Increased microbial growth, biomass, and turnover drive soil organic carbon accumulation at higher plant diversity.

Species-rich plant communities have been shown to be more productive and to exhibit increased long-term soil organic carbon (SOC) storage. Soil microorganisms are central to the conversion of plant organic matter into SOC, yet the relationship between plant diversity, soil microbial growth, turnover as well as carbon use efficiency (CUE) and SOC accumulation is unknown. As heterotrophic soil microbes are primarily carbon limited, it is important to understand how they respond to increased plant-derived carbon inputs at higher plant species richness (PSR). We used the long-term grassland biodiversity experiment in Jena, Germany, to examine how microbial physiology responds to changes in plant diversity and how this affects SOC content. The Jena Experiment considers different numbers of species (1-60), functional groups (1-4) as well as functional identity (small herbs, tall herbs, grasses, and legumes). We found that PSR accelerated microbial growth and turnover and increased microbial biomass and necromass. PSR also accelerated microbial respiration, but this effect was less strong than for microbial growth. In contrast, PSR did not affect microbial CUE or biomass-specific respiration. Structural equation models revealed that PSR had direct positive effects on root biomass, and thereby on microbial growth and microbial biomass carbon. Finally, PSR increased SOC content via its positive influence on microbial biomass carbon. We suggest that PSR favors faster rates of microbial growth and turnover, likely due to greater plant productivity, resulting in higher amounts of microbial biomass and necromass that translate into the observed increase in SOC. We thus identify the microbial mechanism linking species-rich plant communities to a carbon cycle process of importance to Earth's climate system.

Nitrate supply and uptake in the Atlantic Arctic sea ice zone: seasonal cycle, mechanisms and drivers.

Nutrient supply to the surface ocean is a key factor regulating primary production in the Arctic Ocean under current conditions and with ongoing warming and sea ice losses. Here we present seasonal nitrate concentration and hydrographic data from two oceanographic moorings on the northern Barents shelf between autumn 2017 and summer 2018. The eastern mooring was sea ice-covered to varying degrees during autumn, winter and spring, and was characterized by more Arctic-like oceanographic conditions, while the western mooring was ice-free year-round and showed a greater influence of Atlantic water masses. The seasonal cycle in nitrate dynamics was similar under ice-influenced and ice-free conditions, with biological nitrate uptake beginning near-synchronously in early May, but important differences between the moorings were observed. Nitrate supply to the surface ocean preceding and during the period of rapid drawdown was greater at the ice-free more Atlantic-like western mooring, and nitrate drawdown occurred more slowly over a longer period of time. This suggests that with ongoing sea ice losses and Atlantification, the expected shift from more Arctic-like ice-influenced conditions to more Atlantic-like ice-free conditions is likely to increase nutrient availability and the duration of seasonal drawdown in this Arctic shelf region. The extent to which this increased nutrient availability and longer drawdown periods will lead to increases in total nitrate uptake, and support the projected increases in primary production, will depend on changes in upper ocean stratification and their effect on light availability to phytoplankton as changes in climate and the physical environment proceed. This article is part of the theme issue 'The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning'.

Full 15N tracer accounting to revisit major assumptions of 15N isotope pool dilution approaches for gross nitrogen mineralization.

The 15N isotope pool dilution (IPD) technique is the only available method for measuring gross ammonium (NH4 +) production and consumption rates. Rapid consumption of the added 15N-NH4 + tracer is commonly observed, but the processes responsible for this consumption are not well understood. The primary objectives of this study were to determine the relative roles of biotic and abiotic processes in 15N-NH4 + sconsumption and to investigate the validity of one of the main assumptions of IPD experiments, i.e., that no reflux of the consumed 15N tracer occurs during the course of the experiments. We added a 15N-NH4 + tracer to live and sterile (autoclaved) soil using mineral topsoil from a beech forest and a grassland in Austria that differed in NH4 + concentrations and NH4 + consumption kinetics. We quantified both biotic tracer consumption (i.e. changes in the concentrations and 15N enrichments of NH4 +, dissolved organic N (DON), NO3 - and the microbial N pool) and abiotic tracer consumption (i.e., fixation by clay and/or humic substances). We achieved full recovery of the 15N tracer in both soils over the course of the 48 h incubation. For the forest soil, we found no rapid consumption of the 15N tracer, and the majority of tracer (78%) remained unconsumed at the end of the incubation period. In contrast, the grassland soil showed rapid 15N-NH4 + consumption immediately after tracer addition, which was largely due to both abiotic fixation (24%) and biotic processes, largely uptake by soil microbes (10%) and nitrification (13%). We found no evidence for reflux of 15N-NH4 + over the 48 h incubation period in either soil. Our study therefore shows that 15N tracer reflux during IPD experiments is negligible for incubation times of up to 48 h, even when rapid NH4 + consumption occurs. Such experiments are thus robust to the assumption that immobilized labeled N is not re-mobilized during the experimental period and does not impact calculations of gross N mineralization.

Nutrient pathways and their susceptibility to past and future change in the Eurasian Arctic Ocean.

Climate change is altering nutrient cycling within the Arctic Ocean, having knock-on effects to Arctic ecosystems. Primary production in the Arctic is principally nitrogen-limited, particularly in the western Pacific-dominated regions where denitrification exacerbates nitrogen loss. The nutrient status of the eastern Eurasian Arctic remains under debate. In the Barents Sea, primary production has increased by 88% since 1998. To support this rapid increase in productivity, either the standing stock of nutrients has been depleted, or the external nutrient supply has increased. Atlantic water inflow, enhanced mixing, benthic nitrogen cycling, and land-ocean interaction have the potential to alter the nutrient supply through addition, dilution or removal. Here we use new datasets from the Changing Arctic Ocean program alongside historical datasets to assess how nitrate and phosphate concentrations may be changing in response to these processes. We highlight how nutrient dynamics may continue to change, why this is important for regional and international policy-making and suggest relevant research priorities for the future.

The patronizing character and status-preserving function of leniency for outgroup offenders.

This research investigates cases in which leniency for offenders from low-status (out)groups reflects a strategy of high-status (in)groups to consolidate intergroup status differentials. In Study 1, we found that participants from a high-status ingroup recommended a more lenient punishment for a low-status outgroup offender only when intergroup status differentials were likely to remain stable. This leniency, however, disappeared when status differentials were fragile. In Study 2, we found that patronizing leniency can even consolidate intergroup status differentials: When participants learned that their ingroup had punished an outgroup offender leniently, they considered an outgroup member who legitimately complained about discrimination more as being a hypersensitive complainer than when they learned that their ingroup had punished the outgroup offender more harshly or similarly as an ingroup offender. These findings suggest that leniency for outgroup offenders can indeed be used strategically by the in-group to secure its advantaged status.

Description of a Program for Psychiatric Consultations in the Nursing Home.

The authors describe a psychiatric consultation program ad-ministered by a geropsychiatric clinical nurse specialist in a nursing home and present data on its effectiveness. Residents referred for psychiatric consultation were similar with regard to demographic characteristics, but were more cognitively intact. The most common reasons for referral were depressive symptoms, agitated behavior, and perceptual distortions. Interventions involving medication were the most frequently used, followed by relocating the resident, staff interventions, and psychotherapy. Treatments that involved moving the resident were rated as less effective. Overall, significant improvement was noted in slightly more than half of all residents referred for psychiatric consultation.