NUTRIENT CYCLING AND RETENTION

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

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

16. Fig 19.13 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 Molles: Ecology 2nd Ed.

17. Fig 19.13 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 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. 19.14 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. 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. 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. 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.