Chronic N deposition can impact ecosystem C storage by increasing aboveground productivity and by altering decomposition processes, leading to greater soil C storage. These responses have clear implications for the global C cycle and climate change, due to their impact on the strength of the C sink in terrestrial ecosystems. Chronic experimental N deposition (3 g N m-2 y-1 above ambient) was applied to four northern hardwood forests from 1994 to 2017. In August of 2017, we sampled soil to a depth of 70 cm, by depth increment (0-10, 10-30, 30-50 and 50-70 cm) to assess final effect of the long-term N additions on ecosystem C and N storage in soil and roots. Roots were sorted from all soil samples by size class (< 0.5, 0.5-1, 1-2, 2-5 and >5 mm diameter), and all root and soil samples were quantified for mass and C and N concentrations.
Results/Conclusions
The N deposition treatment significantly increased total soil C storage, with greater than a 10% increase in soil C content. Much of the increase occurred in the 0-10 cm depth increment. Comparison to previous samplings in 2004 and 2009 suggest that much of the increase occurred in the earlier portion of the long-term experiment. Soil N content was similarly increased. Root system biomass was not altered, but root N concentrations were greater for larger diameter roots at all soil depths, presumably due to storage of excess N. For roots, comparison to previous samplings suggests that storage of excess N in coarse roots has been steadily increasing during the experiment. Over the experiment, the increase in ecosystem C storage in soil has approximately equaled that due to enhance aboveground woody growth.