PS 37-90
Evaluating the invasive potential of South American spongeplant, Limnobium laevigatum, in California's Sacramento-San Joaquin Delta
California’s Sacramento-San Joaquin Delta is a highly invaded, novel ecosystem. South American spongeplant (Limnobium laevigatum) is a floating macrophyte that has recently arrived in the Delta. I assessed spongeplant’s invasive potential in the Delta by examining its competitive ability against that of water hyacinth (Eichhornia crassipes) and native pennywort (Hydrocotlye verticillata) in both current and anticipated future conditions.
I investigated the macrophytes’ ability to impact its competitor’s growth and the importance of initial plant density on this competition. I then assessed the macrophytes’ performance across a low-salinity gradient. I believed spongeplant would be more competitive than pennywort because the spongeplant has coevolved with water hyacinth in South America, which is known to be highly competitive. I further hypothesized that in future conditions, with elevated salinity, pennywort would gain a competitive edge because, as a native, it has evolved in the Delta which has historically experienced seasonal fluctuations in salinity.
Plants were harvested from the same location in Big Break near Oakley, California. The experiments were conducted in five-gallon containers in the Oxford tract greenhouse in Berkeley, California. 16 hours of light per day mimicked summer conditions. The metric for performance was the change in area covered via vegetative growth as measured by digital photography and ImageJ.
Results/Conclusions
Among the mixed plants, a one-way ANOVA revealed no difference in performance due to the competitor. Additionally, I found no significant difference in the performance of plants due to the varied initial densities, F (4, 44) =1.146, ns. Not surprisingly, the performance of water hyacinth was significantly higher than pennywort, F (2, 44) = 14.13, p < 0.001. Under medium salinity, spongeplant significantly outperformed pennywort, F (2, 15) = 4.692, p < 0.05, with water hyacinth in between the two. And in high salinity, spongeplant significantly outperformed water hyacinth and pennywort, F (2, 15) = 15.82, p < 0.001.
These results confirm that in current conditions water hyacinth is clearly a superior competitor to spongeplant and pennywort. However, with elevated salinity spongeplant may be able to outperform the others which could promote a successful invasion. Furthermore, because the Delta presents a salinity gradient as one travels west to the San Francisco Bay, it is likely that spongeplant will invade oligohaline waters between the two.