Phytoplankton Photosynthesis

Transcription

1 Phytoplankton Photosynthesis RedOx Reactions Some more history Quantum Yields Photosynthetic Units Physical Structure The Z-Scheme The Calvin-Benson Cycle Measuring Photosynthesis Phytoplankton Zooplankton Nutrients 1

2 A Brief History. Otto von Warburg, 1920 s Insisted that the quantum yield of oxygen evolution (the number of oxygen molecules evolved per photon, or quanta, absorbed) was about 0.25 Emerson and Arnold, 1932, described the PSU 2

3 Emerson and Arnold, 1932, determined that the functional unit of photosynthesis could be called a Photosynthetic Unit, and was made up of about 2400 pigment molecules PSI PSII Antenna Apparent PSU Cross-Section Emerson Red-Drop Effect 1952, Emerson determined that photosynthesis is maximal when blue AND red light is available 3

4 Growth on CO 2 and the Macronutrients N and P It is convenient (and often necessary) to consider the growth and decomposition of an average phytoplankter. Redfield showed strong relationships between elements that were consistent with the growth and decomposition of phytoplankton: C:N:P ~ 106:16:1 - Termed the Redfield Ratios 106 CO H 2 O +16 HNO 3 + H 3 PO 4 "# (CH 2 O) 106 +(NH 3 ) 16 +H 3 PO O 2 This suggests that there is a cellular currency related to photosynthesis (growth) and that we can measure ANY ONE variable to get the other variables. 4

5 Photosynthesis Photosynthesis 5

6 Fluorescence HEAT 6

7 The Z-Scheme. The Manganese Clock 7

8 ...embedded in a membrane. Z-Scheme membranes Thylakoid becomes acidic 8

9 Non-Cyclic Photophosphorilation (Z- Scheme) Cyclic Photophosphorylation Only PS I used NO O2 formed Produces ATP 9

10 Dark vs. Light Reactions Light Reactions: Require light energy to run Dark Reactions: technically don t require light, but they stop very quickly in the dark Measuring Photosynthesis Change in biomass Change in H 2 0, O 2 Change in CO 2 Production of Heat Production of Fluorescence 10

11 Photosynthesis Measurements Method 14C Oxygen Fluorescence PROS Easy to use Tracer method Measures carbon Cheap Very Sensitive Measures GPP Not complicated Instantaneous No bottle First principles CONS Requires a bottle Deck vs. In situ? Radioactive! Neither gross nor net productivity Not easy to do Not very sensitive BIG assumptions Instrumentation Photosynthesis Measurements Method 18-Oxygen PROS VERY sensitive GPP, NPP, R Very Sensitive CONS Requires a bottle Very Expensive, hard to do Heat Biomass Really cool! Non-invasive First principles Incredibly simple Community NPP Lab only VERY difficult! Instrumentation Space, Time-scale dependent Not a rate! 11

12 Variable Fluorescence 1 F Start with a pulse of weak light--this will cause weak (background) fluorescence and is called the probe flash 0 Time Variable Fluorescence 1 F 0 Time Turn the lights all the way up (actinic light) and you get maximum fluorescence, directly proportional to the # of functional chl molecules 12

13 Variable Fluorescence 1 F 0 Fm Fv Fo Time Turn the lights all the way up (actinic light) and you get maximum fluorescence, directly proportional to the # of functional chl molecules Variable Fluorescence 1 F 0 Time Leave the light on long enough, and the dark reactions (photochemical quenching) take over..leave it on even longer, and non-photochemical quenching starts 13

14 Variable Fluorescence 1 F 0 Time Leave the light on long enough, and the dark reactions (photochemical quenching) take over..leave it on even longer, and non-photochemical quenching starts Variable Fluorescence Fv/Fm (Fm-Fo/Fm) provides an indication of relative health, or whether there is damage to the photosystem Short-term changes (seconds) provide an indication of photosynthetic efficiency (quantum yield) Long-term changes (seconds-minutes) provide an indication of adaptability Do the same thing in ambient light, get an indication of photosynthetic rates 14

15 Photosynthesis versus Irradiance Curves Photosynthesis Irradiance Photosynthesis versus Irradiance Curves P max Photosynthesis beta alpha E k Irradiance 15

16 Photosynthesis versus Irradiance Curves Photosynthesis Irradiance 16