Primary Producer Carbon Isotopes

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1 Primary Producer Carbon Isotopes

2 The Beginnings Craig 1953

3 Isotope Fractionations: A Review EQUILIBRIUM KINETIC A k 1 B A k 12C B k 2 k 13C Fractionation Factor: k 1 /k 2 Mass-Dependent k 12C > k 13C Rates are Important! Light isotopes ( 12 C) react faster than heavy ( 13 C) ones.

4 O Leary s Isotope Laws First Law: The lighter isotope ( 12 C or 14 N) reacts faster and requires less energy of activation. Second Law: The heavier isotope ( 13 C or 15 N) makes the strongest bonds. Zero th Law: Beware of differences of <1 in d 13 C, d 15 N, or d 18 O! Or <10 in d 2 H!

5 Carbon Isotope (d 13 C) Variation Carbon Isotope Value (d 13 C) Craig 1953

6 D 13 C versus d 13 C

7 Photosynthesis: Two Kinetic Isotope Effects 6CO 2 + 6H 2 O + C 6 H 12 O 6 + 6O 2 d 13 C: -8 d 13 C: -12 to CO 2 Diffusion 13 CO 2 12 CO 2 13 CO 2 Rubisco 12 C 13 C

8 C 3 and C 4 Plants (Australia) Count δ 13 C Fogel et al., unpublished

9 1 st Product of CO 2 Fixation: 3-Carbon (C 3 ) Sugar 1 st Product of CO 2 Fixation: 4-Carbon (C 4 ) Sugar

10 Calvin Cycle: CO 2 + RPB = PGAL (Glucose) Atmospheric CO 2 Rubulose Bisphosphate (Rubisco) Glucose (food)

$fractionation that$

11 Rubisco is the Key Enzyme Guy, Fogel, and Berry 1993 High affinity for 12 C, hence large d 13 C kinetic fractionation that ranges from (average = 27 )

12 D 13 C = d 13 C CO2 d 13 C plant D = ~ CO 2 Count δ 13 C

13 Farquhar, O Leary, and Berry (1982)

14 C 3 Discrimination (D) Equation D = a + (b-a) (c i /c a ) a = Gas-Phase Diffusion (kinetic) b = Carboxylation by Rubisco (kinetic) C i = [CO 2 ] Inside Leaf C a = [CO 2 ] Atmosphere a = b =

15 C 3 vs C 4 Plants: Influence of C i / C a D = a + (b a) (c i /c a ) Discrimination ( ) C i / C a

16 Discrimination (D 13 C) Driven By Stomata

17 Leaf Stomates Control C i / C a d 13 C Atmospheric CO 2-8 ( 12 CO CO 2 ) Water Leaf Stomata 13 CO 2 d 13 C Atmospheric CO 2-8 Internal CO 2 (Prefers 12 CO 2 ) Rubsico Prefers 12 CO 2 Light ( 12 C) Biomass (-27 )

What Causes d 13 C Variation in C 3 Plants 300 250 200 40 35 30 Acacia Australian Plants from Acacia Australia Count

19 What Causes d 13 C Variation in C 3 Plants Acacia Australian Plants from Acacia Australia Count Count δ C δ 13 C Fogel et al. unpublished

20 Factors Controlling D and d 13 C in C 3 Plants 40 Acacia Australian Plants from Acacia Australia 1. Source of CO 2 2. Wet versus Dry 3. Shade versus Sun 4. Temperature 5. Nitrogen Metabolism 6. Salinity Count δ 13 C

21 1. Source of CO 2 : Keeling Plots d 13 C a = c b (d 13 C b - d 13 C S )(1/c a ) + d 13 C S Pataki et al. 2003

22 2. Water Stress C 3 plants discriminate less when exposed to H 2 O stress. Guy et al High H 2 O Stress Low H 2 O Stress

23 A Wet Environment d 13 C Atmospheric CO 2-8 ( 12 CO CO 2 ) Water Leaf Stomata 13 CO 2 d 13 C Atmospheric CO 2-8 High Internal [CO 2 ] (Prefers 12 CO 2 ) Rubsico Prefers 12 CO 2 Very Light ( 12 C) Biomass (-32 )

24 A Dry, Hot, or Saline Environment d 13 C Atmospheric CO 2-8 ( 12 CO CO 2 ) Water Leaf Stomata 13 CO 2 d 13 C Atmospheric CO 2-8 Low Internal [CO 2 ] ( 12 CO CO 2 ) Rubsico Uses Both 12 CO CO 2 Heavy ( 12 C + 13 C) Biomass (-22 )

25 Rainfall Decreases d 13 C Pataki et al. 2003

26 3. Sun versus Shade Ehleringer et al. 1986

27 Canopy Effects

28 C 3 and C 4 Plants Count δ 13 C Fogel et al. unpublished

29 C 4 Photosynthesis Two primary groups within Angiosperms contain different abundances of C 3 and C 4 species. C 3 C 4 Monocots ~6,000 ~6,000 Dicots ~300,000 ~2,000

30 C 4 Photosynthesis C 4 present only in advanced angiosperms Available data suggest multiple, independent evolutionary events Acanthaceae (tropical herbs) Aizoaceae (ice plants) Amaranthaceae (amaranth) Boraginaceae Capparidaceae (capers) Caryophyllaceae Chenopodiaceae (chenopods) Cleomaceae (brassicales) Compositae (aster) Cyperaceae (sedges) Euphorbiaceae (spurge) Gramineae (grasses) Nyctaginaceae Polygonaceae (buckwheat) Portulacaceae Scrophulariaceae (fogworts) Zygophyllaceae (caltrop)

31 C 4 Photosynthesis C 3 and C 4 species appear in a single genus several times suggesting multiple, independent evolutionary events. Family Aizoaceae Amaranthaceae Asteraceae Boraginaceae Chenopodiaceae Cyperaceae Euphorbiaceae Nyctaginaceae Poaceae Zygophyllaceae Genus Mollugo Aerva, Alteranthera Flaveria, Pectis Heliotropium Atriplex, Bassia, Kochia, Suaeda Cyperus, Scirpus Chamaesyce, Euphorbia Boerhaavia Alloteropsis, Panicum Kallstroemia, Zygophyllum

32 C 3 versus C 4 Photosynthesis C 3 C 4

33 C 4 Plants Are Not Perfect (some fixed CO 2 leaks out) Carbonic Anhydrase (CO 2 to HCO 3 ) HCO 3 Some CO 2 Leaks Back Out

34 C 4 Discrimination Equation D = a + (b 4 + b 3 (f) - a) (c i /c a ) a = Gas-Phase Diffusion (4.4 ) b 3 = Carboxylation Rubisco Fractionation (27 30 ) b 4 = PEP Carboxylase Fractionation (5.7 ) f = Leakiness Factor 70 Australian C 4 Grasses Count δ 13 C Fogel et al. unpublished

Factors Controlling D and d 13 C in C 4 Plants

(NADP-ME or NAD-ME ) Wet versus Dry Count 70 60

Australian C 4 Grasses Tight 0-16 -15-14 -13-12

35 Factors Controlling D and d 13 C in C 4 Plants Bundle Sheath Leakiness (f) Metabolic Type (NADP-ME or NAD-ME ) Wet versus Dry Count Australian C 4 Grasses Leaky Australian C 4 Grasses Tight δ 13 C C 4 Plants Leak 35 40% of Fixed CO 2

36 Factors Controlling D and d 13 C in C 4 Plants

37 Crassulacean Acid Metabolism (CAM) Photosynthesis Stomates Open at Night Stomates Closed During Day

38 CAM Plants: A Mix of C 3 and C 4 Photosynthesis d 13 C = -12 to -27 C 4 Night Fixation d 13 C = -12 to -19 Cold and Wet (Stomata Open) C 3 Day Fixation d 13 C = -20 to -27 Hot and Dry (Stomata Closed)

39 Reading Report: Ehleringer et a Graphic support plot from Lambers, Chapin and Pons 2008

41 Photosynthesis in the Ocean

$2010 Basic photosynthetic fractionations are similar to C 3 terrestrial plants Marine plants use CO 2 and HCO 3 as inorganic sources of carbon.$

42 Spatial Gradients in d 13 C Goal: Understand spatial variation in phytoplankton d 13 C d 13 C Graham et al Basic photosynthetic fractionations are similar to C 3 terrestrial plants Marine plants use CO 2 and HCO 3 as inorganic sources of carbon. Principal Components of d 13 C Variation: (1) Type of Primary Producer (2) Source(s) and Supply of Inorganic Carbon (3) Temperature (4) Algal Growth Rate (5) Cell Size/Geometry (Taxa)

43 CO 2 Source? CO 2(dissolved) or Bicarbonate (HCO 3 ) Carbon Isotopes (d 13 C) Craig 1953

44 Calvin Cycle: CO 2 + RPB = PGAL (Glucose) Atmospheric CO 2 Rubulose Bisphosphate Calvin Cycle Glucose (food)

45 C 3 Discrimination (D) Equation D = a + (b a) (c i /c a ) a = Gas-Phase Diffusion (kinetic) b = Carboxylation by Rubisco (kinetic) C i = [CO 2 ] Inside Leaf C a = [CO 2 ] Atmosphere a = b =

46 Effects of Microalgal Growth Rate on D D = a + ((b a) x (c i /c a )) Growth rate is proportional to net flux of CO 2 into cell: Microalgal growth rate (µ) = K 1 C a K 2 C i K 12C > K 13C Substitute (K 1 C a µ) / K 2 for C i D = a + (b-a) x (K 1 µ/c a ) / K 2 Equation Predicts: Linear relationship between D and µ/c a

47 b = Phaeodactylum tricornutum Low Growth Laws et al d 13 C D ( ) High Growth d 13 C µ / [CO 2 ] (kg µmol -1 day -1 ) in growth rate yields in D CO2-algal cells = d 13 C

48 It Works for Lots of Phytoplankton Taxa But slope of the relationship varies among taxa. Popp et al D ( ) µ / [CO 2 ] (kg µmol -1 day -1 )

49 The Relative Influence of Temperature vs Growth Rate High Growth Temperate = [CO 2 ] [CO 2 ] yields D Low Growth

50 The Relative Influence of Temperature vs Growth Rate High Growth Temperate = [CO 2 ] [CO 2 ] yields D Low Growth Temperature wins, but there is lots of local variation due to growth rate (especially at temperate latitudes). Growth Rate Temperature

51 Sources of Inorganic Carbon: CO 2 vs HCO 3 Inorganic Carbon Speciation in the Ocean d 13 C = -7 d 13 C = 0 d 13 C = +1

52 Carbonic Anhydrase: Convert CO 2 to HCO 3 Recyling Leaked CO 2 Leak Barrier Energy Carbonic Anhydrase Active Ci Pumps Cell Localized CO 2 Elevation and Fixation Accumulated HCO 3 ph Regulation (high ph) (Cool) rapidly growing marine plants (kelp and seagrass) do this very well! Why?

53 Bicarbonate (HCO 3 ) Pumping D = d + b (F 3 /F 1 ) d = Equilibrium Isotope Fractionation Between CO 2 and HCO 3 (8 ) b = Carboxylation Rubisco Fractionation (27 ) d F 1 F 3

Seagrasses are C 3 plants with C 4 d 13 C

3 as a carbon source) Phytoplankton can use C

54 Seagrasses are C 3 plants with C 4 d 13 C values because of CO 2 diffusion problems (use HCO 3 as a carbon source) Kelp are C 3 plants with CO 2 diffusion problems (use HCO 3 as a carbon source) Phytoplankton can use C 3 and C 4 pathways (mostly use CO 2 as a carbon source)

55 Paleoceanographic d 13 C Records Schneider-Mor et al. 2005

56 C 3 versus C 4 Abundance Varies Along Gradients

57 Light Use Efficiencies of C 3 and C 4 Plants Quantum Yield (umol/mol) C 3 Quantum Yields Are Sensitive to [CO 2 ]; C 4 Are Not! C 4 C 3 Leaf Temperature (C)

58 Distribution of C 3 and C 4 Plants: CO 2 and Temperature Atmospheric [CO 2 ] (ppm) Growing-Season Temperature (C)

59 Distribution of C 3 and C 4 Plants: Elevation Leaf d 13 C Altitude (km)

60 Distribution of C 3 and C 4 Plants: Latitude Great Plains Relative Carbon Gain Latitude

61 C 4 Abundance Decreases in Cool Growing Seasons Tucson, AZ Daily Carbon Gain (% of maximum) Month

Isotopes as tracers of biogeochemical processes Scott Saleska, 2/11/11

Isotopes as tracers of biogeochemical processes Scott Saleska, 2/11/11 Outline 1. Isotope Definitions and terms a) Isotopes and isotope ratios. b) Kinetic fractionation; thermodynamic fractionation c)