Carbon Fractionation within Individual Plants

MEAS 760

Lori Skidmore & Jonathon Harris

C13 within Plants

• Does C13 vary within individual plants?• Is there a difference in internal

fractionation between C3 and C4 plants?• Many studies examining effects of C4

metabolism:– Winkler et al. 1978– Farquhar et al. 1983– Hobbie and Werner 2004

• Prairie Ridge Data Summary

Does C13 vary within plants?

• YES!

• Carbon fractionation within plants can be described by differences in:– Plant organs– Plant compounds

Fractionation in Plant Organs

• Differences in bulk 13C of different plant parts (leaves, roots) are common.

• Since most 13C measurements are made on leaves, it is important to indicate the plant part measured.

• Fractionation in plant organs differs among C3 and C4 plants (see figure on next slide).

(From Hobbie and Werner, 2003)

Root to shoot variation

• Roots are slightly depleted in heavier isotope, compared to shoots but not when compared to leaves.

Table 3 Werth & Kuzyakov 2006

Organs: C3 versus C4

C3 Plants• Roots are typically

enriched by 1–3‰ relative to leaves.

• Grains enriched by 1–4‰ relative to leaves.

C4 Plants• Roots similar or

slightly lower in δ13C relative to leaves.

• Grains enriched by ≈ 1.5‰ relative to leaves in maize.

(Hobbie and Werner, 2003)

Fractionation in Plant Compounds

• Variations in the isotopic composition of plant organs can be shown to correspond to isotopic differences between organic compounds in the plant.

• Figure shows carbon isotope fractionation between amino-acids in Chlorella pyrenoides (Abelson and Hoering, 1961).

Fractionation in Plant Compounds

• Hobbie & Werner 2004– Suggest early isotopic fractionation in

derivatives of photosynthesis lead to large differences later on.

– If HCO3- becomes enriched in C13 early on in

C4 metabolism all of the later derivatives of that molecule will show the signs of that early discrimination.

– Plant tissues higher in certain compounds than other tissues such as lignin or certain waxes will then reflect this on a plant wide level.

Fractionation in Plant Compounds

• Reactions and transport processes affect composition of compounds in different plant tissues.

• Movement and isotopic fractionation of carbon between leaves and roots results in 13C-depleted products and 13C enrichment in residuals

• Isotopic depletion of lignin and lipids depends on the fraction (f ) of available substrate transformed to lignin and lipids and the isotopic fractionation (∆) of the reaction.

• (Hobbie and Werner, 2003).

Compounds: C3 versus C4

C3 Plants• Alkanes and lipids 4–6‰

depleted (Collister et al., 1994).

C4 Plants• Alkanes and lipids 8–

10‰ depleted (Collister et al., 1994).

• In C4 plants, lipid concentration was found to be about half that in C3 plants (Chikaraishi and Naraoka, 2001).

• Isotopic enrichment of cellulose relative to lignin is slightly greater in leaves of C4 plants.

Prairie Ridge ResultsBROADLEAF PLANTS

Plant type Plant name Sample ID Leaf Flower Stem Root

C3Ambrosia artemisiifolia

(Ragweed)

PRP-3 -31.53   -31.91 -18.82

PRP-4 -31.61 -30.72 -30.12 -16.1

    -30.73    

C3Solanaceae carolinense PRP-8 -30.29   -28.37 -27.5

(Horsenettle)          

GRASSES

Plant type Plant name Sample ID Green blade Brown blade Stem Root

C3Festuca (Fescue)

PRP-9 -29.35 -29.9   -25.6

PRP-12   -28.63   -26.01

C4Cynodon dactyla (Bermuda grass)

PRP-6 -13.28 -13.58 -12.41 -28.73

PRP-11 -12.47 -13.6 -12.94 -12.48

    -13.63    

PRP-13   -13.82 -14.43  

PRP-14 -13.89 -13.17    

Results: Broadleaf plants

Average 13C (%o) [*Part* 13C – Leaf 13C]

• Ragweed– Leaf = -31.57 – Flower = -30.73 [ +0.845]– Stem = -31.02 [ +0.555]– Root = -17.46 [ +14.11]

• Horsenettle– Leaf = -30.29– Stem = -28.37 [+1.92]– Root = -27.50 [ +2.79]

Ragweed

Horsenettle

Results: Grasses

Average 13C (%o) [*Part* 13C – Green blade 13C]

• Bermuda grass– Green blade = -13.21– Brown blade = -13.56 [ -0.347]– Stem = -13.26 [-0.047]– Root = -12.48 [+0.733]

• Fescue– Green blade = -29.35– Brown blade = -29.27 [+0.085]– Root = -25.81 [+3.545]

Bermuda grass

Fescue

Conclusions

• Isotopic composition can vary by:– Plant organ measured– Plant organic compound measured

• Degree of fractionation variable among C3 and C4 plants

• Variations in plant organ 13C correspond to isotopic variations in plant organic compounds (metabolites).

Conclusions: Prairie Ridge

• Roots enriched relative to leaves in C3 and C4 plants.– Isotopic fractionation greater within C3 plants– Isotopic fractionation greater in broadleaf plants than

grasses

• Bermuda grass root data too varied to reliably describe behavior.

• Ragweed exhibited greatest variation between roots (-17.46 %o) and leaves (-31.57 %o)

Differences in Prairie Ridge Data

• Differences between different plant groups

• Perhaps different compound abundances in Cynodon dactlyon roots than in Zea maize roots

• Sample preparation flawed (Bermuda grass root samples?!?)

REFERENCES• Abelson, P.H. and T.C. Hoering. 1961. Carbon isotope fractionation in

formation of aminoacids by photosynthetic organisms. Biogeochemistry, 47: 623-632.

• Chikaraishi Y, Naraoka H. 2001. Organic hydrogen–carbon isotope signatures of terrestrial higher plants during biosynthesis for distinctive photosynthetic pathways. Geochemical Journal 35: 451–458.

• Collister JW, Rieley G, Stern B, Eglinton G, Fry B. 1994. Compound specific 13C analyses of leaf lipids from plants with differing carbon dioxide metabolisms. Organic Geochemistry 21: 619–627.

• Hillaire-Marcel, G. 1986. Isotopes and Food in Handbook of Environmental Isotope Geochemistry, Volume 2. The Terrestrial Environment, B. (Eds. P. Fritz and J.C. Fontes). Elservier Science Publishers, Amsterdam. Chapter 12, p. 507-548.

• Hobbie, E.A. and R.A. Werner. 2004. Intramolecular, compound-specific, and bulk carbon isotope patterns in C3 and C4 plants: a review and synthesis. New Phytologist, Vol. 161: 371-385.

• O’Leary, M.H. 1981. Review: Carbon Isotope Fractionation in Plants. Phytochemistry, Vol. 20, No. 4, pp. 5- 567.