Home field effects on the assimilation of inorganic nitrogen fertiliser into proteinaceous amino acids

The local adaption of soil microbial communities to native litter inputs, the so-called home field effect (HFE), is well established, though this phenomenon has yet to be demonstrated for agriculturally relevant inorganic nutrient sources. Using compound-specific ¹⁵N-stable isotope probing of proteinaceous amino acids (AAs), we investigated if continuous long-term grassland fertilisation with either ammonium or nitrate resulted in preferential assimilation by the soil microbial community of the ‘home’ N fertiliser. Relative ammonium uptake was maximal in historic ammonium treated soils and previously unfertilised soil, confirming a general microbial preference for ammonium likely due to biochemical transformation efficiencies. Assimilation of nitrate and ammonium into AAs was comparable for the historic nitrate fertilisation, indicating that microbial adaptive processes governed by historical land use can dictate the immobilisation efficiency of different fertilisers. This is the first observation of the HFE in long-term fertilised grassland soils, with further work required to investigate abiotic or biotic mechanisms underpinning this phenomena.