Ecological relevance of carbon isotope fractionation during dark respiration
Final Report Abstract
As carbon (C) travels from the atmosphere through plants and is respired back to the atmosphere by leaf, stems, roots and soil, there are many processes, which alter the C isotope ratio. However, for the interpretation of the stable carbon isotope composition as environmental tracer profound knowledge of postcarboxylation fractionation is essential. Particularly, the metabolic origin of large diurnal variation in isotopic signature of dark respiration has long been a matter of debate. However, closing this knowledge gap is essential for the application of stable isotope approaches tracing carbon flow through plants and ecosystems and disentangling key physiological processes in carbon metabolism of plants. This project aimed at closing the gap between recent advances on mechanisms of fractionation during dark respiration and its ecological significance by combining metabolic, whole-plant and ecosystem approaches. It analysed short-term variations of the isotopic composition of respiratory CO2 (δ13Cres) in selected functional groups under different environmental conditions considering diurnal dynamics of metabolite pools in leaves, shoots and roots. Possible implications of diurnal dynamics in δ13Cres at larger scales were assessed by evaluating the processes at the leaf, whole-plant and the ecosystem scale in natural Mediterranean ecosystems. The results shed new light into the metabolic causes and environmental drivers and contributed to the overwhelming evidence for large diurnal dynamics in respiratory carbon isotope fractionation during respiration ranging from 4.0 to 14.8‰ at the metabolic, leaf, plant and ecosystem scale: in particular, the impact of postcarboxylation fractionation on the δ13C of respired CO2 was detected in various plant organs and along the vertical axes in plant tissues. Field studies underlined the influence of environmental parameters on post-carboxylation fractionation in different species and seasons. Further, the coupling of post-carboxylation fractionation and carbon allocation in response to source and sink strength within the plant were detected. Finally, ecosystem component fluxes and their isotopic signatures revealed the impact of single ecosystem components (e.g. soil microorganism) reflecting on total ecosystem carbon dynamics and the close linkage between carbon and water cycle in the studies Mediterranean ecosystems. Innovative approaches of 13CO2, compound and position-specific 13C-labeling and novel chambers were used to trace carbon isotope fractionation in the metabolic branching points and partition above and belowground carbon allocation. A new technique termed dynamic 13C-pulse chasing, combining isotopic analysis of volatile organic compounds (VOCs) and 13CO2 with 13C positional pyruvate labeling allowed real-time tracing of the three C atoms of pyruvate during biosynthetic processes or decarboxylation to CO2. It yielding first evidence for a direct and fast coupling of carbon primary metabolism, 13CO2 fractionation and volatile organic compound (VOC) synthesis. Overall, this project provided new insight into the coupling of post-carboxylation 13C fractionation with carbon allocation, respiration and secondary metabolism, which are all important components of the plant carbon metabolism. A better knowledge of these processes will advance investigations on larger scales, e.g. plant response to global change, ecosystem and global C-flux partitioning or air quality studies. Better understanding the processes driving the dynamics of δ13C of ecosystem respiration has significant implications for the evaluation of ecosystem response to global change.
Publications
- (2010) Disentangling drought-induced variation in ecosystem and soil respiration by stable isotope partitioning. Oecologia 163:1043–1057
Unger S., Máguas C., Pereira J.S., Aires L.M., David T.S. & Werner C.
(See online at https://doi.org/10.1007/s00442-010-1576-6) - (2010) Do isotopic respiratory signals trace changes in metabolic fluxes? New Phytologist 186: 569–571
Werner C.
(See online at https://doi.org/10.1111/j.1469-8137.2010.03248.x) - (2010) On the use of phloem sap d13C as an indicator of canopy carbon discrimination. Tree Physiology 30: 1499-1514
Rascher K.G., Máguas C. & Werner C.
(See online at https://doi.org/10.1093/treephys/tpq092) - (2010) The magnitude of diurnal variation in carbon isotopic composition of leaf dark respired CO2 correlates with the difference between δ13C of leaf and root material. Functional Plant Biology 37: 849–858
Wegener F., Beyschlag W. & Werner C.
(See online at https://doi.org/10.1071/FP09224) - (2011) Diel variations in the carbon isotope composition of respired CO2 and associated carbon sources: a review of dynamics and mechanisms. Biogeosciences 8, 2437–2459
Werner C. & Gessler A.
(See online at https://doi.org/10.5194/bg-8-2437-2011) - (2012) Interpreting postdrought rewetting effects on soil and ecosystem carbon dynamics in a Mediterranean oak savannah. Agricultural and Forest Meteorology. 154-155: 9-18
Unger S., Máguas C., Pereira J.S., David T.S. & Werner C.
(See online at https://doi.org/10.1016/j.agrformet.2011.10.007) - (2012) Progress and challenges in using stable isotopes to trace plant carbon and water relations across scales. Biogeosciences, 9, 3083-3111
Werner C., H. Schnyder, M. Cuntz, F., C. Keitel, M. J. Zeeman, T. E. Dawson, F.W. Badeck, E. Brugnoli, J. Ghashghaie, T.E.E. Grams, Z. Kayler, M. Lakatos, X. Lee, C. Máguas, J. Ogée, K.G. Rascher. R. Siegwolf, S. Unger, J. Welker, L. Wingate, A. Gessler
(See online at https://doi.org/10.5194/bg-9-3083-2012) - (2012). Species-specific differences in temporal and spatial variation in δ13C of plant carbon pools and dark-respired CO2 under changing environmental conditions. Photosynthesis Research 113:297-309
Dubbert M., Rascher K.G., Werner C.
(See online at https://doi.org/10.1007/s11120-012-9748-3) - (2014). Phytogenic Biosynthesis of Methyl Acetate. Plant, Cell and Environment, 37, 414-424
Jardine, K., Wegener, F., Abrell, L., vam Haren, J., Werner, C.
(See online at https://doi.org/10.1111/pce.12164) - (2015) Dynamic carbon allocation into source and sink tissues determine within-plant differences in carbon isotope ratios. Functional Plant Biology 42(7) 620-62. Published: 16 April 2015
Wegener F., Beyschlag W. & Werner C.
(See online at https://doi.org/10.1071/FP14152)
