The effects of fire on ant trophic assemblage and sex allocation

Caut S., Jowers M.J., Arnan X., Pearce-Duvet J., Rodrigo A., Cerda X., Boulay R.R. (2014) The effects of fire on ant trophic assemblage and sex allocation. Ecology and Evolution. 4: 35-49.
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Doi: 10.1002/ece3.714

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Fire plays a key role in ecosystem dynamics worldwide, altering energy flows and species community structure and composition. However, the functional mechanisms underlying these effects are not well understood. Many ground-dwelling animal species can shelter themselves from exposure to heat and therefore rarely suffer direct mortality. However, fire-induced alterations to the environment may change a species' relative trophic level within a food web and its mode of foraging. We assessed how fire could affect ant resource utilization at different scales in a Mediterranean forest. First, we conducted isotopic analyses on entire ant species assemblages and their potential food resources, which included plants and other arthropods, in burned and unburned plots 1 year postfire. Second, we measured the production of males and females by nests of a fire-resilient species, Aphaenogaster gibbosa, and analyzed the differences in isotopic values among workers, males, and females to test whether fire constrained resource allocation. We found that, in spite of major modifications in biotic and abiotic conditions, fire had little impact on the relative trophic position of ant species. The studied assemblage was composed of species with a wide array of diets. They ranged from being mostly herbivorous to completely omnivorous, and a given species' trophic level was the same in burned and unburned plots. In A. gibbosa nests, sexuals had greater δ15N values than workers in both burned and unburned plots, which suggests that the former had a more protein-rich diet than the latter. Fire also appeared to have a major effect on A. gibbosa sex allocation: The proportion of nests that produced male brood was greater on burned zones, as was the mean number of males produced per nest with the same reproductive investment. Our results show that generalist ants with relatively broad diets maintained a constant trophic position, even following a major disturbance like fire. However, the dramatically reduced production of females on burned zones compared to unburned zones 1 year postfire may result in considerably reduced recruitment of new colonies in the mid to long term, which could yield genetic bottlenecks and founder effects. Our study paves the way for future functional analyses of fire-induced modifications in ant populations and communities. © 2013 The Authors.

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Does soil moisture overrule temperature dependence of soil respiration in Mediterranean riparian forests?

Chang C.T., Sabaté S., Sperlich D., Poblador S., Sabater F., Gracia C. (2014) Does soil moisture overrule temperature dependence of soil respiration in Mediterranean riparian forests?. Biogeosciences. 11: 6173-6185.
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Doi: 10.5194/bg-11-6173-2014

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Soil respiration (SR) is a major component of ecosystems' carbon cycles and represents the second largest CO2 flux in the terrestrial biosphere. Soil temperature is considered to be the primary abiotic control on SR, whereas soil moisture is the secondary control factor. However, soil moisture can become the dominant control on SR in very wet or dry conditions. Determining the trigger that makes soil moisture as the primary control factor of SR will provide a deeper understanding on how SR changes under the projected future increase in droughts. Specific objectives of this study were (1) to investigate the seasonal variations and the relationship between SR and both soil temperature and moisture in a Mediterranean riparian forest along a groundwater level gradient; (2) to determine soil moisture thresholds at which SR is controlled by soil moisture rather than by temperature; (3) to compare SR responses under different tree species present in a Mediterranean riparian forest (Alnus glutinosa, Populus nigra and Fraxinus excelsior). Results showed that the heterotrophic soil respiration rate, groundwater level and 30 cm integral soil moisture (SM30) decreased significantly from the riverside moving uphill and showed a pronounced seasonality. SR rates showed significant differences between tree species, with higher SR for P. nigra and lower SR for A. glutinosa. The lower threshold of soil moisture was 20 and 17% for heterotrophic and total SR, respectively. Daily mean SR rate was positively correlated with soil temperature when soil moisture exceeded the threshold, with Q10 values ranging from 1.19 to 2.14; nevertheless, SR became decoupled from soil temperature when soil moisture dropped below these thresholds. © 2014 Author(s).

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SMOS and climate data applicability for analyzing forest decline and forest fires

Chaparro D., Vayreda J., Martinez-Vilalta J., Vall-Llossera M., Banque M., Camps A., Piles M. (2014) SMOS and climate data applicability for analyzing forest decline and forest fires. International Geoscience and Remote Sensing Symposium (IGARSS). : 1069-1072.
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Doi: 10.1109/IGARSS.2014.6946613

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Forests partially reduce climate change impact but, at the same time, this climate forcing threatens forest's health. In recent decades, droughts are becoming more frequent and intense implying an increase of forest decline episodes and forest fires. In this context, global and frequent soil moisture observations from the ESA's SMOS mission could be useful in controlling forest exposure to decline and fires. In this paper, SMOS observations and several climate variables are analyzed together with decline and fire inventories, to study the effect of soil moisture on forest decline during an important drought on summer 2012, and on forest fires in the period 2010-2013. Results show that SMOS-derived soil moisture is a complementary variable in forest decline models. Some of the studied tree species exhibit high probability of decline occurrence under dry conditions. First results showed burned areas to be drier than unburned ones previous to the fire occurrences. © 2014 IEEE.

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Toxicity of phenmedipham and carbendazim to Enchytraeus crypticus and Eisenia andrei (Oligochaeta) in Mediterranean soils

Chelinho S., Domene X., Campana P., Andres P., Rombke J., Sousa J.P. (2014) Toxicity of phenmedipham and carbendazim to Enchytraeus crypticus and Eisenia andrei (Oligochaeta) in Mediterranean soils. Journal of Soils and Sediments. 14: 584-599.
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Doi: 10.1007/s11368-013-0818-8

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Purpose: The main objective of the present study was to evaluate the toxicity of two reference chemicals, Carbendazim and Phenmedipham, for the compostworm Eisenia andrei (effects of Carbendazim) and the potworm Enchytraeus crypticus (effects of Phenmedipham) in 12 Mediterranean soils with contrasting soil properties. The observed toxicity was also compared to that obtained for OECD standard soil, used as a control. Materials and methods: The soils were selected to be representative for the Mediterranean region and to cover a broad range of soil properties. The evaluated endpoints were avoidance behavior and reproduction. Soils were also assembled in two groups according to their pedological properties. Results and discussion: Toxicity benchmarks (AC50s) obtained for E. andrei avoidance behavior in carbendazim-contaminated soils were generally higher for sandy soils with low pH. The toxic effects on the reproduction of the compostworms were similar in the six tested soils, indicating a low influence of soil properties. The avoidance response of E. crypticus towards Phenmedipham was generally highly variable in all tested soils. Even though, a higher toxicity was observed for more acidic soils. The EC50s for reproduction of the latter species varied by a factor of 9 and Phenmedipham toxicity also tended to be increasing in soils with lower pH, except for the soils with extreme organic matter content (0.6 and 5.8%). Conclusions: A soil effect on chemical toxicity was clearly confirmed, highlighting the influence that test soils can have in site-specific ecological risk assessment. Despite some relationships between soil properties and toxicity were outlined, a clear and statistically significant prediction of chemical toxicity could not be established. The range of soil properties was probably narrow to give clearer and more consistent insights on their influence. For the four groups of tests, the toxicity observed for OECD soil was either similar, lower, or generally higher if compared with Mediterranean soils. Moreover, it did represent neither the organic matter content found in Mediterranean soils nor their textural classes. © 2013 Springer-Verlag Berlin Heidelberg.

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Factors controlling the geochemical composition of Limnopolar Lake sediments (Byers Peninsula, Livingston Island, South Shetland Island, Antarctica) during the last ca. 1600 years

Cortizas A.M., Muniz I.R., Taboada T., Toro M., Granados I., Giralt S., Pla-Rabes S. (2014) Factors controlling the geochemical composition of Limnopolar Lake sediments (Byers Peninsula, Livingston Island, South Shetland Island, Antarctica) during the last ca. 1600 years. Solid Earth. 5: 651-663.
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Doi: 10.5194/se-5-651-2014

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We sampled a short (57 cm) sediment core in Limnopolar Lake (Byers Peninsula, Livingston Island, South Shetland Islands), which spans the last ca. 1600 years. The core was sectioned at high resolution and analyzed for elemental and mineralogical composition, and scanning electron microscope and energy dispersive X-ray spectrometer (SEM-EDS) analysis of glass mineral particles in selected samples. The chemical record was characterized by a contrasted pattern of layers with high Ca, Ti, Zr, and Sr concentrations and layers with higher concentrations of K and Rb. The former were also enriched in plagioclase and, occasionally, in zeolites, while the latter were relatively enriched in 2 : 1 phyllosilicates and quartz. This was interpreted as reflecting the abundance of volcaniclastic material (Ca rich) versus Jurassic-Lower Cretaceous marine sediments (K rich) - the dominant geological material in the lake catchment. SEM-EDS analysis revealed the presence of abundant volcanic shards in the Ca-rich layers, pointing to tephras most probably related to the activity of Deception Island volcano (located 30 km to the SE). The ages of four main peaks of volcanic-rich material (AD ca. 1840-1860 for L1, AD ca. 1570-1650 for L2, AD ca. 1450-1470 for L3, and AD ca. 1300 for L4) matched reasonably well the age of tephra layers (AP1 to AP3) previously identified in lakes of Byers Peninsula. Some of the analyzed metals (Fe, Mn, Cu, and Cr) showed enrichments in the most recent tephra layer (L1), suggesting relative changes in the composition of the tephras as found in previous investigations. No evidence of significant human impact on the cycles of most trace metals (Cu, Zn, Pb) was found, probably due to the remote location of Livingston Island and the modest research infrastructures; local contamination was found by other researchers in soils, waters and marine sediments on areas with large, permanent research stations. Chromium is the only metal showing a steady enrichment in the last 200 years, but this cannot be directly attributed to anthropogenic pollution since recent research supports the interpretation that climatic variability (reduced moisture content and increased wind intensity) may have resulted in enhanced fluxes of mineral dust and trace elements (Cr among them) to Antarctica. At the same time, some features of the chemical record suggest that climate may have also played a role in the cycling of the elements, but further research is needed to identify the underlying mechanisms. © Author(s) 2014.

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Functional diversification within bacterial lineages promotes wide functional overlapping between taxonomic groups in a Mediterranean forest soil

Curiel Yuste J., Fernandez-Gonzalez A.J., Fernandez-Lopez M., Ogaya R., Penuelas J., Lloret F. (2014) Functional diversification within bacterial lineages promotes wide functional overlapping between taxonomic groups in a Mediterranean forest soil. FEMS Microbiology Ecology. : 0-0.
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Doi: 10.1111/1574-6941.12373

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We investigated the relationship between taxonomy and functioning of soil bacterial communities in soils from a Mediterranean holm oak forest using a high-throughput DNA pyrosequencing technique. We used nonparametric tests (Mann-Whitney U-test) to evaluate the sensitivity of each single bacterial genus within the community to the fluctuations of plant physiological and environmental abiotic variables, as well as to fluctuations in soil microbial respiration. Within-lineage (phylum/class) functional similarities were evaluated by the distribution of the Mann-Whitney U-test standardized coefficients (z) obtained for all genera within a given lineage. We further defined different ecological niches and within-lineage degree of functional diversification based on multivariate analyses (principal component analyses, PCA). Our results indicate that strong within-lineage functional diversification causes extensive functional overlapping between lineages, which hinders the translation of taxonomic diversity into a meaningful functional classification of bacteria. Our results further suggest a widespread colonization of possible ecological niches as taxonomic diversity increases. While no strong functional differentiation could be drawn from the analyses at the phylum/class level, our results suggest a strong ecological niche differentiation of bacteria based mainly on the distinct response of Gram-positive and Gram-negative bacteria to fluctuations in soil moisture. We investigated the relation between taxonomy and functioning of soil bacterial communities in soils from a Mediterranean Holm-oak forest using a high throughput DNA pyrosequencing technique. © 2014 Federation of European Microbiological Societies.

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Strong functional stability of soil microbial communities under semiarid Mediterranean conditions and subjected to long-term shifts in baseline precipitation

Curiel Yuste J., Fernandez-Gonzalez A.J., Fernandez-Lopez M., Ogaya R., Penuelas J., Sardans J., Lloret F. (2014) Strong functional stability of soil microbial communities under semiarid Mediterranean conditions and subjected to long-term shifts in baseline precipitation. Soil Biology and Biochemistry. 69: 223-233.
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Doi: 10.1016/j.soilbio.2013.10.045

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We investigated the effect of soil microclimate on the structure and functioning of soil microbial communities in a Mediterranean Holm-oak forest subjected to 10 years of partial rain exclusion manipulations, simulating average drought conditions expected in Mediterranean areas for the following decades. We applied a high throughput DNA pyrosequencing technique coupled to parallel measurements of microbial respiration (RH) and temperature sensitivity of microbial respiration (Q10). Some consistent changes in the structure of bacterial communities suggest a slow process of community shifts parallel to the trend towards oligotrophy in response to long-term droughts. However, the structure of bacterial communities was mainly determined by short-term environmental fluctuations associated with sampling date (winter, spring and summer) rather than long-term (10 years) shifts in baseline precipitation. Moreover, long-term drought did not exert any chronic effect on the functioning of soil microbial communities (RH and Q10), emphasizing the functional stability of these communities to this long-term but mild shifts in water availability. We hypothesize that the particular conditions of the Mediterranean climate with strong seasonal shifts in both temperature and soil water availability but also characterized by very extreme environmental conditions during summer, was acting as a strong force in community assembling, selecting phenotypes adapted to the semiarid conditions characterizing Mediterranean ecosystems. Relations of climate with the phylogenetic structure and overall diversity of the communities as well as the distribution of the individual responses of different lineages (genera) to climate confirmed our hypotheses, evidencing communities dominated by thermotolerant and drought-tolerant phenotypes. © 2013 Elsevier Ltd.

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Intercropping trees' effect on soil oribatid diversity in agro-ecosystems

Doblas-Miranda E., Paquette A., Work T.T. (2014) Intercropping trees' effect on soil oribatid diversity in agro-ecosystems. Agroforestry Systems. 88: 671-678.
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Doi: 10.1007/s10457-014-9680-y

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The benefits of tree-based intercropping (TBI) compared to conventional agro-ecosystems in North America could include climate change mitigation and adaptation, although enhancing resilience to climate change through increasing soil diversity remains poorly explored. Diversity of soil microarthropods supports a series of ecological services that may be altered by soil desiccation due to climate change. Here we study the effect of red oak and hybrid poplar TBI on soil oribatid mite species assemblages associated to forage crops (mix of Timothy-grass and red clover). Abundance and species density of oribatids were affected by treatment, depth and the interaction of both variables. Abundance of oribatid mites was significantly lower in the oak TBI, showing a homogeneous vertical distribution in opposition to a decreasing with depth distribution under poplar TBI and conventional crops. Species density was significantly higher in the conventional crop, showing again significant differences in depth that were not present in both TBI treatments. Distance to tree did not affect mite abundance nor species density. TBI increased oribatid richness (obtained by sample-based rarefaction and extrapolation) only in the presence of oaks. The distribution of oribatids was strongly associated to tree fine root biomass and stress the importance of underground organic resources for the oribatid fauna and their ecological functions. If increasing drought associated with climate change desiccates superficial levels of agro-ecosystem soils, deeper sources of organic resources, such as tree roots, should become crucial in the maintenance of diverse microarthropod communities. © 2014 Springer Science+Business Media Dordrecht.

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Medium-term effects of corn biochar addition on soil biota activities and functions in a temperate soil cropped to corn

Domene X., Mattana S., Hanley K., Enders A., Lehmann J. (2014) Medium-term effects of corn biochar addition on soil biota activities and functions in a temperate soil cropped to corn. Soil Biology and Biochemistry. 72: 152-162.
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Doi: 10.1016/j.soilbio.2014.01.035

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Biochar addition to soil has been generally associated with crop yield increases observed in some soils, and increased nutrient availability is one of the mechanisms proposed. Any impact of biochar on soil organisms can potentially translate to changes in nutrient availability and crop productivity, possibly explaining some of the beneficial and detrimental yield effects reported in literature. Therefore, the main aim of this study was to assess the medium-term impact of biochar addition on microbial and faunal activities in a temperate soil cropped to corn and the consequences for their main functions, litter decomposition and mineralization. Biochar was added to a corn field at rates of 0, 3, 12, 30tonsha-1 three years prior to this study, in comparison to an annual application of 1tha-1.Biochar application increased microbial abundance, which nearly doubled at the highest addition rate, while mesofauna activity, and litter decomposition facilitated by mesofauna were not increased significantly but were positively influenced by biochar addition when these responses were modeled, and in the last case directly and positively associated to the higher microbial abundance. In addition, in short-term laboratory experiments after the addition of litter, biochar presence increased NO2+NO3 mineralization, and decreased that of SO4 and Cl. However, those nutrient effects were not shown to be of concern at the field scale, where only some significant increases in SOC, pH, Cl and PO4 were observed.Therefore, no negative impacts in the soil biota activities and functions assessed were observed for the tested alkaline biochar after three years of the application, although this trend needs to be verified for other soil and biochar types. © 2014 Elsevier Ltd.

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Site-specific factors influence the richness and phenology of snowbed plants in the Pyrenees

Domenech M., Komac B., Penuelas J., Conesa J.A. (2014) Site-specific factors influence the richness and phenology of snowbed plants in the Pyrenees. Plant Biosystems. : 0-0.
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Doi: 10.1080/11263504.2014.990941

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Although the timing of snowmelt and growth temperatures appear to be the main factors that influence the species richness and phenology of snowbed plants, site-specific characteristics may also play a role in modifying the effects of the timing of snowmelt and temperature. In this study, the effects of site-specific factors (microtopography and snow origin) on species richness and plant phenology were evaluated in 72 plots in two snowbeds in the Andorran Pyrenees. Snowmelt patterns influenced the spatial distribution of species richness and abundance. Site-specific factors had significant effects on the responses of species (shortening or lengthening the duration of the phenophase) and on the extent to which the timing of snowmelt influenced leaf expansion and flowering. Notably, the highest rates of leaf expansion occurred on late snowmelt isoclines, where, nevertheless, the time taken to reach peak flowering was significantly longer than on the early snowmelt isoclines. The results of this study highlight the fact that, in addition to the effects of interannual variability in climate, site-specific factors have a significant effect on the phenology and reproductive success of the commonest plants in the snowbed communities of the Pyrenees.

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