δ¹³C of CO₂ respired in the dark in relation to δ¹³C of leaf metabolites: comparison between Nicotiana sylvestris and Helianthus annuus under drought

Abstract

505Plant, Cell and Environment (2001) 24, 505-515 intercellular partial pressure of CO 2 ; PPFD, photosynthetic photon flux density; R, dark respiration; R VPDB , 13 C/ 12 C ratio of standard VPDB; R s , 13 C/ 12 C ratio of sample; Rubisco, ribulose 1,5 bisphosphate carboxylase-oxygenase; RWC, leaf relative water content; VPD, vapour pressure deficit; d 13 C, carbon isotopic composition. INTRODUCTIONCarbon isotope discrimination during leaf CO 2 assimilation has been extensively studied and models have been developed (Farquhar, O'Leary & Berry 1982;Evans et al. 1986). The simple version of these models, which does not include the discrimination during respiration, has been validated for many species, suggesting that the discrimination during respiration is negligible and does not significantly modify the net discrimination during on-line measurements compared to the predicted values (for a recent review see Brugnoli & Farquhar 2000). Yet, the carbon isotope signature of plant dry matter integrates not only the discrimination during net CO 2 assimilation in the light (including CO 2 diffusion from the atmosphere to the chloroplasts, carboxylation, photorespiration and day respiration) but also the discrimination that could occur during the night-time respiration. Therefore, any fractionation during the night and/or the use of heavy or light substrates for dark respiration (releasing 13 C-enriched or 13 C-depleted CO 2 compared with leaf material) should change the isotopic signature of the remaining leaf material. Moreover, when non-photosynthesizing organs are taken into account, the release of 13 C-enriched or 13 C-depleted CO 2 will further contribute to changes in whole-plant carbon isotopic signature. Henderson, von Caemmerer & Farquhar (1992) observed in some C 4 species that the discrimination determined on leaf dry matter was significantly greater than that measured on-line. Using a modelling approach, they proposed that at least a part of this difference could be explained by the fractionation during dark respiration, releasing CO 2 enriched in 13 C relative to the plant material. We obtained similar results on Phaseolus vulgaris (unpublished results) and Nicotiana sylvestris (Duranceau, ABSTRACTThe variations of d 13 C in leaf metabolites (lipids, organic acids, starch and soluble sugars), leaf organic matter and CO 2 respired in the dark from leaves of Nicotiana sylvestris and Helianthus annuus were investigated during a progressive drought. Under well-watered conditions, CO 2 respired in the dark was 13 C-enriched compared to sucrose by about 4‰ in N. sylvestris and by about 3‰ and 6‰ in two different sets of experiments in H. annuus plants. In a previous work on cotyledonary leaves of Phaseolus vulgaris, we observed a constant 13 C-enrichment by about 6‰ in respired CO 2 compared to sucrose, suggesting a constant fractionation during dark respiration, whatever the leaf age and relative water content. In contrast, the 13 C-enrichment in respired CO 2 increased in dehydrated N. sylvestris and decrea...

Effects of Water Stress on Respiration in Soybean Leaves

“…Nevertheless, this observation agrees with some published studies in other species (Lawlor, 1976;Loboda, 1993;Flexas et al, 2005). However, several other authors have found different results on the effect of water stress on respiration, ranging from decrease (Brix, 1962;Brown and Thomas, 1980;Palta and Nobel, 1989;Escalona et al, 1999;Ghashghaie et al, 2001;Haupt-Herting et al, 2001) to stimulation (Upchurch et al, 1955;Shearmann et al, 1972;Zagdań ska, 1995). In all cases, as in this study, changes in respiration were much less than those in photosynthesis, causing a significant increase in the respiration/photosynthesis ratio under water stress, indicating that the role of respiration becomes more important as water stress develops.…”

Diel variations in the carbon isotope composition of respired CO<sub>2</sub> and associated carbon sources: a review of dynamics and mechanisms

“…During the night the 13 C-enriched transitory starch is used for sucrose synthesis. As a result, a ∼4 ‰ δ 13 C oscillation between light-and dark-exported sucrose has been predicted and observed (Ghashghaie et al, 2001;Tcherkez et al, 2004;Gessler et al, 2008Gessler et al, , 2009a.…”

Progress and challenges in using stable isotopes to trace plant carbon and water relations across scales

“…Despite early evidence by Park and Epstein (1961), carbon isotope fractionation during dark respiration has long been considered negligible (Lin and Ehleringer, 1997). Systematic studies by Duranceau et al (1999) and Ghashghaie et al (2001) with a range of C 3 species again provided clear evidence for substantial and systematic variation in carbon isotope ratios of leaf dark respiration (see review by Ghashghaie et al, 2003). These authors introduced the term "apparent respiratory fractionation" to describe the manifested differences between carbon isotope compositions of leaf dark-respired CO 2 and its putative substrates (mainly carbohydrates), caused by multiple processes in the respiratory pathways (see below).…”