Does soil organic matter variation affect the retention of 15NH4+ and 15NO3− in forest ecosystems?

▶ Retention of ammonium in soil is substantially higher than the retention of nitrate. ▶ Ammonium retention is positively correlated to the quantity of soil organic matter. ▶ Nitrification reduces N retention in soil. ▶ The fate of atmospherically deposited N in forest ecosystems is soil dependent. ▶ Low soil organic matter and high nitrification lead to low N retention.