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Figure 7.14

Figure 7.14. Negative and positive feedbacks to atmospheric [CO2]. Can Elevated CO 2 Stimulate a Negative Feedback through plant growth?. atm CO 2. atm CO 2. NPP. plant CO 2 uptake. Leaf Level Photosynthesis. net photosynthesis (umol m -2 sec -1 ). 350. 700. CO 2 (ppm).

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Figure 7.14

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  1. Figure 7.14

  2. Negative and positive feedbacks to atmospheric [CO2]

  3. Can Elevated CO2 Stimulate a Negative Feedback through plant growth? atm CO2 atm CO2 NPP plant CO2 uptake

  4. Leaf Level Photosynthesis net photosynthesis (umol m-2 sec-1) 350 700 CO2 (ppm)

  5. Greenhouse Experiments Ps not saturated at 380 ppm Increased CO2 decreases photorespiration Increased CO2 decreases stomatal conductance (H2O loss) 100’s of studies -- evidence is strong

  6. Greenhouse Experiments: Problems What is response of plant to CO2 when other factors (light, nutrients) are limiting? Does increased Ps and NPP really lead to more carbon storage in the ecosystem (NEP)?

  7. Chambers have room for extra paneling to make them taller as thevegetation grows Fans blow air into the chambers either ambient air, or air with added CO2 Technique to manipulate CO2:Open-top chambers Air exits the chambers through the open tops Florida Scrub-Oak Elevated CO2 Experiment Photo B. G. Drake

  8. Free Air CO2 Enrichment (FACE) at the Duke Forest

  9. Another FACE experiment looking at effects of CO2 and O3 (ozone)on growth of Aspens (Rhinelander, Wisconsin)

  10. Nevada Desert FACE Site

  11. Sweetgum forest FACE site at Oak Ridge National Lab

  12. Manipulations: 2 CO22 Temperature 2 Precipitation2 N deposition + all combinations 2 x 2 x 2 x 2 design8 replicates 128 plots Close-up of ‘baby-FACE’CO2 injectors Infrared heat lamp used to increase air T by 3.5 ºC

  13. The Duke Forest Free-Air CO2 Enrichment Experiment: Effects on Net Primary Productivity (DeLucia et al. 1999, Science)

  14. Cedar Creek: Biocon

  15. Free Air CO2 Enrichment (FACE) Done in relatively few ecosystems, biased towards short statured vegetation, and/or early succession But, shows C exchange of entire ecosystem

  16. FACE: Plant response Smaller and less consistent than leaf-level greenhouse response Modest increase (≈15%) in aboveground biomass accumulation Response depends strongly on availability of other resources Largest response in dry ecosystems (or dry years), fertile sites, or early in succession

  17. FACE: Decomposition response, a negative feedback? atm CO2 decomposition NPP leaf C:N ratio

  18. FACE: Decomposition response Leaf C:N ratios do increase, but mostly due to increased starch Starch is retranslocated at leaf senescence, so increases in litter C:N ratio are small No consistent effect of elevated CO2 on decomposition rates

  19. FACE: Decomposition response, a negative feedback? Not really… atm CO2 ~decomposition NPP leaf C:N ratio

  20. FACE: Belowground allocation With elevated CO2, more C allocated belowground Explains increased Ps, but small increase in ANPP Belowground allocation may be a result of increased demand for nutrients

  21. Fate of Belowground allocation Root biomass Root production Root exudation Mycorrhizae Most extra C ends up in high turnover pools Little potential for long term C storage

  22. Where can we store carbon?

  23. Marine Primary Production

  24. Production is low in ‘blue water’ despite sometimes high [N] and [P]

  25. Iron stimulates production in high nutrient blue waters (Graph courtesy U.S. Joint Global Ocean Flux Study, based on data from K. Johnson and K. Coale.)

  26. “Give me half a tanker filled with iron, and I’ll give you another ice age” -John Martin (1989)

  27. Dust Atm CO2 Ice core records show that dust inputs are correlated with depletion of atmospheric CO2, presumably by stimulating ocean productivity

  28. Large-scale, open-ocean experiments: the true test of the iron hypothesis During the 1993 Iron Enrichment Experiment (IRONEX), researchers dumped iron into a 64-square-kilometer area and measured the response of phytoplankton. The photograph above shows researchers at the Naval Postgraduate School preparing iron to be dumped in the sea.

  29. Monitoring CO2 levels in the water showed increasedphotosynthetic activity where the iron had been released

  30. But the results were truly dramatic, as reported in Science News, 148:220 (1995), “Nothing had prepared them for the color of the water. The oceanographers watched in awe as the R. V. Melville pliedPacific waves dyed a soupy green by a bumper crop of tinyocean plants. The tint was abnormal. Only a day before, this patch of water near the Galapagos Islands had sparkled with electric blue clarity, a quality owing to the general absence of phytoplankton. They had transformed this marine desert into a garden simply by sprinkling a dilute solution of iron into the water.”

  31. The results of the Southern Ocean Iron Enrichment Experiment (SOIREE) experiment in 1999 were captured by the Sea-viewing Wide Field-of-view Sensor (SeaWiFS). The bright comma in the image indicates phytoplankton growth stimulated by iron added during the course of the experiment.(Image courtesy Jim Acker, Goddard Distributed Active Archive Center, the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE

  32. + Fe + NPP + Ocean carbon storage  Atmospheric[CO2] ??? “We have demonstrated that we have the key now for turningthis system on and off. I think some will be encouraged bythese findings. Therein lies the dilemma.” Kenneth Coale, lead scientist in the IRONEX experiments

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