To predict emissions of nitrous oxide (N2O) and nitric oxide (NO) from forest soils, we have developed a process-oriented model by integrating several new features with three existing models, PnET, Denitrification-Decomposition (DNDC), and a nitrification model. In the new model, two components were established to predict (1) the effects of ecological drivers (e. g., climate, soil, vegetation, and anthropogenic activity) on soil environmental factors (e. g., temperature, moisture, pH, redox potential, and substrates concentrations), and (2) effects of the soil environmental factors on the biochemical or geochemical reactions which govern NO and N2O production and consumption. The first component consists of three submodels for predicting soil climate, forest growth, and turnover of soil organic matter. The second component contains two submodels for nitrification and denitrification. A kinetic scheme, a so-called "anaerobic balloon," was developed to calculate the anaerobic status of the soil and divide the soil into aerobic and anaerobic fractions. Nitrification is only allowed to occur in the aerobic fraction, while denitrification occurs only in the anaerobic fraction. The size of the anaerobic balloon is defined by the simulated oxygen partial pressure which is calculated based on oxygen diffusion and consumption rates in the soil. As the balloon swells or shrinks, the model dynamically allocates substrates (e. g., dissolved organic carbon, ammonium, nitrate, etc.) into the aerobic and anaerobic fractions. With this approach, the model is able to predict both nitrification and denitrification in the same soil at the same time. This feature is important for soils where aerobic and anaerobic microsites often exist simultaneously. With the kinetic framework as well as its interacting functions, the PnET-N-DNDC model links ecological drivers to trace gas emissions. Tests for validating the new model are published in a companion paper

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Over the past few years, new technologies for nitrogen removal have been developed mainly because of the increasing financial costs of the traditional wastewater treatment technologies. Newly discovered pathways, like the anaerobic oxidation of ammonium (ANAMMOX), and uses for nitrogen removal technologies are under discussion. Processes and technologies such as: Partial nitrification; Single reactor systems for High Ammonium Removal Over Nitrite (SHARON); Anammox; Aerobic/anoxic deammonification; Oxygen Limited Autotrophic Nitrification‐Denitrification (OLAND); Completely Autotrophic Nitrogen Removal Over Nitrite (CANON); wetland based systems, all have a high potential for nitrogen removal. However, the pathways of nitrogen transformation processes are very complex. An understanding of how various environmental factors affect these processes and a sound knowledge of existing, worldwide experience pertaining to these novel technologies are the key if the nitrogen removal rates are to be improved and success is to be realized in full‐scale applications. This review describes the present knowledge of the new treatment technologies for wastewater with high nitrogen loads. Special emphasis is given to the influence of environmental factors and the reactor configuration on the nitrogen transformation process and microbial activity.

Summary• In contrast to terrestrial plants, epiphytic tank bromeliads take up nutrients mainly over their tank leaf surface. The form in which nutrients are available in the tanks is determined by the source and the complex interplay between tank microbes, which transform them and the epiphytes that take them up.• To elucidate the importance of different nitrogenous compounds for the nitrogen (N) nutrition of Vriesea gigantea from the Atlantic Rainforest, Brazil, N transformation processes in tank water as well as foliar uptake rates were estimated by 15 N labelling techniques.• Microorganisms actively transformed N compounds in the tank. Specifically, organic N compounds were rapidly mineralized to NH 4 + , while nitrification was negligible.• Plants took up both organic and inorganic N forms, with a clear preference for NH 4 + . NH 4 + comprised the largest and, because of fast mineralization rates, the most constant dissolved N pool in the tank water. Excretion of ureases by the plants together with an unusual uptake kinetic for urea also suggests that urea may be potentially important as an N source.

Plant roots strongly influence C and N availability in the rhizosphere via rhizodeposition and uptake of nutrients. This study aimed at investigating the effect of resource availability on microbial processes and community structure in the rhizosphere. We analyzed C and N availability, as well as microbial processes and microbial community composition in rhizosphere soil of European beech and compared it to the bulk soil. Additionally, we performed a girdling experiment in order to disrupt root exudation into the soil. By this novel approach we were able to demonstrate that enhanced resource availability positively affected N mineralization and hydrolytic enzyme activities in the rhizosphere, but negatively affected nitrification rates and oxidative enzyme activities, which are involved in the degradation of soil organic matter. Both rhizosphere effects on N mineralization and oxidative enzyme activities disappeared in the girdling treatment. Microbial community structure in the rhizosphere, assessed by phospholipid fatty acid analysis, differed only slightly from bulk soil but was markedly altered by the girdling treatment, indicating additional effects of the girdling treatment beyond the reduction of root exudation. Differences in oxidative enzyme activities and nitrification rates between rhizosphere soil and bulk soil, however, suggest considerable differences in the (functional) microbial community composition.