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Carbon isotope composition of C4 grasses is influenced by light and water supply
Author(s) -
BUCHMANN N.,
BROOKS J. R.,
RAPP K. D.,
EHLERINGER J. R.
Publication year - 1996
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.1996.tb00331.x
Subject(s) - isotopes of carbon , photosynthesis , carbon fibers , isotope , botany , stable isotope ratio , ecophysiology , crassulacean acid metabolism , biology , environmental chemistry , chemistry , total organic carbon , physics , mathematics , algorithm , quantum mechanics , composite number
The carbon isotope composition of C 4 grasses has the potential to be used as an indicator of changes in the isotopic composition and concentration of atmospheric CO2, especially for climate reconstruction. The usefulness of C 4 grasses for this purpose hinges on the assumption that their photosynthetic discrimination against 13 C remains constant in a wide range of environmental conditions. We tested this assumption by examining the effects of light and water stress on the carbon isotope composition of C 4 grasses using different biochemical subtypes (NADP‐ME, NAD‐ME, PCK) in glasshouse experiments. We grew 14 different C 4 grass species in four treatments: sun‐watered, sun‐drought, shade‐watered and shade‐drought. Carbon isotope discrimination (Δ) rarely remained constant. In general, Δ values were lowest in sun‐watered grasses, greater for sun‐drought plants and even higher for plants of the shade‐watered treatment. The highest Δ values were generally found in the most stressed grasses, the shade‐drought plants. Grasses of the NADP‐ME subtype were the least influenced by a change in environmental variables, followed by PCK and NAD‐ME subtypes. Water availability affected the carbon isotope discrimination less than light limitation in PCK and NAD‐ME subtypes, but similarly in NADP‐ME subtypes. In another experiment, we studied the effect of increasing light levels (150 to 1500 μmol photons m −2 s −1 ) on the Δ values of 18 well‐watered C 4 grass species. Carbon isotope discrimination remained constant until photon flux density (PFD) was less than 700 μmol photons m −2 s −1 . Below this light level, Δ values increased with decreasing irradiance for all biochemical subtypes. The change in A was less pronounced in NADP‐ME and PCK than in NAD‐ME grasses. Grasses grown in the field and in the glasshouse showed a similar pattern. Thus, caution should be exercised when using C4 plants under varying environmental conditions to monitor the concentration or carbon isotopic composition of atmospheric CO2 in field/glasshouse studies or climate reconstruction.