1. NUTRIENT CYCLING AND RETENTION
Chapter 19
Molles: Ecology 2nd Ed.

2. Disturbance increases ecosystem nutrient loss
Chapter Concepts
Decomposition rate influenced by temperature, moisture, and chemical composition of litter and environment
Plants and animals modify distribution and cycling of nutrients in ecosystems
Disturbance increases ecosystem nutrient loss
Molles: Ecology 2nd Ed.

3. Global phosphorus cycle doesn’t include substantial atmospheric pool
Largest quantities of P are in mineral deposits and marine sediments
Much of this not directly available to plants
Slowly released in terrestrial and aquatic ecosystems – weathering of rocks
Molles: Ecology 2nd Ed.

4. Molles: Ecology 2nd Ed.

5. Includes major atmospheric pool – N2
Nitrogen Cycle
Includes major atmospheric pool – N2
Only nitrogen fixers can use atmospheric supply directly
Blue-green algae, soil bacteria, bacteria of legume roots, some fungi
= energy-demanding process
N2 reduced to ammonia (NH3)
Molles: Ecology 2nd Ed.

6. Nitrogen fixers fix nitrogen = anaerobic (stinks)
Once N fixed – available to organisms
Upon death of organism, N can be released by fungi and bacteria during decomposition
Molles: Ecology 2nd Ed.

7. Molles: Ecology 2nd Ed.

8. Carbon Cycle
Moves between organisms and atmosphere due to photosynthesis and respiration
In aquatic ecosystems, CO2 dissolves into water – then used by primary producers
Although some C cycles rapidly, some remains stored in unavailable forms for long time
Molles: Ecology 2nd Ed.

9. Molles: Ecology 2nd Ed.

10. Occurs primarily during decomposition
Decomposition Rates
Rate at which nutrients are made available to primary producers is determined largely by rate of mineralization
Occurs primarily during decomposition
Rate in terrestrial systems influenced by temperature, moisture, and chemical compositions
Molles: Ecology 2nd Ed.

11. Decomposition in Temperate Forest Ecosystems
Melillo et.al. (1982)
Litter bags to study decomposition in temperate forests:
Leaves with higher lignin:nitrogen ratios lost less mass
= higher N availability in soil might have contributed to higher decomposition rates
Molles: Ecology 2nd Ed.

12. Fig. 19.7
Molles: Ecology 2nd Ed.

13. Decomposition in Aquatic Ecosystems
Gessner and Chauvet (1994)
Stream in French Pyrenees
Leaves with more lignin decomposed slower
Higher lignin inhibits fungi colonization of leaves
Molles: Ecology 2nd Ed.

14. Suberkropp and Chauvet
Tulip tree leaves degraded faster in Alabama streams with higher nitrate concentrations
Molles: Ecology 2nd Ed.

15. Nutrient Cycling in Streams
Webster (1975) – nutrients in streams are subject to downstream transport
Little nutrient cycling in one place
Nutrient Spiraling
Fig 19.13
Molles: Ecology 2nd Ed.

16. Webster (1975)
Spiraling Length = length of stream required for a nutrient atom to complete a cycle
Related to rate of nutrient cycling and velocity of downstream nutrient movement
Fig 19.13
Molles: Ecology 2nd Ed.

17. Nutrient Cycling in Streams
Spiraling Length:
S = VT
S = Spiraling Length
V = Average velocity of nutrient atom
T = Average time to complete cycle
Short lengths = high nutrient retentiveness
Long lengths = low nutrient retentiveness
Fig 19.13
Molles: Ecology 2nd Ed.

18. Stream Invertebrates and Spiraling Length
Grimm (1988):
Sycamore Creek, AZ
Collector-gatherer insect larvae
Mayflies + chironomids
Aquatic invertebrates increase rate of N cycling
Molles: Ecology 2nd Ed.

19. How much N do invert’s contribute to nutrient dynamics of stream?
Rapid recycling of N by macroinvertebrates increases primary production
Excreted and recycled 15-70% of nitrogen pool as ammonia
Molles: Ecology 2nd Ed.

20. Fig
Molles: Ecology 2nd Ed.

21. Animals and Nutrient Cycling in Terrestrial Ecosystems
Huntley and Inouye (1988)
Pocket gophers alter N cycle by bringing N-poor subsoil to surface
Molles: Ecology 2nd Ed.

22. MacNaughton et al. (1988)
Positive relationship between grazing intensity and rate of turnover in plant biomass in Serengeti Plain
Without grazing, nutrient cycling occurs more slowly through decomposition and feeding of small herbivores
Molles: Ecology 2nd Ed.

23. Molles: Ecology 2nd Ed.

24. Plants and Ecosystem Nutrient Dynamics
Fynbos is a South African temperate shrub/woodland known for high plant diversity and low soil fertility
Two species of Acacia introduced to stabilize shifting sand dunes
Molles: Ecology 2nd Ed.

25. Witkowski (1991)
Compared nutrient dynamics under canopy of native shrub and introduced Acacia
Amount of litter similar, but nutrient content was significantly different
Acacia – N fixer
Molles: Ecology 2nd Ed.

26. Introduced Tree and Hawaiian Ecosystem
Native flora = 1,200 species
> 90% endemic
~ 4,600 new species introduced to Hawaii
Firetree
Myrica faya
Molles: Ecology 2nd Ed.

27. Nitrogen fixation by Myrica large N input
Vitousek and Walker (1989)
Invading N-fixing tree Myrica faya is altering N dynamics of Hawaiian ecosystems
Introduced in late 1800’s as ornamental or medicinal plant – later used for watershed reclamation
Nitrogen fixation by Myrica large N input
Leaves contain high N content
High decomposition rate
Molles: Ecology 2nd Ed.

28. Molles: Ecology 2nd Ed.

29. Disturbance and Nutrient Loss From the Hubbard Brook Forest
Vitousek et al.
19 forests around N. America
11 deciduous, 8 coniferous
Acidic to neutral soils
Effects of disturbance and environmental conditions on N loss
Molles: Ecology 2nd Ed.

30. Dig trenches around them, line w/plastic
Vitousek studies:
Square meter plots
Dig trenches around them, line w/plastic
Trenching increased concentrations of nitrate in soil water up to 1,000X
Nitrate losses higher at sites with rapid decomposition
Uptake by vegetation most important in ecosystems with fertile soils and warm, moist conditions
Molles: Ecology 2nd Ed.

31. Similar study on disturbance by forest clearcutting:
Fig 19.21
Molles: Ecology 2nd Ed.

32. Flooding and Nutrient Export by Streams
Meyer and Likens found P exports were highly episodic and associated with periods of high flow
Annual peak in P input associated with spring snowmelt
Most export was irregular because it was driven by flooding caused by intense periodic storms
Molles: Ecology 2nd Ed.

33. Disturbance increases ecosystem nutrient loss
Summary
Decomposition rate influenced by temperature, moisture, and chemical composition of litter and environment
Plants and animals modify distribution and cycling of nutrients in ecosystems
Disturbance increases ecosystem nutrient loss
Molles: Ecology 2nd Ed.

34. Molles: Ecology 2nd Ed.