Document: ADA-3-34-24

Carbon sink activity and nitrogen nutrition of ectomycorrhizal roots in response to elevated CO₂.

LANGLEY, A.* and B.A.HUNGATE

Northern Arizona University, Flagstaff, AZ 86011-5640 ¹

Abstract:
The roles of ectomycorrhizal associations in Florida scrub oak under elevated CO₂ were evaluated on the basis of conventional colonization rates, as well as more innovative measures such as coarse mycorrhizal biomass, and isotopic composition. Neither EM colonization rate nor coarse mycorrhizal mass showed a consistent treatment effect over the sampling period. Isotopic analysis however revealed a trend of enhanced dependence on ectomycorrhizal roots for nitrogen uptake under elevated CO₂ culminating in 86% stronger ¹⁵N tracer signal in mycorrhizal versus nonmycorrhizal roots. Under ambient conditions, mycorrhizal status had no effect on root ¹⁵N composition. These results suggest that elevated CO₂ may increase plant dependence on ectomycorrhizae for nitrogen nutrition without corresponding increases in coarse EM biomass or colonization and therefore would not be detected by conventional measures. Enhanced mycorrhizal functioning could be a result of more extensive hyphal proliferation or more rapid mycorrhizal turnover, either of which could represent a globally significant terrestrial carbon sink. The C:N ratio of ectomycorrhizal roots (28.8) was 60% lower than that of uninfected roots of the same diameter (72.8). Since root turnover can account for a majority of plant matter entering the soil, subtle shifts in carbon allocation between these two distinct root types could have profound consequences for the system's nutrient cycling rates that have been overlooked in global change research.

Keywords: Roots, ectomycorrhizae, CO₂

This abstract is being presented at: 8:30 AM in session:
Oral Session #40: Elevated CO₂ In Forest Systems.