Impact of Plant Invasion and Increasing Floods on Total Soil Phosphorus and its Fractions in the Minjiang River Estuarine Wetlands, China

Wang W.-Q., Sardans J., Zeng C.-S., Tong C., Wang C., Peñuelas J. (2015) Impact of Plant Invasion and Increasing Floods on Total Soil Phosphorus and its Fractions in the Minjiang River Estuarine Wetlands, China. Wetlands. : 0-0.
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Doi: 10.1007/s13157-015-0712-9

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Plant invasion and increased flooding intensity projected by climate change models can change the soil capacity of marine wetland to store P. This is a key question to the nutrient balances and eutrophication processes of coastal areas, especially in China coastal area that is receiving the freshwaters of a country in fast economical developing process. We studied the impact of changes in flooding intensity and plant invasion on total soil-P concentrations in the Minjiang River estuarine wetland. Flooding had a weak positive effect on soil P-fractions concentrations, but this effect was largely counteracted by the negative effect of salinity. Soil clay concentration and pH, both of which were related more with species community composition than with flooding intensity, were directly related to the P-fraction concentrations. The replacement of the native mangrove community by the invasive plant Phragmites australis was related to a decrease in the soil capacity to store P. A suitable management to maintain this wetland area in optimum conditions to act as a natural eutrophication buffer should tend to favor mangrove communities in the new areas that reach more than 220 days y-1 of flooding, and a combination of the three tall-grasses communities below this level of flooding. © 2015 Society of Wetland Scientists

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Plant invasive success associated with higher N-use efficiency and stoichiometric shifts in the soil–plant system in the Minjiang River tidal estuarine wetlands of China

Wang W.-Q., Wang C., Sardans J., Zeng C.-S., Tong C., Penuelas J. (2015) Plant invasive success associated with higher N-use efficiency and stoichiometric shifts in the soil–plant system in the Minjiang River tidal estuarine wetlands of China. Wetlands Ecology and Management. : 0-0.
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Doi: 10.1007/s11273-015-9425-3

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The tidal estuarine wetlands of China are rich in plant diversity, but several human-driven processes, such as species invasion, can affect the biogeochemical cycles of these ecosystems, and by changing soil conditions can inhibit the regeneration of native vegetation. We seasonally analyzed the carbon (C), nitrogen (N) and phosphorus (P) concentrations in soils and in leaves, stems and roots of the invasive species Spartina alterniflora and of the native species Cyperus malaccensis var. brevifolius Boeckeler. This latter species was analyzed both in natural non-invaded stands and in stands that had been invaded by Spartina but from which it had been removed and replaced by Cyperus. The aim was to investigate the effect of plant invasion, subsequent removal and replanting with a native species on C, N and P stoichiometry of the plant–soil system in the tidal wetlands of the Minjiang River. C and N concentrations averaged across seasons did not differ significantly among the plant species. P concentration was lower in the stems of Spartina than in the stems of the native species Cyperus but was not significantly different in the roots of the two species. The soil C and N concentrations were higher in the Spartina stand than in the Cyperus stand, whereas the soil P concentrations were not significantly different. The invasive species had a higher N-resorption capacity, N:P ratios in stem and roots, biomass, absolute growth and biomass N and had a lower relative growth rate and litter production than the native species. After the removal of the invasive plants, the regenerating native plants have a higher capacity to resorb N and lower relative growth rates. All these traits show that a conservative strategy and a high N-use efficiency and internal plant control of the N in the ecosystem underlie the invasive success of Spartina in this N-limited wetland. Relative growth rate was associated with lower plant N:P ratios, whereas absolute growth rate was associated with higher nutrient-use efficiency and lower C and N turnover and storage capacities in the biomass. Changes in soil properties produced by the establishment of an invasive plant can condition the later regeneration of native plants. © 2015 Springer Science+Business Media Dordrecht

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Ecological stoichiometry of C, N, and P of invasive Phragmites australis and native Cyperus malaccensis species in the Minjiang River tidal estuarine wetlands of China

Wang W.Q., Sardans J., Wang C., Zeng C.S., Tong C., Asensio D., Penuelas J. (2015) Ecological stoichiometry of C, N, and P of invasive Phragmites australis and native Cyperus malaccensis species in the Minjiang River tidal estuarine wetlands of China. Plant Ecology. : 0-0.
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Doi: 10.1007/s11258-015-0469-5

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Tidal estuarine wetlands of China are rich in plant diversity, but several global change drivers, such as species invasion, are currently affecting the biogeochemical cycles of these ecosystems. We seasonally analyzed the carbon (C), nitrogen (N), and phosphorus (P) concentrations in litters and soils and in leaves, stems, and roots of the C3 invasive species Phragmites australis (Cav.) Trin. ex Steud. and of the C4 native species Cyperus malaccensis var. brevifolius Boeckeler to investigate the effect of C3 plant invasion on C, N, and P stoichiometry in the C4 plant-dominated tidal wetlands of the Minjiang River. When averaged across seasons, the invasive species P. australis had higher N concentrations and lower P concentrations in leaves than the native species C. malaccensis. N and P concentrations were lower in litter (stem and leaf), whereas C concentrations in leaf litter were higher in P. australis than in C. malaccensis. The C, N, and P concentrations of the soil also did not differ, but plants had a lower C:N and much higher N:P ratios than soils. Root C:P and N:P ratios were lower in the growing season both in the invasive and the native species. The leaf C:N, C:P and N:P ratios peaked in summer. The invasive species had lower C:N ratio in leaves and roots, and higher N:P ratios in all biomass organs and litter than the native species, an effect related with the higher N-resorption capacity of the invasive species. Interspecific differences in C:N, C:P, and N:P ratios may likely reflect the differences in plant morphology, nutrient-use efficiency, and photosynthetic capacity between the C3 (P. australis) and C4 (C. malaccensis) plants. Our results generally suggested that the success of P. australis in these wetlands was related to its slow growth and higher resorption capacity of N and P. This implies a more conservative use of limited nutrients, particularly N, by P. australis, and to higher N concentration in its biomass thus potentially contributing to its invasiveness in these estuarine wetlands. © 2015 Springer Science+Business Media Dordrecht

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The climate space of fire regimes in north-western North America

Whitman E., Batllori E., Parisien M.-A., Miller C., Coop J.D., Krawchuk M.A., Chong G.W., Haire S.L. (2015) The climate space of fire regimes in north-western North America. Journal of Biogeography. 42: 1736-1749.
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Doi: 10.1111/jbi.12533

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Aim: Studies of fire activity along environmental gradients have been undertaken, but the results of such studies have yet to be integrated with fire-regime analysis. We characterize fire-regime components along climate gradients and a gradient of human influence. Location: We focus on a climatically diverse region of north-western North America extending from northern British Columbia, Canada, to northern Utah and Colorado, USA. Methods: We used a multivariate framework to collapse 12 climatic variables into two major climate gradients and binned them into 73 discrete climate domains. We examined variation in fire-regime components (frequency, size, severity, seasonality and cause) across climate domains. Fire-regime attributes were compiled from existing databases and Landsat imagery for 1897 large fires. Relationships among the fire-regime components, climate gradients and human influence were examined through bivariate regressions. The unique contribution of human influence was also assessed. Results: A primary climate gradient of temperature and summer precipitation and a secondary gradient of continentality and winter precipitation in the study area were identified. Fire occupied a distinct central region of such climate space, within which fire-regime components varied considerably. We identified significant interrelations between fire-regime components of fire size, frequency, burn severity and cause. The influence of humans was apparent in patterns of burn severity and ignition cause. Main conclusions: Wildfire activity is highest where thermal and moisture gradients converge to promote fuel production, flammability and ignitions. Having linked fire-regime components to large-scale climate gradients, we show that fire regimes - like the climate that controls them - are a part of a continuum, expanding on models of varying constraints on fire activity. The observed relationships between fire-regime components, together with the distinct role of climatic and human influences, generate variation in biotic communities. Thus, future changes to climate may lead to ecological changes through altered fire regimes. © 2015 John Wiley & Sons Ltd.

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Key molecular processes of the diapause to post-diapause quiescence transition in the alfalfa leafcutting bee Megachile rotundata identified by comparative transcriptome analysis

Yocum G.D., Rinehart J.P., Horvath D.P., Kemp W.P., Bosch J., Alroobi R., Salem S. (2015) Key molecular processes of the diapause to post-diapause quiescence transition in the alfalfa leafcutting bee Megachile rotundata identified by comparative transcriptome analysis. Physiological Entomology. : 0-0.
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Doi: 10.1111/phen.12093

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Insect diapause (dormancy) synchronizes an insect's life cycle to seasonal changes in the abiotic and biotic resources required for development and reproduction. Transcription analysis of diapause to post-diapause quiescent transition in the alfalfa leafcutting bee Megachile rotundata Fabricius identifies 643 post-diapause up-regulated gene transcripts and 242 post-diapause down-regulated transcripts. The log2 fold change in gene expression levels ranges from -5 to 7. Transcripts from several pivotal diapause-related processes, including chromatin remodelling, cellular signalling pathways, microRNA processing, anaerobic glycolysis, cell cycle arrest and neuroendocrine control, are identified as being differentially expressed during the diapause to post-diapause transition. In conjunction with studies from other insect species, the data indicate that there are several common mechanisms of diapause control and maintenance. © 2015 The Royal Entomological Society.

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Five Years of Experimental Warming Increases the Biodiversity and Productivity of Phytoplankton

Yvon-Durocher G., Allen A.P., Cellamare M., Dossena M., Gaston K.J., Leitao M., Montoya J.M., Reuman D.C., Woodward G., Trimmer M. (2015) Five Years of Experimental Warming Increases the Biodiversity and Productivity of Phytoplankton. PLoS Biology. 13: 0-0.
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Doi: 10.1371/journal.pbio.1002324

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Phytoplankton are key components of aquatic ecosystems, fixing CO2 from the atmosphere through photosynthesis and supporting secondary production, yet relatively little is known about how future global warming might alter their biodiversity and associated ecosystem functioning. Here, we explore how the structure, function, and biodiversity of a planktonic metacommunity was altered after five years of experimental warming. Our outdoor mesocosm experiment was open to natural dispersal from the regional species pool, allowing us to explore the effects of experimental warming in the context of metacommunity dynamics. Warming of 4°C led to a 67% increase in the species richness of the phytoplankton, more evenly-distributed abundance, and higher rates of gross primary productivity. Warming elevated productivity indirectly, by increasing the biodiversity and biomass of the local phytoplankton communities. Warming also systematically shifted the taxonomic and functional trait composition of the phytoplankton, favoring large, colonial, inedible phytoplankton taxa, suggesting stronger top-down control, mediated by zooplankton grazing played an important role. Overall, our findings suggest that temperature can modulate species coexistence, and through such mechanisms, global warming could, in some cases, increase the species richness and productivity of phytoplankton communities. © 2015 Yvon-Durocher et al.

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The application of ecological stoichiometry to plant-microbial-soil organic matter transformations

Zechmeister-Boltenstern S., Keiblinger K.M., Mooshammer M., Peñuelas J., Richter A., Sardans J., Wanek W. (2015) The application of ecological stoichiometry to plant-microbial-soil organic matter transformations. Ecological Monographs. 85: 133-155.
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Doi: 10.1890/14-0777.1

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Elemental stoichiometry constitutes an inherent link between biogeochemistry and the structure and processes within food webs, and thus is at the core of ecosystem functioning. Stoichiometry allows for spanning different levels of biological organization, from cellular metabolism to ecosystem structure and nutrient cycling, and is therefore particularly useful for establishing links between different ecosystem compartments. We review elemental carbon : nitrogen : phosphorus (C:N:P) ratios in terrestrial ecosystems (from vegetation, leaf litter, woody debris, and dead roots, to soil microbes and organic matter). While the stoichiometry of the plant, litter, and soil compartments of ecosystems is well understood, heterotrophic microbial communities, which dominate the soil food web and drive nutrient cycling, have received increasing interest in recent years. This review highlights the effects of resource stoichiometry on soil microorganisms and decomposition, specifically on the structure and function of heterotrophic microbial communities and suggests several general patterns. First, latitudinal gradients of soil and litter stoichiometry are reflected in microbial community structure and function. Second, resource stoichiometry may cause changes in microbial interactions and community dynamics that lead to feedbacks in nutrient availability. Third, global change alters the C:N, C:P, and N:P ratios of primary producers, with repercussions for microbial decomposer communities and critical ecosystem services such as soil fertility. We argue that ecological stoichiometry provides a framework to analyze and predict such global change effects at various scales. © 2015 by the Ecological Society of America.

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Environmental factors prevail over dispersal constraints in determining the distribution and assembly of Trichoptera species in mountain lakes

de Mendoza G., Ventura M., Catalan J. (2015) Environmental factors prevail over dispersal constraints in determining the distribution and assembly of Trichoptera species in mountain lakes. Ecology and Evolution. 5: 2518-2532.
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Doi: 10.1002/ece3.1522

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Aiming to elucidate whether large-scale dispersal factors or environmental species sorting prevail in determining patterns of Trichoptera species composition in mountain lakes, we analyzed the distribution and assembly of the most common Trichoptera (Plectrocnemia laetabilis, Polycentropus flavomaculatus, Drusus rectus, Annitella pyrenaea, and Mystacides azurea) in the mountain lakes of the Pyrenees (Spain, France, Andorra) based on a survey of 82 lakes covering the geographical and environmental extremes of the lake district. Spatial autocorrelation in species composition was determined using Moran's eigenvector maps (MEM). Redundancy analysis (RDA) was applied to explore the influence of MEM variables and in-lake, and catchment environmental variables on Trichoptera assemblages. Variance partitioning analysis (partial RDA) revealed the fraction of species composition variation that could be attributed uniquely to either environmental variability or MEM variables. Finally, the distribution of individual species was analyzed in relation to specific environmental factors using binomial generalized linear models (GLM). Trichoptera assemblages showed spatial structure. However, the most relevant environmental variables in the RDA (i.e., temperature and woody vegetation in-lake catchments) were also related with spatial variables (i.e., altitude and longitude). Partial RDA revealed that the fraction of variation in species composition that was uniquely explained by environmental variability was larger than that uniquely explained by MEM variables. GLM results showed that the distribution of species with longitudinal bias is related to specific environmental factors with geographical trend. The environmental dependence found agrees with the particular traits of each species. We conclude that Trichoptera species distribution and composition in the lakes of the Pyrenees are governed predominantly by local environmental factors, rather than by dispersal constraints. For boreal lakes, with similar environmental conditions, a strong role of dispersal capacity has been suggested. Further investigation should address the role of spatial scaling, namely absolute geographical distances constraining dispersal and steepness of environmental gradients at short distances. © 2015 The Authors.

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