Fate of atmospherically deposited NH4+ and NO3- in two temperate forests in China: temporal pattern and redistribution

The impacts of anthropogenic nitrogen (N) deposition on forest ecosystems depend in large part on its fate. However, our understanding of the fates of different forms of deposited N as well as the redistribution over time within different ecosystems is limited. In this study, we used the 15N-tracer method to investigate both the short-term (1 week to 3 months) and long-term (1 to 3 years) fates of deposited NH4+ or NO3- by following the recovery of the 15N in different ecosystem compartments in a larch plantation forest and a mixed forest located in northeastern China. The results showed similar total ecosystem retention for deposited NH4+ and NO3-, but their distribution within the ecosystems (plants vs soil) differed distinctly particularly in the short-term, with higher 5NO3- recoveries in plants (while lower recoveries in organic layer) than found for 15NH4+. The different short-term fate was likely related to the higher mobility of 15NO3- than 15NH4+ in soils instead of plant uptak..., ,

人为源氮（anthropogenic nitrogen）沉降对森林生态系统的影响，在很大程度上取决于其归趋。然而，当前学界对不同形态沉降氮的归趋，以及不同生态系统内氮素随时间的再分布过程的认知仍存在局限。本研究采用15N示踪法（15N-tracer method），以中国东北地区的落叶松人工林与混交林为研究对象，通过追踪不同生态系统组分（ecosystem compartments）中的15N回收率，探究了沉降态铵态氮（NH4+）与硝态氮（NO3-）的短期（1周至3个月）和长期（1至3年）归趋。研究结果显示，沉降态NH4+与NO3-的生态系统总滞留量相近，但二者在生态系统内的分布格局（植物组分与土壤组分）差异显著，尤其在短期阶段：植物中15NO3-的回收率更高（而有机层回收率更低），这一特征与15NH4+的表现截然不同。这种短期归趋的差异，可能与15NO3-在土壤中的迁移性强于15NH4+有关，而非植物吸收……