Date of Award:


Document Type:


Degree Name:

Master of Science (MS)


Plants, Soils, and Climate

Committee Chair(s)

Youping Sun


Youping Sun


Larry Rupp


Jeanette Norton


Heidi Kratsch


Shepherdia ×utahensis ‘Torrey’ (Elaeagnaceae) is a hybrid of two native actinorhizal plants in the Intermountain West, S. argentea (silver buffaloberry) and S. rotundifolia (roundleaf buffaloberry). Due to actinorhizal symbiosis, atmospheric nitrogen (N2) can be converted to ammonium, a bioavailable form. Actinorhizal plants have great value in sustainable nursery production and urban landscape use. However, nitrogen fertilizer negatively affects the nodulation of actinorhizal plants. As a newly developed hybrid, both the symbiont identity and nodule formation of S. ×utahensis ‘Torrey’ remain largely unknown. Therefore, experiments were conducted to investigate the nodule formation of S. ×utahensis ‘Torrey’ inoculated with field soils from the Greenville Research Farm at Utah State University, North Logan, UT, or Mohave County, AZ. Further, S. ×utahensis ‘Torrey’ inoculated with field soils from the Greenville Research Farm were topdressed with controlled-released fertilizer (CRF) at eight application rates or irrigated with nutrient solutions at two nitrogen levels to study the impacts of nitrogen levels on nodule formation of S. ×utahensis ‘Torrey’. Nodules from S. ×utahensis ‘Torrey’ were used to identify the symbiont using nifH sequence and phylogenetic analysis. The results of our study showed that plants in a low organic substrate (e.g., perlite) and irrigated with a nutrient solution at pH 7.5 developed nodules 7 weeks earlier than in a commercial substrate (e.g., Metro-Mix® 820) irrigated with a nutrient solution at pH 6.5. Nodulated plants need less nitrogenous fertilizer to maintain plant growth and quality compared with uninoculated plants. However, S. ×utahensis ‘Torrey’ plants had fewer nodules when the nitrogen level of the fertilizer increased, and nodulation was completely inhibited when applying 2.9 g·L-1 CRF or 2 mM ammonium nitrate to plants. Phylogenetic analysis suggested that the symbiont of S. ×utahensis ‘Torrey’ could also induce nodules on plants in the Elaeagnaceae and Rhamnaceae to fix atmospheric nitrogen. According to the results in this research, to induce nodules earlier, S. ×utahensis ‘Torrey’ plants should be grown in a substrate with low organic-matter content and irrigated with a nitrogen-free nutrient solution at a relatively high pH when they are inoculated with Frankia-contained soil. Fertilizer lower than the manufacturer’s recommended rate may be applied to S. ×utahensis ‘Torrey’ plants, if inoculated with field soils, to promote nodule formation for nitrogen fixation and reduce nitrogen runoff.