Marklein CNP stoichiometry


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Presentation by Alison Marklein at UC Davis in ECL290: Ecological Stoichiometry

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Marklein CNP stoichiometry

  1. 1. Ecological Stoichiometry Alison marklein Ecl 290 37 Alan hastings Oct 16, 2012
  2. 2. Why is stoichiometry important?• Conservation of mass and energy• Growth is limited by nutrients, that are required in fairly strict ratios• Ecosystems have a finite amount of elements and inputs/outputs• Without limiting nutrients, energy, or space, theoretical population dynamics may give infinite growth (implicitly included in carrying capacity)
  3. 3. • Humans have much more C,N,P as a fraction of total mass than occurs in the earth as a whole• Must be preferentially accumulating these elements Sterner and Elser, 2002
  4. 4. Stoichiometry of bio-chemicals Sterner and Elser, 2002
  5. 5. N vs. P• P available in rock form and decreases as ecosystem age• N can be fixed by organisms from the atmosphere to inorganic bio-available forms (but this is energetically expensive and requires lots of P as ATP)• Aquatic ecosystems often thought to be P limited because N can be brought in via fixation. Also affected by anthropogenic N inputs (runoff, dep) Walker and Syers 1976; Vitousek et al. 2010
  6. 6. N, P, and co- limitation Large purple bars suggests co- limitation of N and P. This could be supported by re-allocation of one nutrient to get another to optimize growth Elser et al., Ecology Letters, 2008
  7. 7. Reiners 1986
  8. 8. Background info: Redfield Ratios• Phytomass displays an average C:N:P of 106:16:1• This is similar to the C:N:P of dissolved matter in the ocean Redfield, American Naturalist, 1958
  9. 9. NO3- from PO43- Oceaninferred and CNP deviations N* - processes Mean Phytoplankton 106:16:1 1:16 P:N lineN* = NO3- – 16PO43- + 2.9 Gruber and Sarmiento 199
  10. 10. N/P Tropical TemperateLeaf litter (reg) 43:1 12:1Leaf: 43:1 25:1Leaf litter: 63:1 27:1 All forest microbes 9:1 Fungi 15:1 Bacteria 7:1 Enzymes 1:1McGroddy et al. 2004; Townsendet al. ; Cleveland et al. 2007;Reiners 1986; Sinsabaugh et al.;
  11. 11. N/P Plant Tropical Temperate Litterfall Leaf litter (reg) 43:1 12:1 Uptake Leaf: 43:1 25:1 Leaf litter: 63:1 27:1 Litter All forest microbes 9:1 Fungi 15:1 Bacteria 7:1 Enzymes 1:1 McGroddy et al. 2004; TownsendMicrobial Inorganic et al. ; Cleveland et al. 2007;Biomass nutrients Reiners 1986; Sinsabaugh et al.;
  12. 12. Pelagic CNP in eutrophic lake with food web manipulation• Q: How do tropic dynamics and biogeochemistry interact in regulating lake ecosystem dynamics during a whole-lake food-web manipulation?• HYP: elimination of planktivorous fishes would result in a pelagic food web in which P-rich zooplankton (for example, Daphnia) would have a greatly enhanced role in regulating internal nutrient availability and would differentially increase the availability of N relative to P. Elser et al. 2000 Ecosystems
  13. 13. Responses to Pike• + Pike• 3 yrs later: - minnows• 4 yrs later: + cladoceranDaphnia - zooplankton N:P - seston C:P + DON and DOP Elser et al. 2000 Ecosystems
  14. 14. N fixation• Low external N/P ratio• Internal processes driven by food-web changes fixed enough N relative to P in the early season to allow phytoplankton to grow similarly to 25 years previously• Then cyanobacteria crashed• Suggests threshold N/P ratio for N fixation to be energetically favorable Elser et al. 2000 Ecosystems
  15. 15. 5 aspects of stoichiometric effects• Zooplankton became more P rich (lower C:P and N:P ratio)• The importance of zooplankton as a nutrient pool in the water column greatly increased• Increased zooplankton biomass increased overal dissolved nutrient availability (more for N than P). This caused shift away from N-fixing cyanobacteria• Seston C:P and N:P ratios were low, indicating relatively rapid groth rates of remaining phytoplankton biomass. Decreased phytoplankton bioass reflected less of the limiting nutrient P• Sedimentation appears to have been altered by food web manipulation Elser et al. 2000 Ecosystems
  16. 16. Conclusions• Consumer-driven nutrient cycling processes appeared to have increased N:P ratio in the available nutrient supply.• This should result in decreased dominance of cyanobacteria in phytoplankton community• Introduction of piscivorous pike and elimination of planktivorous fish generated low N:P sink (Daphnia zooplankton community) counteracted the low N:P source of nutrients entering the lake, drastically altering the response of the lake Elser et al. 2000 Ecosystems
  17. 17. Modeling implications• Eutrophic lakes are characterized by alternative stable states• These dynamics are consistent with stoichiometric models of grazer-algae interactions• These models predict the existence of intrinsic high grazer and grazer-free stable states under eutrophic conditions• Nutrient loading ,tropic cascades and stoichiometric theories provide a fundamental understanding of eutrophic lake dynamics• Our ability to make specific predictions of the occurrence and intensity of cyanobacteria biomass may be limited by the nonlinear mechanisms underpinning the nutrient- phytoplankton-zooplankton systems Elser et al. 2000 Ecosystems
  18. 18. Biological stoichiometry• Biological stoichiometry: coupling the first laws of thermodynamics; evolution by natural selection; and central dogma of molecular biology• Roots: optimal foaging; resource ratio competition theory; Redfield ratio; nutrient use efficiency Elser et al. 2000 Ecology Letters
  19. 19. Biological stoichiometry from genes to ecosystems• Q: What determines the C:N:P of living biomass?• HYP: a connection between growth rate and C:N:P stoichiometry based on rRNA allocation and the organization of ribosomal genes in diverse biota Elser et al. 2000 Ecology Letters
  20. 20. Autotroph N:P rules of thumb• Biomass N:P tracks N:P of the nutrient supply• At fixed supply rate of nutrient X, biomass C:X increases as light intensity and/or pCO2 increase• Under concentrations of X-limited growth, biomass C:X increases steeply as realized specific growth rate declines• High variation of C:N:P in base of food web Elser et al. 2000 Ecology Letters
  21. 21. Growth rate and P relationships• Organisms with high max specific growth rate have high [RNA]• RNA makes up 50-60% of the ribosome, which promotes cell growth• RNA is 10% P by weight• P-rich, low N:P is a signature of rapid growth and is a cellular necessity• Most variation occurs in chromosomal rDNA copy number Elser et al. 2000 Ecology Letters
  22. 22. Growth Rate Hypothesis• rRNA is needed for protein synthesis; rRNA is ~80% of all RNA in organisms• RNA has a relatively low N/P• Thus, growth rate is limited by P and N/P variation is largely driven by investment in rRNA Sterner and Elser, 2002
  23. 23. Molecular genetics of food web dynamics hypothesis• Goal: generate functionally realistic model of ecological dynamics informed by modern genetic understanding• Evolution of growth rate related to RNA allocation and organism P content/CNP stoich• HYP: variation in the relative abundance of high growth rate, low C:P and N:P consumers with high rDNA should be higher in systems with good quality (low C:N and C:P food). Elser et al. 2000 Ecology Letters
  24. 24. Resource Ratio TheoryMiller, American Naturalist 2005
  25. 25. Questions and discussion:1. How might results differ if the lake were not eutrophic?2. How do terrestrial and lake ecosystems differ, and what are the problems?3. In what situations is it worth incorporating nutrient dynamics and stoichiometry, and when might it be unneccessarily complicating the model?4. Does Elser’s RNA hypotheses make sense when comparing across global scales, like tropics vs. temperate? Elser et al. 2000 Ecology Letters
  26. 26. Thanks!