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The effects of soil succession after glacial retreat and fertilisation by marine animals are known to have major impacts on soil greenhouse gas (GHG) fluxes in polar terrestrial ecosystems. While in many polar coastal areas retreating glaciers open up new ground for marine animals to colonise, little is known about the combination of both factors on the local GHG budget. We studied the magnitude of GHG fluxes (CO2, CH4 and N2O) on the combined effect of glacial retreat and penguin-induced fertilisation along a transect protruding into the world's largest King Penguin (Aptenodytes patagonicus) colony at Saint Andrews Bay on sub-Antarctic South Georgia. GHG production and consumption rates were assessed based on laboratory incubations of intact soil cores and nutrients and water additional experimental incubations. The oldest soils along the transect show significant higher contents of soil carbon, nutrients and moisture and were strongly influenced by penguin activity. We found a net CH4 consumption along the entire transect with a marked decrease within the penguin colony. CO2 production strongly increased along the transect, while N2O production rates were low near the glacier front and increased markedly within the penguin colony. Controlled applications of guano resulted in a significant increase in CO2 and N2O production, and decrease in CH4 consumption, except for sites already strongly influenced by penguin activity. The results show that soil microbial activity promptly catalyses a turnover of soil C and atmospheric methane oxidation in de-glaciated forelands. The methane oxidizers, however, may increase relatively slowly in their capacity to oxidise atmospheric CH4. Results show also that the increase of nutrients by penguins reduces CH4 oxidation whereas N2O production is greatly increased. A future expansion of penguins into newly available ice-free polar coastal areas may therefore markedly increase the local GHG budget.

In the permafrost-affected landscape, surface and near-surface water movement links areas of higher elevation with lowlands and surface water bodies. Water supply is dominated by snow melt and is thus highly seasonal, as most water moves on the frozen surface in spring, passing only a thin layer of thawed soil. Soluble nutrients mobilized by soil thaw may thus be transported laterally from upslope to downslope ecosystems, which in nutrient-limited cold ecosystems may affect vegetation, ecosystem respiration and surface-atmosphere interaction. In a nitrogen (N) limited ecosystem, however, released inorganic N may in reality not travel far downslope. This study quantifies the potential effect of the snowmelt water nutrient transport by tracing dissolved N in meltwater moving downslope on the frozen surface in a W Greenlandic slope with a snow fan supplying meltwater throughout most of the summer. We use the stable isotopes 15N and D applied simultaneously on top of the frozen surface upslope in a combined solution to investigate the behavior of water and dissolved N flow patterns. We further address the effect of season by tracing N supplied in the early thaw season (30 cm to the frozen surface) and in the late thaw season (90 cm to the frozen surface). Monitoring the slope in detail, we then use the numerical coupled heat-and-mass transfer Coup model to simulate the biotics and abiotics of the receiving ecosystem and study the importance of the lateral N input and the effect of increased N transport in a warmer future. About 50 % of the N tracer was retained in the ecosystem immediately below injection in the early growing season (30 cm active layer), whereas about 35 % was retained in the later growing season (90 cm active layer). Most of the applied 15N was rapidly immobilized by microbes and into the bulk soil, whereas only a few percentages was taken up by the vegetation. D recovery seemed to follow the pattern of microbial N uptake, suggesting that N and D moved

Recent advances in laser spectroscopy have allowed for real-time measurements of the 13C/12C isotopic ratio in CO2, thereby providing new ways to investigate carbon cycling in natural ecosystems. In this study, we combined an Aerodyne quantum cascade laser spectrometer for CO2 isotopes with a LI-COR LI-8100A/8150 automated chamber system to measure the δ13C of CO2 during automated closed-chamber measurements. The isotopic composition of the CO2 flux was determined for each chamber measurement by applying the Keeling plot method. We found that the δ13C measured by the laser spectrometer was influenced by water vapour and CO2 concentration of the sample air and we developed a method to correct for these effects to yield accurate measurements of δ13C. Overall, correcting for the CO2 concentration increased the δ13C determined from the Keeling plots by 3.4%‰ compared to 2.1%‰ for the water vapour correction. We used the combined system to measure δ13C of the CO2 fluxes automatically every two hours from intact soil, trenched soil, tree stems and coarse roots during a two-month campaign in a Danish beech forest. The mean δ13C was -29.8 ± 0.32%‰ for the intact soil plots, which was similar to the mean δ13C of -29.8 ± 1.2%‰ for the trenched soil plots. The lowest δ13C was found for the root plots with a mean of -32.6 ± 0.78%‰. The mean δ13C of the stems was -30.2 ± 0.74%‰, similar to the mean δ13C of the soil plots. In conclusion, the study showed the potential of using a quantum cascade laser spectrometer to measure δ13C of CO2 during automated closed-chamber measurements, thereby allowing for measurements of isotopic ecosystem CO2 fluxes at a high temporal resolution. It also highlighted the importance of proper correction for cross-sensitivity with water vapour and CO2 concentration of the sample air to get accurate measurements of δ13C.

Elevated atmospheric CO2 concentration (eCO2) and climate change may substantially alter soil carbon (C) dynamics and thus feedback to future climate. However, only very few field experiments world‐wide have combined eCO2 with both warming and changes in precipitation in order to study the potential combined effects of changes in these fundamental drivers of C cycling in ecosystems. We exposed a temperate heath/grassland to eCO2, warming, and drought, in all combinations for 8 years. At the end of the study, soil C stocks were on average 0.927 kg C m−2 higher across all treatment combinations with eCO2 compared to ambient CO2 treatments (equal to an increase of 0.120 ± 0.043 kg C m−2 y−1), and showed no sign of slowed accumulation over time. However, if observed pre‐treatment differences in soil C are taken into account, the annual rate of increase caused by eCO2 may be as high as 0.177 ± 0.070 kg C m−2 y−1. Further, the response to eCO2 was not affected by simultaneous exposure to warming and drought. The robust increase in soil C under eCO2 observed here, even when combined with other climate change factors, suggests that there is continued and strong potential for enhanced soil carbon sequestration in some ecosystems to mitigate increasing atmospheric CO2 concentrations under future climate conditions. The feedback between land C and climate remains one of the largest sources of uncertainty in future climate projections, yet experimental data under simulated future climate, and especially including combined changes, are still scarce. Globally coordinated and distributed experiments with long‐term measurements of changes in soil C in response to the three major climate change‐related global changes, eCO2, warming, and changes in precipitation patterns, are therefore urgently needed.

Soil N availability for plants and microorganisms depends on the breakdown of soil polymers such as proteins into smaller, assimilable units by microbial extracellular enzymes. Changing climatic conditions are expected to alter protein depolymerization rates over the next decades, and thereby affect the potential for plant productivity. We here tested the effect of increased CO2 concentration, temperature, and drought frequency on gross rates of protein depolymerization, N mineralization, microbial amino acid and ammonium uptake using N-15 pool dilution assays. Soils were sampled in fall 2013 from the multifactorial climate change experiment CLIMAITE that simulates increased CO2 concentration, temperature, and drought frequency in a fully factorial design in a temperate heathland. Eight years after treatment initiation, we found no significant effect of any climate manipulation treatment, alone or in combination, on protein depolymerization rates. Nitrogen mineralization, amino acid and ammonium uptake showed no significant individual treatment effects, but significant interactive effects of warming and drought. Combined effects of all three treatments were not significant for any of the measured parameters. Our findings therefore do not suggest an accelerated release of amino acids from soil proteins in a future climate at this site that could sustain higher plant productivity.

Long-term climate change experiments are extremely valuable for studying ecosystem responses to environmental change. Examination of the vegetation and the soil should be non-destructive to guarantee long-term research. In this paper, we review field methods using isotope techniques for assessing carbon dynamics in the plant–soil–air continuum, based on recent field experience and examples from a European climate change manipulation network. Eight European semi-natural shrubland ecosystems were exposed to warming and drought manipulations. One field site was additionally exposed to elevated atmospheric CO2. We discuss the isotope methods that were used across the network to evaluate carbon fluxes and ecosystem responses, including: (1) analysis of the naturally rare isotopes of carbon (13C and 14C) and nitrogen (15N); (2) use of in situ pulse labelling with 13CO2, soil injections of 13C- and 15N-enriched substrates, or continuous labelling by free air carbon dioxide enrichment (FACE) and (3) manipulation of isotopic composition of soil substrates (14C) in laboratory-based studies. The natural 14C signature of soil respiration gave insight into a possible long-term shift in the partitioning between the decomposition of young and old soil carbon sources. Contrastingly, the stable isotopes 13C and 15N were used for shorter-term processes, as the residence time in a certain compartment of the stable isotope label signal is limited. The use of labelled carbon-compounds to study carbon mineralisation by soil micro-organisms enabled to determine the long-term effect of climate change on microbial carbon uptake kinetics and turnover. Based on the experience with the experimental work, we provide recommendations for the application of the reviewed methods to study carbon fluxes in the plant–soil–air continuum in climate change experiments. 13C-labelling techniques exert minimal physical disturbances, however, the dilution of the applied isotopic signal can be challenging. In