Sierra Nevada Aquatic Research Laboratory

03 Aug, 05 AM - 07 Aug, 08 AM

Background Submersed aquatic weeds cause tremendous ecological and economic damage worldwide (Ashton and Mitchell 1989, Anderson 2011). While many studies have focused on controlling aquatic weeds once they have proliferated (Ashton and Mitchell 1989, Anderson 2011, Genovesi 2011), very few have addressed the abiotic factors that influence the ability of aquatic plants to establish in the first place (Xie et al. 2010). Because submersed aquatic weeds are notoriously difficult to eradicate once established (Genovesi 2011), it is important to understand the factors that lead to, or help prevent, initial establishment. Light is often a limiting resource for aquatic plants (Lacoul and Freedman 2006, Engelhardt 2011). Riparian zone restoration can alter light levels through either removal of invasive overstory vegetation (which increases instream insolation) or replanting of native overstory (which ultimately decreases instream insolation). However, the effects of these light-altering actions on instream invasibility to aquatic weeds are poorly understood. Shade has been experimentally shown to negatively impact the growth of established aquatic weeds in several studies (Abernethy et al. 1996, Sabbatini and Murphy 1996, Bunn et al. 1998, Wilcock et al. 2002). However, to my knowledge, no literature details the effect of shade on the rate of initial establishment of aquatic plants. Current theories suggest different possible effects of varying light levels on instream invasibility. The fluctuating resource hypothesis says that when resources in a plant community become more available, the probability of invasion increases (Davis et al. 2000). This would suggest that aquatic weeds may have higher rates of establishment in higher light conditions. In contrast, some studies have shown that weedy species may be exceptionally efficient at utilizing scarce resources (Lacoul and Freedman 2006, Funk and Vitousek 2007); also, submersed aquatic plants have been shown to have a high degree of phenotypic plasticity (Riis et al. 2010). These findings imply that the aquatic weeds may be just as successful at establishing in low light as in high light conditions by using light efficiently and/or responding plastically to different shade levels. Objectives To better understand the effects of different light levels on instream invasibility to submersed aquatic weeds, I plan to initiate a manipulative study in the artificial channels at the Sierra Nevada Aquatic Research Lab (SNARL). I will use Elodea spp. as a model organism: Elodea is a weedy plant that is native to California and present at SNARL, but is invasive in other parts of the world. Shade cloth will be used as a proxy for different levels of riparian canopy cover that are present in natural systems. This study will complement observational and manipulative studies that I will be conducting in natural streams, and will contribute to my PhD dissertation. The channels at SNARL will allow me to control confounding factors that I may encounter in my studies in natural systems, so that I can isolate light levels as the main factor influencing the results of my experiments. Experimental design and methods My experiments will be initiated in mid-June, 2011. I will divide each of four 100m long artificial channels at SNARL into 24 two-meter long plots (I will exclude the most upstream and downstream meter of each channel). Each of these plots will be randomly assigned to one of four different shade treatments: 0%, 30%, 60%, or 90% shade. Shade cloth of the assigned light reduction level will be fastened over the plots (except 0%, which will be left uncovered). This will yield a total of 24 replicates per shade treatment. I will use a light meter to verify the level of light reduction provided by each type of shade cloth. I will collect stems of Elodea from sites on or near the reserve. The collected plant material will be cut into three-inch fragments, which will be mixed in a large bucket or tub. Each plot will be randomly assigned ten fragments (propagules) of Elodea. Fragments of Elodea will be secured to the bottom of the channel with ground staples, within the inner 0.5 square meter of each plot. I intend for this to mimic the process of Elodea fragments getting caught on instream debris. After one month, the number of established (rooted) propagules in each plot will be counted. All surviving biomass from each plot will be collected and put into paper bags, which will be placed into a drying oven for 24 hours at 70˚C. This experiment will be re-initiated in mid-July and mid-August to give three full replications of the experiment (experimental runs). Plots will be randomly reassigned shade treatments for each experimental run. The final experiment will conclude in mid-September. Data from all 24 replicates within each shade treatment for all three experimental runs will be averaged to yield a mean number of established propagules and a mean total dry biomass for each treatment level. To determine whether light levels cause significant differences in establishment and growth of Elodea, treatment means will be compared using one-way blocked analysis of variance, with light level as the predictor variable and total dry biomass and number of established propagules per plot as response variables. Each experimental run will be treated as a block effect in the model. To determine the shape of the response, the data will also be analyzed using a priori polynomial contrasts. Expected results: In accordance with the fluctuating resource hypothesis, I anticipate the number of established propagules and the total plant biomass to increase with increasing light levels. I expect the shape of the relationship to have significant linear and quadratic components, with greater differences between the 60% and 90% shade levels than between 0% and 30%. Significance and relevance to the UC Natural Reserve System The effects of light levels on aquatic plant establishment have yet to be studied, but could have profound management implications. For example, if invasibility increases with greater light levels, removing shade-producing invasive riparian overstory may increase the need for managers to enact preventative measures against submersed invasives. Also, restoring native riparian cover may represent a tool for concurrently restoring adjacent instream habitats by reducing the threat of submersed invasives. My research will both advance theories in the field of invasion biology and inform responsible management decisions, which supports the stated mission of the UC Natural Reserve System: ?to contribute to the understanding and wise management of the Earth and its natural systems??. More specifically, invasive species pose a threat to all the UC reserves, creating management problems throughout the reserve system. While many studies on UC reserves target invasive terrestrial plants, studies of aquatic invasives are uncommon. In addition I will be examining invasibility in the context of riparian restoration, another UCNRS goal. References cited Abernethy, V. J., M. R. Sabbatini, and K. J. Murphy. 1996. Response of Elodea canadensis Michx. and Myriophyllum spicatum L. to shade, cutting, and competition experimental culture. Hydrobiologia 340:219-224. Anderson, L. 2011. Freshwater Plants and Seaweeds.in D. Simberloff and M. Rejmanek, editors. Encyclopedia of Biological Invasions. University of California Press, Berkeley and Los Angeles. Ashton, P. J. and D. S. Mitchell. 1989. Aquatic Plants: Patterns and Modes of Invasion, Attributes of Invading Species ans Assessment of Control Programs.in J. A. Drake, H. A. Mooney, F. d. Castri, R. H. Groves, F. J. Kruger, M. Rejmanek, and M. Williamson, editors. Biological Invasions: A Global Perspective. John Wiley & Sons, New York. Bunn, S. E., P. M. Davies, D. M. Kellaway, and I. P. Prosser. 1998. Influence of invasive macrophytes on channel morphology and hydrology in an open tropical lowland stream, and potential control by riparian shading. Freshwater Biology 39:171-178. Davis, M. A., J. P. Grime, and K. Thompson. 2000. Fluctuating resources in plant communities: A general theory of invasibility. Journal of Ecology 88:528-534. Engelhardt, K. A. M. 2011. Aquatic Eutrophication.in D. Simberloff and M. Rejmanek, editors. Encyclopedia of Biological Invasions. University of California Press, Berkeley and Los Angeles. Funk, J. L. and P. M. Vitousek. 2007. Resource-use efficiency and plant invasion in low-resource systems. Nature (London) 446:1079-1081. Genovesi, P. 2011. Eradication.in D. Simberloff and M. Rejmanek, editors. Encyclopedia of Biological Invasions. University of California Press, Berkely and Los Angeles. Lacoul, P. and B. Freedman. 2006. Environmental influences on aquatic plants in freshwater ecosystems. Environmental Reviews 14:89-136. Riis, T., C. Lambertini, B. Olesen, J. S. Clayton, H. Brix, and B. K. Sorrell. 2010. Invasion strategies in clonal aquatic plants: are phenotypic differences caused by phenotypic plasticity or local adaptation? Annals of Botany (London) 106:813-822. Sabbatini, M. R. and K. J. Murphy. 1996. Response of Callitriche and Potamogeton to cutting, dredging and shade in English drainage channels. Journal of Aquatic Plant Management 34:8-12. Wilcock, R. J., M. R. Scarsbrook, K. J. Costley, and J. W. Nagels. 2002. Controlled release experiments to determine the effects of shade and plants on nutrient retention in a lowland stream. Hydrobiologia 485:153-162. Xie, D., D. Yu, L.-F. Yu, and C.-H. Liu. 2010. Asexual propagations of introduced exotic macrophytes Elodea nuttallii, Myriophyllum aquaticum, and M. propinquum are improved by nutrient-rich sediments in China. Hydrobiologia 655:37-47.

Visit #24320 @Sierra Nevada Aquatic Research Laboratory

Approved

Under Project # 23047 | Research

The influence of light levels on stream invasibility to a weedy aquatic plant

graduate_student - University of California, Davis

Reservation Members(s)

Group of 2 Graduate Student Aug 3 - 7, 2011 (5 days)

Reserve Resources(s) | Create Invoice

Lab 3 2 Aug 3 - 7, 2011
Lab 5 2 Aug 3 - 7, 2011
Q1 2 Aug 3 - 7, 2011