This project is concerned with testing the significance of dissolved organic nitrogen (DON) for plant nutrition and resource partitioning by co-existing species of semi-natural grassland ecosystems. The project is testing whether co-existing plant species have realised niches based on differential uptake of different chemical forms of N, both organic and inorganic, and whether such niche differentiation is constrained by ecosystem productivity, and especially the rate of microbial turnover of the DON pool. Our overarching hypothesis is that the availability of DON to plants, and the existence of realised niches based on chemical forms of N, is greatest in low productivity ecosystems where DON dominates the soil N pool. These ideas are being tested using a productivity gradient based on a well-characterized sequence of semi-natural grasslands in Snowdonia, North Wales. The project is joint with Davey Jones, John Farrah, and Paul Hill of Bangor University.