Growth response of Populus fremontii, Salix gooddingii, and Tamarix ramosissima seedlings under different nitrogen and phosphorus concentrations

Treated effluent can potentially be used to restore riparian ecosystems to the many stream reaches in the south-western United States that have been dewatered. We undertook this study to determine how elevated nutrient levels in effluent influence riparian tree seedling performance. Seedlings of Fremont cottonwood (Populus fremontii), Goodding willow (Salix gooddingii), and exotic saltcedar (Tamarix ramosissima) were grown in a greenhouse for 43 days to address how concentration increases of ammonium-N and nitrate-N (5·56, 55·6, 278 and 556 mmol m−3), and phosphate-P (3·23, 32·3, 162 and 323 mmolm−3) would influence height, leaf or stem number, and biomass production. Seedlings of all species grew significantly taller, produced more leaves or stems, and produced greater biomass at the two larger treatments than at the two smaller treatments. Populus fremontii grew significantly taller, and produced more leaves and biomass than S. gooddingii or T. ramosissima at all nutrient concentrations, whereas T. ramosissima produced significantly less biomass than either P. fremontii or S. gooddingii at all concentrations. Only T. ramosissima showed a significant increase in stem number, shoot biomass and total biomass from the third to highest treatment. All species increased their shoot: root biomass ratio as nutrient concentration increased. Concentrations above the third highest nutrient treatment may favor establishment of T. ramosissima seedlings, while concentrations below these levels may provide the greatest potential for reestablishment of cottonwood-willow riparian forests along streams of the south-western United States.