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Depolymerization of high‐molecular weight organic nitrogen (N) represents the major bottleneck of soil N cycling and yet is poorly understood compared to the subsequent inorganic N processes. Given the importance of organic N cycling and the rise of global change, we investigated the responses of soil protein depolymerization and microbial amino acid consumption to increased temperature, elevated atmospheric CO2, and drought. The study was conducted in a global change facility in a managed montane grassland in Austria, where elevated CO2 (eCO2) and elevated temperature (eT) were stimulated for 4 years, and were combined with a drought event. Gross protein depolymerization and microbial amino acid consumption rates (alongside with gross organic N mineralization and nitrification) were measured using 15N isotope pool dilution techniques. Whereas eCO2 showed no individual effect, eT had distinct effects which were modulated by season, with a negative effect of eT on soil organic N process rates in spring, neutral effects in summer, and positive effects in fall. We attribute this to a combination of changes in substrate availability and seasonal temperature changes. Drought led to a doubling of organic N process rates, which returned to rates found under ambient conditions within 3 months after rewetting. Notably, we observed a shift in the control of soil protein depolymerization, from plant substrate controls under continuous environmental change drivers (eT and eCO2) to controls via microbial turnover and soil organic N availability under the pulse disturbance (drought). To the best of our knowledge, this is the first study which analyzed the individual versus combined effects of multiple global change factors and of seasonality on soil organic N processes and thereby strongly contributes to our understanding of terrestrial N cycling in a future world. [ABSTRACT FROM AUTHOR]

Climate change is altering the frequency and severity of drought events. Recent evidence indicates that drought may produce legacy effects on soil microbial communities. However, it is unclear whether precedent drought events lead to ecological memory formation, i.e., the capacity of past events to influence current ecosystem response trajectories. Here, we utilize a long-term field experiment in a mountain grassland in central Austria with an experimental layout comparing 10 years of recurrent drought events to a single drought event and ambient conditions. We show that recurrent droughts increase the dissimilarity of microbial communities compared to control and single drought events, and enhance soil multifunctionality during drought (calculated via measurements of potential enzymatic activities, soil nutrients, microbial biomass stoichiometry and belowground net primary productivity). Our results indicate that soil microbial community composition changes in concert with its functioning, with consequences for soil processes. The formation of ecological memory in soil under recurrent drought may enhance the resilience of ecosystem functioning against future drought events. Legacies of past ecological disturbances are expected but challenging to demonstrate. Here the authors report a 10-year field experiment in a mountain grassland that shows ecological memory of soil microbial community and functioning in response to recurrent drought. [ABSTRACT FROM AUTHOR]

Nitrogen dioxide (NO2), produced as a result of fossil fuel combustion, biomass burning, lightning, and soil emissions, is a key urban and rural tropospheric pollutant. In this case study, ground-based remote sensing has been coupled with the in situ network in Vienna, Austria, to investigate NO2 distributions in the planetary boundary layer. Near-surface and path-averaged NO2 mixing ratios within the metropolitan area of Vienna are estimated from car DOAS (differential optical absorption spectroscopy) zenith-sky and tower DOAS horizon observations. The latter configuration is innovative in the sense that it obtains horizontal measurements at more than a hundred different azimuthal angles – within a 360 ∘ rotation taking less than half an hour. Spectral measurements were made with a DOAS instrument on nine days in April, September, October, and November 2015 in the zenith-sky mode and on five days in April and May 2016 in the off-axis mode. The analysis of tropospheric NO2 columns from the car measurements and O4 normalized NO2 path averages from the tower observations provide interesting insights into the spatial and temporal NO2 distribution over Vienna. Integrated column amounts of NO2 from both DOAS-type measurements are converted into mixing ratios by different methods. The estimation of near-surface NO2 mixing ratios from car DOAS tropospheric NO2 vertical columns is based on a linear regression analysis including mixing height and other meteorological parameters that affect the dilution and reactivity in the planetary boundary layer – a new approach for such conversion. Path-averaged NO2 mixing ratios are calculated from tower DOAS NO2 slant column densities by taking into account topography and geometry. Overall, lap averages of near-surface NO2 mixing ratios obtained from car DOAS zenith-sky measurements, around a circuit in Vienna, are in the range of 3.8 to 26.1 ppb and in good agreement with values obtained from in situ NO2 measurements for days with wind from the southeast. Path-averaged NO2 mixing ratios at 160 m above the ground as derived from the tower DOAS measurements are between 2.5 and 9 ppb on two selected days with different wind conditions and pollution levels and show similar spatial distribution as seen in the car DOAS zenith-sky observations. We conclude that the application of the two methods to obtain near-surface and path-averaged NO2 mixing ratios is promising for this case study. [ABSTRACT FROM AUTHOR]

The integrated modelling of coupled socio-ecological systems in land-change science requires innovative model concepts capable of grasping the interrelations between socioeconomic and natural components. Here, we discuss the integrated socio-ecological model SERD (Simulation of Ecological Compatibility of Regional Development) that was developed for the municipality of Reichraming in Upper Austria in a participative 2-year process involving local stakeholders. SERD includes three main components: (1) an agent-based actors module that simulates decisions of farmsteads, the municipal administration and other important actors; (2) a spatially explicit (GIS based) land-use module that simulates land-use change at the level of individual parcels of land and (3) an integrated socio-ecological stock-flow module that simulates carbon and nitrogen flows through both socioeconomic and ecological system compartments. We report on outcomes of a scenario analysis that outlines possible future trajectories depending on both external (e.g. agricultural subsidies and prices) and internal (e.g. innovation, willingness to co-operate) factors. We find that both external and internal factors can affect the behaviour of the integrated system considerably. Local and regional policies are found to be able to counteract adverse global socioeconomic conditions to some extent, but not to reverse the trend altogether. We also find strong interdependencies between socioeconomic and ecological components of the system. Fully evaluating these interdependencies is, however, not possible at the local scale alone and will require explicit consideration of higher-level effects in future research. [ABSTRACT FROM AUTHOR]

We investigated the nitrogen (N) dynamics of an alpine–nival ecotone on Mt. Schrankogel, Tyrol, Austria, in relation to temperature. Natural abundance of 15N was used as a tool to elucidate differences in N cycling along an altitudinal transect ranging from 2,906 to 3,079 m, corresponding to a gradient in mean annual temperature of 2.4 °C. The amount of total soil N, of plant available N and soil C/N ratio decreased significantly with increasing altitude, whereas soil pH increased. Soil δ 15N decreased with increasing altitude from +2.2 to −2.1‰ and δ 15N of plant tissues (roots and leaves) decreased from −3.7 to −5.5‰. The large shift in soil δ 15N of 4.3‰ from the lowest to the highest site suggested substantial differences in N cycling in alpine and nival ecosystems in the alpine nival ecotone investigated. We concluded that N cycling at the alpine–nival ecotone is likely to be controlled by various factors: temperature, soil age and development, atmospheric N deposition and plant competition. Our results furthermore demonstrate that the alpine–nival ecotone may serve as a sensitive indicator of global change. [ABSTRACT FROM AUTHOR]

This article provides an overview of the selected papers of the 1st Joint European Stable Isotope Users Group Meeting (JESIUM) in Vienna, Austria from August 30 through September 3, 2004. The intention of JESIUM 2004 was to harness the spirit of the established national meetings and scale it up to a European level, to broaden the scope beyond national borders in order to discuss ideas and methodologies, foster new collaborations and provide a platform to air future ideas and applications in stable isotope research.

Abstract: Glucans like cellulose and starch are a major source of carbon for decomposer food webs, especially during early- and intermediate-stages of decomposition. Litter quality has previously been suggested to notably influence decomposition processes as it determines the decomposability of organic material and the nutrient availability to the decomposer community. To study the impact of chemical and elemental composition of resources on glucan decomposition, a laboratory experiment was carried out using beech (Fagus sylvatica, L.) litter from four different locations in Austria, differing in composition (concentration of starch, cellulose and acid unhydrolyzable residue or AUR fraction) and elemental stoichiometry (C:N:P ratio). Leaf litter was incubated in mesocosms for six months in the laboratory under controlled conditions. To investigate the process of glucan decomposition and its controls, we developed an isotope pool dilution (IPD) assay using 13C-glucose to label the pool of free glucose in the litter, and subsequently measured the dilution of label over time. This enabled us to calculate gross rates of glucose production through glucan depolymerization, and glucose consumption by the microbial community. In addition, potential activities of extracellular cellulases and ligninases (peroxidases and phenoloxidases) were measured to identify effects of resource chemistry and stoichiometry on microbial enzyme production. Gross rates of glucan depolymerization and glucose consumption were highly correlated, indicating that both processes are co-regulated and intrinsically linked by the microbial demand for C and energy and thereby to resource allocation to enzymes that depolymerize glucans. At early stages of decomposition, glucan depolymerization rates were correlated with starch content, indicating that starch was the primary source for glucose. With progressing litter decomposition, the correlation with starch diminished and glucan depolymerization rates were highly correlated to cellulase activities, suggesting that cellulose was the primary substrate for glucan depolymerization at this stage of decomposition. Litter stoichiometry did not affect glucan depolymerization or glucose consumption rates early in decomposition. At later stages, however, we found significant negative relationships between glucan depolymerization and litter C:N and AUR:N ratio and a positive relationship between glucan depolymerization and litter N concentration. Litter C:N and C:P ratios were negatively related to cellulase, peroxidase and phenoloxidase activities three and six months after incubation, further corroborating the importance of resource stoichiometry for glucan depolymerization after the initial pulse of starch degradation. [Copyright &y& Elsevier]

Soil microbial communities have a prominent role in regulating carbon (C) dynamics in terrestrial ecosystems. Climate change factors that alter the composition of the soil microbial community therefore can influence ecosystem processes. While effects of elevated atmospheric CO2 (eCO2) and temperature (eT) on soil microbial community composition have been extensively studied, their combined effect in concomitance with extreme stress events (such as drought) are not well understood. The aim of this study was to examine the impact of different climate change factors, either individually or in combination, on soil microbial community composition of a montane grassland in Styria, Austria. At the experimental site, field plots were subjected to either ambient conditions or simulated future climate, with combinations of eT (+1.5 or +3 °C) and eCO2 (+150 or +300 ppm), for 3 years in a response surface design. A summer drought treatment was superimposed on ambient climate plots and future climate plots (combined +3 °C and +300 ppm CO2), in a full factorial design in 2017. Samples were collected in 3 different seasons: May, July (peak drought) and October (drought recovery). To estimate soil microbial biomass and microbial community composition, phospholipid fatty acids (PLFA) were extracted and quantified. Neutral lipid fatty acids (NLFA) in soils and roots were used to estimate the abundance of arbuscular mycorrhizal fungi (AMF; based on the neutral lipid biomarker 16:1ω5). Multivariate analysis demonstrated distinct differences in microbial community composition of control soils between the three sampling dates, indicating a strong seasonal change in microbial community composition. In addition, individual PLFA biomarkers showed a clear separation of drought versus non-drought treatments as well as of ambient and future climate treatments, indicating shifts in microbial community composition caused by these climate change factors. During drought, in both the future climate and the ambient climate plots, we detected a decrease in all bacterial groups, but not in saprotrophic fungi. However, the strongest negative effect of drought was found in the NLFA biomarker of AMF in roots. Using a response surface model (RSM) approach we examined the individual and combined effects of eT and eCO2 on the biomass of different microbial groups. Significant effects of elevated CO2 and temperature on microbial biomass and community composition were only detected during the first sampling (May) but not during the other sampling dates.Our study demonstrates that climate change strongly affects soil microbial community composition in montane grasslands. Extreme stress events, such as prolonged droughts, induced the strongest shifts in both, microbial community composition and in the biomass of various microbial groups, including bacteria and AMF, but not saprotrophic fungi. Elevated temperature and CO2 did not modulate these drought effects. Moreover, eT and eCO2 showed weaker effects on soil microbial community composition and these effects were dependent on season, highlighting the importance of seasonality when analysing climate change effects on soil microbial community composition and function. [ABSTRACT FROM AUTHOR]

Soils store more than double the amount of carbon (C) than currently present in the biosphere and atmosphere combined. Microbial physiology ultimately controls soil C storage, depending on the proportion of organic C taken up being allocated to microbial catabolism (energy production, respiration) in comparison to microbial anabolism (growth and biosynthesis). Changes in this balance lead to either soil C losses or to the build-up of microbial necromass, which is thought to represent the most important part of stable C in soil. This partitioning of organic C taken up is estimated as microbial carbon use efficiency (CUE), a key parameter in describing the effectiveness of organic C conversion to either potentially stable soil organic matter (SOM) versus C losses from soil to the atmosphere in the form of respiratory CO2. The aim of this study was to assess potential effects of seasonality and of climate change on microbial physiology (growth, turnover, respiration, and CUE). In a managed montane grassland in Styria, Austria, field plots were subjected to either ambient climate conditions or to simulated future climate conditions, with combinations of elevated temperature (+1.5 or +3 °C) and/or elevated atmospheric CO2 (+150 or +300 ppm) for 3 years in a response surface design. A summer drought treatment was also superimposed on ambient climate plots and on future climate plots (combined +3 °C and +300 ppm CO2), in a full factorial design in 2017. Samples were collected in 3 different periods: May, July and October 2017. To determine microbial growth, CUE and turnover we used a novel technique based on the incorporation of 18O-labelled water into microbial DNA. Our results demonstrate that overall season had a significant effect on microbial physiology, with reduced activity in autumn compared to spring and summer. Season modulated climate change effects, especially of elevated temperature which showed the most prominent effects. In July (peak plant growing season), elevated temperature significantly decreased microbial growth, and respiration, leading to slow-down of microbial turnover. However, the resulting CUE exhibited strong non-linearity (quadratic response) to temperature, with highest values at intermediate temperature (+1.5 °C). In contrast, both growth and respiration increased with temperature in autumn. Elevated atmospheric CO2 did not play a major role in modulating microbial physiology, with significant effects only on growth rate and turnover early in the season (May). Drought increased microbial activity (growth and respiration) in combination with the combined climate change treatment (+3 °C, + 300 ppm) only, leading to an increased microbial turnover under these conditions. Our study demonstrates that climate change can have strong effects on microbial physiology, mainly caused by elevated temperatures. Moreover, the strong seasonal, interactive and non-linear effects of global change drivers highlight the complexity of understanding climate change effects on soil microbial processes and the necessity of studying these effects in multiple time points over the growing season and at multiple levels of experimental factors. [ABSTRACT FROM AUTHOR]

To evaluate a new N-monitoring program in the framework of the UN-ECE ICP-Vegetation program using mosses as bioindicators, 490 moss samples were collected at 220 sites in Austria and analyzed for total N (N content) and delta(15)N signatures. Within-site variability of N content and delta(15)N signatures was tested for the first time on a large scale and was extremely low compared to between-site variability. N content in moss tissue ranged between 0.76% and 1.99% and delta(15)N signatures between -10.04 and -2.45. Altitude was significantly correlated with N content (P=0.021) and delta(15)N signatures (P<0.001). When comparing moss data to deposition data from 35 measurement sites, significant correlations between N content and N deposition (P=0.014) were found. Increasing delta(15)N signatures provided evidence for a change in N source and its respective isotopic composition with altitude, e.g., due to long-distance transport of reactive N or as a result of changes in the wetdry deposition ratio. Our study underlines that N deposition can generally be estimated by N content in mosses on a large scale, but that this approach has certain limitations, especially in areas with large differences in altitude and precipitation.