The Effect of Nitrogen and Phosphorus on Competition between a Non-native and a Native Dune Plant

Overview

Objectives/Goals This study was designed to test whether the invasive plant ripgut brome (Bromus diandrus) has a competitive advantage over the native dune plant beach buckwheat (Eriogonum latifolium). In addition the study will test how the outcome of this competition is affected by elevated levels of nitrogen and phosphorus. I chose these two nutrients to test because invasive Bromus tends to grow where another invasive species, yellow bush lupine (Lupinus arboreus) has previously grown. This lupine elevates nitrogen levels in the soil. I chose phosphorous because it is very limiting in the dunes. Methods/Materials I collected seedlings of Bromus and Eriogonum from the dunes at Humboldt Bay National Wildlife Refuge, and (after measuring their height) planted them in flats at different ratios of Bromus:Eriogonum (0:1, 1:1, and 2:1). I watered them with different fertilizer solutions (no fertilizer, nitrogen, phosphorous, and nitrogen+phosphorous). After 6 weeks I remeasured the plants and calculated the average amount of growth. Results Eriogonum, in the absence of Bromus, grew the most in the nitrogen and control groups. When the two species were planted together Bromus always did better than Eriogonum. The nitrogen and phosphorus treatments separately gave a greater competitive advantage to Bromus than the control or nitrogen+phosphorus treatments. In the 2:1 ratio Bromus did not do as well as it did in the 1:1 ratio. Conclusions/Discussion This experiment demonstrates that invasive Bromus outcompetes native Eriogonum in conditions that imitate nature, possibly because Bromus germinates before most California native, perennial, dune plants. Bromus grew less in the 2:1 ratio than in the 1:1 ratio, possibly due to increased intraspecific competition. In addition, the experiment supports the concept that elevated nitrogen and phosphorus levels make Bromus even more competitive. This explains why, in nature, the nonnative Bromus can outcompete native dune plants such as Eriogonum, especially if yellow bush lupine leaves behind elevated nitrogen when it dies or is removed.

Competition history

• CSEF 2012 Plant Biology · Entry J1925

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