Fleming, 2014, plant ecology research lesson, S1 Lab 1
Lab 1: Biodiversity and Ecosystem Functioning (a.k.a Competition)
Background
Extinction rates are currently orders of magnitude higher than throughout much of Earth’s history. Should we care? You are probably familiar with some arguments for protecting species such as utilitarian values (of use to humans: “That plant might have the chemical that cures cancer!”) to existence values (“Every living thing has a right to life.”). One argument of interest to biologists regarding protecting species from extinction is the role of biological diversity in ecosystem functioning.
Biological diversity (or “biodiversity”) refers to differences among living things at genetic, species, and ecosystem levels. Technically, species diversity refers to both the number of species and the relative abundance of them. Biologists refer to the number of species as species richness . Ecosystem function refers to the bio-geo-physical processes carried out by living things in conjunction with their environment; these functions can often be categorized as ecosystem services. Examples include production of biomass, nutrient cycling, erosion control, water retention, decomposition and so forth.
Biomass refers to the total mass of organisms in a population and is a good indicator of the photosynthetic capacity, or productivity , of a system, which in turn is a good indicator of the biodiversity of the system. This may seem a bit circular, but let’s go with it for now. This lab focuses on species diversity and plant biomass as an indicator of productivity of an ecosystem.
Does a relationship exist between biodiversity (as measured by plant species richness) and productivity? If so, then this relationship would be considered an emergent property of the community of organisms involved. An emergent property refers to a relationship that is not evident at lower levels of organization (e.g. when only individual organisms are considered), but which emerge at higher levels of organization. The key variable here is to consider community composition , which refers to all the species found in a place, taking into account that some are common and some are rare. Over the course of this lab you should try to link data about particular species to understanding why a relationship between species richness and biomass production may emerge when all of the species in a community are considered together. Some questions to help you link data from this lab to understanding the concepts described here might be (1) Does species “A” help or hinder species “B” and “C”? (2) Do all species respond to light/nutrients/water the same way? (3) Is competition within a species strong or weak relative to competition between species? What other relevant questions can you come up with?
This lab takes several weeks. Today, you will set up the experiment by planting seeds as described below. In about 7 weeks, you will record data from this planting. Again, keep in mind your central question is generally: “How is plant biomass related to the number of plant species?” With your lab group you should do some brainstorming about other questions similar to the examples above.
So, today is planting seeds, and later you will examine the data with respect to interactions among plant species, especially focusing on one question brainstormed with your lab partners. After analyzing your data, you will briefly present your question and analysis to the rest of the lab.

Fleming, 2014, plant ecology research lesson, S1 Lab 1
Set-up
First we must plant seeds in greenhouse “pony flats,” each measuring 26 x 52 cm. Seed density will be kept constant at ~0.12 seeds/cm
2
by planting 160 seeds in each pony flat . However, the proportion of the 160 seeds for a particular plant species will vary. Plants are chosen from a total pool of 12 species.
The characteristics of these species are described in the following table.
Functional group Species
Leafy herbaceous (LH) Mustard greens
Basil
Lettuce
Seed size (mm) Description
Grass-like (G)
Spinach
Hairgrass
Corn
Annual ryegrass
Rough and Tumble grass
Enlarged taproot (ER) Radish
Carrot
Nitrogen fixing (NF) Clover
Bean
Species richness per flat will either be 1, 2, 4, or 8. Given our pool of 10 species, there are only
10 possible ways to grow monocultures (single-species combinations), but 45 different ways to grow two species in combination (e.g. AB, AC, AD, ... EH, EI, EJ, ... HI, HJ,…IJ) and even more ways to grow 4 or
8 species together. Clearly there is not enough greenhouse space to grow all of these combinations!
Thus, only a few combinations will be set up to represent each level of species richness. These different combinations are replicates of the different levels of species richness .
For this lab there will be 8 groups, each with 3 students. Each group will plant and later examine five flats. Two will be monocultures of different species, one will be two species grown in combination, another will be 4 species grown together, and the last will be 8 species grown together. Another lab group will plant and examine similar community compositions as your group. In total, you will have access to data for multiple replicates of community composition . Each flat will have 1 – 4 functional groups represented, depending on the number of species grown together.
The following table shows you the eight different sets of communities that you will plant and later examine as a class.
Group
A
Monoculture a
LH1
Monculture b
LH2
B
C
G1
LH
G2
ER
Two species
G1, G2 (1 FG)
LH, ER (2 FG)
Four species
LH1, LH2 (1FG) LH1, LH2, LH3,
LH4 (1 FG)
G1, G2, G3, G4 (1
FG)
Eight species
LH1, LH2, LH3,
LH4, G1, G2, G3,
G4 (2 FG)
LH1, G1, LH2,
G2, LH3, G3,
LH4, G4 (2 FG)
LH1, LH2, ER1, G
(3 FG)
LH1, LH2, ER1,
ER2, LH3, G1,
G2, G3 (3 FG)

Fleming, 2014, plant ecology research lesson, S1 Lab 1
D
E
F
G
H
G
ER1
NF1
G
LH
NF
ER2
NF2
ER
NF
G, NF (2 FG)
ER1, ER2 (1 FG) ER1, ER2, LH1,
LH2 (2 FG)
NF1, NF2 (1 FG) NF1, NF2, ER1 (2
FG)
G, ER (2 FG)
LH, NF (2 FG)
G1, LH1, NF1,
ER1 (4 FG)
G, ER, LH1, LH2
(3 FG)
LH, NF, G, ER (4
FG)
G1, LH1, NF1,
ER1, G2, ER2,
LH2, LH3 (4 FG)
ER1, ER2, LH,
LH2, LH3, G1,
G2, G3 (3 FG)
NF1, NF2, ER1,
ER2, LH1, LH2,
LH3, LH4 (3 FG)
G1, ER1,
LH1,LH2, NF1,
NF2, G2, ER2 (4
FG)
LH, NF, G, ER,
LH2, NF2, G2,
ER2 (4 FG)
Count out the exact number of seeds needed in each combination for each. For example, for monoculture flats you need 160 seeds of one species; for flats with two species you need 80 seeds each, and so forth. For polyculture flats, combine the correct number of seeds from each species and mix the seeds gently with your fingers to distribute them evenly for sowing. Fill your flats about ¾ full with soil and gently level the soil in the flat. Water the soil thoroughly to settle it. Sprinkle your seed mix as evenly as possible over the wet soil surface and cover with a thin layer of additional soil. Gently water again and label your flat with the date, your group code, and number of species in the flat (ex: B1a, B4, etc). NOTE: very important…please record which actual species you planted! If you planted two species of leafy herbs, you had thee to choose from, so which two did you plant? This will be important later!
Greenhouse interns (and your instructor) will water the flats regularly for you. We will check in a couple of times between today and harvest day to note germination and generally see how our plants are progressing. In about 7 weeks, we will retrieve the flats, harvest the plants, and assay biomass to collect a large data set for analysis.
Get your hands dirty, have fun, and be ready to analyze data next month!