氮沉降模拟实验亟待研究大气氨浓度增加的影响

Ammonia should be considered in field experiments mimicking nitrogen deposition

大气活性氮污染及其过量沉降是全球变化重要议题。为研究氮沉降对自然生态系统结构和功能的影响,基于喷淋加氮的控制实验在草地或林下广泛开展。该实验体系假定氮沉降是通过增加土壤氮的有效性从而影响整个生态系统,没有考虑植被与大气活性氮的相互作用,也未能反映氮沉降以干沉降为主的自然过程。考虑到大气氨是氮沉降的主要前体物,且全球氨气浓度呈现上升趋势,未来的氮沉降模拟实验亟待研究氨气干沉降的重要影响,以期更加完整的刻画大气氮沉降过程及其生态环境效应。

Excess nitrogen deposition has significant impacts on water eutrophication,soil acidification,eleveted greenhouse gas emissions,and biodiversity loss.These impacts mostly derive from conventional manipulative experiments in the field by adding nitrogen solution directly onto grassland or forest floors.For forest ecosystems,previous field experiments have usually ignored the nitrogen cycles in the canopy,which are important in responses to airborne nitrogen input.Although whole-forest canopy nitrogen fertilization has recently been conducted to promote our understanding of nitrogen deposition processes,spraying nitrogen solution onto plants still largely ignores the dry deposition of ammonia(as well as other gaseous reactive nitrogen species).To date,there have been a limited number of field studies that have investigated the bi-directional exchange of ammonia between the atmosphere and plants,not to mention the impacts of ammonia on natural ecosystems.Due to the increasing trend of atmospheric ammonia concentrations worldwide and its dominant role in nitrogen deposition and haze pollution,the next generation of experiments should mimick nitrogen deposition on natural ecosystems by further considering the dry deposition of ammonia.