Soil retention of N in a simulated N deposition study: effects of live plant and soil organic matter content.

Background and aims: The impacts of atmospheric nitrogen (N) deposition on terrestrial ecosystem processes remain controversial, mostly because of the uncertainty regarding the fates of deposited N. We conducted a 16-week simulated deposition study to experimentally trace N in a greenhouse plant-soil system. Methods: Using a two-way factorial design, we added (NH)SO solution twice a week to pots containing different soil organic matter (SOM) content and with or without a live plant ( Salix dasyclados). The recoveries of N in soil, plant biomass, and leaching solution were quantified. Results: We found most N was retained in soil (18.0-59.2%), with significantly more N recovered from high-SOM soils than from low-SOM soils. Plant presence significantly increased N retention in soil. Plant biomass accounted for 10-20% of the N input, with proportionally more N assimilated when plants were grown in low-SOM soils. Leaching loss of N was relatively low (10-17%). Conclusion: Our study suggests that SOM content and plant presence significantly affect the fates of deposited N. Indeed, N would be preferentially retained in soils with high SOM content and live plant, while plants would assimilate more deposited N when grown in low SOM soils. Global biogeochemical models thus need to incorporate such soil-specific N retention and plant N assimilation. [ABSTRACT FROM AUTHOR]