| Summary: | This study set out to investigate the effects of level of nitrogen supply on the root dynamics, carbon (C) and nitrogen (N) return to soil from root turnover, decomposition, and stability of improved grasslands. Field studies involved a two-year field experiment, where plant species composition, above ground biomass production, root production, litter decomposition and short term soil organic matter (SOM) dynamics, as a response to varying levels of inorganic fertiliser nitrogen supply were studied. The results showed that root dynamics are strongly affected by N fertilisation, with an increase in root production and death with increasing N supply. Reduced water availability lead to a greater root disappearance rate and the production of roots with a shorter lifespan. Root decomposition was strongly influenced by the age of the grass ley, which also exerted a strong influence on the structure of the soil microbial communities (SMC). Rate of litter decomposition and SMC structure were also influenced by the level of N supply. Level of mineral N supply and age of the grass ley also influenced the formation and stability of water stable aggregates, the microbial community structure and microbial community function within the aggregates. Mineral N applications are likely to influence SOM and soil nutrient dynamics. The finding that climatic conditions, and in particular water availability, had the strongest impact on both above and below ground productivity, and strongly influenced the amount of C, N and root/shoot biomass returned to soils, is of great importance in helping to make more accurate predictions of the response of plant communities to projected changes in the global climate.
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