ALBERT

Description: Our paper tracks for the first time the different development pathways of varying peatland vegetation types in response to long‐term water level drawdown. We found that the so‐called tipping point, a drop of water table at which an open peatland undergoes significant vegetation change or transitions to a forest system, is inversely proportional to the nutrient level of the system. Abstract Questions Peatland ecosystems are a globally important carbon storage that is predicted to turn into a carbon source due to water level drawdown (WLD) associated with climate change. The predictions assume stable plant communities but how realistic is this assumption? If the vegetation is not stable, what are the nature and rate of changes? Location Peatland complex in Southern Finland. Methods We conducted a water level drawdown (WLD of ~10 cm) experiment over 17 years in three peatland types differing in their fertility. On each peatland type, we included an adjacent forestry drained (FD, with water table ca. 40 cm lower than in control) area for comparison. Results Peatland type had a clear impact on the response to WLD: at the ecosystem level, the two minerotrophic fens underwent rapid species turnover, while the vegetation in nutrient‐poor bog was more resilient to change. In nutrient‐rich sites, WLD initiated tree canopy development and created understorey conditions that strengthened impact of WLD. In nutrient‐poor site, tree establishment was seen only in the FD area. In addition to high nutrient level, high wetness accelerated change at the plant community level, where we found three types of responses: accelerating change, decelerating change, and stability. Succession resulted in an overall loss of community heterogeneity. Conclusions Interaction between hydrology, nutrient availability, and biological factors in boreal peatlands is important: the drop in water table required to achieve the shift from open peatland to forested system is inversely proportional to the nutrient level of the system. The results suggest that predictive models of peatland functions under climate change should consider compositional change for fens and their diverse plant communities but are more realistic for bogs. The response of bog vegetation to climate change may, however, be more dependent on changes in rainfall regime and therefore needs to be further addressed.

Description: Abstract Understanding how variation in hosts, parasites, and the environment shapes patterns of disease is key to predicting ecological and evolutionary outcomes of epidemics. Yet in spatially structured populations, variation in host resistance may be spatially confounded with variation in parasite dispersal and environmental factors that affect disease processes. To tease apart these disease drivers, we paired surveys of natural epidemics with experiments manipulating spatial variation in host susceptibility to infection. We mapped epidemics of the wind‐dispersed powdery mildew pathogen Podosphaera plantaginis in five populations of its plant host, Plantago lanceolata. At 15 replicate sites within each population, we deployed groups of healthy potted ‘sentinel’ plants from five allopatric host lines. By tracking which sentinels became infected in the field and measuring pathogen connectivity and microclimate at those sites, we could test how variation in these factors affected disease when spatial variation in host resistance and soil conditions was minimized. We found that the prevalence and severity of sentinel infection varied over small spatial scales in the field populations, largely due to heterogeneity in pathogen prevalence on wild plants and unmeasured environmental factors. Microclimate was critical for disease spread only at the onset of epidemics, where humidity increased infection risk. Sentinels were more likely to become infected than initially healthy wild plants at a given field site. However, in a follow‐up laboratory inoculation study we detected no significant differences between wild and sentinel plant lines in their qualitative susceptibility to pathogen isolates from the field populations, suggesting that primarily non‐genetic differences between sentinel and wild hosts drove their differential infection rates in the field. Our study leverages a multi‐faceted experimental approach to disentangle important biotic and abiotic drivers of disease patterns within wild populations.

Description: Abstract Northern peatlands form a major soil carbon (C) stock. With climate change, peatland C mineralization is expected to increase, which in turn would accelerate climate change. A particularity of peatlands is the importance of soil aeration, which regulates peatland functioning and likely modulates the responses to warming climate. Our aim is to assess the impacts of warming on a southern boreal and a sub‐arctic sedge fen carbon dioxide (CO2) exchange under two plausible water table regimes: wet and moderately dry. We focused this study on minerotrophic treeless sedge fens, as they are common peatland types at boreal and (sub)arctic areas, which are expected to face the highest rates of climate warming. In addition, fens are expected to respond to environmental changes faster than the nutrient poor bogs. Our study confirmed that CO2 exchange is more strongly affected by drying than warming. Experimental water level draw‐down (WLD) significantly increased gross photosynthesis and ecosystem respiration. Warming alone had insignificant impacts on the CO2 exchange components, but when combined with WLD it further increased ecosystem respiration. In the southern fen, CO2 uptake decreased due to WLD, which was amplified by warming, while at northern fen it remained stable. As a conclusion, our results suggest that a very small difference in the WLD may be decisive, whether the C sink of a fen decreases, or whether the system is able to adapt within its regime and maintain its functions. Moreover, the water table has a role in determining how much the increased temperature impacts the CO2 exchange. This article is protected by copyright. All rights reserved.

Description: We introduce an inversion method that uses dimension reduction for the retrieval of atmospheric methane (CH 4 ) profiles. Uncertainty analysis is performed using the Markov chain Monte Carlo (MCMC) statistical estimation. These techniques are used to retrieve CH 4 profiles from the ground-based spectral measurements by the Fourier Transform Spectrometer (FTS) instrument at Sodankylä (67.4 ∘ N, 26.6 ∘ E), Northern Finland. The Sodankylä FTS is part of the Total Carbon Column Observing Network (TCCON), a global network that observes solar spectra in near-infrared wavelengths. The high spectral resolution of the data provides approximately three degrees of freedom about the vertical structure of CH 4 between around 0 and 40 km. We reduce the dimension of the inverse problem by using principal component analysis. Smooth and realistic profiles are sought by estimating three parameters for the profile shape. We use Bayesian framework with adaptive MCMC to better characterize the full posterior distribution of the solution and uncertainties related to the retrieval. The retrieved profiles are validated against in-situ AirCore soundings which provide an accurate reference up to 20–30 km. The method is presented in a general form, so that it can easily be adapted for other applications, such as different trace gases or satellite-borne measurements where more accurate profile information and better analysis of the uncertainties would be highly valuable.

Description: We discuss trend analysis of non-stationary ionosonde hmF 2 time-series measured at Sodankylä Geophysical Observatory (67.4◦N, 26.7◦4 E), Finland, 1957{2014. We model the hmF 2 with a dynamic regression time-series model with the following components: a slowly varying background level, seasonal variations and solar effects. We analyze the time-series with a dynamic linear state-space model. Such an approach allows model components to vary in time, allowing us to study the dynamic stochastic nature of the underlying long-term trend. This feature is lacking in most time-series models used in atmospheric and environmental long-term trend analyses. Our objective is to understand the long-term hmF 2 trend with respect to increased levels of carbon dioxide and methane in the atmosphere. Based on model estimates, this phenomenon is predicted to cool the thermosphere, and, leads to decrease of the altitude of the so-called F2-layer peak. After accounting for the effects of solar activity variations on the data, we see that the estimated trend shows an almost 30 km decrease of the F2-layer peak during the observation period. The decrease of the peak during 1990–2010 is significantly greater than during earlier observation period.

Description: Question Measurements of ecosystem carbon (C) exchange are usually labour-intensive and expensive. In peatlands, these temporally and spatially limited measurements are often up-scaled over comparable ecosystems, such as ombrotrophic bogs, to provide an estimate for ecosystem level carbon dioxide (CO 2 ) fluxes. Peatlands typically have moisture variations reflected in the presence of microforms (e.g. hummocks and hollows), each with characteristic plant life forms. However, so far the applicability of peatland type (e.g. bog, fen) or microforms for up-scaling has not been assessed. Does the vegetation composition or function of associated species differ so greatly between the same types of peatland that up-scaling is impossible? Location Five ombrotrophic bogs in Northern Europe; in Ireland, Finland and western Russia. Methods We described the variation in vegetation of microforms within and between ombrotrophic bogs using multivariate analyses. Thereafter, we measured CO 2 exchange at different microforms and evaluated the relationship between vegetation structure and the light response of photosynthesis. Results Our results show that the community composition of hummocks, lawns and hollows was rather uniform at the plant life-form level. The photosynthetic capacity per leaf area unit was quite similar within microform classes over the different bogs. The observed differences between sites in capacity were mainly related to variation in leaf area. Conclusions A reliable estimate of ecosystem-level photosynthesis requires knowledge of the proportion of different microforms in an area and the leaf area characteristics for each microform in the year(s) in question. Assessments of ecosystem-level photosynthesis are important with regard to current and future changes in climate, as the most dramatic changes in peatlands involve water level drawdown, which in turn is likely to lead to changes in the relative proportions of microforms within peatlands. We described the variation in ombrotrophic bog vegetation and light response of photosynthesis at the level of microforms by using multivariate analyses. Our aim was to find out if gas fluxes measured at one mire could be generalized over other similar mires, and at which level the upscaling should be done. We found out that bogs are similar enough for such upscaling and microforms are good units for upscaling as long as their proportion in an area and the leaf area characteristic in the year(s) in question are known. Assessments of ecosystem-level photosynthesis are important with regard to current and future changes in climate, as the most dramatic changes in peatlands involve water-level drawdown, which in turn is likely to lead to changes in the relative proportions of microforms within peatlands.

Description: Abstract Phase‐pure [NiO]0.5[Al2O3]0.5 spinel nanoparticles (NPs) with limited aggregation were obtained via liquid‐feed flame spray pyrolysis (LF‐FSP) by combusting metalloorganic precursor solutions. Thereafter “chocolate chip‐like” Nix[NiO0.5‐x][Al2O3]0.5 nanoparticles consisting of primary [NiO0.5‐x][Al2O3]0.5 particles with average particle sizes of 40‐60 nm decorated with Ni metal particles (〈10 nm in diameter) dispersed on the surface were synthesized by heat treating the spinel NPs at 800°C/7 h in flowing 5% H2:N2 100 mL/min in a fluidized bed reactor. The synthesized materials were characterized using TEM, XRD, FTIR, and TGA/DTA. The Ni depleted areas consist primarily of γ‐Al2O3. The Ni content (800°C) was determined by TGA to be ≈11.3 wt.% based on TGA oxidation behavior. The successful synthesis of such nanocomposites with limited aggregation on a high temperature support provides a facile route to synthesize well‐defined NP catalysts. This work serves as a baseline study for an accompanying paper, wherein thin, flexible, dense films made from these same NPs are used as regenerable catalysts for carbon nanotube syntheses.

Description: Rapeseed ( Brassica napus L.) is a crop requiring high levels of nitrogen (N) fertilizer for growth and to optimize yield and seed quality. To limit the environmental pollution associated with intensive N fertilizer use, rapeseed–clover ( Trititcum incarnatum L.) mixtures were grown in lysimeters under low N conditions (100 kg N ha −1 ). Considering the high sulfur (S) requirements of both rapeseed and clover, two inputs of S fertilizer (30 and 60 kg S ha −1 ) were applied. The effects S input on the agronomic performance of rapeseed in mixture and monocrops considered as reference, the N 2 -fixing capacity of clover, and the leaching of nitrate and sulfate were monitored. This study showed that the N 2 -fixing capacity (%Ndfa) of clover was improved (1.3-fold) when it was grown in mixture with rapeseed at S60. However, irrespective of the type of cropping (monocrops or mixtures) and S application level (30 or 60 kg S ha −1 ), the biomasses and total N and S contents of both plants were not significantly different, nor was the rapeseed seed quality. Moreover, the yield of rapeseed grown in mixture at S60 was significantly lower than the yield of rapeseed grown as a monocrop (331.5 ± 9.8 versus 380.8 ± 3.5 g DW m −2 , respectively). The results demonstrate that, in our field conditions, rapeseed mixed with clover required only 30 kg S ha −1 to maintain yield and seed quality, despite the high S needs of both plants. More surprisingly, compared to the rapeseed monocrop, the rapeseed–clover mixture led to an increase in N ( -N) and S ( -S) leaching during the early winter period of cultivation.

Description: Here we demonstrate the potential utility of using chemical modification to reorganize metastable nanoparticles into nanostructured nanoparticles without coincidentally inducing extensive necking/sintering. The motivation for this effort derives from the concept that chemical reduction of a single component in a mixed-metal nanoparticle will create segregated islands of a second immiscible phase. Given the very high chemical energies inherent in nanoparticles, the formation of even smaller islands of a second phase can be anticipated to lead to extremely high interfacial energies that may drive these islands to diffuse to cores or surfaces to form core-shell structures that minimize such interfacial energies. Thus, ammonolysis of (TiO 2 ) 0.43 (Al 2 O 3)0.57 composition nanopowders where both elements are approximately uniformly mixed at atomic length scales, under selected conditions (1000 °C) for various periods of time at constant NH 3 flow rates leads primarily to the reduction of the Ti species to form TiN or TiON which then appears to diffuse to the surface of the particles. The final products consist of Al 2 O 3 @TiON core-shell nanopowders that remain mostly unaggregated pointing to a new mechanism for modifying nanopowder chemistries and physical properties. This article is protected by copyright. All rights reserved.