Dynamics and multi‐annual fate of atmospherically deposited nitrogen in montane tropical forests

• Published in: Global change biology 2021-05, Vol.27 (10), p.2076-2087
• Main Authors: Wang, Ang, Chen, Dexiang, Phillips, Oliver L., Gundersen, Per, Zhou, Xulun, Gurmesa, Geshere A., Li, Shanlong, Zhu, Weixing, Hobbie, Erik A., Wang, Xueyan, Fang, Yunting
• Format: Article
• Language: English
• Subjects: 15N tracer; Ammonium; ammonium and nitrate; Ammonium compounds; Carbon sequestration; China; Deposition; Ecosystem; Ecosystems; Environmental changes; Forest ecosystems; Forest growth; Forests; long‐term fate; Montane environments; Mountain forests; N deposition; N retention and redistribution; Nitrogen; Nitrogen isotopes; Organic soils; Recovering; Recovery; Retention; Soil; Soils; Temperate forests; Tracers; Trees; Tropical climate; Tropical forests; tropical montane forests
• ISSN: 1354-1013; 1365-2486
• DOI: 10.1111/gcb.15526

The effects of nitrogen (N) deposition on forests largely depend on its fate after entering the ecosystem. While several studies have addressed the forest fate of N deposition using 15N tracers, the long‐term fate and redistribution of deposited N in tropical forests remains unknown. Here, we applied 15N tracers to examine the fates of deposited ammonium (NH4+) and nitrate (NO3‐) separately over 3 years in a primary and a secondary tropical montane forest in southern China. Three months after 15N tracer addition, over 60% of 15N was retained in the forests studied. Total ecosystem retention did not change over the study period, but between 3 months and 3 years following deposition 15N recovery in plants increased from 10% to 19% and 13% to 22% in the primary and secondary forests, respectively, while 15N recovery in the organic soil declined from 16% to 2% and 9% to 2%. Mineral soil retained 50% and 35% of 15N in the primary and secondary forests, with retention being stable over time. The total ecosystem retention of the two N forms did not differ significantly, but plants retained more 15NO3‐ than 15NH4+ and the organic soil more 15NH4+ than NO3‐. Mineral soil did not differ in 15NH4+ and 15NO3‐ retention. Compared to temperate forests, proportionally more 15N was distributed to mineral soil and plants in these tropical forests. Overall, our results suggest that atmospherically deposited NH4+ and NO3‐ is rapidly lost in the short term (months) but thereafter securely retained within the ecosystem, with retained N becoming redistributed to plants and mineral soil from the organic soil. This long‐term N retention may benefit tropical montane forest growth and enhance ecosystem carbon sequestration. 15NH4+ and 15NO3‐ tracers were applied to tropical montane forests to explore the fate and redistribution of atmospherically deposited N over 3 years. More than 60% of the 15N tracer was retained within the two forests after 3 years. 15N tracer was redistributed over time from the organic soil to plants and mineral soil.