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Rayna Gasik Drew Groshong Fran Novak 12/08/2013 Does Ivy Growth in Riverview Natural Area Affect Soil Nutrients Required for Miner’s Lettuce to Grow? Introduction The effects of non-native species are widely misunderstood and to some extent, unknown, throughout the globe. Few newly introduced species are able to survive, and many of those that do survive appear to live innocuously alongside natives. However, some non-native species become invasive, wreaking havoc on native ecosystems. This damage to ecosystem function puts native species, and local economies at risk. Humans have altered ecosystems by both intentionally and unintentionally introducing species. For example, fire clearing for agricultural purposes can change the way an entire ecosystem functions by allowing one species (grass) to dominate over others (Mack et al 2000). English Ivy, once unknown to the Pacific Coast of the United States is now common in many forested areas. It was originally planted as a decorative climber in home gardens, however it spread quickly into natural habitats after birds consumed the berries and spread the seeds. Ivy’s hardiness in gardening also makes it a powerful adversary for eradication. Many have voiced concerns over ivy’s effect on native plants, diversity and the surrounding habitat (Bierzychudek 2013). However, few studies on the effects of ivy in the Pacific Northwest have taken place. Biggerstaff has studied ivy in the Southeastern US, finding that ivy did have an effect on germination rate for Coreopsis lanceolata seeds, but only when the ivy was physically present. No difference between ivy soil or non ivy soil was detected in the germination rate (Biggerstaff 2007). Dlugosch performed one of the only studies on ivy in Pacific Northwest, in which areas with English Ivy had a lower percent cover of native species due to a smaller presence of native bushes (Dlugosch 2005). Though neither study confirmed that ivy was detrimental to the surrounding environment, both indicated that ivy could have a larger impact than was previously thought. Further knowledge concerning this subject will be valuable because complete ivy eradication will be both labor and cost intensive. Determining the effect an invader has on primary producers is key to understanding its impact on the entire ecosystem. Soil nutrients are vital to the growth and function of primary producers. Plants require a myriad of nutrients, however the ones that most often limit growth are nitrogen and phosphorous. Ivy differs in many ways from native plant species, so it makes sense to question whether ivy requires different concentrations of soil nutrients than species which previously inhabited the area. For example, due to its nutrient requirements, ivy might deplete nitrogen levels in the soil, reducing availability to native plants. In our study, we are measuring the effect of English Ivy on soil nutrients by comparing the growth of the native plant species, Miner’s Lettuce (Claytonia Perfoliata) in ivy and non ivy soils. This study will determine if ivy limits Miner’s Lettuce growth through competition for soil nutrients. We are measuring the biomass and root/shoot ratio as well as the number of seeds germinated over a six-week study. We have collected soil samples from ten plots, five of which currently have ivy growth and five of which have not had ivy present for two years, all in the Riverview Natural Area. With ample sunlight and water, we hypothesize that there will be a noticeable difference in the growth between the Miner’s Lettuce in soil from plots containing ivy and from plots without ivy. Though we do not have the funding necessary to measure the nutrients within the soil, we believe that the germination, biomass and root/shoot ratio will be sufficient indicators for our study. High biomass and germinations indicate a healthy plant and a low root/shoot ratio indicates that nutrients are readily available from the soil. We hope that this study will accurately depict English Ivy’s effect on native plant species and determine if English Ivy limits their growth. Methods On September 28th 2013, we collected soil samples from ten different plots in Riverview Natural Area (RVNA), Riverview Cemetery and the Lewis & Clark campus. There were five plots in RVNA, which is adjacent to the Lewis & Clark campus, in which the ivy was removed two years prior. The five plots with ivy were on the Lewis & Clark campus or on the Riverview Cemetery, which is also adjacent to the Lewis & Clark campus. We used a greenhouse on the Lewis & Clark campus to keep the conditions (ie temperature, sunlight, water, etc.) for each of the different pots as uniform as possible. In each of the plots, we collected three samples. We divided each plot in to fifty 1m x 1m subplots and then we used randomization to select three for each plot. At each subplot we used a hand shovel to dig about three inches deep to obtain a small amount of dirt and placed it in a plastic bag. For each plot, we mixed the samples of the three subplots in the same plastic bag. After collecting all thirty samples, we took all ten plastic bags into the greenhouse where we removed some soil, sifted it through a sieve to remove plant material and filled each pot to the same level to make sure each had roughly the same amount of dirt. We then added enough water to moisten the soil before we planted four seeds of Miner’s Lettuce (Claytonia perfoliata) in each pot. After that we used randomization to place the pots in the greenhouse. Every 3-4 days, one of us would come in, mark all of the newly germinated seeds with toothpicks, count and record the germination data and then water the plants. The amount of water added to the plants was different each day but every plant would receive the same amount of water as the rest on that given day. After 5 weeks, we removed the plants from the soil in order to weigh them. To do this, we first had to remove both soil and plant from the pot and wash off all of the dirt. Finally, we separated the roots and shoots and placed them in separate paper bags labeled with the sample number and either “root” or “shoot.” All of these bags were then taken back to the lab and placed in a dryer, which was set at 60°C, for 48 hours, which is relatively a large amount of time, in order to attempt to remove all of the water content from the plants so we would only be measuring the biomass of each root and shoot. When weighing the plants we placed a tray on the balance, zeroed out the balance and then poured the contents of one of the bags into a tray. This reading was then recorded in a table with its sample number and identity of either “root” or “shoot.” The contents were then poured back in the bag, and the bag was placed back in the dryer. This method was repeated for all of the bags. After leaving the plants in the dryer for another two hours, we weighed all of the plants again using the same method as before. We did this in order to ensure that the plants were completely dry and we were only measuring biomass. Because all of the masses were the same as before, we knew they were completely dry. Results Our results did not support our hypothesis. The difference between the total number of plants that germinated and survived at the end of the study in the two soil types was only by one plant, so it was insignificant enough that further analysis was not necessary. The mean biomass per plant per pot (Fig. 1) was 6% higher in ivy absent soil but differences were not found to be significant (t-test, dif= .0009, t=.184, p=.855). The mean root/shoot ratio (Fig. 2) was 40% higher for plants grown in soil where ivy was absent than present; this test was not statistically significant (t-test, dif=.218, t=1.01, p=.322). Figure 1. Averages of Biomass per plant per pot in ivy and non ivy soil with two standard errors (95% confidence) Figure 2. Averages of root to shoot ratios in ivy and non ivy soil with two standard errors (95% confidence) Discussion Upon analysis of our data, we can conclude that our study did not support our hypothesis. Though the graph of root/shoot ratio appears to show a large difference of forty percent higher in ivy present pots, a statistical analysis determined that this difference is insignificant. Also, the mean biomass per plant per pot was insignificant upon statistical analysis. We did not feel that it was necessary to include a graph of plants that had germinated and survived because the difference between the soil types was only by one plant. Overall, this data would support the null hypothesis that ivy’s presence does not affect soil quality because a difference in the success of Miner’s Lettuce was not observed between pots where ivy was present and pots were ivy was absent. Because our study only measured success of Miner’s Lettuce in soil that ivy had grown in previously compared to soil that did not have ivy growing in it, we were not measuring the direct effect of ivy on Miner’s Lettuce but rather its effect on soil nutrients. However, we feel that we can conclude that ivy’s presence did not have an effect on soil quality and that Miner’s Lettuce is not competing with ivy for soil nutrients. Since we concluded that ivy was not responsible for variation amongst the different plots, other factors must have been influencing Miner’s Lettuce growth. For instance, there could be differences in soil quality in the different sampling locations, unrelated to ivy’s presence or absence. We observed that some of the sites had very claylike soil while others had more fine soil, so it is likely that this affected plant growth. Germination also depends largely on the environment inside the individual seed, more than the surrounding environment, so seed germination is also highly variable. Other variation, such as varied levels of sun exposure could have contributed to our large standard error bars, though randomization should have checked for variation causing differences between the two different categories. A few of our pots did experience some weed growth, but the amount of weeds was small enough that it was unlikely to have affected overall biomass and caused much variation. There were a few factors in our experimental method which could also contribute to the variation we saw. For example, we kept the soil samples from each of the individual plots separate instead of mixing together all samples of ivy soil and all of non ivy soil. If we had mixed the soil, there would have been fewer differences in the soil between plots within each category and variation would be smaller. Another possible source of variation was that different people washed the plants in order to obtain the biomass of roots and shoots. Two different washers could cause an inconsistency in how much of the soil was washed from the plants and thus cause variation in biomass measured. The largest issue with our study was that the time period of six weeks was not long enough to assert whether or not ivy presence was affecting soil quality. In this time, our plants did not gain a large enough biomass to really see the differences between plots. It is also likely that, due to their small biomass, the plants did not have enough time to run out of nutrients. Given this, a study over 6 months instead of 6 weeks would yield more comprehensive results. If longer studies produce similar results, we could more confidently accept the null hypothesis and turn to other possibilities for ivy’s effect on Miner’s Lettuce. For example, if we know that soil nutrients are not a factor for competition, we could do a field study to see other ways ivy might compete with Miner’s Lettuce, such as limiting sunlight. We could also improve the study by sampling more sites, which would reduce the effect variation had on our results. Growing plants in the soil is just one way of measuring soil quality. Further studies would benefit from chemical analysis of the soil and would likely give more definite results since plant growth is determined many different factors. Although our study could be improved with more sampling sites and an extended time period, we have shown that it is unlikely that ivy depletes the soils nutrients enough to negatively affect Miner’s Lettuce. Similar to the other studies that have been performed on ivy, we are unable to conclude that ivy’s presence has an effect on the environment. However, in order to conclude this, further experiments must be performed. Knowing the ways in which ivy does not affect the environment allows us to explore other possibilities of ivy’s influence. Ivy has a large presence in the Pacific Northwest and any impacts, even subtle ones, could significantly alter the surrounding environment and influence future conservation methods. Ivy is an invasive species and as such, the possibility that it will outcompete its native counterparts should make it an important topic for further study. Acknowledgements We would like to thank Professor Bierzychudek for assisting us with SPSS difficulties and for guiding us throughout the study. We would also like to thank our TAs Rebecca Kidder and Ben Hanson for teaching us procedure in the greenhouse as well as giving us helpful input on our project. We would like to thank Riverview Natural Area for allowing us to take soil samples from their property. Literature Cited Bierzychudek, G.Binford, W. McLennan, and P. Kennedy. 2013. Laboratory Manual for Bio 141, Lewis and Clark College Biggerstaff, M.S. and C. Beck 2007. Effects of English Ivy (hedera helix) on seed bank formation and germination. American Midland Naturalist 158 (1): 206-220 Dlugosch, K.M. 2005. Understory community changes associated with English Ivy invasions in Seattle’s urban parks. Northwest Science 79 (1): 52-59. Mack, R.N.,D. Simberloff, W.M Lonsdale, H. Evans, M. Clout, and F. Bazzaz. 200. Biotic invasions:epidemiology, global consequences, and control. Issues in Ecology 5: 120.