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Aims: The possibility of NOx (NO + NO2) emissions from plants and the underlying mechanisms are still under discussion. Excess NO created possibly as a result of nitrite accumulation in plant leaves has been suggested to result in emissions. Such emission has been observed in laboratory conditions due to nitrate fertilization. In this study, we tested whether nitrate fertilization of Scots pine seedlings growing outdoors leads to accumulation of NO3- or NO2- in the needles and subsequent NOx emission. Methods: The experiment was done at the SMEAR II station in Southern Finland. The seedlings received nitrate or ammonium fertilizer or neither. Shoot NOx emissions were measured with dynamic chambers. Total dissolved nitrogen, inorganic nitrogen, NO3-, NO2- and NH4+ concentrations in the soil and needles were determined. Results: NOx fluxes from the shoots were, on average, deposition. There was no indication of fertilization-induced NO or NOx emissions. The highest NO fluxes were observed at night and were humidity-related. Conclusions: It seems unlikely that additional nitrate in the soil could cause significant NOx emission from boreal Scots pine forests in field conditions, possibly because of soil chemistry. [ABSTRACT FROM AUTHOR]

Background: Wetlands store a substantial amount of carbon (C) in deep soil organic matter deposits, and play an important role in global fluxes of carbon dioxide and methane. Fine roots (i.e., ephemeral roots that are active in water and nutrient uptake) are recognized as important components of biogeochemical cycles in nutrient-limited wetland ecosystems. However, quantification of fine-root dynamics in wetlands has generally been limited to destructive approaches, possibly because of methodological difficulties associated with the unique environmental, soil, and plant community characteristics of these systems. Non-destructive minirhizotron technology has rarely been used in wetland ecosystems. Scope: Our goal was to develop a consensus on, and a methodological framework for, the appropriate installation and use of minirhizotron technology in wetland ecosystems . Here, we discuss a number of potential solutions for the challenges associated with the deployment of minirhizotron technology in wetlands, including minirhizotron installation and anchorage, capture and analysis of minirhizotron images, and upscaling of minirhizotron data for analysis of biogeochemical pools and parameterization of land surface models. Conclusions: The appropriate use of minirhizotron technology to examine relatively understudied fine-root dynamics in wetlands will advance our knowledge of ecosystem C and nutrient cycling in these globally important ecosystems. [ABSTRACT FROM AUTHOR]