Leaf N resorption efficiency and litter N mineralization rate have a genotypic tradeoff in a silver birch population

Plants enhance N use efficiency by resorbing N from senescing leaves. This can affect litter N mineralization rate due to the C:N-ratio requirements of microbial growth. We examined genotypic links between leaf N resorption and litter mineralization by collecting leaves and litter from 19 Betula pendula genotypes and following the N release of litter patches on forest ground. We found significant genotypic variation for N resorption efficiency, litter N concentration, cumulative three-year patch N-input and litter N release with high broad-sense heritabilities (H-2 = 0.28-0.65). The genotype means of N resorption efficiency varied from 46% to 65% and correlated negatively with the genotype means of litter N concentration, cumulative patch N-input and litter N release. NH4+ yield under patches had a positive genotypic correlation with the cumulative patch N-input. During the first year of litter decomposition, genotypes varied from N immobilization (max 2.71 mg/g dry litter) to N release (max 1.41 mg/g dry litter), creating a genotypic tradeoff between the N conserved by resorption and the N available for root uptake during the growing season. We speculate that this tradeoff is one likely reason for the remarkably wide genotypic range of N resorption efficiencies in our birch population.Peer reviewe

Insect herbivory dampens Subarctic birch forest C sink response to warming

Climate warming is anticipated to make high latitude ecosystems stronger C sinks through increasing plant production. This effect might, however, be dampened by insect herbivores whose damage to plants at their background, non-outbreak densities may more than double under climate warming. Here, using an open-air warming experiment among Subarctic birch forest field layer vegetation, supplemented with birch plantlets, we show that a 2.3 degrees C air and 1.2 degrees C soil temperature increase can advance the growing season by 1-4 days, enhance soil N availability, leaf chlorophyll concentrations and plant growth up to 400%, 160% and 50% respectively, and lead up to 122% greater ecosystem CO2 uptake potential. However, comparable positive effects are also found when insect herbivory is reduced, and the effect of warming on C sink potential is intensified under reduced herbivory. Our results confirm the expected warming-induced increase in high latitude plant growth and CO2 uptake, but also reveal that herbivorous insects may significantly dampen the strengthening of the CO2 sink under climate warming. Warming is expected to increase C sink capacity in high-latitude ecosystems, but plant-herbivore interactions could moderate or offset this effect. Here, Silfver and colleagues test individual and interactive effects of warming and insect herbivory in a field experiment in Subarctic forest, showing that even low intensity insect herbivory strongly reduces C sink potential

Towards constraining the circumpolar nitrous oxide budget

Arctic soils and sediments are well known for their huge carbon stocks and the significant positive feedback carbon dioxide (CO2) and methane (CH4) emissions can have on climate change. However, the vast amounts of nitrogen (N) and possible emissions of the strong greenhouse gas nitrous oxide (N2O) from Arctic soils are much less considered in this context. Arctic soils have been neglected in global N2O accounting, since their N2O emissions were traditionally thought to be low due to the general N-limitation of biological processes. Recent results suggest, however, that this assumption is unwarranted and needs to be revised. Still, although we know about the risk for increasing N2O emissions from the Arctic with warming, data are available only from a handful of sites and we are lacking any estimate on the circumarctic N2O budget even under the present climate. This presentation will introduce our plan to produce the first circumarctic N2O budget, an important baseline scenario against which changes in circumarctic N2O emissions can be observed with ongoing warming and global change. In order to estimate the first circumarctic N2O budget, we synthesize existing data and organize large-scale surveys of N2O fluxes across the Circumarctic. In our synthesis effort, we collect published and unpublished data on N2O emissions and N2O soil gas concentrations and analyze the data for driving variables and mechanisms underlying the N2O fluxes from various sites with different soil and vegetation characteristics. In addition, we organize measurement campaigns (via the INTERACT remote access program) to quantify N2O fluxes across a wide variety of Arctic sites using a network of collaborator stations with simple, standardized methods, and combine this N2O screening with GIS approaches to scale up the N2O fluxes step-wise from plot to regional and circumarctic levels. Ultimately, these data will be combined with existing data-sets and archived in a database that will be made available for process modelers in order to develop and improve the performance N2O models for permafrost soils. N2O flux data were published in 21 articles from 16 Arctic sites. In the frame of this project, N2O flux measurements were conducted in 2018 at 18 study sites located in Russia, Scandinavia, Svalbard, Canada and Alaska. First analyses show that N2O is released from a range of environmentally distinct sites and at variable magnitudes with soil N content, soil C/N ratios, vegetation cover, water availability, and nutrient content likely playing significant roles. Ultimately, this project will not only provide a valuable input towards the first estimate of the circumarctic N2O budget but also towards understanding the controls of Arctic N2O fluxes which is necessary for future projections. There is urgent need for collaboration among partners in this effort and we would thus like to invite interested researchers to contribute with further published or unpublished data on N2O fluxes/concentrations from Arctic sites to support our synthesis effort. Scientists are also highly requested to sample additional N2O data from “their” Arctic sites with the simple methods introduced here, in order to help us filling large data gaps

Extracting DNA from soil or directly from isolated nematodes indicate dissimilar community structure for Europe-wide forest soils

Nematodes are numerous in soils and play a crucial role in soil food-webs. DNA metabarcoding offers a time-effective alternative to morphology-based assessments of nematode diversity. However, it is unclear how different DNA extraction methods prior to metabarcoding could affect community analysis. We used soils with woody vegetation from a European latitudinal gradient (29 sites, 39 to 79°N, ∼4500 km, covering six biomes) to systematically evaluate the effect of two sources of nematode DNA either directly extracted from soils vs. extracted from nematodes previously isolated from soils hypothesizing that the DNA source material may produce different diversities, community structures and abundances of feeding types. Nematode-sample DNA exhibited a higher richness, while no difference in Shannon diversity was found between the approaches. The DNA sources also created significantly different community structures, with greater differences observed across soil-extracted DNA than nematode-sample DNA. The most overrepresented species in nematode-sample DNA were Heterocephalobus elongatus, Eucephalobus striatus and Hexatylus sp., whereas Phasmarhabditis sp. and Eumonhystera filiformis were overrepresented in soil-extracted DNA. Read abundances of feeding types significantly differed between the DNA sources and across sites, with a significant effect of biome on both ecto- and endoparasitic herbivores in soil-extracted DNA and for ectoparasitic herbivores only in nematode-sample DNA. Collectively, our data suggest that choice of the DNA source material may lead to different patterns of nematode community composition across space and environmental conditions. Improving the sensitivity of the soil-extracted DNA method by developing protocols using larger amounts of soil and designing nematode-specific primers will make this approach an efficient screening tool to analyse nematode diversity and community structure complementing the labour-intensive isolation of intact nematodes from soils (nematode-sample DNA)

Just a game? Unjustified virtual violence produces guilt in empathetic players

Many avid gamers discount violent conduct in video games as morally insignificant as "it is just a game." However, recent debates among users, regarding video games featuring inappropriate forms of virtual violence, suggest a more complex truth. Two ex- periments (

"It’s not my dream, actually" : students' identity work across figured worlds of construction engineering in Sweden

Background: Research in engineering education has pointed to the need for new engineers to develop a broader skillsetwith an emphasis on “softer” social skills. However, there remains strong tensions in the identity work that engineersmust engage in to balance the technical demands of the discipline with the new emphasis on heterogeneous skills(Faulkner, Social Studies of Science 37:331–356, 2007). This study explores how three unconventional students experiencethese tensions in the final year of their construction engineering program, and as they move in and out of workplacefield experiences.Results: Using a figured worlds framework (Holland et al., Identity and agency in cultural worlds, 1998), we explore thedominant subject positions for students in construction engineering classroom and workplaces in a 3-year Swedishengineering program. Results demonstrate that dominant subject positions for construction engineers can troublestudents’ identity work as they move across classroom and workplace settings.Conclusions: This study expands our knowledge of the complexity of students’ identity work across classroom andworkplace settings. The emergence of classroom and workplace masculinities that shape the dominant subject positionsavailable to students are shown to trouble the identity work that students engage in as they move across these learningspaces. We examine students’ identity strategies that contribute to their persistence through the field. Finally, we discussimplications for teaching and research in light of students’ movements across these educational contexts

Gender equality as a resource and a dilemma : interpretative repertoires in engineering education in Sweden

This article explores how female university students' abilities to present themselves as 'authentic' engineers are imbricated with discursive constructions of gender and gender equality. The empirical data comes from interviews and video diaries collected with three female engineering students. The analysis demonstrates the power of the Swedish gender equality discourse to inform the students' talk as they negotiate their gendered identities to become intelligible as engineering students and engineers. We suggest that gender equality is used as a resource in the repertoires, but we also demonstrate that this discourse becomes a dilemma in that it limits possibilities for gender performances to go beyond old patterns. Despite this, the article still shows three unique ways of negotiating gender and other social categories in different situations connected to university learning and participation in internships

The Pride and Joy of Engineering? The Identity Work of Male Working-Class Engineering Students

In this article, we explore the identity work done by four male, working-class students who participate in a Swedish mechanical engineering program, with a focus on their participation in project work. A focus on how individuals negotiate their participation in science and technology disciplines has proven to be a valuable way to study inclusion and exclusion in such disciplines. This is of particular relevance in engineering education where it is widely argued that change is needed in order to attract new groups of students and provide students with knowledge appropriate for the future society. In this study we conceptualized identity as socially and discursively produced, and focus on tracing students’ identity trajectories. The empirical data consists of ethnographic field notes from lectures, video-recordings of project work, semi-structured interviews, and video-diaries recorded by the students. The findings show that even though all four students unproblematically associate with the ‘technicist’masculinity of their chosen program it takes considerable work to incorporate the project work into their engineering trajectories. Further, ‘laddish’ masculinities re/produced in higher education in engineering also contribute to a ‘troubled’ identity trajectory for one of the interviewed students.Special Issue</p