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.

The development of new options to reduce ammonia (NH₃) emissions during slurry manure storage is still required due to the shortcomings of the current technologies. This study aimed to identify to what extent untreated and acid-treated biochar (BC) and pure acids could reduce ammonia nitrogen (NH₃-N) volatilization and increase nitrogen retention in slurry digestate. The NH₃-N emissions were effectively reduced by H₂SO₄ and H₃PO₄ acids, untreated BC when applied mixed into the digestate and acidified BC treatments applied on the surface of the digestate. Acidification increased the specific surface area and number of O-containing surface functional groups of the BC and decreased the pH, alkalinity and the hydrophobic property. Compared to untreated BC, the ability of BC to reduce NH₃-N emissions was greater when it was acidified with H₂SO₄ and applied to the digestate surface. The effect on digestate pH of acidified BC when applied mixed into the digestate was not different, except for H₂O₂, from that of the addition of the respective pure acid to digestate. The total N concentration in digestate was not significantly correlated with NH₃-N emissions. These findings indicate that acidified BC could be an effective conditioner to reduce NH₃-N emissions from slurry digestate storage.

Tree stems play an important role in forest methane (CH₄) and nitrous oxide (N₂O) flux dynamics. Our paper aimed to determine the unknown diurnal variability of CH₄ and N₂O exchange in grey alder tree stems. The gas fluxes in tree stems and adjacent soil were measured using manual static and dynamic chamber systems with gas chromatographic and laser-spectroscopic analysis, respectively. The alder trees were predominant emitters of CH₄ and N₂O; however, N₂O emission from stems was negligible. The soil mainly emitted N₂O into the atmosphere and was both a source and sink of CH₄, depending on environmental conditions. Neither the tree stems nor the riparian forest soil showed significant differences in their CH₄ and N₂O fluxes between the daytime and nighttime, independently of the exchange rates. In contrast to several previous studies revealing a diurnal variability of greenhouse gas fluxes from tree stems, our investigation did not show any clear daytime–nighttime differences. On the other hand, we found quite clear seasonal dynamics initiated by changing environmental conditions, such as temperature and soil water conditions and tree physiological activity. Our results imply a transport role of tree stems for soil-produced CH₄ and N₂O rather than the production of these gases in tree tissues, even though this cannot be excluded.

Nutrient-rich northern peatlands are often drained to enhance forest productivity, turning peatland soils into sinks of methane (CH₄) and sources of nitrous oxide (N₂O). However, further attention is needed on CH₄ and N₂O dynamics during the winter period to fully understand the spatio-temporal variability of fluxes. Besides soil, tree stems can also emit CH₄ and N₂O. However, stem contribution is not considered in most biogeochemical models. We determined the temporal dynamics of winter-time CH₄ and N₂O fluxes in a drained peatland forest by simultaneously measuring stem and soil fluxes and exploring the relationships between gas fluxes and soil environmental parameters. During sampling (October 2020–May 2021), gas samples from Downy Birch (Betula pubescens) and Norway Spruce (Picea abies) trees were collected from different tree heights using manual static chambers and analysed using gas chromatography. Soil CH₄ and N₂O concentrations were measured using an automated dynamic soil chamber system. Tree stems were a net source of CH₄ and N₂O during the winter period. The origin of stem CH₄ emissions was unclear, as stem and soil CH₄ fluxes had opposite flux directions, and the irregular vertical stem flux profile did not indicate a connection between stem and soil fluxes. Stem N₂O emissions may have originated from the soil, as emissions decreased with increasing stem height and were driven by soil N₂O emissions and environmental parameters. Soil was a net sink for CH₄, largely determined by changes in soil temperature. Soil N₂O dynamics were characterised by hot moments—short periods of high emissions related to changes in soil water content. Tree stem emissions offset the soil CH₄ sink by 14% and added 2% to forest floor N₂O emissions. Therefore, CH₄ and N₂O budgets that do not incorporate stem emissions can overestimate the sink strength or underestimate the total emissions of the ecosystem.

Biochar has been proposed as an amendment that can improve soil conditions, increase harvest yield, and reduce N losses through NO₃⁻ leaching and N₂O emissions. We conducted an experiment to test the hay biochar mitigation effect on N₂O emissions depending on its production temperature. The pot experiment consisted of the soil amendment with three different production temperature biochars (300 °C, 550 °C, 850 °C) alone and in combination with three different organic fertilizers (cattle slurry, slurry digestate, vinasse), in growth chamber conditions. The effects of biochar and fertilizer were both significant, but the interaction biochar:fertilizer was not. The amendment with the three fertilizer types and with the highest production temperature biochar resulted in significantly higher cumulative N₂O fluxes. Biochar did not show a mitigation effect on N₂O emissions when applied with organic fertilizer. Cumulative emissions were higher with biochar addition, with increasing emissions for increasing biochar production temperature. Our results support the idea that biochar cannot be considered as a universal tool for the reduction of N₂O emissions.

Biochar, a carbon-rich material resulting from pyrolysation, is one of the proposed alternatives as a substrate component to peat. The aim of this study was to investigate the effect of different ratios of peat substitution with a locally available hardwood biochar on the chemical characteristics of growing media, seed germination, plant morphological and nutritional parameters of Tagetes patula. Experimental results show that biochar can be used as a partial peat replacement, showing a complementary liming effect, rising the initial pH of peat (2.8) to values of 4.5 and 7.3 in mixtures with 50% and 75% substitution of peat by biochar, respectively. The mixture with a 50% biochar rate exhibited the strongest change between initial and final pH, rising from 4.5 to 5.7. Increasing content of biochar in the mixtures corresponded to increasing content of total K, Ca, Mg, available K and decreasing level of available Mg. The highest germination percentage was observed in the mixtures with biochar rates from 50% to 100%. Among all substrates, the greatest plant diameter, true leaf area and total root length were measured in the 50% peat substitution mixture, where the highest contents of P, K and Ca in plant shoots were found.