conditions over a period of a few weeks in order to generate different levels of isoprenoid production potential. Volatile isoprenoid emission potentials and carotenoid concentrations were measured in all species, and dimethylallyl diphosphate (DMAPP) concentrations were measured in E. globulus, E. gunnii, M. pruriens and L. esculentum. Generally, instantaneously emitted isoprenoid emission potentials were positively correlated with carotenoid concentrations, and were negatively correlated with DMAPP concentrations. In contrast, emission potentials of monoterpenes stored in tissue pools were negatively correlated with carotenoid concentrations, and positively correlated with DMAPP concentrations. Our results support the possibility of a link (either direct, e.g. via substrate availability, or indirect, e.g. via complementary functionality) between emission potential of the volatile isoprenoid compounds studied here, and carotenoid synthesis at time scales of days to weeks. © 2013 Franciszek Górski Institute of Plant Physiology, Polish Academy of Sciences, Kraków.
Paneque-Galvez J., Mas J.-F., Gueze M., Luz A.C., Macia M.J., Orta-Martinez M., Pino J., Reyes-Garcia V. (2013) Land tenure and forest cover change. The case of southwestern Beni, Bolivian Amazon, 1986-2009. Applied Geography. 43: 113-126.EnllaçDoi: 10.1016/j.apgeog.2013.06.005
As land use change continues to increase throughout the Amazon basin, there is a pressing need to accurately map, quantify and assess the effects of different factors on forest cover change (FCC). Land tenure may sometimes have important effects on forest cover, yet such effects remain poorly understood in Amazonia, particularly outside Brazil. In this paper we assess whether significant differences in trends of FCC can be partially explained by different land tenure arrangements, using a case study in southwestern Beni (Bolivian Amazon). We examine spatio-temporal dynamics of FCC across four land tenure systems (indigenous titled territory, protected area, logging concession, and private land) by classifying forests using a time-series of Landsat satellite imagery consisting of four dates (1986, 1996, 2001, 2009). Specifically, we unravel (1) trends in early growth and old-growth forest extent, including changes in total cover area, annual change rates, and spatial change dynamics, and (2) trends in old-growth forest fragmentation. To better understand the association between land tenure and FCC, we qualitatively assess the potential role that other underlying and proximate drivers may have had in FCC over the study period. We found that private lands underwent, by far, the largest FCC, that indigenous territories and the protected area had little FCC, and that logging concessions were responsible for the lowest FCC. Our findings suggest that land tenure played a key role in FCC except in private areas, where many other drivers had operated. Our study sheds light into the potential role of land tenure in FCC and has important implications for public policies aimed at socioeconomic development and environmental conservation in the Amazon. We give some policy recommendations drawn from a biocultural conservation perspective that could contribute to implement more inclusive conservation policies in the region. © 2013 Elsevier Ltd.
Paneque-Gálvez J., Mas J.-F., Moré G., Cristóbal J., Orta-Martínez M., Luz A.C., Guèze M., Macía M.J., Reyes-García V. (2013) Enhanced land use/cover classification of heterogeneous tropical landscapes using support vector machines and textural homogeneity. International Journal of Applied Earth Observation and Geoinformation. 23: 372-383.EnllaçDoi: 10.1016/j.jag.2012.10.007
Land use/cover classification is a key research field in remote sensing and land change science as thematic maps derived from remotely sensed data have become the basis for analyzing many socio-ecological issues. However, land use/cover classification remains a difficult task and it is especially challenging in heterogeneous tropical landscapes where nonetheless such maps are of great importance. The present study aims at establishing an efficient classification approach to accurately map all broad land use/cover classes in a large, heterogeneous tropical area, as a basis for further studies (e.g., land use/cover change, deforestation and forest degradation). Specifically, we first compare the performance of parametric (maximum likelihood), non-parametric (k-nearest neighbor and four different support vector machines - SVM), and hybrid (unsupervised-supervised) classifiers, using hard and soft (fuzzy) accuracy assessments. We then assess, using the maximum likelihood algorithm, what textural indices from the gray-level co-occurrence matrix lead to greater classification improvements at the spatial resolution of Landsat imagery (30 m), and rank them accordingly. Finally, we use the textural index that provides the most accurate classification results to evaluate whether its usefulness varies significantly with the classifier used. We classified imagery corresponding to dry and wet seasons and found that SVM classifiers outperformed all the rest. We also found that the use of some textural indices, but particularly homogeneity and entropy, can significantly improve classifications. We focused on the use of the homogeneity index, which has so far been neglected in land use/cover classification efforts, and found that this index along with reflectance bands significantly increased the overall accuracy of all the classifiers, but particularly of SVM. We observed that improvements in producer's and user's accuracies through the inclusion of homogeneity were different depending on land use/cover classes. Early-growth/degraded forests, pastures, grasslands and savanna were the classes most improved, especially with the SVM radial basis function and SVM sigmoid classifiers, though with both classifiers all land use/cover classes were mapped with producer's and user's accuracies of ~90%. Our classification approach seems very well suited to accurately map land use/cover of heterogeneous landscapes, thus having great potential to contribute to climate change mitigation schemes, conservation initiatives, and the design of management plans and rural development policies. © 2012 Elsevier B.V.
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