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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