Seed loss before seed predation: experimental evidence of the negative effects of leaf feeding insects on acorn production

Canelo T., GaytÁn Á., GonzÁlez-Bornay G., Bonal R. (2018) Seed loss before seed predation: experimental evidence of the negative effects of leaf feeding insects on acorn production. Integrative Zoology. 13: 238-250.
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Doi: 10.1111/1749-4877.12292

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Insect herbivory decreases plant fitness by constraining plant growth, survival and reproductive output. Most studies on the effects of herbivory in trees rely on correlational inter-individual comparisons and could, thus, be affected by confounding factors linked to both herbivory and plant performance. Using the Mediterranean Holm oak (Quercus ilex) as a study model, we followed an experimental approach in which leaf-feeding insects (mainly Lepidoptera caterpillars) were excluded from some shoots in all study trees. Shoots subjected to herbivore exclusion exhibited lower defoliation rates and produced more acorns than control shoots. Defoliation constrained shoot growth throughout the study period, but had no effect on the number of female flowers produced per shoot. Acorn production was, however, lower in control shoots due to their higher abortion rates, and also to their greater mortality risk during summer drought, as shoots with fewer leaves were less likely to survive. Plant reaction to herbivory inhibits certain physiological pathways involved in plant growth, which, together with the effects of physical damage, reduces the amount and efficiency of the photosynthetic tissue. This increases their vulnerability to environmental stresses, such as water deficit, which limit resource assimilation. Defoliation is likely a key factor affecting oak regeneration, as it may be a significant source of seed loss prior to pre-dispersal acorn predation. Further experimental studies could help to elucidate its effects in contrasting environments. In Mediterranean regions, the harsher droughts predicted by climate change models could worsen the effects of insect herbivory on oak reproductive output. © 2017 International Society of Zoological Sciences, Institute of Zoology/Chinese Academy of Sciences and John Wiley & Sons Australia, Ltd

Llegeix més

Sewage sludge as an organic amendment for quarry restoration: Effects on soil and vegetation

Carabassa V., Ortiz O., Alcañiz J.M. (2018) Sewage sludge as an organic amendment for quarry restoration: Effects on soil and vegetation. Land Degradation and Development. 29: 2568-2574.
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Doi: 10.1002/ldr.3071

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Quarry restoration in Mediterranean environments usually needs organic amendments to improve the substrates used for technosol construction. Digested sewage sludges from municipal wastewater treatment plants are rich in organic matter, N, and P and constitute an available and economically interesting alternative for substrate amendment. However, their pollutant burden and labile organic matter content involve an environmental risk that must be controlled. Moreover, ecological succession in restored areas can be influenced by the use of sludge and should be assessed. To minimize these risks, a new sewage sludge dose criterion relating to its labile organic matter and heavy metal content has been established. Sewage sludge doses currently range between 10 and 50 Mg ha−1. In order to verify the suitability of this dose criterion, 16 areas rehabilitated using sewage sludge located in limestone quarries in a Mediterranean climate in Catalonia (NE Spain) have been assessed. These evaluations focused on physicochemical properties of rehabilitated soils, land degradation processes, and ecological succession. In the short term, 6 months after sludge application, an increment of organic matter content in the restored soils was observed, without significant increases in electrical conductivity or heavy metals content, and with a dense plant cover that contributes to effective soil erosion control. Two years after, ruderal plants were still present but later successional species colonized the restored zones in different degrees. These results suggest that sewage sludge, used as a soil amendment according to the proposed methodology, can safely improve technosol quality without constraints that compromise ecological succession. © 2018 John Wiley & Sons, Ltd.

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Oldest skeleton of a fossil flying squirrel casts new light on the phylogeny of the group

Casanovas-Vilar I., Garcia-Porta J., Fortuny J., Sanisidro Ó., Prieto J., Querejeta M., Llácer S., Robles J.M., Bernardini F., Alba D.M. (2018) Oldest skeleton of a fossil flying squirrel casts new light on the phylogeny of the group. eLife. 7: 0-0.
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Doi: 10.7554/eLife.39270

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Flying squirrels are the only group of gliding mammals with a remarkable diversity and wide geographical range. However, their evolutionary story is not well known. Thus far, identification of extinct flying squirrels has been exclusively based on dental features, which, contrary to certain postcranial characters, are not unique to them. Therefore, fossils attributed to this clade may indeed belong to other squirrel groups. Here we report the oldest fossil skeleton of a flying squirrel (11.6 Ma) that displays the gliding-related diagnostic features shared by extant forms and allows for a recalibration of the divergence time between tree and flying squirrels. Our phylogenetic analyses combining morphological and molecular data generally support older dates than previous molecular estimates (~23 Ma), being congruent with the inclusion of some of the earliest fossils (~36 Ma) into this clade. They also show that flying squirrels experienced little morphological change for almost 12 million years. © Casanovas-Vilar et al.

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Foliar C, N, and P stoichiometry characterize successful plant ecological strategies in the Sonoran Desert

Castellanos A.E., Llano-Sotelo J.M., Machado-Encinas L.I., López-Piña J.E., Romo-Leon J.R., Sardans J., Peñuelas J. (2018) Foliar C, N, and P stoichiometry characterize successful plant ecological strategies in the Sonoran Desert. Plant Ecology. 219: 775-788.
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Doi: 10.1007/s11258-018-0833-3

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Ecological processes are centered to water availability in drylands; however, less known nutrient stoichiometry can help explain much of their structure and ecological interactions. Here we look to the foliar stoichiometry of carbon (C), nitrogen (N), and phosphorus (P) of 38 dominant plant species from the Sonoran Desert, grouped in four different functional types to describe ecological characteristics and processes. We found that foliar N, C:N, C:P, and N:P stoichiometric ratios, but not P, were higher than those known to most other ecosystems and indicate P but not N limitations in leaves. Biological N fixers (BNF) had even higher leaf N concentrations, but bio-elemental concentrations and stoichiometry ratios were not different to other non-N-fixing legume species which underscores the need to understand the physiological mechanisms for high N, and to how costly BNF can succeed in P-limiting drylands environments. Stoichiometry ratios, and to lesser extent elemental concentrations, were able to characterize BNF and colonizing strategies in the Sonoran Desert, as well as explain leaf attribute differences, ecological processes, and biogeochemical niches in this dryland ecosystem, even when no direct reference is made to other water-limitation strategies. © 2018, Springer Science+Business Media B.V., part of Springer Nature.

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Behind the Scenes: Mechanisms Regulating Climatic Patterns of Dissolved Organic Carbon Uptake in Headwater Streams

Catalán N., Casas-Ruiz J.P., Arce M.I., Abril M., Bravo A.G., del Campo R., Estévez E., Freixa A., Giménez-Grau P., González-Ferreras A.M., Gómez-Gener L., Lupon A., Martínez A., Palacin-Lizarbe C., Poblador S., Rasines-Ladero R., Reyes M., Rodríguez-Castillo T., Rodríguez-Lozano P., Sanpera-Calbet I., Tornero I., Pastor A. (2018) Behind the Scenes: Mechanisms Regulating Climatic Patterns of Dissolved Organic Carbon Uptake in Headwater Streams. Global Biogeochemical Cycles. 32: 1528-1541.
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Doi: 10.1029/2018GB005919

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Large variability in dissolved organic carbon (DOC) uptake rates has been reported for headwater streams, but the causes of this variability are still not well understood. Here we assessed acetate uptake rates across 11 European streams comprising different ecoregions by using whole-reach pulse acetate additions. We evaluated the main climatic and biogeochemical drivers of acetate uptake during two seasonal periods. Our results show a minor influence of sampling periods but a strong effect of climate and dissolved organic matter (DOM) composition on acetate uptake. In particular, mean annual precipitation explained half of the variability of the acetate uptake velocities (VfAcetate) across streams. Temperate streams presented the lowest VfAcetate, together with humic-like DOM and the highest stream respiration rates. In contrast, higher VfAcetate were found in semiarid streams, with protein-like DOM, indicating a dominance of reactive, labile compounds. This, together with lower stream respiration rates and molar ratios of DOC to nitrate, suggests a strong C limitation in semiarid streams, likely due to reduced inputs from the catchment. Overall, this study highlights the interplay of climate and DOM composition and its relevance to understand the biogeochemical mechanisms controlling DOC uptake in streams. ©2018. American Geophysical Union. All Rights Reserved.

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Knowledge gaps about mixed forests: What do European forest managers want to know and what answers can science provide?

Coll, L., Ameztegui, A., Collet, C., Löf, M., Mason, B., Pach, M., Verheyen, K., Abrudan, I., Barbati, A., Barreiro, S., Bielak, K., Bravo-Oviedo, A., Ferrari, B., Govedar, Z., Kulhavy, J., Lazdina, D., Metslaid, M., Mohren, F., Pereira, M., Peric, S., Rasztovits, E., Short, I., Spathelf, P., Sterba, H., Stojanovic, D., Valsta, L., Zlatanov, T., Ponette, Q. (2018) Knowledge gaps about mixed forests: What do European forest managers want to know and what answers can science provide?. Forest Ecology and Management. 407: 106-115.
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Doi: 10.1016/j.foreco.2017.10.055

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Weed suppression greatly increased by plant diversity in intensively managed grasslands: A continental-scale experiment

Connolly, J., Sebastià, M.-T., Kirwan, L., Finn, J.A., Llurba, R., Suter, M., Collins, R.P., Porqueddu, C., Helgadóttir, Á., Baadshaug, O.H., Bélanger, G., Black, A., Brophy, C., Čop, J., Dalmannsdóttir, S., Delgado, I., Elgersma, A., Fothergill, M., Frankow-Lindberg, B.E., Ghesquiere, A., Golinski, P., Grieu, P., Gustavsson, A.-M., Höglind, M., Huguenin-Elie, O., Jørgensen, M., Kadziuliene, Z., Lunnan, T., Nykanen-Kurki, P., Ribas, A., Taube, F., Thumm, U., De Vliegher, A., Lüscher, A. (2018) Weed suppression greatly increased by plant diversity in intensively managed grasslands: A continental-scale experiment. Journal of Applied Ecology. 55: 852-862.
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Doi: 10.1111/1365-2664.12991

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Correction to: Spatial Variation of Soil CO2, CH4 and N2O Fluxes Across Topographical Positions in Tropical Forests of the Guiana Shield (Ecosystems, (2018), (1-14), 10.1007/s10021-018-0232-6)

Courtois E.A., Stahl C., Van den Berge J., Bréchet L., Van Langenhove L., Richter A., Urbina I., Soong J.L., Peñuelas J., Janssens I.A. (2018) Correction to: Spatial Variation of Soil CO2, CH4 and N2O Fluxes Across Topographical Positions in Tropical Forests of the Guiana Shield (Ecosystems, (2018), (1-14), 10.1007/s10021-018-0232-6). Ecosystems. : 0-0.
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Doi: 10.1007/s10021-018-0281-x

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This paper was published with several formatting errors. It will be republished with corrections in place. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.

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Spatial Variation of Soil CO2, CH4 and N2O Fluxes Across Topographical Positions in Tropical Forests of the Guiana Shield

Courtois E.A., Stahl C., van Den Berge J., Bréchet L., van Langenhove L., Richter A., Urbina I., Soong J.L., Peñuelas J., Janssens I.A. (2018) Spatial Variation of Soil CO2, CH4 and N2O Fluxes Across Topographical Positions in Tropical Forests of the Guiana Shield. Ecosystems. : 1-14.
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Doi: 10.1007/s10021-018-0232-6

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The spatial variation of soil greenhouse gas fluxes (GHG; carbon dioxide—CO2, methane—CH4 and nitrous oxide—N2O) remains poorly understood in highly complex ecosystems such as tropical forests. We used 240 individual flux measurements of these three GHGs from different soil types, at three topographical positions and in two extreme hydric conditions in the tropical forests of the Guiana Shield (French Guiana, South America) to (1) test the effect of topographical positions on GHG fluxes and (2) identify the soil characteristics driving flux variation in these nutrient-poor tropical soils. Surprisingly, none of the three GHG flux rates differed with topographical position. CO2 effluxes covaried with soil pH, soil water content (SWC), available nitrogen and total phosphorus. The CH4 fluxes were best explained by variation in SWC, with soils acting as a sink under drier conditions and as a source under wetter conditions. Unexpectedly, our study areas were generally sinks for N2O and N2O fluxes were partly explained by total phosphorus and available nitrogen concentrations. This first study describing the spatial variation of soil fluxes of the three main GHGs measured simultaneously in forests of the Guiana Shield lays the foundation for specific studies of the processes underlying the observed patterns. © 2018 Springer Science+Business Media, LLC, part of Springer Nature

Llegeix més

Isotopic evidence for oligotrophication of terrestrial ecosystems

Craine J.M., Elmore A.J., Wang L., Aranibar J., Bauters M., Boeckx P., Crowley B.E., Dawes M.A., Delzon S., Fajardo A., Fang Y., Fujiyoshi L., Gray A., Guerrieri R., Gundale M.J., Hawke D.J., Hietz P., Jonard M., Kearsley E., Kenzo T., Makarov M., Marañón-Jiménez S., McGlynn T.P., McNeil B.E., Mosher S.G., Nelson D.M., Peri P.L., Roggy J.C., Sanders-DeMott R., Song M., Szpak P., Templer P.H., Van der Colff D., Werner C., Xu X., Yang Y., Yu G., Zmudczyńska-Skarbek K. (2018) Isotopic evidence for oligotrophication of terrestrial ecosystems. Nature ecology & evolution. 2: 1735-1744.
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Doi: 10.1038/s41559-018-0694-0

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Human societies depend on an Earth system that operates within a constrained range of nutrient availability, yet the recent trajectory of terrestrial nitrogen (N) availability is uncertain. Examining patterns of foliar N concentrations and isotope ratios (δ15N) from more than 43,000 samples acquired over 37 years, here we show that foliar N concentration declined by 9% and foliar δ15N declined by 0.6-1.6‰. Examining patterns across different climate spaces, foliar δ15N declined across the entire range of mean annual temperature and mean annual precipitation tested. These results suggest declines in N supply relative to plant demand at the global scale. In all, there are now multiple lines of evidence of declining N availability in many unfertilized terrestrial ecosystems, including declines in δ15N of tree rings and leaves from herbarium samples over the past 75-150 years. These patterns are consistent with the proposed consequences of elevated atmospheric carbon dioxide and longer growing seasons. These declines will limit future terrestrial carbon uptake and increase nutritional stress for herbivores.

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