LEAF DECOMPOSITION Leaf litter entering streams and ponds provides an important source of allochthonous organic matter and nutrients. After a period of conditioning in the water where leaves are leached of organic and inorganic components, they begin to break down and are colonized (conditioned) by bacteria and fungi. Once the leaves have been conditioned, macroinvertebrates begin feeding on them. Bacteria and fungi provide an important source of nutrients to macroinvertebrates. Macroinvertebrate species serving as shredders (species that shred leaves) assist in breaking down leaves from coarse particulate organic matter (CPOM) to fine particulate organic matter (FPOM). In turn, FPOM is consumed by collector-gatherers (species that gather FPOM) and collectorfilterers (species that filter FPOM), which are themselves consumed by macroinvertebrate predators (Allan, 1995). The rate of leaf decomposition varies depending on leaf structural content and the presence of macroinvertebrates. Stream studies have found that leaves with higher carbon content tied up in cellulose and lignin and less nitrogen content take longer to break down. Leaves higher in carbon and lower in nitrogen are also less palatable to many macroinvertebrates (Allan, 1995; Royer and Minshall, 2001). The purpose of this lab is to 1) quantify the difference in leaf decomposition between two leaf species that differ in “toughness” (as a crude index of cellulose and lignin), and 2) determine if the presence of macroinvertebrates affects leaf decomposition. Hypotheses and predictions H1: Structural differences between leaf species will cause them to decompose at different rates. Leaves higher in carbon content (cellulose and lignin) will break down more slowly than leaves with lower carbon content. P1: Structurally tough southern magnolia leaves will have a significantly lower mass loss than softer bigleaf magnolia leaves. H2: Macroinvertebrates cause an increase in leaf breakdown by consuming leaf tissue and bacteria and fungi. P2: Leaves in coarse-mesh bags will have significantly more mass lost compared to leaves in fine-mesh bags. The statistical null hypotheses for these predictions are, “anything but the predicted outcome” and that means that a result in the opposite direction from your prediction is evidence for rejection of the alternative hypothesis. Methods Week 1 Note: Old shoes are good for this lab as we will go into the field. The lab will divide into four groups with as equal numbers of people as possible. Each group will be responsible for one of four treatments and will make four identical bags (replicates) for their assigned treatment. The treatments are: 1) 2) 3) 4) Water oak (Quercus nigra ) in fine mesh (~1 mm—window screen) packs Water oak in coarse mesh (~6 mm—onion bags) packs Sweetgum (Liquidambar styraciflua) in fine mesh packs Sweetgum in coarse mesh packs Leaves must be dry before you weigh them. Cut out and weigh 3.0g of dried leaves for each of your bags. Add your leaves to the bag making sure all the leaf matter goes into the bag. Don’t include any material other than your assigned species of leaf. Watch out for small sticks etc. Wrap a zip tie around the bag near its open end, but before you tighten it, insert a piece of flagging and a 0.5m-long section of string between the tie and the bag. With a sharpie, write the lab time, group name, the species of leaf, and course or fine mesh on the flagging. Cut a 3.0m piece of string, tie a loop in one end, and tie one of each of the four treatments to the loop. After you have assembled the leaf packs, we will drive to the field site and place them in the creek. Tie packs to stakes or rebar. They will sink within a few hours. Place a flag on the bank so your leaves will be easy to find. Week 2 Note: It is a good idea to wear old shoes for this lab. At least some people will go into the field. After about five weeks we will collect the leaf packs. As you pull them from the water, quickly and carefully place them in a zip-lock bag to prevent macroinvertebrates from escaping. After returning from the field, each student group will have four bags of each treatment. Cut the zip ties (not the bags!) with a knife or scissors and empty the contents on a dissection tray one bag at a time. If a zip-lock bag has water in it, pour it all into a tray or pour it into the sink through an aquarium net. Then rinse what is in the net into your tray. It is important to get all the material out of the mesh bag. One missed small piece of leaf can bias the data. Rinse the bag upside down and inside-out with a squirt bottle so that the water falls onto the tray. Using the squirt bottle, rinse off each leaf individually so that the water falls into the tray. Also, rinse the bags holding them upside down. Animals will try to cling to the bag. This will get your insects onto the tray where you can see them. Put your rinsed leaves in a paper bowl and label the bowl with your bag number, bag type, leaf species, name, and day of the week. Each leaf bag must have its own bowl. Leave your leaves to dry. We will weigh them next lab period. Using forceps, a pipette, and a microscope, identify your inverts using the Aquatic Macroinvertebrate Field Guide for Georgia’s Streams and the other pictures at the end of this section of the manual (this guide can be found at http://www.georgiaadoptastream.com/Manuals_etc/Bio_Chem/Macro_Key.pdf. Consult your instructor if you need help identifying animals, and feel free to share anything interesting with fellow students. Record them on the data sheet, “Invertebrate counts.” Then record the functional feeding group (see the list at the end of this lab section) of each animal on the data sheet “Leaf Decomposition Data Sheet.” Only record animals found on the list, “Macroinvertebrate Functional Feeding Groups and notes on identification.” Don’t spill anything on the microscope and carry it with two hands. Cleanup: Rinse the fine and coarse leaf bags in the sink. Rinse off your dissecting tray and zip lock bags. Do not allow anything but water to enter the drain. Please leave your lab station straightened out. Week 3 (Statistics) For both of our hypotheses, we want to know whether there is a difference between the mean mass lost between two groups: water oak vs. sweetgum leaves (H1) and presence vs. absence of macroinvertebrates (H2). We can test for this difference by using COMBINED CLASS DATA and a t-test. If your t value is high, the means are relatively far apart. You will use the “t-test” function in Excel for this. Remember that a p-value less than 0.05 means there is a significant difference between the means of the two samples you are comparing. Data Analysis 1. Is there a difference in decomposition between water oak and sweetgum leaves? Weigh your dry leaves and enter your data into an Excel spreadsheet in the same format as on your data sheet “Leaf Decomposition Data Sheet.” Calculate your leaf mass lost by bag. Calculate the average and standard deviation for all water oak values and all sweetgum values (so two averages, two standard deviations). Calculate a t-value as you have done in past labs. 2. Does the presence of macroinvertebrates affect leaf decomposition? Repeat the procedure above (performing a t-test) except this time your columns will be “fine mesh” and “coarse mesh”. To help explain the results of your second hypothesis, conduct a t-test comparing the numbers of shredders and grazers in coarse mesh versus shredders and grazers in fine mesh. Why shredders and grazers? 3. Create your Graphs Make a column graph to show the average mass lost for the two leaf species, and between coarse mesh and fine mesh bags (already calculated). This graph will have four columns. Note: at no time will you conduct a summary, analysis, or graph based on the categories water oak fine mesh, water oak coarse mesh, sweetgum fine mesh, and sweegum coarse mesh—only water oak, sweet gum, coarse mesh, and fine mesh. Questions Why would decomposition rate vary between leaf species? Would either structural differences in the leaves or differential macroinvertebrate abundance play a bigger role in this difference? Why? Which macroinvertebrates colonize leaves first? How would your results differ if we left the leaves in the water for longer or shorter periods of time? Which macroinvertebrate functional feeding groups did you find in your bags and which groups were most/least abundant? How did their presence affect your results? Why did we use different mesh-sizes of bags? Was this effective? Did you notice anything interesting about the numbers of the different kinds of macroinvertebrates and which treatments they were found in? Literature Cited Allan, J.D. 1995. Stream ecology: Structure and function of running waters. 388 pp. Chapman and Hall, New York. Royer, T.V., and G.W. Minshall. 2001. Effects of nutrient enrichment and leaf quality on the breakdown of leaves in a hardwater stream. Freshwater Biology 46:603-610. Unit 1 Water Oak coarse Water Oak fine Sweet Gum coarse Sweet gum fine Unit 2 Water Oak coarse Water Oak fine Sweet Gum coarse Sweet gum fine Unit 3 Water Oak coarse Water Oak fine Sweet Gum coarse Sweet gum fine % loss 22.58 9.38 43.75 70.00 % loss 16.70 6.67 63.30 16.70 % loss 16.00 20.00 46.70 36.70 Unit 4 Water Oak coarse Water Oak fine Sweet Gum coarse Sweet gum fine 0.17 0.07 0.40 0.27 Unit 5 Water Oak coarse Water Oak fine Sweet Gum coarse Sweet gum fine 13.30 16.60 23.30 30.00 Unit 6 Water Oak Coarse Water Oak Fine Sweet Gum Coarse Sweet Gum Fine % loss 7.00 20.00 33.30 46.70 Unit 7 Water Oak Coarse Water Oak Fine Sweet Gum Coarse Sweet Gum Fine % loss 13.33 20.00 33.33 13.33 Unit 8 Water Oak Coarse Water Oak Fine Sweet Gum Coarse % loss 20.00 10.00 86.70 Sweet Gum Fine 60.00 Unit 9 Water Oak Coarse Water Oak Fine Sweet Gum Coarse Sweet Gum Fine % loss 20.00 26.70 36.70 36.70 Unit 10 Water Oak Coarse Water Oak Fine Sweet Gum Coarse Sweet Gum Fine % loss 23.33 23.33 30.00 70.00 Unit 1 Order # individuals Water Oak coarse Diptera Oligochaeta Oligochaeta Diptera Oligochaeta Diptera Oligochaeta Diptera 1 1 4 8 9 1 9 1 Order ⎯ Oligochaeta Mollusca Oligochaeta Oligochaeta # individuals ⎯ 1 4 2 3 Order Diptera Diptera Oligochaeta Diptera Oligochaeta Diptera # individuals 9 3 5 9 14 6 Order Mollusca Megaloptera Mollusca Oligochaeta Amphopoda Oligochaeta Megaloptera Oligochaeta Mollusca Megaloptera # individuals 4 2 2 4 1 3 1 2 1 1 Sweet gum fine Order ⎯ Diptera Mollusca Oligochaeta Oligochaeta # individuals ⎯ 2 1 2 2 Unit 6 Order # individuals Water Oak fine Sweet Gum coarse Sweet gum fine Unit 2 Water Oak coarse Water Oak fine Sweet Gum coarse Sweet gum fine Unit 3 Water Oak coarse Water Oak fine Sweet Gum coarse Sweet gum fine Unit 4 Water Oak coarse Water Oak fine Sweet Gum coarse Sweet gum fine Unit 5 Water Oak coarse Water Oak fine Sweet Gum coarse Water Oak Coarse Water Oak Fine Sweet Gum Coarse Sweet Gum Fine Unit 7 Water Oak Coarse Water Oak Fine Sweet Gum Coarse Sweet Gum Fine Unit 8 Water Oak Coarse Water Oak Fine Sweet Gum Coarse Sweet Gum Fine Unit 9 Water Oak Coarse Water Oak Fine Sweet Gum Coarse Sweet Gum Fine Unit 10 Water Oak Coarse Water Oak Fine Sweet Gum Coarse Sweet Gum Fine Mollusca Oligochaeta Mollusca Oligochaeta Diptera Mollusca 4 2 5 1 1 3 Order Coleoptera Oligochaeta Coleoptera Ephemeroptera Oligochaeta Oligochaeta Oligochaeta # individuals 1 3 1 1 1 8 15 Order ⎯ Oligochaeta Mollusca Oligochaeta Mollusca Oligochaeta # individuals ⎯ 4 2 5 1 21 Order Diptera Trichoptera Oligochaeta Mollusca # individuals 2 1 13 2 1 1 Order Olgiochaeta Oligochaeta Tricohoptera Diptera Megloptera Oligochaeta Mulosca Coleoptera Oligochaeta Tricohoptera # individuals 2 9 2 1 1 7 1 1 12 1 Oligochaeta Plecoptera Final Lab!!!!!!!!!!! Sections Name, Section, Title, Date, Location, Physical conditions Introduction Draft an introduction narrative that adequetaly discusses the background knowledge needed to set up your study. (Not methodology) Include a relevant citation to assist in the understanding of concepts of the study. Inclusion of Hypothesis and predictions in the appropriate position Possible 0.05 2.15 0.75 0.30 Methods Appropriately describe the methodology used at all stages of the study using proper spelling, units, and labeling Results Appropriate narrative results section Correct positioning for references to tables, figures, and equations Appropriate tables, figures, and equations Inclusion of T-test, Shannon diversity, Relative abundance, Coefficient of community Discussion Appropriate discussion of results Restate the concet/hypoythesis for the study and how your results support or do not support your hypothesis Comparison with published study with citation References AMA Format by ordr of appearance 2.00 2.00 0.50 1.00 1.00 3.00 0.25 1.00 0.50 Overall Writing Correct spelling, grammar, sentence structure, word choice 0.50 TOTAL 15.00 Earned Troy University BIO L229 - Guidelines for General Ecology Lab Reports - Fall 2018 General features of lab reports: Labs must be typed; use a standard 12-point font (Times New Roman, Arial, etc.) for the text of the report. Labs must be written in complete sentences, with correct spelling and punctuation. Lab reports are due prior to the beginning of lab class of the specified due date. You will lose one point per day for labs turned in late; no lab report will be accepted more than three days late. An unexcused absence on the day of lab will also result in a deduction of one point (even if the report is turned in on time). Lab reports must be written in your own words. Do not copy from other members of your group, from the internet, or from other sources. Do not copy and paste from the lab handouts into your write-up. Do not use direct quotes; the information must be in your own words. Numbering the pages: Number each of the pages at the bottom. Don’t use a cover page. Terminology and other notes on grammar, calculations etc: Tenses for different sections of the report – The introduction should use past tense when referring to previous studies and future tense when referring to what will be presented in the report. The methods section should be in past tense. The results and discussion sections are generally in past tense, except when referring to information presented further along in the report, areas for future study, etc. Spacing – Double space the text throughout the report. Text in tables and figures, as well as references, may be single spaced. Numbers – A zero must always be put before a decimal point if there is not another number before it, e.g. 0.45 not .45. Do not use more than two decimal places. In the text, numbers less than 10 are written out in letters, e.g., three not 3. However, numbers associated with a unit of measurement are always written as Arabic numerals, e.g., 1 m2, not one m2 . Calculations – When reporting calculated values, show your work! You must retain the computer files of your work for this course until the semester is over and you have received the final grade for the class. 1 Format for General Ecology Lab Reports (unless otherwise specified) Name: Lab Section: Title of Lab: Date of Lab: Location of the lab: Briefly describe the site and location, i.e., the lab was performed in the wooded area of the Troy University Arboretum. Include the latitude and longitude (available from Google Maps) reported in decimal degrees, e.g. 31.784°N, 85.975°W. Physical conditions: Describe the weather during the lab, e.g., sunny and 30 °C. Species studied: Give the common and scientific names of all species observed in the lab. The scientific names of species must be accompanied by the authority (the last name of the person who named the species or an abbreviation). The primary source for plant scientific names and authorities is the Alabama Plant Atlas. Put the information in the following format: Common Name Tuberous Vervain Southern Crabgrass Scientific Name Verbena rigida Digitaria ciliaris Authority Spreng. (Retzius) Koeler The genus is always capitalized, and the species is not. Scientific names should be italicized. The authority is not italicized. Introduction: The introduction defines the general purpose of the lab and introduces specific terminology and concepts related to the lab. Methods: The Methods section describes the step-by-step procedure that was used in the field. Include all equipment that was used in the performance of the lab exercise. Do not write instructions. Typically, you should cite the lab handout as your source of information. Results: This section contains tables and/or figures. You should have an introductory sentence or two that refers to the tables and/or figures. Pictures, maps, graphs, and diagrams are all figures. You need to have “stand alone” titles for figures and tables. For example: Figure 1. Species-area curve for herbaceous plant species collected at Troy Arboretum. Figure 2. Logarithmic plot of species-area relationship for herbaceous plant species collected at Troy Arboretum. Tables and figures should be numbered in increasing Arabic numerals, e.g., 1, 2, 3, 4, in the order that they are first cited in the text. The word table or figure is always capitalized in the text when referring to a specific table or figure, e.g., Table 1, Figure 1. 2 Discussion: This section should summarize the main findings of the experiment. Do not repeat the results in paragraph form. Explain how the findings of your work compare with the expectations of the study. Unless otherwise instructed, your discussion should include an outside reference from a published scientific peer-reviewed journal study that was conducted on the topic and used a similar method for collecting data. The publication date of the study should be within the last 10 years. Print out the first page of the article and attach to the end of the report for verification of your source. References: All references cited should be put into the References section. Wikipedia, blogs, and other similar sources are not acceptable. References are listed in alphabetic order of the first author’s last name. Examples of proper reference listings are shown below: Gotelli, N.J. and L.G. Abele. 1982. Statistical distributions of West Indian land-bird families. Journal of Biogeography 9: 421-435. • This should be cited as (Gotelli and Abele 1982) in the text. Keener, B. R., A.R. Diamond, L. J. Davenport, P. G. Davison, S. L. Ginzbarg, C. J. Hansen, C. S. Major, D. D. Spaulding, J. K. Triplett, and M. Woods. 2017. Alabama Plant Atlas. University of West Alabama, Livingston, Alabama. • This should be cited in the text as (Keener et al. 2017) Smith, T.M. and R.L. Smith. 2015. Elements of Ecology. 9th ed. Pearson Education. • This should be cited as (Smith and Smith 2015) in the text. Troy University, Dept. of Biological and Environmental Sciences. 2017. Title of lab. General Ecology Lab Handout 1 {or relevant number}. • This should be cited as (Troy University 2017) in the text. 3
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