Tuesday, November 14, 2006 - 8:50 AM

Root System Responses to Chronic N Additions.

Andrew Burton, 100b U.j. Noblet Foresty Bldg., Michigan Tech. Univ., MI Tech University, School of Forest Resources & Environmental Science, Houghton, MI 49931

Twelve years of chronic nitrate additions to four northern hardwood forests in Michigan have not caused changes in fine root biomass or respiration rates, but have led to decreased rates of mycorrhizal infection.  During the last several years of N additions, root N concentrations have gradually increased, but concurrent increases in root metabolic activity have not been observed.  Consistent and significant decreases in soil respiration with N addition at these sites appear to be the combined result of reduced mycorrhizal respiration and turnover and altered decomposition processes.  Results from this long-term study will be compared with findings from other N addition experiments to assess the range of potential responses of root systems to chronic N additions and examine the temporal trends that occur in response to long-term elevated N inputs.