PARENT SESSION
Poster Session #44: Plant Ecology II.
Friday, August 10, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall

Comparison of parental and growth condition effects between the invasive annual grass Bromus madritensis ssp. rubens and two native Mojave Desert annual species.

Smith-Longozo, Vickie¹, Defalco, Lesley^1,2, Nowak, Robert¹, ^{1 2}

ABSTRACT- In desert environments, the unpredictability of soil resources can have a profound impact on seed production and quality and consequent species diversity of annual plants. In a controlled greenhouse experiment, we compared the fecundity of the invasive annual grass Bromus madritensis ssp. rubens to the native annual grass Vulpia octoflora and the native forb Descurainia pinnata. We distinguished between the effects of parental investment and growth conditions on seed viability of the parental, filial 1 and filial 2 generations for the three annual species. Parental investment was inferred from seed mass and C:N ratio of seeds. Seeds of the successive generations were grown under two nitrogen levels (1.5 and 12.0 g N m²) and two planting densities (80 and 800 ind m²). Planting density had a greater effect on seed number than did nitrogen availability for all three species. Seed viability was more than 60% for Bromus, except under high density and high soil nitrogen availability where no viable seed was produced. Conversely, seed viability for Descurainia and Vulpia was significantly lower than Bromus for all treatment combinations (range = 20 - 40%). Seed mass was greatest for Bromus, then Vulpia and then Descurainia. We discuss the trade-offs associated with seed size, number and quality and the implications for the different reproductive strategies between this invasive and the two native species.

KEY WORDS: invasive species, mojave desert, seed ecology