Soil retention of N-15 in a simulated N deposition study: effects of live plant and soil organic matter content

摘要

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. Using a two-way factorial design, we added ((NH4)-N-15)(2)SO4 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-15 in soil, plant biomass, and leaching solution were quantified. We found most N-15 was retained in soil (18.0-59.2%), with significantly more N-15 recovered from high-SOM soils than from low-SOM soils. Plant presence significantly increased N-15 retention in soil. Plant biomass accounted for 10-20% of the N-15 input, with proportionally more N-15 assimilated when plants were grown in low-SOM soils. Leaching loss of N-15 was relatively low (10-17%). 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.