Segregation of nitrogen use between ammonium and nitrate of ectomycorrhizas and beech trees

Here, we characterized nitrogen (N) uptake of beech ( Fagus sylvatica ) and their associated ectomycorrhizal (EM) communities from NH 4 + and NO 3 − . We hypothesized that a proportional fraction of ectomycorrhizal N uptake is transferred to the host, thereby resulting in the same uptake patterns of plants and their associated mycorrhizal communities. 15 N uptake was studied under various field conditions after short‐term and long‐term exposure to a pulse of equimolar NH 4 + and NO 3 − concentrations, where one compound was replaced by 15 N. In native EM assemblages, long‐term and short‐term 15 N uptake from NH 4 + was higher than that from NO 3 − , regardless of season, water availability and site exposure, whereas in beech long‐term 15 N uptake from NO 3 − was higher than that from NH 4 + . The transfer rates from the EM to beech were lower for 15 N from NH 4 + than from NO 3 − . 15 N content in EM was correlated with 15 N uptake of the host for 15 NH 4 + , but not for 15 NO 3 − ‐derived N. These findings suggest stronger control of the EM assemblage on N provision to the host from NH 4 + than from NO 3 − . Different host and EM accumulation patterns for inorganic N will result in complementary resource use, which might be advantageous in forest ecosystems with limited N availability.