Chapter 7: Decomposition and Decomposers

1
Lecture 4

• Chapter 7 Decomposition and Decomposers

2
Learning Objectives

• Rank macromolecules for quality as energy source
  to decomposers
• Recall
• Details of Swift, Heal, Anderson study
• 4 types of aquatic arthropods
• Contrast POM vs. DOM

3
Carbon Compound Quality

• Typically, glucose and other simple sugars are
  quickly used by decomposers
• Remember, glucose is the universal power source
• More complex macromolecules, such as proteins,
  cellulose next
• Lignin, a mixture of large, complex molecules
  which makes wood hard, breaks down very slowly
• Only a few fungi can consume these (Basidiomycota)

4
Decaying Straw

• Swift, Heal, Anderson 1979

5
Litterbag Experiments

• Smith 2002, Virginia
• 30 pouches made from synthetic bags
• Different leaves put inside
• 5 bags harvested, 6 times in a year

6
Leaf Litter Mass vs. Lignin Content

• A) terrestrial (Smith, 2002)
• B) aquatic (Klapp, et al. 1999)

7
Spartina Decomposition

• From aquatic litterbag experiment with Spartina
  (a salt marsh grass)
• Water surface vs. buried under mud
• Many fungi require oxygen
• In anaerobic environments, bacteria do the job

8
Animal Material

• Animal bodies and feces decompose much more
  readily than plants (ie cells not protected by
  cellulose, lignin)
• Dung beetles consume feces

9
7th Inning Stretch
10
Precipitation and Leaf Decomposition

• Litterbag study from many sites in Hawaii

11
Climate Affects Decomposition

• Red maple (Acer rubrum) litter bags
• 3 sites (all have similar lignin content)
• Wetter, warmer climates hasten decomposition

12
Soil Microbe CO2 Release

• Respiration rate is greatest with higher temps

13
Nitrogen Content of Leaf Litter

• 3 stages 1st initital leaching, 2nd rise, 3rd
  fall
• N content can actually exceed 100 of original
  (why?)
• This graph is idealized

14
Actual Nitrogen Content
15
Other Nutrients Similar
16
Stream Arthropods Aid in Decomposition

• Shredders break up leaves, twigs
• Collectors live downstream, filter out leftovers
  feces from shredders
• Grazers, scrapers feed on algae, fungi, and
  materials on rocks and twigs
• See the following
• Stream Invertebrate Guide website
• U of Michigan website

17
Organic Matter in Lakes, Ponds

• POM particulate organic matter
• Often formed from leaves
• DOM dissolved organic matter
• In ocean, algae are major contributors
• Sometimes break up in minutes after death