Nitrogen partitioning between plant species and soil microbes in alpine heath

Nitrogen is rapidly taken up by plants and microbes, but questions remain as to which forms are preferred. Using in situ stable isotope labelling ( 13 C and 15 N), we show that co-existing plant species of alpine heath mainly take up ammonium and nitrate, passing 15 N from root to shoot over time, leading to accumulated nitrogen in the shoots (over 10-fold increase compared with roots), with more complex organic nitrogen forms such as amino acids taken up to a lesser extent. Conversely, soil microbes preferred amino acids, potentially as a side-effect of satisfying their carbon requirements to build cellular structures. We show that competition for nitrogen can be alleviated by differing growth rates in plants and varying microbial preference of nitrogen forms. • Microbes prefer carbon rich organic molecules such as amino acids over nitrate. • Plants and microbes compete for ammonium, which may lead to partitioning. • Positive links between plant relative abundance and uptake strengthen with time.