Nocturnal and seasonal patterns of carbon isotope composition of leaf dark-respired carbon dioxide differ among dominant species in a semiarid savanna

Abstract

The C isotope composition of leaf dark-respired CO(2) (δ(13)C(l)) integrates short-term metabolic responses to environmental change and is potentially recorded in the isotopic signature of ecosystem-level respiration. Species differences in photosynthetic pathway, resource acquisition and allocation patterns, and associated isotopic fractionations at metabolic branch points can influence δ(13)C(l), and differences are likely to be modified by seasonal variation in drought intensity. We measured δ(13)C(l) in two deep-rooted C(3) trees (Prosopis velutina and Celtis reticulata), and two relatively shallow-rooted perennial herbs (a C(3) dicot Viguiera dentata and a C(4) grass Sporobolus wrightii) in a floodplain savanna ecosystem in southeastern Arizona, USA during the dry pre-monsoon and wet monsoon seasons. δ(13)C(l) decreased during the nighttime and reached minimum values at pre-dawn in all species. The magnitude of nocturnal shift in δ(13)C(l) differed among species and between pre-monsoon and monsoon seasons. During the pre-monsoon season, the magnitude of the nocturnal shift in δ(13)C(l) in the deep-rooted C(3) trees P. velutina (2.8 ± 0.4‰) and C. reticulata (2.9 ± 0.2‰) was greater than in the C(3) herb V. dentata (1.8 ± 0.4‰) and C(4) grass S. wrightii (2.2 ± 0.4‰). The nocturnal shift in δ(13)C(l) in V. dentata and S. wrightii increased to 3.2 ± 0.1‰ and 4.6 ± 0.6‰, respectively, during the monsoon season, but in C(3) trees did not change significantly from pre-monsoon values. Cumulative daytime net CO(2) uptake was positively correlated with the magnitude of the nocturnal decline in δ(13)C(l) across all species, suggesting that nocturnal δ(13)C(l) may be controlled by (13)C/(12)C fractionations associated with C substrate availability and C metabolite partitioning. Nocturnal patterns of δ(13)C(l) in dominant plant species in the semiarid savanna apparently have predictable responses to seasonal changes in water availability, which is important for interpreting and modeling the C isotope signature of ecosystem-respired CO(2).

Rain pulse response of soil CO2exchange by biological soil crusts and grasslands of the semiarid Colorado Plateau, United States

“…The δ 13 C of respiration from C 3 and C 4 plants generally reflects that of their bulk tissues [ Lin and Ehleringer , 1997; Sun et al , 2010]. There are important isotope effects associated with plant C allocation and metabolism [ Bowling et al , 2008], but these are small relative to the difference in δ 13 C of leaf tissue of the C 3 and C 4 photosynthetic types.…”

The efficiency of C4 photosynthesis under low light conditions in Zea mays, Miscanthus x giganteus and Flaveria bidentis

“…2007; Bathellier et al . 2008; Sun, Resco & Williams 2010). In this study, we consider e = 0‰ (Pengelly et al .…”

The influence of light quality on C4 photosynthesis under steady‐state conditions in Zea mays and Miscanthus × giganteus: changes in rates of photosynthesis but not the efficiency of the CO2 concentrating mechanism

“…2008); e′ is fractionation associated with dark respiration, which is calculated as (Wingate et al . 2007): where e is fractionation during decarboxylation, assumed to equal −6‰ (Ghashghaie, Duranceau & Badeck 2001; Sun, Resco & Williams 2010); δ 13 C measurement (–31‰) is the carbon isotope signature of CO 2 used for the online discrimination measurement, which was measured by the TDLAS; and δ 13 C growth is the carbon isotope composition of CO 2 in the greenhouse, which is assumed to be −8‰.…”