Announcements

1. Announcements • Handouts • Wagener et al. article “Rivers and Soils…” • Questions: written assignment due in your section this week (Oct. 7th or 8th) • Writing guidelines will help you with the assignment • You can get all of these online: www.es.ucsb.edu/classes/envs100/ • Lecture notes online

2. Summary from Friday… • Biology controls the flow of energy between organisms • Plant and animal allocation of energy • Endotherms vs. ectotherms and the energy available in a food chain • Limits on Primary Productivity • Light • Temperature • Nutrients

3. Two-minute Quiz Imagine that you are a limnologist. (What is a limnologist?)

4. Two-minute Quiz Imagine that you are a limnologist. (What is a limnologist?) You are doing your research at Zaca Lake in Santa Barbara County.

5. Two-minute Quiz Imagine that you are a limnologist. (What is a limnologist?) You are doing your research at Zaca Lake in Santa Barbara County. You make measurements of phytoplankton and macrophyte biomass over the course of the year as part of a calculation of the net uptake of CO2 by the lake. Which of the following occurrences could influence plant biomass in the lake? How?

6. The watershed surrounding Zaca Lake burns. • El Niño weather patterns cause a drop in the mean air temperatures in Santa Barbara County during the winter months. • Mount Saint Helens erupts. • A dirt road surrounding the lake is paved. • A group of anglers successfully lobby to stock the lake with more fish.

7. Global Nitrogen Cycle Fixation by lightning N deposition Denitri-fication Biological fixation Biological fixation Human activities Denitrification Internal cycling River flow Internal cycling Long-term burial

8. Global Nitrogen Cycle Fixation by lightning N deposition Denitri-fication Biological fixation Biological fixation Human activities Denitrification Internal cycling River flow Internal cycling Human activity: More fixation, more N emissions Cycle becomes more “open” Long-term burial

9. Rhizobium Nitrogen fixation N2 NH4+ Mycorrhizal fungi Fungal hyphae take up nutrients  used by plant Photosynthate from plants  used by fungi Plant-Microbe Mutualisms

10. Mycorrhizal Fungi • Increase volume of soil exploited by plants • Absorbing length increased by 2-3 orders of magnitude • 80% of angiosperms, all gymnosperms, some ferns • 4-20% of GPP from plant goes to fungus • Can enhance both N and P uptake • Mining of P only  induces N limitation • Orchids depend on mycorrhizae for carbon as well as nutrients

11. What controls nutrient availability to plants? • Decomposition NH4+ NO3- organic N

15. Decomposition The physical and chemical breakdown of dead organic matter • Decomposition is crucial because it: • Provides energy for microbial growth • Releases nutrients for plant uptake • Influences ecosystem carbon storage and therefore climate

16. Fungi • Most decomposition in aerobic environments • 60-90% of microbial biomass in forests • 50% of microbial biomass in grasslands • Broad enzymatic capability • Cell walls (lignin, cellulose, hemicellulose) • Cell contents (proteins, sugars, lipids) • Can transport metabolites through hyphae • Surface litter (import nitrogen from soil) • Wood degraders (import nitrogen from soil) • Mycorrhizae (trade carbohydrates for nutrients)

17. Laetiporus gilbertsonii “chicken of the woods” Often grows on eucalyptus stumps Massive fruiting at the end of the dry season A fungus among us:

18. Announcements • Handouts • Wagener et al. article “Rivers and Soils…” • Questions: written assignment due in your section this week (Oct. 7th or 8th) • Writing guidelines will help you with the assignment • You can get all of these online: www.es.ucsb.edu/classes/envs100/ • Lecture notes online

19. Summary from Monday • Global Nitrogen Cycle • Without humans, cycling within a system dominates • Human impacts make a system more “open”

20. Summary from Monday • Global Nitrogen Cycle • Without humans, cycling within a system dominates • Human impacts make a system more “open” • Plant-microbe Mutualisms • Mycorrhizae: very common, fungus gives nutrients to plant in exchange for carbon • Nitrogen-fixers: plant roots make nodules, bacteria give N to plant in exchange for carbon

21. Summary from Monday • Global Nitrogen Cycle • Without humans, cycling within a system dominates • Human impacts make a system more “open” • Plant-microbe Mutualisms • Mycorrhizae: very common, fungus gives nutrients to plant in exchange for carbon • Nitrogen-fixers: plant roots make nodules, bacteria give N to plant in exchange for carbon • Decomposition: breakdown of organic matter • Who does it? Macrofauna, mesofauna, microfauna • Fungus

22. Two-minute Quiz • You are hunting for truffles (the yummy underground fruiting body of a fungus) in the forest with your trusty pig. Where are you most likely to find them and why? a) In a forest gap where there is a grassy meadow b) Near the base of a tree c) Near a rocky outcrop where the soils are thin and there is not much vegetation

23. Can fungi photosynthesize? • All fungi are heterotrophs • they cannot photosynthesize and gather energy from the sun • they must take carbon from dead organic matter • Some fungi are green, but they do not photosynthesize

24. Main Players in Decomposition Macrofauna (greater than 2 mm): ecosystem engineers, turn soil over • earthworms • termites Mesofauna (0.1-2 mm): fragment litter, injest litter covered with microfauna • collembola Microfauna (less than 0.1 mm): main decomposers, larger ones prey on bacteria • nematodes • amoebas • fungi • bacteria

25. How does it decomposition work? • smaller molecules can get engulfed completely (phagocytosis) • larger molecules must be broken down outside of the decomposer’s body • hyphae are small! • bacteria are even smaller!! • bacteria and fungus produce exoenzymes to break things down

26. Fungi • Why are there so many in forests? • fungi specialize in breaking down wood fruiting bodies high C C N high N hyphae

27. Bacteria • Grow rapidly • Specialize on labile substrates • Some bacteria function anaerobically • Dependent on diffusion • Spatial specialists • Rhizosphere, macropores, interior of aggregates • Biofilms on particle surfaces • Chemical specialists • Different bacteria produce different enzymes (consortia)

28. Why do Decomposers Decompose Stuff? • Decomposition does release nutrients into the soil, BUT… • Decomposers don’t care that they are performing an “ecosystem process” • Decomposers need C and nutrients too! • They get energy (C) and nutrients from breaking down organic matter

29. Climate Quantity of dead material (also known as “substrate”) Quality of substrate Size Bond Strength Regularity Toxicity Nutrient Content What controls decomposition?

30. Substrate Quality 1. Size of molecule • Large molecules must be broken down outside of cells • Exoenzymes

31. Substrate Quality 2. Bond Strength • Peptide bonds compared to aromatic rings • peptide bonds are easy to break • aromatic rings have double bonds & are stronger • The same amount of nitrogen: • fresh litter is high in protein • older organic matter in soil has aromatic rings

32. Substrate Quality 3. Regularity of structure • Cellulose has a regular structure • Lignin has an irregular structure 4. Toxicity • Toxins protect plants from herbivory & pathogens • May also affect decomposers 5. Nutrient content • Nutrients are essential for microbial growth

33. Predictors of Decomposition Rate • C:N ratio • Index of ratio of cytoplasm to cell walls • Measure of nitrogen concentration • Directly affects decomposition ONLY in presence of labile C • Lignin:N ratio (this is a better predictor) • Integrated measure of N concentration and substrate size/complexity

35. Announcements • Office hours on Monday: • Look for Kevin in my office (Girvetz 2307) • Online fun!

36. cellulose cellulose fragment 1 2 glucose Summary from Wednesday • How decomposition occurs • microbes exude exoenzymes that attack substrate • Bacteria • small, grow quickly, spatial specialization • chemical specialization more labile more recalcitrant

37. Summary from Wednesday • Why decomposition occurs • microbes don’t care that they are performing an “ecosystem service”, they just need energy and nutrients • Controls on decomposition • Climate • Quantity of substrate • Quality of substrate • size of molecule • bond strength • regularity of structure • toxicity • nutrient content

39. Soils • "We know more about the movement of celestial bodies than about the soil underfoot." - Leonardo Da Vinci, circa 1500's

40. Soils • "Be it deep or shallow, red or black, sand or clay, the soil is the link between the rock core of the earth and the living things on its surface. It is the foothold for the plants we grow. Therein lies the main reason for our interest in soils." - Roy W. Simonson, USDA Yearbook of Agriculture, 1957

41. What is Soil? • Natural body comprised of solids, liquids, & gases • On the surface of the land • Has one or both of the following: • horizons • the ability to support rooted plants • Upper limit: • boundary between soil and air, shallow water, live plants, or plant materials that have not begun to decompose • Lower limit: • bedrock or 200m

43. additions translocations transformations losses

46. Soil Formation Factors Cl.O.R.P.T.H. • Climate • Organisms • Relief • Parent material • Time • Human activity

47. Biome: A large climatic region where plants are similar to each other