Decomposition and nitrogen release from foliage of cottonwood (Populus deltoides) and Russian-olive (Elaeagnus angustifolia) in a riparian ecosystem

The exotic tree, Russian-olive (Elaeagnus angustifolia L.), is an invader o f riparian zones and grasslands throughout the plains and western United St ates. Mie compared the rate of litter decomposition and nitrogen loss from foliage of this species and the native cottonwood, (Populus deltoides Marsh all). Nitrogen concentrations of foliage of I:he nitrogen-fixing Russian-ol ive were initially much higher than cottonwood. Using new litter and litter allowed to overwinter in the held before being placed in litterbags, Russi an-olive lost 42 to 58% of initial mass over a 224 day interval and cottonw ood lost 29 to 38% of initial mass (P < 0.001). Foliage litter of cottonwoo d initially functions as a nitrogen sink, removing nitrogen from the enviro nment. Over the study period, cottonwood lost 0.3 g nitrogen (N) for every 100 grams of new litter. In contrast, Russian-olive lost 1.4 g N for every 100 g of new litter (P < 0.01). These nitrogen contributions of Russian-oli ve foliage to soils may facilitate invasion by other exotic plant species.