Despite the ecological connection between natural and managed systems, they are often studied separately, by different research groups. This echoes the focus of this session that, despite the tight coupling of carbon (C) and nitrogen (N), global change investigations of these element cycles may be carried out by different research groups. This talk will address the contrasting approach to integrating element cycles between researchers in natural and managed systems.

Global change research in natural systems has focused on predicting the C balance of the system. Integrating research between C and other element cycles makes sense in this situation, because the growth and activity of the research organisms (animals, plants, microorganisms) are limited by other elements. This stoichiometric theory (multiple limitation hypothesis) has been investigated for at least three decades, and although C and other elements are often studied independently, many researchers in natural systems have embraced this elemental integration in their global change research. 

Managed systems also have a long history of element limitation research, primarily NPK, with a focus on maximising plant growth and the economy of fertiliser use efficiency. However, natural climate solutions - necessary because mandatory reductions in fossil fuel emissions are insufficient to meet climate targets – often rely on sequestering C in biomass and soils, changing the focus of managed system research to include C. As we know from our research in natural systems, the process of C sequestration is tightly coupled to N (and other elements). Unfortunately, most soil C process models or earth system models do not include N (or other elements). Very few soil C sequestration predictions include the C-cost of N₂O losses - an important trade-off in N-saturated systems - primarily because there has been insufficient research into the microbial interdependency of C and N in managed soils.

In this talk I will discuss recent insights into how the integration of C and N (and other elements) in the ecological research of managed systems can improve our ability to mitigate the consequences of global change.

How to cite: Buckeridge, K.: The integration of element cycles: contrasting perspectives from natural and managed systems in global change research, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14296, https://doi.org/10.5194/egusphere-egu21-14296, 2021.

Wildfire frequency in the Arctic has increased in recent years and is projected to increase further with changes in climatic conditions due to warmer and drier summers. Yet, there is a lack of knowledge about the impacts such events may have on the net greenhouse gas (GHG) balances in ecosystems. During three consecutive growing seasons, we investigated the immediate and short-term effects of experimental fire on carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) surface fluxes in a well-drained tundra ecosystem in West Greenland. During the fire, we monitored litter and surface temperature, as well as the soil temperature in the top 0-5 cm. The results showed that surface temperatures exceeded 400 °C during the burning process and combusted all aboveground biomass, which significantly affected the ecosystem carbon (C) balance. Burned plots continued to be a net CO₂ source for at least two years after burning. Meanwhile, soil temperature did not exceed 60 °C during the fire, and soil GHG cycling appeared relatively resistant to these conditions. Burning had an effect on soil properties and CH₄ fluxes only immediately after the fire event and it had no significant effect on ecosystem respiration (ER). Instead net CH₄ uptake and ER correlated (p<0.05) with soil moisture and soil temperature, respectively. No significant fire effects were observed in net N₂O fluxes which suggests that processes linked to the nitrogen (N) cycle are driven by factors that were not affected by this moderate fire event.   

How to cite: Hermesdorf, L., D'Imperio, L., Elberling, B., and Ambus, P. L.: Short-term effects of experimental fire on CO2, CH4 and N2O exchange in a well-drained arctic tundra, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13480, https://doi.org/10.5194/egusphere-egu21-13480, 2021.

The ecosystem carbon (C) dynamics after permafrost thaw depends on more than just climate change since soil nutrient status may also impact ecosystem C balance. It has been advocated that the potential nitrogen (N) release upon permafrost thaw could promote plant growth and thus offset soil C loss. However, compared with the widely accepted C-N interactions, little is known about the potential role of soil phosphorus (P) availability. Here we combined two-year field observations along a permafrost thaw sequence (constituted by four thaw stages, i.e., non-collapse and 5, 14, and 22 years since collapse) with an in-situ fertilization experiment (included N and P additions at the level of 10 g N m^-2 yr^-1 and 10 g P m^-2 yr^-1, respectively) in a Tibetan swamp meadow to evaluate ecosystem C-nutrient interactions upon permafrost thaw. Our results showed that changes in soil P availability rather than N availability played an important role in regulating the increases in gross primary productivity and the decreases in net ecosystem exchange along the thaw sequence. The fertilization experiment further confirmed that P addition had stronger effects on plant growth than N addition in this permafrost ecosystem. These two lines of evidence highlight the crucial role of soil P availability in altering the trajectory of permafrost C cycle under climate warming.

How to cite: Yang, Y., Yang, G., Peng, Y., Abbott, B. W., Biasi, C., Wei, B., Zhang, D., Wang, J., Yu, J., Li, F., Wang, G., Kou, D., and Liu, F.: Phosphorus regulates ecosystem carbon dynamics after permafrost thaw, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-376, https://doi.org/10.5194/egusphere-egu21-376, 2020.

Permafrost affected soils store a huge amount of organic matter including carbon and nitrogen. But especially permafrost is expected to degrade significantly through deepening and erosion processes with important consequences for freshwater systems. Although Arctic ecosystems are strongly limited by bioavailable nitrogen (N), the loss of vegetation by thermokarst and lack of vegetation on riverbanks probably establish conditions for imbalance in the nitrogen cycle, therefore higher N-availability for microbial transformations and in consequence loss of reactive nitrogen.

Here we present data from expeditions in 2008 and 2019, where we found indeed relatively high concentrations of dissolved inorganic nitrogen, mainly as ammonium (up to approx. 10 µg N g dw^-1 ) in the active layer of dry no vegetated carbon poor mineral soils of the riverbank and cliff (recently eroded by the Lena river). In the stratified permafrost-affected soils of the riverbank nitrate accumulated during the summer period, especially in more organic silty layers (4 % SOM) to extremely high concentrations (up to approx. 90 µg N-nitrate g dw^-1). Decreasing ammonium and increasing nitrate concentrations during the vegetation period hint to the aerobic nitrification process, which is the main source of nitrate in terrestrial ecosystem. Together with high nitrate concentrations in the field, these soil layers showed high potential nitrification rates in aerobic incubation experiments (max. 14.4 µg N g dw^-1 d^-1, 21,6 g N m^-3 d^-1, 5 °C) combined with high varying but significant N₂O production rates (max. 150 µg N-N₂O m^-3 d^-1, 5 °C). Since nitrification rates positively respond to temperature (max. Q₁₀ of 4) and ammonium availability, climate change may cause an increasing release of gaseous N-loss (N₂O) or leaching of nitrate and dissolved organic nitrogen (DON) to aquatic ecosystems with further consequences. Hot spots of high N-availability in no vegetated river and erosion banks likely influence the microbial induced C cycle as C-mineralization but also atmospheric methane oxidation, which might be the interest of future studies.

How to cite: Fiencke, C., Sanders, T., Zell, N., Pfeiffer, E.-M., and Beer, C.: Nitrogen loss in river and erosion banks in form of reactive dissolved nitrogen and nitrous oxide via microbial nitrification in permafrost-affected soils in the Lena Delta in the Siberian Arctic, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14915, https://doi.org/10.5194/egusphere-egu21-14915, 2021.

Coastal ecosystems are suffering increasing degradation in many parts of the world and the ecological integrity and biodiversity of those ecosystems have been greatly threatened due to the high load of pollutants produced largely through anthropogenic processes. Agricultural, industrial and domestic applications pollution mainly affect coastal zones via riverine inputs from contaminated urban and rural areas near shore, atmospheric deposition and direct dumping. Beside the different other pollutants, excessive nutrients have become major concerns which can completely change the functioning and appearance of coastal ecosystems. A variety of plants complete the ecological system of coasts and coastal vegetation may even govern the microbial processes and greenhouse gas emissions. With the need to better protect and manage the coastal areas, it is important to understand the decisive microbial processes of nutrients cycling in coastal ecosystem, especially in the face of the changing climate.

The aim of this study was to assess the abundances of soil bacteria and archaea and their potential to perform different carbon and nitrogen cycling processes in coastal zones and relate these nutrient transformation processes to greenhouse gas emissions. The study was carried out in Estonian and Chinese coasts which were affected by brackish water (mixed saline and fresh water) because of riverine inputs. Twice a month during the most intensive vegetation period, the gas samples (CO₂, CH₄, and N₂O) were taken and different parameters of plant (Schoenoplectus tabernaemontanii and Phragmites australis in Estonia; Spartina alterniflora and Scirpus mariqueter in China) and water were measured in situ. Soil (from the 0–10 cm top layer) and plant samples were collected in the end of study. Besides different chemical parameters measured of soil samples, the archaeal and bacterial community abundance was evaluated by quantitative PCR. To characterise methane cycle, the abundances of methanogenic marker gene mcrA and methanotrophic marker gene pmoA were assessed. Genetic potential of nitrogen transformation processes was evaluated by targeting the following functional genes: bacterial, archaeal and COMAMMOX(complete oxidation of ammonium)-specific amoA (nitrification); nirS, nirK, nosZ clade I and nosZ clade II (denitrification); nifH (N₂ fixation); nrfA (DNRA, dissimilatory nitrate reduction to ammonium); ANAMMOX- (anaerobic ammonium oxidation), and n-damo-specific 16S rRNA genes (nitrite dependent anaerobic methane oxidation).

The results concluded that different plant species played a critical role in mediating gas emissions, where their age composition and biomass was important. Relevance of n-damo process and its high genetic potential for CH₄ reduction was detected in coastal areas. Still, four times higher CH₄ emissions were observed on the Chinese coast compared to Estonia. DNRA process showed the greatest genetic potential in the Chinese research area, but this process was less likely to occur in the soil of Estonian Phragmites australis. As a result of nitrification and denitrification, N₂O was emitted from the coasts to the atmosphere.

How to cite: Espenberg, M., Yang, B., Pille, K., Maddison, M., Li, X., and Mander, Ü.: Different plant species drive the microbial methane and nitrogen cycles and CH4 and N2O emissions on coasts affected by brackish water, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9314, https://doi.org/10.5194/egusphere-egu21-9314, 2021.

Accurate annual greenhouse gas (GHG) budgets are the crucial baseline for global climate change forecast scenarios. On the other hand, the parameterization of these forecast models requires more than high-quality GHG datasets, but also the constant improvement of the representation of GHG producing and consuming processes. Extensive research efforts are therefore focusing on increasing our knowledge of the main GHG producing carbon (C) and nitrogen (N) cycles, though surprisingly not so much into their direct interaction. Most annual GHG budgets from pristine northern ecosystems are based on interpolated datasets from sampling campaigns mainly taken during the growing season. Within the ERC funded FluxWIN project, we are investigating how soil and pore water C & N interact and their biogeochemical GHG drivers change over seasons. Freeze-thaw events have previously been identified as significant GHG drivers by rapidly changing moisture and oxygen conditions in the soil matrix, but it remains unclear if and how C & N coupling contributes to these non-growing season emissions. Therefore, a fully automated static chamber system is monitoring GHG fluxes in high frequency at a boreal peatland ecosystem in Siikaneva, Finland. Nutrient stocks and biogeochemical dynamics within the soil matrix are compared to GHG soil-atmosphere exchange in the form of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) all year-round. We control for climatic variability and isolate differences in non-growing season emissions by using a moisture gradient from well-drained upland soils to adjacent wetland ecosystems. The use of these automated high-frequency GHG measurements in combination with year-round biogeochemical monitoring maximizes the likelihood of capturing episodic emissions and their drivers, which are particularly important during fall freeze and spring thaw periods. The gained information on the coupled C & N biogeochemical cycles will improve feedback estimates of climate change by including non-growing season processes in global-scale process-based models.

How to cite: van Delden, L., Boike, J., Tuittila, E.-S., Vesala, T., and Treat, C.: Inter-seasonal investigation of coupled C & N greenhouse gas fluxes in pristine northern ecosystems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10669, https://doi.org/10.5194/egusphere-egu21-10669, 2021.

Non-growing season greenhouse gas emissions are still underrepresented in observation systems as well as process-based models despite growing evidence of their importance to annual budgets in high latitude regions. We therefore investigate ecological and biogeochemical processes in global carbon and nitrogen cycles during the non-growing and shoulder seasons at Siikaneva, nearby Hyytiälä Research Station in boreal Finland. The FluxWIN project investigates the current underestimation of annual methane (CH₄) emissions from boreal ecosystems by combining high-frequency greenhouse gas measurements and biogeochemical monitoring. Identifying the processes leading to the large observed CH₄ emissions requires thorough analysis of potential meteorological drivers controlling the soil temperature, including radiative forcing, surface energy balance and snow pack characteristics. The location of our research site within extensive long-term scientific infrastructure allows us to compare the measurements obtained from our newly set up meteorological station at a well-drained upland forest site to the ones recorded about 1 km south-east at an ICOS station in open fen. While both stations are subject to the same large-scale meteorological forcing due to their spatial proximity, the different ecosystem types might produce very different microclimates with differing freeze-thaw and soil temperature dynamics, which has potential implications for local carbon and nitrogen cycling leading to CH₄ exchange. Controlling for spatial microclimatic variability will help us to evaluate the representativeness of our flux measurements and identified soil, geophysical and biogeochemical drivers when expanded to a larger spatial scale.

How to cite: Jentzsch, K., van Delden, L., Boike, J., Tuittila, E.-S., Vesala, T., and Treat, C.: Impact of spatial microclimatic variability on carbon and nitrogen cycling leading to methane emissions during the non-growing season of Siikaneva, Finland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8744, https://doi.org/10.5194/egusphere-egu21-8744, 2021.