Carbon isotope composition of C4 grasses is influenced by light and water supply

Abstract

The carbon isotope composition of C4 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 C4 grasses for this purpose hinges on the assumption that their photosynthetic discrimination against 13C 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 C4 grasses using different biochemical subtypes (NADP‐ME, NAD‐ME, PCK) in glasshouse experiments. We grew 14 different C4 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 C4 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.

Paleovegetation reconstruction using δ<sup>13</sup>C of Soil Organic Matter

“…Relative to C 3 plants, the δ 13 C of C 4 plants is not sensitive to water availability Henderson et al, 1992;Wang et al, 2005Wang et al, , 2006. Studies on C 4 species mostly showed slight increases in δ 13 C with increasing water availability (Buchmann et al, 1996;Schulze et al, 1996;Wang et al, 2005Wang et al, , 2006. A counter example, however, is provided by Liu et al (2005) who observed an opposite pattern in Bothriochloa ischaemum (C 4 ), i.e., δ 13 C decreasing significantly with increasing precipitation (−0.61‰/100 mm).…”

History of Animals using Isotope Records (HAIR): A 6-year dietary history of one family of African elephants

“…1E, uses the average ␦ 13 C values for the Ͼ250 plant samples from the Samburu. C 3 plants tend to become more positive and C 4 plants tend to be slightly more negative in xeric environments (35,36); thus the mixing lines are likely to be slightly compressed during the dry season and slightly expanded in the wet season compared with the nominal case. To better assess the possible variability in actual C 4 biomass contributions, we used C 3 and C 4 end-member values based on samples collected during the wet and dry seasons of Ϫ28.5‰ and Ϫ12‰ (''wet-season'' mixing line) and Ϫ26 and Ϫ14‰ (''dry-season'' mixing line).…”

Variability in oxidative degradation of charcoal: Influence of production conditions and environmental exposure

“…Within the C 4 photosynthetic 133 pathway, variations in δ 13 C can be primarily attributed to availability of water and light 134 (Buchmann et al, 1996;Ehleringer, 1993). 135…”