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How does water and nitrogen availability impact seed production of a native species in competition with an invasive species?
Rising rates of nitrogen deposition are threatening the stability of the serpentine grassland ecosystem around the California Bay Area by changing the soil to be more accessible habitat for invasive nonnative species. The recent increase in nitrogen is largely attributed to air pollution from automotive traffic throughout the region. This area hosts 10% of California’s endemic species in only 1% of the state's land, making it a critical area for ecological conservation efforts. The plant species native to this area have persisted by inhabiting the characteristically low-resource soil of the serpentine grasslands, giving them competitive advantage over invasive species that require higher resource levels.
To study the variation in reproductive success of these plants under different environmental constraints typical of polluted serpentine grasslands, I worked on a greenhouse experiment using a nitrogen-water resource gradient in serpentine-amended soil. Plantago erecta, a native, resource-conservative herb, was sown in competition with Bromus hordeaceus, a nonnative, resource-acquisitive grass. My findings showed that Plantago produces the most seeds when there is no competition from Bromus, low availability of water, and high levels of nitrogen. With low Bromus competition, water availability had less impact on Plantago, while increased nitrogen continued to increase Plantago seed production, suggesting that Plantago may not inhabit a low-nitrogen niche, but potentially a low-water niche. However, with high Bromus competition, Plantago seed production was consistently low regardless of nitrogen and water treatments, suggesting that Bromus competition was too great for the availability of resources to support the population of Plantago.
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