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

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Presentation on theme: "Molles: Ecology 2 nd Ed. NUTRIENT CYCLING AND RETENTION Chapter 19."— Presentation transcript:

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

2 Molles: Ecology 2 nd Ed. 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

3 Molles: Ecology 2 nd Ed. 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

4 Molles: Ecology 2 nd Ed.

5 Nitrogen Cycle Includes major atmospheric pool – N 2  Only nitrogen fixers can use atmospheric supply directly  Blue-green algae, soil bacteria, bacteria of legume roots, some fungi  = energy-demanding process  N 2 reduced to ammonia (NH 3 )

6 Molles: Ecology 2 nd Ed. 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

7 Molles: Ecology 2 nd Ed.

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

9 Molles: Ecology 2 nd 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

11 Molles: Ecology 2 nd Ed. 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

12 Molles: Ecology 2 nd Ed. Fig. 19.7

13 Molles: Ecology 2 nd Ed. 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

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

15 Molles: Ecology 2 nd Ed. 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

16 Molles: Ecology 2 nd Ed. 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

17 Molles: Ecology 2 nd Ed. 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

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

19 Molles: Ecology 2 nd Ed. 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

20 Molles: Ecology 2 nd Ed. Fig

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

22 Molles: Ecology 2 nd Ed. 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

23 Molles: Ecology 2 nd 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

25 Molles: Ecology 2 nd Ed. 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

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

27 Molles: Ecology 2 nd Ed. 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

28 Molles: Ecology 2 nd 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

30 Molles: Ecology 2 nd Ed. 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

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

32 Molles: Ecology 2 nd Ed. 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

33 Molles: Ecology 2 nd Ed. 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

34 Molles: Ecology 2 nd Ed.


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