Nitrogen contribution by antelope bitterbrush in Mesa Verde National Park, Colorado, USA

Antelope bitterbrush (Purshia tridentata (Pursh) DC, Rosaceae), an actinorhizal shrub of intermountain western North America, is an important member of the pinyon-juniper communities of the Colorado Plateau and Great Basin. In Mesa Verde National Park, Colorado, Purshia is an early seral species sprouting from rodent-cached seeds following wildfire. Purshia-fixed nitrogen has the potential of contributing substantially to the recovery of the community from fire disturbance. Across a chronosequence of sites of differing stand ages following fire, we measured nitrogen fixation by Purshia with the ¹⁵N dilution method and decomposition and nitrogen release from Purshia leaf litter over 21 months. Nitrogen derived from fixation (%Ndff) in Purshia leaves ranged from 82-100% across the chronosequence. Estimates ranged from 4 kg ha^-1 yr^-1 nitrogen fixed in the site with the lowest Purshia density (4% cover) to 36 kg ha^-1 yr^-1 nitrogen fixed in the sites with the highest Purshia density (32% cover). Litter decomposition returned to the soil an estimated 8 kg N ha^-1 yr^-1 in the youngest site with the lowest Purshia density and 65 kg N ha^-1 yr^-1 in the site with the highest Purshia density