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Climate change induced mild and rainy winters may expose soils to more frequent and prolonged waterlogging in boreal regions. Resulting oxygen depletion induces reductive dissolution of iron (Fe) oxides further altering the stability of Fe-associated organic matter. Thus far, the impact of waterlogging on the coupled cycling of Fe and carbon (C) in upland arable soils remains unknown. We constructed a monolithic experimental system with 32 soil profiles (l = 63 cm, d = 15.2 cm) collected from two agricultural fields (silty clay, sandy loam) to study the effects of off-season waterlogging, overwintering cover crop and soil type on soil redox potential (Eh), Fe solubility, and movement of C and nitrogen (N) within the soil–plant-atmosphere continuum. Soil moisture, temperature, electrical conductivity, and Eh were continuously monitored, and soil pore water samples were collected at three soil depths. Here, we assess the systems suitability for studying coupled Fe and C dynamics in boreal climate, and investigate the treatment impacts on soil Eh, pH, reductive Fe dissolution and N concentration in pore water. Waterlogging led to reducing conditions in both soils down to 30 cm depth at the soil temperature (+4 to 12 °C) matching those of spring and autumn in southern Finland. The declining Eh and the slightly rising Fe concentration in porewater (max ∼ 10 µmol l−1) suggest that reductive dissolution of Fe could proceed even during mild winters if the duration of waterlogging exceeds 1–2 weeks. The study demonstrated that cover crops may accelerate the drop in soil Eh by removing bioavailable N, and hence controlling the availability of alternative electron acceptors (nitrate) in the soil. Thus, the simultaneous effects of cover crops on C inputs, and on N and water dynamics, all influencing redox reactions, emphasize the importance of incorporating vegetation into studies exploring the impacts of waterlogging on coupled dynamics of Fe and C.

Exploring data aids in the comprehension of the dataset and the system’s essence. Various approaches exist for managing numerous sensors. This study perceives operational states to clarify the physical dynamics within a soil environment. Utilizing Principal Component Analysis (PCA) enables dimensionality reduction, offering an alternative perspective on the spring soil dataset. The K-means algorithm clusters data densities, forming the groundwork for an operational state description. Soil data, integral to an ecosystem, entails evident attributes. Employing dynamic visualization, including animations, constitutes a vital exploration angle. Greenhouse gas variables have been added to PCA to achieve more understanding in the interconnection of gas exchange and soil properties. Pit data and flux data are analysed both separately and together using a data-driven approach. The results look promising, showing the potential to add new values and more detailed state structures to ecological models. All experiments are conducted within the Jupyter programming environment, utilizing Python 3. The relevant literature on data visualization is examined. Through combined techniques and tools, the potential features of the soil ecosystem are observed and identified.

Abstract A multitude of biogeochemical feedback mechanisms govern the climate sensitivity of Earth in response to radiation balance perturbations. One feedback mechanism, which remained missing from most current Earth System Models applied to predict future climate change in IPCC AR6, is the impact of higher temperatures on the emissions of biogenic volatile organic compounds (BVOCs), and their subsequent effects on the hydroxyl radical (OH) concentrations. OH, in turn, is the main sink term for many gaseous compounds including methane, which is the second most important human-influenced greenhouse gas in terms of climate forcing. In this study, we investigate the impact of this feedback mechanism by applying two models, a one-dimensional chemistry-transport model, and a global chemistry-transport model. The results indicate that in a 6 K temperature increase scenario, the BVOC-OH-CH4 feedback increases the lifetime of methane by 11.4% locally over the boreal region when the temperature rise only affects chemical reaction rates, and not both, chemistry and BVOC emissions. This would lead to a local increase in radiative forcing through methane (ΔRFCH4) of approximately 0.013 Wm−2 per year, which is 2.1% of the current ΔRFCH4. In the whole Northern hemisphere, we predict an increase in the concentration of methane by 0.024% per year comparing simulations with temperature increase only in the chemistry or temperature increase in chemistry and BVOC emissions. This equals approximately 7% of the annual growth rate of methane during the years 2008–2017 (6.6 ± 0.3 ppb yr−1) and leads to an ΔRFCH4 of 1.9 mWm−2 per year.

Organic soil amendments such as manure, biochar and compost are among the most efficient and widely used methods to increase soil carbon sequestration in agricultural soils. Even though their benefits are well known, many wood-derived materials are not yet utilized in Nordic agriculture due to a lack of incentives and knowledge of their effects in the local climate. We studied greenhouse gas exchange, plant growth and soil properties of a clay soil cultivated with oat in southern Finland in an extremely dry year. Two years earlier, the field was treated with three ligneous soil amendments—lime-stabilized fiber from the pulp industry, willow biochar and spruce biochar—which we compared against fertilized and non-fertilized controls. We found that the soil amendments increased porosity and the mean soil water holding capacity, which was most noticeable in plots amended with spruce biochar. There was a trend indicating that the mean yield and overall biomass production were larger in plots with soil amendments; however, the difference to unamended control was seldom significant due to the high variance among replicates. Manual chamber measurements revealed that carbon dioxide and methane exchange rates were reduced most probably by the exceptionally hot and dry weather conditions, but no differences could be found between the amended and unamended treatments. The nitrous oxide emissions were significantly smaller from the vegetated soil amended with willow biochar compared with the unamended control. Emissions from non-vegetated soil, representing heterotrophic respiration, were similar but without significant differences between treatments. Overall, the studied soil amendments indicated positive climatic impact two years after their application, but further research is needed to conclusively characterize the specific effects of organic soil amendments on processes affecting greenhouse gas exchange and plant growth.

Abstract Riparian forests are known as hot spots of nitrogen cycling in landscapes. Climate warming speeds up the cycle. Here we present results from a multi-annual high temporal-frequency study of soil, stem, and ecosystem (eddy covariance) fluxes of N2O from a typical riparian forest in Europe. Hot moments (extreme events of N2O emission) lasted a quarter of the study period but contributed more than half of soil fluxes. We demonstrate that high soil emissions of N2O do not escape the ecosystem but are processed in the canopy. Rapid water content change across intermediate soil moisture was a major determinant of elevated soil emissions in spring. The freeze-thaw period is another hot moment. However, according to the eddy covariance measurements, the riparian forest is a modest source of N2O. We propose photochemical reactions and dissolution in canopy-space water as reduction mechanisms.

Biochars have potential to provide agricultural and environmental benefits such as increasing soil carbon sequestration, crop yield, and soil fertility while reducing greenhouse gas (GHG) emissions and nitrogen leaching. However, whether these effects will sustain for the long-term is still unknown. Moreover, these effects were observed mostly in highly weathered (sub-) tropical soils with low pH and soil organic carbon (SOC). The soils in northern colder boreal regions have typically higher SOC and undergo continuous freeze-thaw cycles. Therefore, effects of biochars in these regions may be different from those observed in other climates. However, only a few biochar studies have been conducted in boreal regions. We aimed to assess the long-term effects of biochars on GHG emissions, yield-normalized non-CO2 GHG emissions (GHGI), and N dynamics in boreal soils. For this, we collected data from four existing Finnish biochar field experiments during 2018 growing season. The experiments were Jokioinen (Stagnosol), Qvidja (Cambisol), Viikki-1 (Stagnosol), and Viikki-2 (Umbrisol), where biochars were applied, 2, 2, 8, and 7 years before, respectively. The GHG emissions, crop yield, soil mineral N, and microbial biomass were measured from all fields, whereas, additional measurements of plant N contents and N leaching were conducted in Qvidja. Biochars increased CO2 efflux in Qvidja and Viikki-2, whereas, there were no statistically significant effects of biochars on the fluxes of N2O or CH4, but in Qvidja, biochars tended to reduce N2O fluxes at the peak emission points. The tendency of biochars to reduce N2O emissions seemed higher in soils with higher silt content and lower initial soil carbon. We demonstrated the long-term effects of biochar on increased crop yield by 65% and reduced GHGI by 43% in Viikki-2. In Qvidja, the significant increment of plant biomass, plant N uptake, nitrogen use efficiency, and crop yield, and reduction of NO3−–N leaching by the spruce biochar is attributed to its ability to retain NO3−–N, which could be linked to its significantly higher specific surface area. The ability of the spruce biochar to retain soil NO3−–N and hence to reduce N losses, has implications for sustainable management of N fertilization.

Forest soil is known to be a source of the greenhouse gas N2O, but the impact of what is planted in that soil has long been overlooked. Here Machacova and colleagues quantify seasonal N2O fluxes from common boreal tree species in Finland, finding that all trees are net sources of this gas.

Understanding mechanisms of soil organic matter (SOM) decomposition and stabilisation improves soil-climate feedback predictions. Here the authors show that roots in boreal forest promote organic nitrogen economy and provide a framework on how roots affect decomposition and stabilisation of SOM.

In the northern hemisphere, boreal forests are a major source of biogenic volatile organic compounds (BVOCs), which drive atmospheric processes and lead to cloud formation and changes in the Earth’s radiation budget. Although forest vegetation is known to be a significant source of BVOCs, the role of soil and the forest floor, and especially interannual variations in fluxes, remains largely unknown due to a lack of long-term measurements. Our aim was to determine the interannual, seasonal and diurnal dynamics of boreal forest floor volatile organic compound (VOC) fluxes and to estimate how much they contribute to ecosystem VOC fluxes. We present here an 8-year data set of forest floor VOC fluxes, measured with three automated chambers connected to the quadrupole proton transfer reaction mass spectrometer (quadrupole PTR-MS). The exceptionally long data set shows that forest floor fluxes were dominated by monoterpenes and methanol, with relatively comparable emission rates between the years. Weekly mean monoterpene fluxes from the forest floor were highest in spring and in autumn (maximum 59 and 86 μg m-2 h-1, respectively), whereas the oxygenated VOC fluxes such as methanol had highest weekly mean fluxes in spring and summer (maximum 24 and 79 μg m-2 h-1, respectively). Although the chamber locations differed from each other in emission rates, the inter-annual dynamics were very similar and systematic. Accounting for this chamber location dependent variability, temperature and relative humidity, a mixed effects linear model was able to explain 79–88% of monoterpene, methanol, acetone, and acetaldehyde fluxes from the boreal forest floor. The boreal forest floor was a significant contributor in the forest stand fluxes, but its importance varies between seasons, being most important in autumn. The forest floor emitted 2–93% of monoterpene fluxes in spring and autumn and 1–72% of methanol fluxes in spring and early summer. The forest floor covered only a few percent of the forest stand fluxes in summer.