Representation of dissolved organic carbon in the JULES land surface model (vn4.4-JULES-DOCM)

Nakhavali M., Friedlingstein P., Lauerwald R., Tang J., Chadburn S., Camino-Serrano M., Guenet B., Harper A., Walmsley D., Peichl M., Gielen B. (2018) Representation of dissolved organic carbon in the JULES land surface model (vn4.4-JULES-DOCM). Geoscientific Model Development. 11: 593-609.
Link
Doi: 10.5194/gmd-11-593-2018

Abstract:

Current global models of the carbon (C) cycle consider only vertical gas exchanges between terrestrial or oceanic reservoirs and the atmosphere, thus not considering the lateral transport of carbon from the continents to the oceans. Therefore, those models implicitly consider all of the C which is not respired to the atmosphere to be stored on land and hence overestimate the land C sink capability. A model that represents the whole continuum from atmosphere to land and into the ocean would provide a better understanding of the Earth's C cycle and hence more reliable historical or future projections. A first and critical step in that direction is to include processes representing the production and export of dissolved organic carbon in soils. Here we present an original representation of dissolved organic C (DOC) processes in the Joint UK Land Environment Simulator (JULES-DOCM) that integrates a representation of DOC production in terrestrial ecosystems based on the incomplete decomposition of organic matter, DOC decomposition within the soil column, and DOC export to the river network via leaching. The model performance is evaluated in five specific sites for which observations of soil DOC concentration are available. Results show that the model is able to reproduce the DOC concentration and controlling processes, including leaching to the riverine system, which is fundamental for integrating terrestrial and aquatic ecosystems. Future work should include the fate of exported DOC in the river system as well as DIC and POC export from soil. © Author(s) 2018.

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How to spend a dwindling greenhouse gas budget

Obersteiner, M., Bednar, J., Wagner, F., Gasser, T., Ciais, P., Forsell, N., Frank, S., Havlik, P., Valin, H., Janssens, I.A., Peñuelas, J., Schmidt-Traub, G. (2018) How to spend a dwindling greenhouse gas budget. Nature Climate Change. 8: 7-10.
Link
Doi: 10.1038/s41558-017-0045-1

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High planktonic diversity in mountain lakes contains similar contributions of autotrophic, heterotrophic and parasitic eukaryotic life forms

Ortiz-Álvarez R., Triadó-Margarit X., Camarero L., Casamayor E.O., Catalan J. (2018) High planktonic diversity in mountain lakes contains similar contributions of autotrophic, heterotrophic and parasitic eukaryotic life forms. Scientific Reports. 8: 0-0.
Link
Doi: 10.1038/s41598-018-22835-3

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A rich eukaryotic planktonic community exists in high-mountain lakes despite the diluted, oligotrophic and cold, harsh prevailing conditions. Attempts of an overarching appraisal have been traditionally hampered by observational limitations of small, colorless, and soft eukaryotes. We aimed to uncover the regional eukaryotic biodiversity of a mountain lakes district to obtain general conclusions on diversity patterns, dominance, geographic diversification, and food-web players common to oligotrophic worldwide distributed freshwater systems. An unprecedented survey of 227 high-altitude lakes comprising large environmental gradients was carried out using Illumina massive tag sequencing of the 18S rRNA gene. We observed a large Chrysophyceae dominance in richness, abundance and novelty, and unveiled an unexpected richness in heterotrophic phagotrophs and parasites. In particular, Cercozoa and Chytridiomycota showed diversity features similar to the dominant autotrophic groups. The prominent beta-dispersion shown by parasites suggests highly specific interactions and a relevant role in food webs. Interestingly, the freshwater Pyrenean metacommunity contained more diverse specific populations than its closest marine oligotrophic equivalent, with consistently higher beta-diversity. The relevance of unseen groups opens new perspectives for the better understanding of planktonic food webs. Mountain lakes, with remarkable environmental idiosyncrasies, may be suitable environments for the genetic diversification of microscopic eukaryotic life forms. © 2018 The Author(s).

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Denitrification Temperature Dependence in Remote, Cold, and N-Poor Lake Sediments

Palacin-Lizarbe C., Camarero L., Catalan J. (2018) Denitrification Temperature Dependence in Remote, Cold, and N-Poor Lake Sediments. Water Resources Research. 54: 1161-1173.
Link
Doi: 10.1002/2017WR021680

Abstract:

The reservoir size and pathway rates of the nitrogen (N) cycle have been deeply modified by the human enhancement of N fixation, atmospheric emissions, and climate warming. Denitrification (DEN) transforms nitrate into nitrogenous gas and thus removes reactive nitrogen (Nr) back to the atmospheric reservoir. There is still a rather limited knowledge of the denitrification rates and their temperature dependence across ecosystems; particularly, for the abundant cold and N-poor freshwater systems (e.g., Arctic and mountain lakes). We experimentally investigated the denitrification rates of mountain lake sediments by manipulating nitrate concentration and temperature on field collected cores. DEN rates were nitrate limited in field conditions and showed a large potential for an immediate DEN increase with both warming and higher Nr load. The estimated activation energy (Ea) for denitrification at nitrate saturation was 46 ± 7 kJ mol−1 (Q10 1.7 ± 0.4). The apparent Ea increased with nitrate (μM) limitation as Ea = 46 + 419 [NO2 −]−1. Accordingly, we suggest that climate warming may have a synergistic effect with N emission reduction to readjusting the N cycle. Changes of nitrate availability might be more relevant than direct temperature effects on denitrification. © 2018. American Geophysical Union. All Rights Reserved.

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Climatic Suitability Derived from Species Distribution Models Captures Community Responses to an Extreme Drought Episode

Pérez Navarro M.Á., Sapes G., Batllori E., Serra-Diaz J.M., Esteve M.A., Lloret F. (2018) Climatic Suitability Derived from Species Distribution Models Captures Community Responses to an Extreme Drought Episode. Ecosystems. : 1-14.
Link
Doi: 10.1007/s10021-018-0254-0

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The differential responses of co-occurring species in rich communities to climate change—particularly to drought episodes—have been fairly unexplored. Species distribution models (SDMs) are used to assess changes in species suitability under environmental shifts, but whether they can portray population and community responses is largely undetermined, especially in relation to extreme events. Here we studied a shrubland community in SE Spain because this region constitutes an ecotone between the Mediterranean biome and subtropical arid areas, and it has recently suffered its driest hydrological year on record. We used four different modeling algorithms (Mahalanobis distance, GAM, BRT, and MAXENT) to estimate species’ climatic suitability before (1950–2000) and during the extreme drought. For each SDM, we related species’ climatic suitability with their remaining green canopy as a proxy for species resistance to drought. We consistently found a positive correlation between remaining green canopy and species’ climatic suitability before the event. This relationship supports the hypothesis of a higher vulnerability of populations living closer to their species’ limits of aridity tolerance. Contrastingly, climatic suitability during the drought did not correlate with remaining green canopy, likely because the exceptional episode led to almost zero suitability values. Overall, our approach highlights climatic niche modeling as a robust approach to standardizing and comparing the behavior of different co-occurring species facing strong climatic fluctuations. Although many processes contribute to resistance to climatic extremes, the results confirm the relevance of populations’ position in the species’ climatic niche for explaining sensitivity to climate change. © 2018 Springer Science+Business Media, LLC, part of Springer Nature

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Critical temperature and precipitation thresholds for the onset of xylogenesis of Juniperus przewalskii in a semi-arid area of the north-eastern Tibetan Plateau

Ren P., Rossi S., Camarero J.J., Ellison A.M., Liang E., Peñuelas J. (2018) Critical temperature and precipitation thresholds for the onset of xylogenesis of Juniperus przewalskii in a semi-arid area of the north-eastern Tibetan Plateau. Annals of Botany. 121: 617-624.
Link
Doi: 10.1093/aob/mcx188

Abstract:

Background and Aims The onset of xylogenesis plays an important role in tree growth and carbon sequestration, and it is thus a key variable in modelling the responses of forest ecosystems to climate change. Temperature regulates the resumption of cambial activity, but little is known about the effect of water availability on the onset of xylogenesis in cold but semi-arid regions. Methods The onset of xylogenesis during 2009-2014 was monitored by weekly microcoring Juniperus przewalskii trees at upper and lower treelines on the north-eastern Tibetan Plateau. A logistic regression was used to calculate the probability of xylogenic activity at a given temperature and a two-dimensional reverse Gaussian model to fit the differences between the observed and estimated days of xylogenesis onset at given temperatures and precipitation within a certain time window. Key Results The thermal thresholds at the beginning of the growing season were highly variable, suggesting that temperature was not the only factor initiating xylem growth under cold and dry climatic conditions. The onset of xylogenesis was well predicted for climatic thresholds characterized by a cumulative precipitation of 17.0 ± 5.6 mm and an average minimum temperature of 1.5 ± 1.4 °C for a period of 12 d. Conclusions Xylogenesis in semi-arid regions with dry winters and springs can start when both critical temperature and precipitation thresholds are reached. Such findings contribute to our knowledge of the environmental drivers of growth resumption that previously had been investigated largely in cold regions without water shortages during early growing seasons. Models of the onset of xylogenesis should include water availability to improve predictions of xylem phenology in dry areas. A mismatch between the thresholds of temperature and moisture for the onset of xylogenesis may increase forest vulnerability in semi-arid areas under forecasted warmer and drier conditions. © 2017 The Author(s). Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved.

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Coping with iron limitation: a metabolomic study of Synechocystis sp. PCC 6803

Rivas-Ubach A., Poret-Peterson A.T., Peñuelas J., Sardans J., Pérez-Trujillo M., Legido-Quigley C., Oravec M., Urban O., Elser J.J. (2018) Coping with iron limitation: a metabolomic study of Synechocystis sp. PCC 6803. Acta Physiologiae Plantarum. 40: 0-0.
Link
Doi: 10.1007/s11738-018-2603-1

Abstract:

Iron (Fe) is a key element for all living systems, especially for photosynthetic organisms because of its important role in the photosynthetic electron transport chain. Fe limitation in cyanobacteria leads to several physiological and morphological changes. However, the overall metabolic responses to Fe limitation are still poorly understood. In this study, we integrated elemental, stoichiometric, macromolecular, and metabolomic data to shed light on the responses of Synechocystis sp. PCC 6803, a non-N2-fixing freshwater cyanobacterium, to Fe limitation. Compared to Synechocystis growing at nutrient replete conditions, Fe-limited cultures had lower growth rates and amounts of chlorophyll a, RNA, RNA:DNA, C, N, and P, and higher ratios of protein:RNA, C:N, C:P, and N:P, in accordance with the growth rate hypothesis which predicts faster growing organisms will have decreased biomass RNA contents and C:P and N:P ratios. Fe-limited Synechocystis had lower amounts Fe, Mn, and Mo, and higher amount of Cu. Several changes in amino acids of cultures growing under Fe limitation suggest nitrogen limitation. In addition, we found substantial increases in stress-related metabolites in Fe-limited cyanobacteria such antioxidants. This study represents an advance in understanding the stoichiometric, macromolecular, and metabolic strategies that cyanobacteria use to cope with Fe limitation. This information, moreover, may further understanding of changes in cyanobacterial functions under scenarios of Fe limitation in aquatic ecosystems. © 2018, Franciszek Górski Institute of Plant Physiology, Polish Academy of Sciences, Kraków.

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Glacial refugia and mid-Holocene expansion delineate the current distribution of Castanea sativa in Europe

Roces-Díaz, J.V., Jiménez-Alfaro, B., Chytrý, M., Díaz-Varela, E.R., Álvarez-Álvarez, P. (2018) Glacial refugia and mid-Holocene expansion delineate the current distribution of Castanea sativa in Europe. Palaeogeography, Palaeoclimatology, Palaeoecology. 491: 152-160.
Link
Doi: 10.1016/j.palaeo.2017.12.004

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The spatial level of analysis affects the patterns of forest ecosystem services supply and their relationships

Roces-Díaz, J.V., Vayreda, J., Banqué-Casanovas, M., Díaz-Varela, E., Bonet, J.A., Brotons, L., de-Miguel, S., Herrando, S., Martínez-Vilalta, J. (2018) The spatial level of analysis affects the patterns of forest ecosystem services supply and their relationships. Science of the Total Environment. 626: 1270-1283.
Link
Doi: 10.1016/j.scitotenv.2018.01.150

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Zero-sum landscape effects on acorn predation associated with shifts in granivore insect community in new holm oak (Quercus ilex) forests

Ruiz-Carbayo, H., Bonal, R., Pino, J., Espelta, J.M. (2018) Zero-sum landscape effects on acorn predation associated with shifts in granivore insect community in new holm oak (Quercus ilex) forests. Diversity and Distributions. : 0-0.
Link
Doi: 10.1111/ddi.12701

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