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Arctic and alpine tundra ecosystems are large reservoirs of organic carbon 1,2 . Climate warming may stimulate ecosystem respiration and release carbon into the atmosphere 3,4 . The magnitude and persistency of this stimulation and the environmental mechanisms that drive its variation remain uncertain 5-7 . This hampers the accuracy of global land carbon-climate feedback projections 7,8 . Here we synthesize 136 datasets from 56 open-top chamber in situ warming experiments located at 28 arctic and alpine tundra sites which have been running for less than 1 year up to 25 years. We show that a mean rise of 1.4 °C [confidence interval (CI) 0.9-2.0 °C] in air and 0.4 °C [CI 0.2-0.7 °C] in soil temperature results in an increase in growing season ecosystem respiration by 30% [CI 22-38%] (n = 136). Our findings indicate that the stimulation of ecosystem respiration was due to increases in both plant-related and microbial respiration (n = 9) and continued for at least 25 years (n = 136). The magnitude of the warming effects on respiration was driven by variation in warming-induced changes in local soil conditions, that is, changes in total nitrogen concentration and pH and by context-dependent spatial variation in these conditions, in particular total nitrogen concentration and the carbon:nitrogen ratio. Tundra sites with stronger nitrogen limitations and sites in which warming had stimulated plant and microbial nutrient turnover seemed particularly sensitive in their respiration response to warming. The results highlight the importance of local soil conditions and warming-induced changes therein for future climatic impacts on respiration., (© 2024. The Author(s).)

Targeted removal experiments are a powerful tool to assess the effects of plant species or (functional) groups on ecosystem functions. However, removing plant biomass in itself can bias the observed responses. This bias is commonly addressed by waiting until ecosystem recovery, but this is inherently based on unverified proxies or anecdotal evidence. Statistical control methods are efficient, but restricted in scope by underlying assumptions. We propose accounting for such biases within the experimental design, using a gradient of biomass removal controls. We demonstrate the relevance of this design by presenting (1) conceptual examples of suspected biases and (2) how to observe and control for these biases. Using data from a mycorrhizal association-based removal experiment, we show that ignoring biomass removal biases (including by assuming ecosystem recovery) can lead to incorrect, or even contrary conclusions (e.g. false positive and false negative). Our gradient design can prevent such incorrect interpretations, regardless of whether aboveground biomass has fully recovered. Our approach provides more objective and quantitative insights, independently assessed for each variable, than using a proxy to assume ecosystem recovery. Our approach circumvents the strict statistical assumptions of, for example, ANCOVA and thus offers greater flexibility in data analysis., (© 2023 The Authors. New Phytologist © 2023 New Phytologist Foundation.)

Warming in the Arctic accelerates top-soil decomposition and deep-soil permafrost thaw. This may lead to an increase in plant-available nutrients throughout the active layer soil and near the permafrost thaw front. For nitrogen (N) limited high arctic plants, increased N availability may enhance growth and alter community composition, importantly affecting the ecosystem carbon balance. However, the extent to which plants can take advantage of this newly available N may be constrained by the following three factors: vertical distribution of N within the soil profile, timing of N-release, and competition with other plants and microorganisms. Therefore, we investigated species- and depth-specific plant N uptake in a high arctic tundra, northeastern Greenland. Using stable isotopic labelling ( 15 N-NH 4 + ), we simulated autumn N-release at three depths within the active layer: top (10 cm), mid (45 cm) and deep-soil near the permafrost thaw front (90 cm). We measured plant species-specific N uptake immediately after N-release (autumn) and after 1 year, and assessed depth-specific microbial N uptake and resource partitioning between above- and below-ground plant parts, microorganisms and soil. We found that high arctic plants actively foraged for N past the peak growing season, notably the graminoid Kobresia myosuroides. While most plant species (Carex rupestris, Dryas octopetala, K. myosuroides) preferred top-soil N, the shrub Salix arctica also effectively acquired N from deeper soil layers. All plants were able to obtain N from the permafrost thaw front, both in autumn and during the following growing season, demonstrating the importance of permafrost-released N as a new N source for arctic plants. Finally, microbial N uptake markedly declined with depth, hence, plant access to deep-soil N pools is a competitive strength. In conclusion, plant species-specific competitive advantages with respect to both time- and depth-specific N-release may dictate short- and long-term plant community changes in the Arctic and consequently, larger-scale climate feedbacks., (© 2020 John Wiley & Sons Ltd.)

Aims: The aims of this study were to evaluate health-related quality of life (HRQL) among patients treated with extracorporeal membrane oxygenation (ECMO) in northern Norway over a period of 27 years (1988-2015) and to identify variables related to HRQL., Methods and Results: A retrospective inquiry of the ECMO registry at the University Hospital of North Norway identified 74 ECMO-treated patients (mean age 49 years, 65% males). Acute cardiac failure was the dominant indication (58%), and venoarterial ECMO was the dominant mode of treatment (87%). Mortality for discharged patients was recorded on 20 September 2016. Thirty (41%) survivors were identified. Twenty-three survivors were eligible for the survey and received a set of questionnaires at home. The main outcome measure was HRQL as measured with the 36-item Short-Form health survey (SF-36) (RAND Short Form-36 v1.2). Other questionnaires covered demographic information, problems with functioning in usual daily activities (such as hobbies, household chores, family, or work), employment status, and psychological distress. The survey was completed by 20 (87%) survivors (mean age = 49 years, 12 men). Indications for ECMO treatment (VA = 90%) had been respiratory failure (25%), cardiac failure (60%), and extracorporeal cardiopulmonary resuscitation (15%). The average time since ECMO treatment was 6.5 years. Seventy-five percent reported mental HRQL (SF-36 Mental Component Summary, mean = 43, SD = 5) or physical HRQL (SF-36 Physical Component Summary, mean = 43, SD = 4.5) within the normal range (T = 50 ± 10) in comparison with age-matched population data from national norms. Half of the responders reported problems on the SF-36 subscales general health and role physical. Seventy percent reported problems on the SF-36 subscale role emotional. All but one responder lived independently without any organized care, and 90% reported no problems related to basic self-care. Half of those in working age had returned to work after ECMO treatment. Forty percent of the responders reported some degree of restrictions in usual daily activities, problems with mobility (35%), anxiety/depression (35%), or pain/discomfort (55%). Significant univariate associations were observed for poorer HRQL and higher reports of psychological distress, pain, and experiencing restrictions in usual everyday activities. Improved HRQL was significantly related to an extended time since ECMO treatment., Conclusions: Our survey indicates an overall positive long-term HRQL outcome for our ECMO survivors. A subset reported problems with functioning and HRQL. Future research should focus on identification of the survivors at risk for poor recovery who may benefit from rehabilitation interventions., (© 2019 The Authors. ESC Heart Failure published by John Wiley & Sons Ltd on behalf of the European Society of Cardiology.)