『Abstract
　A microcosm study was conducted outdoors at ambient temperatures in York, UK, to investigate the effects of seasonal temperature changes on NH4⁺-N dynamics associated with litter mineralization. Temporal variations in the effects of a surface litter layer and litter mixed with near-surface mineral soils on the mobility of NH4⁺-N were assessed over 7 months from the start of winter. Litter decomposition and associated N mineralization contributed significantly towards NH4⁺-N production in the soil profiles, especially at 0-10 cm depths, even at low winter temperatures. Increase in temperature over time substantially increased KCl-extractable and water-soluble NH4⁺-N concentrations via enhanced organic matter mineralization. The difference between KCl-extractable and water-soluble NH4⁺-N increased over time, as much of the NH4⁺-N produced and mobilized in the litter layer was retained in the soil profiles. Surprisingly, the presence of litter, especially in the mixed litter treatment, markedly reduced mineral-N concentrations in the leachate in winter. Nitrate-N concentrations in leachate were substantially lowered in summer too, in spite of the absence of vegetation uptake in summer. This indicates that microbial N immobilization in soil and/or abiotic N retention linked with soil organic matter, and not just plant-N uptake, reduce nitrate leaching to freshwaters in summer months.

Keywords: litter; Mineralization; Ammonium; Nitrogen cycle; DOC; Temporal variations』

1. Introduction
2. Materials and methods
　2.1. Site description
　2.2. Sampling and sample preparation
　　2.2.1. Litter sampling
　　2.2.2. Soil sampling
　2.3. Microcosm construction and experimental design
　2.4. Simulated rain formulation, irrigation and leachate collection
　2.5. Soil analysis
　　2.5.1. Soil and litter initial analysis
　　　2.5.1.1. Soil pH
　　　2.5.1.2. Moisture content
　　　2.5.1.3. Soil C, N and C/N ratio
　　　2.5.1.4. Soil texture
　　2.5.2. Soil and litter analysis after each destructive sampling
　　　2.5.2.1. Extractable NH4⁺-N and NO3^--N concentrations in soils and litter
　　　2.5.2.2. Leachate analysis
　　　2.5.2.3. H2O-extractable dissolved organic carbon (DOC)
　2.6. Statistical analysis
3. Results
　3.1. Initial physico-chemical characteristics of soils
　3.2. Changes in extractable NO3^--N concentrations
　3.3. Changes in extractable NH4⁺-N concentrations in the litter layer
　3.4. Effects of litter on KCl-extractable NH4⁺-N concentrations
　3.5. Effects of litter on H2O-extractable NH4⁺-N concentrations
　3.6. Temporal variation in KCl-extractable NH4⁺-N concentrations
　3.7. Temporal variation in H2O-extractable NH4⁺-N concentrations
　3.8. Relationships of NH4⁺-N dynamics to soil physico-chemical properties
　3.9. Pools of NH4⁺-N in the soil profile
　3.10. DOC effects on NH4⁺-N retention dynamics
　3.11. Effects of temperature on NH4⁺-N dynamics
　3.12. Mean weekly NH4⁺-N and NO3^--N concentrations in leachate
4. Discussion
　4.1. Litter addition effects on NH4⁺-N production
　4.2. Temporal NH4⁺-N variations versus changes in temperature and moisture　
　4.3. The importance of soil-physico-chemical properties
　4.4. Storage and mobility of litter-derived NH4⁺-N
　4.5. Potential role of DOC in NH4⁺-N dynamics
5. Conclusions
Acknowledgements
References