Plant respiration

Virtual Issue Articles: In the heat of the night – alternative pathway respiration drives thermogenesis in Philodendron bipinnatifidum Rebecca E. Miller, Nicole M. Grant, Larry Giles, Miquel Ribas-Carbo, Joseph A. Berry, Jennifer R. Watling and Sharon A. Robinson Temperature-sensitive alternative oxidase protein content and its relationship to floral reflectance in natural Plantago lanceolata populations Ann L. Umbach, Elizabeth P. Lacey and Scott J. Richter Leaf respiration and alternative oxidase in field-grown alpine grasses respond to natural changes in temperature and light Stephanie Y. Searle, Samuel Thomas, Kevin L. Griffin, Travis Horton, Ari Kornfeld, Dan Yakir, Vaughan Hurry and Matthew H. Turnbull Steps towards a mechanistic understanding of respiratory temperature responses Jörg Kruse, Heinz Rennenberg and Mark A. Adams Acclimation of respiratory temperature responses in northern and southern populations of Pinus banksiana M.G. Tjoelker, J. Oleskyn, G. Lorenc-Plicinska and P.B. Reich Impacts of drought on leaf respiration in darkness and light in Eucalyptus saligna exposed to industrial-age atmospheric CO2 and growth temperature Gohar Ayub, Renee A. Smith, David T. Tissue and Owen K. Atkin Temperature dependence of respiration in roots colonized by arbuscular mycorrhizal fungi Owen K. Atkin, David Sherlock, Alastair H. Fitter, Susan Jarvis, John K. Hughes, Catherine Campbell, Vaughan Hurry and Angela Hodge Arbuscular mycorrhizal mycelial respiration in a moist tropical forest Andrew T. Nottingham, Benjamin L. Turner, Klaus Winter, Marcel G.A. van der Heijden and Edmund V.J. Tanner Multiple mechanisms of Amazonian forest biomass losses in three dynamic global vegetation models under climate change David Galbraith, Peter E. Levy, Stephen Sitch, Chris Huntingford, Peter Cox, Mathew Williams and Patick Meir Shifts in plant respiration and carbon use efficiency at a large-scale drought experiment in the eastern Amazon D.B. Metcalfe, P. Meir, L.E.O.C. Aragão, R. Lobo-do-Vale, D. Galbraith, R.A. Fisher, M.M. Chaves, J.P. Maroco, A.C.L. da Costa, S.S. de Almeida et al.

Controls on declining carbon balance with leaf age among 10 woody species in Australian woodland: do leaves have zero daily net carbon balances when they die?

Peter B. Reich, Daniel S. Falster, David S. Ellsworth, Ian J. Wright, Mark Westoby, Jacek Oleksyn and Tali D. Lee In folio isotopic tracing demonstrates that nitrogen assimilation into glutamate is mostly independent from current CO2 assimilation in illuminated leaves of Brassica napus Paul P.G. Gauthier, Richard Bligny, Elizabeth Gout, Aline Mahé, Salvador Nogués, Michael Hodges and Guillaume Tcherkez Rapid changes in δ13C of ecosystem-respired CO2 after sunset are consistent with transient 13C enrichment of leaf respired CO2 Margaret M. Barbour, John E. Hunt, Naomi Kodama, Johannes Laubach, Tony M. McSeveny, Graeme N.D. Rogers, Guillaume G.B. Tcherkez and Lisa Wingate Photosythetic carbon isotope discrimination and its relationship to the carbon isotope signals of stem, soil and ecosystem respiration Lisa Wingate, Jérôme Ogée, Régis Burlett, Aledandre Bosc, Marion Devaux, John Grace, Denis Loustau and Arthur Gessler Seasonal patterns of carbon allocation to respiratory pools in 60-yr-old deciduous (Fagus sylvatica) and evergreen (Picea abies) trees assessed via whole-tree stable carbon isotope labelling Daniel Kuptz, Frank Fleischmann, Rainer Matyssek and Thorsten E.E. Grams Day-length effects on carbon stores for respiration of perennial ryegrass Christoph Andreas Lehmeier, Fernando Alfredo Lattanzi, Rud Schäufele and Hans Schnyder Root-derived CO2 efflux via xylem stream rivals soil CO2 efflux Doug. P Aubrey and Robert O. Teskey Antisense inhibition of enolase strongly limits the metabolism of aromatic amino acids, but has only minor effects on respiration in leaves of transgenic tobacco plants Lars M. Voll, Mohammad R. Hajirezaei, Cäcilia Czogalla-Peter, Wolfgang Lein, Mark Stitt, Uwe Sonnewald and Frederik Börnke Iron availability affects the function of mitochondria in cucumber roots Gianpiero Vigani, Dario Maffi and Graziano Zocchi

Turn the page to read the articles...

Introduction New Phytologist has a long history in publishing studies that enhance our understanding of the underlying mechanisms that regulate plant respiratory metabolism, and how environmental gradients impact on respiratory rates. Here, we build on this rich heritage of past respirationrelated research by highlighting recent papers from New Phytologist that further enhance our understanding of: (1) respiration-temperature interactions, both in non-thermogenic and thermogenic tissues; (2) how leaf respiratory metabolism differs in the light and darkness; (3) the importance of respiration for the carbon economy of individual plants and whole ecosystems; (4) sources of carbon used in above and below-ground respiratory metabolism; and, (5) factors regulating respiratory metabolism in plants.

Given the pivotal nature of respiration for plant growth/performance/survival, and importance of respiratory CO2 release for future concentrations of atmospheric CO2, it is vital that the scientific community form a better understanding of the key determinants of respiration, and how variable environments impact on respiratory functioning. The findings of the recent New Phytologist papers contained in this VSI are a substantive step forward in achieving the goal of establishing a holistic understanding of respiration–environment interactions.

In the heat of the night – alternative pathway respiration drives thermogenesis in Philodendron bipinnatifidum Rebecca E. Miller, Nicole M. Grant, Larry Giles, Miquel Ribas-Carbo, Joseph A. Berry, Jennifer R. Watling and Sharon A. Robinson Summary Author for correspondence: Rebecca E. Miller Tel: +61 3 99055217 Email: Rebecca.miller@monash.edu

New Phytologist (2010) 187: 941–956 doi: 10.1111/j.1469-8137.2010.03337.x

Key words: alternative oxidase, Araceae, diffusion limitation, Philodendron bipinnatifidum, plant thermogenesis, plant uncoupling proteins, stable isotope measurements of respiration.

• Philodendron bipinnatifidum inflorescences heat up to 42°C and thermoregulate. We investigated whether they generate heat via the cytochrome oxidase pathway uncoupled by uncoupling proteins (pUCPs), or the alternative oxidase (AOX).

• Contribution of AOX and pUCPs to heating in fertile (FM) and sterile (SM) male florets was determined using a combination of oxygen isotope discrimination, protein and substrate analyses.

• Both FM and SM florets thermoregulated independently for up to 30 h ex planta. In both floret types, AOX contributed > 90% of respiratory flux during peak heating. The AOX protein increased fivefold with the onset of thermogenesis in both floret types, whereas pUCP remained low throughout development. These data indicate that AOX is primarily responsible for heating, despite FM and SM florets potentially using different substrates, carbohydrates or lipids, respectively.

Measurements of discrimination between O2 isotopes in strongly respiring SM florets were affected by diffusion; however, this diffusional limitation was largely overcome using elevated O2.

• The first in vivo respiratory flux measurements in an arum show AOX contributes the bulk of heating in P. bipinnatifidum. Fine-scale regulation of AOX activity is post-translational. We also demonstrate that elevated O2 can aid measurement of respiratory pathway fluxes in dense tissues.

Temperature-sensitive alternative oxidase protein content and its relationship to floral reflectance in natural Plantago lanceolata populations Ann L. Umbach, Elizabeth P. Lacey and Scott J. Richter

Summary Author for correspondence: Elizabeth Lacey Tel: +1 336 334 4955 Fax: +1 336 334 5839 Email: eplacey@uncg.edu

New Phytologist (2009) 181: 662–671 doi: 10.1111/j.1469-8137.2008.02683.x

Key words: alternative oxidase (AOX), floral reflectance, flower, genetic variation, natural populations, phenotypic plasticity, temperature, thermal acclimatization.

• In many plant species, the alternative respiratory pathway consisting of alternative oxidase (AOX) is affected by growth temperature. The adaptive significance of this temperature-sensitivity is unresolved.

• Here, leaf and spike (flower cluster) AOX protein content and spike/floral reflectance of genotypes from European Plantago lanceolata populations found in regions differing in reproductive season temperatures were measured. Cloned genotypes grown at controlled warm and cool temperatures were used to assess the natural within- and between-population variation in AOX content, temperature-sensitive phenotypic plasticity in content, and the relationship between AOX and temperaturesensitive floral/spike reflectance.

• AOX content and plasticity were genetically variable. Leaf AOX content, although greater at cool temperature, was relatively low and not statistically different across populations. Spike AOX content was greater than in leaves. Spike AOX plasticity differed significantly among populations and climate-types and showed significant negative correlation with floral reflectance plasticity, which also varied among populations. Genotypes with more AOX at cool than at warm temperature had greater floral reflectance plasticity; genotypes with relatively more AOX at warm temperature had less floral reflectance plasticity.

• The data support the hypothesis that plasticity of AOX content in reproductive tissues is associated with long-term thermal acclimatization.

Leaf respiration and alternative oxidase in field-grown alpine grasses respond to natural changes in temperature and light Stephanie Y. Searle, Samuel Thomas, Kevin L. Griffin, Travis Horton, Ari Kornfeld, Dan Yakir, Vaughan Hurry and Matthew H. Turnbull Summary • We report the first investigation of changes in electron partitioning via the alternative respiratory pathway (AP) and alternative oxidase (AOX) protein abundance in field-grown plants and their role in seasonal acclimation of respiration.

• We sampled two alpine grasses native to New Zealand, Chionochloa rubra and Chionochloa pallens, from field sites of different altitudes, over 1 yr and also intensively over a 2-wk period.

New Phytologist (2011) 189: 1027–1039 • In both species, respiration acclimated to seasonal changes in temperature doi: 10.1111/j.1469-8137.2010.03557.x through changes in basal capacity (R ) but not temperature sensitivity (E ). In C. 10 0 pallens, acclimation of respiration may be associated with a higher AOX : cytochrome c oxidase (COX) protein abundance ratio. Oxygen isotope discrimination (D), which reflects relative changes in AP electron partitioning, correlated positively with Key words: acclimation, alternative oxidase (AOX), Chionochloa, daily integrated photosynthetically active radiation (PAR) in both cytochrome oxidase, leaf respiration, species over seasonal timescales. Respiratory parameters, the AOX : COX protein oxygen isotope discrimination, ratio and D were stable over a 2-wk period, during which significant temperature photosynthetically active radiation changes were experienced in the field.

(PAR), seasonal variation.

• We conclude that respiration in Chionochloa spp. acclimates strongly to seasonal, but not to short-term, temperature variation. Alternative oxidase appears to be involved in the plant response to both seasonal changes in temperature and daily changes in light, highlighting the complexity of the function of AOX in the field.

Author for correspondence: Stephanie Y. Searle Tel: + 64 3 348 5996 Email: sys15@student.canterbury.ac.nz

Research review Steps towards a mechanistic understanding of respiratory temperature responses

Author for correspondence: Jorg Kruse Tel: +49 (0) 761 203 8300 Fax: +49 (0) 761 203 8302 Email: joerg.kruse@ctp.uni-freiburg.de

Jörg Kruse, Heinz Rennenberg and Mark A. Adams

Summary New Phytologist (2011) 189: 659–677 doi: 10.1111/j.1469-8137.2010.03576.x

Key words: acclimatization, Arrhenius kinetics, Q10-model, respiration, temperature response.

Temperature crucially affects the speed of metabolic processes in poikilotherm organisms, including plants. The instantaneous temperature responses of O2-reduction and CO2-release can be approximated by Arrhenius kinetics, even though respiratory gas exchange of plants is the net effect of many constituent biochemical processes. Nonetheless, the classical Arrhenius equation must be modified to account for a dynamic response to measurement temperatures. We show that this dynamic response is readily explained by combining Arrhenius and Michaelis–Menten kinetics, as part of a fresh appraisal of metabolic interpretations of instantaneous temperature responses. In combination with recent experimental findings, we argue that control of mitochondrial electron flow is shared among cytochrome oxidase and alternative oxidase under in vivo conditions, and is continuously coordinated. In this way, upstream carbohydrate metabolism and downstream electron transport appear to be optimized according to the demand of ATP, TCA-cycle intermediates and anabolic reducing power under differing metabolic states. We provide a link to the ‘Growth and Maintenance Paradigm’ of respiration and argue that respiratory temperature responses can be used as a tool to probe metabolic states of plant tissue, such that we can learn more about the mechanisms that govern longer-term acclimatization responses of plant metabolism.

Acclimation of respiratory temperature responses in northern and southern populations of Pinus banksiana M.G. Tjoelker, J. Oleskyn, G. Lorenc-Plicinska and P.B. Reich

Summary Author for correspondence: Mark G. Tjoelker Tel: +1 979 845 8279 Fax: +1 979 845 6049 Email: m-tjoelker@tamu.edu

New Phytologist (2009) 181: 218–229 doi: 10.1111/j.1469-8137.2008.02624.x

Key words: adaptation, carbohydrates, climate change, jack pine (Pinus banksiana), nitrogen, Q10, respiration, temperature acclimation.

• Temperature acclimation of respiration may contribute to climatic adaptation and thus differ among populations from contrasting climates.

• Short-term temperature responses of foliar dark respiration were measured in 33-yr-old trees of jack pine (Pinus banksiana) in eight populations of wide-ranging origin (44–55°N) grown in a common garden at 46.7°N. It was tested whether seasonal adjustments in respiration and population differences in this regard resulted from changes in base respiration rate at 5°C (R5) or Q10 (temperature sensitivity) and covaried with nitrogen and soluble sugars.

• In all populations, acclimation was manifest primarily through shifts in R5 rather than altered Q10 R5 . was higher in cooler periods in late autumn and winter and lower in spring and summer, inversely tracking variation in ambient air temperature.

Overall, R5 covaried with sugars and not with nitrogen. Although acclimation was comparable among all populations, the observed seasonal ranges in R5 and Q10 were greater in populations originating from warmer than from colder sites.

Population differences in respiratory traits appeared associated with autumnal cold hardening.

• Common patterns of respiratory temperature acclimation among biogeographically diverse populations provide a basis for predicting respiratory carbon fluxes in a wide-ranging species.

Impacts of drought on leaf respiration in darkness and light in Eucalyptus saligna exposed to industrial-age atmospheric CO2 and growth temperature Gohar Ayub, Renee A. Smith, David T. Tissue and Owen K. Atkin

Summary • Our study assessed the impact of a wide range of industrial-age climate scenarios on leaf respiration (R) in Eucalyptus saligna.

• Well-watered or sustained drought-treated plants were grown in glasshouses differing in atmospheric CO2 concentration ([CO2]) (280, 400 and 640 µl l-1) and temperature (26 and 30°C). Rates of R in darkness (Rdark) and light (Rlight), photosynthesis (A) and related leaf traits (mass : area relationships, and nitrogen, phosphorus, starch and New Phytologist (2011) 190: 1003–1018 sugar concentrations) were measured. doi: 10.1111/j.1469-8137.2011.03673.x • Light inhibited R in all cases (R light < Rdark) (well-watered: 40%; drough-treated: 73%).

Growth [CO2] and temperature had little impact on area-based rates of Rdark or Rlight, with Rlight exhibiting minimal thermal acclimation. By contrast, sustained drought resulted in reduced Rdark, Rlight and A, with the inhibitory effect Key words: acclimation, drought, Eucalyptus, leaf respiration, of drought on A and Rlight (c. 50–70%) greater than that on Rdark (c. 15%). photosynthesis, subambient and Drought effects were fully reversible after watering. Variability in Rlight appeared to elevated atmospheric CO2, be dependent on the underlying rate of Rdark and associated Rubisco activity. temperature, water stress.

• Collectively, our data suggest that there is an asynchronous response of leaf carbon metabolism to drought, and a tighter coupling between Rlight and A than between Rdark and A, under both past and future climate scenarios. These findings have important implications for ecosystem ⁄ global models seeking to predict carbon cycling Author for correspondence: Owen Atkin Tel: +61 (0)2 6125 5046 Email: owen.atkin@anu.edu.au

Temperature dependence of respiration in roots colonized by arbuscular mycorrhizal fungi Owen K. Atkin, David Sherlock, Alastair H. Fitter, Susan Jarvis, John K. Hughes, Catherine Campbell, Vaughan Hurry and Angela Hodge Summary Author for correspondence: Angela Hodge Tel: +44 (0)1904 328562 Fax: +44 (0)1904 328564 Email: ah29@york.ac.uk

New Phytologist (2009) 182: 188–199 doi: 10.1111/j.1469-8137.2008.02727.x

Key words: acclimation, arbuscular mycorrhizal (AM) fungi, protein abundance, Q10, root respiration (R), temperature

• The arbuscular mycorrhizal (AM) symbiosis is ubiquitous, and the fungus represents a major pathway for carbon movement in the soil–plant system. Here, we investigated the impacts of AM colonization of Plantago lanceolata and temperature on the regulation of root respiration (R).

• Warm-grown AM plants exhibited higher rates of R than did nonAM plants, irrespective of root mass. AM plants exhibited higher maximal rates of R (Rmax– R measured in the presence of an uncoupler and exogenous substrate) and greater proportional use of Rmax as a result of increased energy demand and/or substrate supply. The higher R values exhibited by AM plants were not associated with higher maximal rates of cytochrome c oxidase (COX) or protein abundance of either the COX or the alternative oxidase.

• Arbuscular mycorrhizal colonization had no effect on the short-term temperature dependence (Q10) of R. Cold-acclimated nonAM plants exhibited higher rates of R than their warm-grown nonAM counterparts. By contrast, chilling had a negligible effect on R of AM-plants. Thus, AM plants exhibited less cold acclimation than their nonAM counterparts.

• Overall, these results highlight the way in which AM colonization alters the underlying components of respiratory metabolism and the response of root R to sustained changes in growth temperature.

Arbuscular mycorrhizal mycelial respiration in a moist tropical forest Andrew T. Nottingham, Benjamin L. Turner, Klaus Winter, Marcel G.A. van der Heijden and Edmund V.J. Tanner Summary Author for correspondence: Andrew T. Nottingham Tel: +44 (0) 1223 333900 Email: atn24@cam.ac.uk

New Phytologist (2010) 186: 957–967 doi: 10.1111/j.1469-8137.2010.03226.x

Key words: carbon cycle, fine roots, mycelia, mycorrhizas, Pseudobombax septenatum, soil CO2 efflux, soil microbes, tropical forest.

• Arbuscular mycorrhizal fungi (AMF) are widespread in tropical forests and represent a major sink of photosynthate, yet their contribution to soil respiration in such ecosystems remains unknown.

• Using in-growth mesocosms we measured AMF mycelial respiration in two separate experiments: (1) an experiment in a semi-evergreen moist tropical forest, and (2) an experiment with 6-m-tall Pseudobombax septenatum in 4.5-m3 containers, for which we also determined the dependence of AMF mycelial respiration on the supply of carbon from the plant using girdling and root-cutting treatments.

• In the forest, AMF mycelia respired carbon at a rate of 1.4 t ha-1 yr-1, which accounted for 14 ± 6% of total soil respiration and 26 ± 12% of root-derived respiration.

For P. septenatum, 40 ± 6% of root-derived respiration originated from AMF mycelia and carbon was respired < 4 h after its supply from roots.

• We conclude that arbuscular mycorrhizal mycelial respiration can be substantial in lowland tropical forests. As it is highly dependent on the recent supply of carbon from roots, a function of aboveground fixation, AMF mycelial respiration is therefore an important pathway of carbon flux from tropical forest trees to the atmosphere.

Multiple mechanisms of Amazonian forest biomass losses in three dynamic global vegetation models under climate change David Galbraith, Peter E. Levy, Stephen Sitch, Chris Huntingford, Peter Cox, Mathew Williams and Patick Meir Summary Author for correspondence: David Galbraith Tel: +44 (0) 131 445 8594 Email: darga@ceh.ac.uk

New Phytologist (2010) 187: 647–665 doi: 10.1111/j.1469-8137.2010.03350.x

Key words: Amazon ‘die-back’, Amazon drought, CO2 fertilization, dynamic global vegetation models (DGVMs), elevated temperatures, photosynthesis, plant respiration.

• The large-scale loss of Amazonian rainforest under some future climate scenarios has generally been considered to be driven by increased drying over Amazonia predicted by some general circulation models (GCMs). However, the importance of rainfall relative to other drivers has never been formally examined.

• Here, we conducted factorial simulations to ascertain the contributions of four environmental drivers (precipitation, temperature, humidity and CO2) to simulated changes in Amazonian vegetation carbon (Cveg), in three dynamic global vegetation models (DGVMs) forced with climate data based on HadCM3 for four SRES scenarios.

• Increased temperature was found to be more important than precipitation reduction in causing losses of Amazonian Cveg in two DGVMs (Hyland and TRIFFID), and as important as precipitation reduction in a third DGVM (LPJ). Increases in plant respiration, direct declines in photosynthesis and increases in vapour pressure deficit (VPD) all contributed to reduce Cveg under high temperature, but the contribution of each mechanism varied greatly across models. Rising CO2 mitigated much of the climate-driven biomass losses in the models.

• Additional work is required to constrain model behaviour with experimental data under conditions of high temperature and drought. Current models may be overly sensitive to long-term elevated temperatures as they do not account for physiological acclimation.

Shifts in plant respiration and carbon use efficiency at a large-scale drought experiment in the eastern Amazon D.B. Metcalfe, P. Meir, L.E.O.C. Aragão, R. Lobo-do-Vale, D. Galbraith, R.A. Fisher, M.M. Chaves, J.P. Maroco, A.C.L. da Costa, S.S. de Almeida et al.

Summary Author for correspondence: Daniel B. Metcalfe Tel.: + 44 1865 285182 Email: daniel.metcalfe@ouce.ox.ac.uk

New Phytologist (2010) 187: 608–621 doi: 10.1111/j.1469-8137.2010.03319.x

Key words: Amazon rain forest, carbon cycling, carbon dioxide, carbon use efficiency, drought, gross primary productivity, net primary productivity, partitioning.

• The effects of drought on the Amazon rainforest are potentially large but remain poorly understood. Here, carbon (C) cycling after 5 yr of a large-scale through-fall exclusion (TFE) experiment excluding about 50% of incident rainfall from an eastern Amazon rainforest was compared with a nearby control plot.

• Principal C stocks and fluxes were intensively measured in 2005. Additional minor components were either quantified in later site measurements or derived from the available literature.

• Total ecosystem respiration (Reco) and total plant C expenditure (PCE, the sum of net primary productivity (NPP) and autotrophic respiration (Rauto)), were elevated on the TFE plot relative to the control. The increase in PCE and Reco was mainly caused by a rise in Rauto from foliage and roots. Heterotrophic respiration did not differ substantially between plots. NPP was 2.4 ± 1.4 t C ha-1yr-1 lower on the TFE than the control. Ecosystem carbon use efficiency, the proportion of PCE invested in NPP, was lower in the TFE plot (0.24 ± 0.04) than in the control (0.32 ± 0.04).

• Drought caused by the TFE treatment appeared to drive fundamental shifts in ecosystem C cycling with potentially important consequences for long-term forest C storage.

Controls on declining carbon balance with leaf age among 10 woody species in Australian woodland: do leaves have zero daily net carbon balances when they die?

Peter B. Reich, Daniel S. Falster, David S. Ellsworth, Ian J. Wright, Mark Westoby, Jacek Oleksyn and Tali D. Lee Summary Author for correspondence: Peter B. Reich Tel: +1 612 624 4270 Email: preich@umn.edu

New Phytologist (2009) 183: 153–166 doi: 10.1111/j.1469-8137.2009.02824.x

Key words: Australia, carbon balance, leaf age, light, nitrogen, photosynthesis, respiration, woody species.

• Here, we evaluated how increased shading and declining net photosynthetic capacity regulate the decline in net carbon balance with increasing leaf age for 10 Australian woodland species. We also asked whether leaves at the age of their mean life-span have carbon balances that are positive, zero or negative.

• The net carbon balances of 2307 leaves on 53 branches of the 10 species were estimated. We assessed three-dimensional architecture, canopy openness, photosynthetic light response functions and dark respiration rate across leaf age sequences on all branches. We used YPLANT to estimate light interception and to model carbon balance along the leaf age sequences.

• As leaf age increased to the mean life-span, increasing shading and declining photosynthetic capacity each separately reduced daytime carbon gain by approximately 39% on average across species. Together, they reduced daytime carbon gain by 64% on average across species.

• At the age of their mean life-span, almost all leaves had positive daytime carbon balances. These per leaf carbon surpluses were of a similar magnitude to the estimated whole-plant respiratory costs per leaf. Thus, the results suggest that a whole-plant economic framework, including respiratory costs, may be useful in assessing controls on leaf longevity

In folio isotopic tracing demonstrates that nitrogen assimilation into glutamate is mostly independent from current CO2 assimilation in illuminated leaves of Brassica napus Paul P.G. Gauthier, Richard Bligny, Elizabeth Gout, Aline Mahé, Salvador Nogués, Michael Hodges and Guillaume Tcherkez Summary Author for correspondence: Paul Gauthier Tel: +33 1 69 15 33 79 Email: paul.gauthier@u-psud.fr

New Phytologist (2010) 185: 988–999 doi: 10.1111/j.1469-8137.2009.03130.x

Key words: day respiration, glutamate, isotopes, labelling, nitrogen assimilation

• Nitrogen assimilation in leaves requires primary NH2 acceptors that, in turn, originate from primary carbon metabolism. Respiratory metabolism is believed to provide such acceptors (such as 2-oxoglutarate), so that day respiration is commonly seen as a cornerstone for nitrogen assimilation into glutamate in illuminated leaves. However, both glycolysis and day respiratory CO2 evolution are known to be inhibited by light, thereby compromising the input of recent photosynthetic carbon for glutamate production.

• In this study, we carried out isotopic labelling experiments with 13 CO2 and 15 Nammonium nitrate on detached leaves of rapeseed (Brassica napus), and performed 13 C- and 15 N-nuclear magnetic resonance analyses.

• Our results indicated that the production of 13 C-glutamate and 13 C-glutamine under a 13 CO2 atmosphere was very weak, whereas 13 C-glutamate and 13 C-glutamine appeared in both the subsequent dark period and the next light period under a 12 CO2 atmosphere.

Consistently, the analysis of heteronuclear (13 C–15N) interactions within molecules indicated that most 15N-glutamate and 15 N-glutamine molecules were not 13 C labelled after 13 C ⁄ 15 N double labelling. That is, recent carbon atoms (i.e. 13C) were hardly incorporated into glutamate, but new glutamate molecules were synthesized, as evidenced by 15 N incorporation.

• We conclude that the remobilization of night-stored molecules plays a significant role in providing 2-oxoglutarate for glutamate synthesis in illuminated rapeseed leaves, and therefore the natural day : night cycle seems critical for nitrogen assimilation.

Rapid changes in δ13C of ecosystem-respired CO2 after sunset are consistent with transient 13C enrichment of leaf respired CO2 Margaret M. Barbour, John E. Hunt, Naomi Kodama, Johannes Laubach, Tony M. McSeveny, Graeme N.D. Rogers, Guillaume G.B. Tcherkez and Lisa Wingate Summary Author for correspondence: Margaret M. Barbour Tel: +61 2 9351 8884 Email: margaret.barbour@sydney.edu.au

New Phytologist (2011) 190: 990–1002 doi: 10.1111/j.1469-8137.2010.03635.x

Key words: carbon isotopes, lightenhanced dark respiration, net ecosystem exchange, photosynthesis, respiration.

• The CO2 respired by darkened, light-adapted, leaves is enriched in 13C during the first minutes, and this effect may be related to rapid changes in leaf respiratory biochemistry upon darkening. We hypothesized that this effect would be evident at the ecosystem scale.

• High temporal resolution measurements of the carbon isotope composition of ecosystem respiration were made over 28 diel periods in an abandoned temperate pasture, and were compared with leaf-level measurements at differing levels of pre-illumination.

• At the leaf level, CO2 respired by darkened leaves that had been preadapted to high light was strongly enriched in 13C, but such a 13C-enrichment rapidly declined over 60– 100 min. The 13C-enrichment was less pronounced when leaves were preadapted to low light. These leaf-level responses were mirrored at the ecosystem scale; after sunset following clear, sunny days respired CO2 was first 13C enriched,but the 13 C-enrichment rapidly declined over 60–100 min. Further, this response was less pronounced following cloudy days.

• We conclude that the dynamics of leaf respiratory isotopic signal caused variations in ecosystem-scale 12CO2 ⁄ 13CO2 exchange. Such rapid isotope kinetics should be considered when applying 13C-based techniques to elucidate ecosystem carbon cycling.

Photosynthetic carbon isotope discrimination and its relationship to the carbon isotope signals of stem, soil and ecosystem respiration Lisa Wingate, Jérôme Ogée, Régis Burlett, Aledandre Bosc, Marion Devaux, John Grace, Denis Loustau and Arthur Gessler Summary Author for correspondence: Lisa Wingate Tel: +44 (0)1223 330212 Email: l.wingate@ed.ac.uk

New Phytologist (2010) 188: 576–589 doi: 10.1111/j.1469-8137.2010.03384.x

Key words: 13CO2, autotrophic respiration, carbon isotopes, forests, maritime pine,photosynthesis, plant allocation, tuneable diode laser.

• Photosynthetic carbon (C) isotope discrimination ΔA) labels photosynthates (δA) and atmospheric CO2 (δa) with variable C isotope compositions during fluctuating environmental conditions. In this context, the C isotope composition of respired CO2 within ecosystems is often hypothesized to vary temporally with ΔA. • We investigated the relationship between ΔA and the C isotope signals from stem (δW), soil (δS) and ecosystem (δE) respired CO2 to environmental fluctuations, using novel tuneable diode laser absorption spectrometer instrumentation in a mature maritime pine forest.

• Broad seasonal changes in ΔA were reflected in δW, δS and δE However, respired .

CO2 signals had smaller short-term variations than ΔA and were offset and delayed by 2–10 d, indicating fractionation and isotopic mixing in a large C pool. Variations in δS did not follow ΔA at all times, especially during rainy periods and when there is a strong demand for C allocation above ground.

• It is likely that future isotope-enabled vegetation models will need to develop transfer functions that can account for these phenomena in order to interpret and predict the isotopic impact of biosphere gas exchange on the C isotope composition of atmospheric CO2.

Seasonal patterns of carbon allocation to respiratory pools in 60-yrold deciduous (Fagus sylvatica) and evergreen (Picea abies) trees assessed via whole-tree stable carbon isotope labeling Daniel Kuptz, Frank Fleischmann, Rainer Matyssek and Thorsten E.E. Grams

Summary Author for correspondence: Daniel Kuptz Tel: 0049 8161 71 4674 Email: kuptz@tum.de

New Phytologist (2011) doi: 10.1111/j.1469-8137.2011.03676.x

Key words: carbon allocation, Fagus sylvatica (European beech), growth (RG) and maintenance (RM) respiration, phloem sugars, Picea abies (Norway spruce), seasonality, stable carbon isotope labeling, trunk and coarse-root CO2 efflux.

• The CO2 efflux of adult trees is supplied by recent photosynthates and carbon (C) stores. The extent to which these C pools contribute to growth and maintenance respiration (RG and RM, respectively) remains obscure.

• Recent photosynthates of adult beech (Fagus sylvatica) and spruce (Picea abies) trees were labeled by exposing whole-tree canopies to 13C-depleted CO2. Label was applied three times during the year (in spring, early summer and late summer) and changes in the stable C isotope composition (δ13 C) of trunk and coarse-root CO2 efflux were quantified.

• Seasonal patterns in C translocation rate (CTR) and fractional contribution of label to CO2 efflux (FLabel-Max) were found. CTR was fastest during early summer.

In beech, FLabel-Max was lowest in spring and peaked in trunks during late summer (0.6 ± 0.1, mean ± SE), whereas no trend was observed in coarse roots. No seasonal dynamics in FLabel-Max were found in spruce.

• During spring, the RG of beech trunks was largely supplied by C stores. Recent photosynthates supplied growth in early summer and refilled C stores in late summer. In spruce, CO2 efflux was constantly supplied by a mixture of stored (c. 75%) and recent (c. 25%) C. The hypothesis that RG is exclusively supplied by recent photosynthates was rejected for both species.

Day-length effects on carbon stores for respiration of perennial ryegrass Christoph Andreas Lehmeier, Fernando Alfredo Lattanzi, Rud Schäufele and Hans Schnyder

Summary Author for correspondence: Christoph Andreas Lehmeier Tel: +49 8161 714136 Email: lehmeier@wzw.tum.de

New Phytologist (2010) 188: 719–725 doi: 10.1111/j.1469-8137.2010.03457.x

Key words: 13C labelling, allocation, compartmental analysis, day length, fructan, Lolium perenne (perennial ryegrass), respiration, sucrose.

• The mechanism controlling the use of stored carbon in respiration is poorly understood. Here, we explore if the reliance on stores as respiratory substrate depends on day length.

• Lolium perenne (perennial ryegrass) was grown in continuous light (275 µmol photons m2 -1) or in a 16 : 8 h day : night regime (425 µmol m -2 -1 during the photoperiod), with the s s same daily photosynthetic photon flux density (PPFD). Plants in stands were labelled with 13 CO : 12 CO for various time intervals. The rates and isotopic signatures of shoot- and 2 2 root-respired CO2 were measured after labelling, and water-soluble carbohydrates were determined in biomass. The tracer kinetics in respired CO2 was analysed with compartmental models to infer the sizes, half-lives and contributions of respiratory substrate pools.

• Stores were the main source for respiration in both treatments (c. 60% of all respired carbon). But, continuous light slowed the turnover (+270%) and increased the size (+160%) of the store relative to the 16 : 8 h day : night regime.

This effect corresponded with a greatly elevated fructan content. Yet, day length had no effect on sizes and half-lives of other pools serving respiration.

• We suggest that the residence time of respiratory carbon was strongly influenced by partitioning of carbon to fructan stores.

Root-derived CO2 efflux via xylem stream rivals soil CO2 efflux

Doug. P Aubrey and Robert O. Teskey

Summary Author for correspondence: Doug P. Aubrey Tel: +1 803 439 4886 Email: daubrey@uga.edu

New Phytologist (2009) 184: 35–40 doi: 10.1111/j.1469-8137.2009.02971.x

Key words: carbon allocation, carbon cycle, CO2 efflux, dissolved inorganic carbon, forests, respiration, roots, xylem transport.

• Respiration consumes a large portion of annual gross primary productivity in forest ecosystems and is dominated by belowground metabolism. Here, we present evidence of a previously unaccounted for internal CO2 flux of large magnitude from tree roots through stems. If this pattern is shown to persist over time and in other forests, it suggests that belowground respiration has been grossly underestimated.

• Using an experimental Populus deltoides plantation as a model system, we tested the hypothesis that a substantial portion of the CO2 released from belowground autotrophic respiration remains within tree root systems and is transported aboveground through the xylem stream rather than diffusing into the soil atmosphere.

• On a daily basis, the amount of CO2 that moved upward from the root system into the stem via the xylem stream (0.26 mol CO2 m−2d−1) rivalled that which diffused from the soil surface to the atmosphere (0.27 mol CO2 m−2d−1). We estimated that twice the amount of CO2 derived from belowground autotrophic respiration entered the xylem stream as diffused into the soil environment.

• Our observations indicate that belowground autotrophic respiration consumes substantially more carbohydrates than previously recognized and challenge the paradigm that all root-respired CO2 diffuses into the soil atmosphere.

Antisense inhibition of enolase strongly limits the metabolism of aromatic amino acids, but has only minor effects on respiration in leaves of transgenic tobacco plants Lars M. Voll, Mohammad R. Hajirezaei, Cäcilia Czogalla-Peter, Wolfgang Lein, Mark Stitt, Uwe Sonnewald and Frederik Börnke Summary • Enolase catalyses the reversible conversion of 2-phosphoglycerate and phosphoenolpyruvate in glycolysis. Phosphoenolpyruvate constitutes an important branch point in plant metabolism. It is converted to pyruvate by pyruvate kinase and organic acids by phosphoenolpyruvate carboxylase. Phosphoenolpyruvate also acts as a precursor for the synthesis of aromatic amino acids in plastids.

• Tobacco (Nicotiana tabacum) enolase antisense plants were analysed for New Phytologist (2009) 184: 607–618 changes in metabolite composition, respiration and photosynthetic parameters. doi: 10.1111/j.1469-8137.2009.02998.x • Antisense repression resulted in up to a 95% reduction in total enolase activity.

It also resulted in fundamental changes in foliar metabolism. Although 2-phosphoglycerate remained largely unaltered, there was a substantial decrease in phosphoenolpyruvate. The levels of aromatic amino acids and secondary phenylpropanoid Key words: amino acids, antisense, enolase, glycolysis, phosphoenolpyruvate. metabolites that are derived from these compounds decreased strongly, as did branched chain amino acids. The level of pyruvate was unaltered, as was the rate of respiration. There were substantial increases in tricarboxylic acid cycle intermediates, including a 16-fold increase in isocitrate, an increase in the total free amino acid content, including a 14-fold increase in asparagine and glutamine, and a 50% decrease in free sugars.

• We conclude that a decrease in enolase activity affects secondary pathways, such as the shikimate branch of amino acid biosynthesis, but does not inhibit the rate of respiration.

Author for correspondence: Frederik Bornke Tel: +49 9131 85 25239 Email: fboernke@biologie.unierlangen.de

Iron availability affects the function of mitochondria in cucumber roots Gianpiero Vigani, Dario Maffi and Graziano Zocchi

Summary Author for correspondence: Gianpiero Vigani Tel: +39 0250316534 Fax: +39 0250316521 Email: gianpiero.vigani@unimi.it

New Phytologist (2009) 182: 127–136 doi: 10.1111/j.1469-8137.2008.02747.x

Key words: citrate synthase, Cucumis sativus, Fe deficiency, mitochondria, respiratory chain.

• In Strategy-I-plants, iron (Fe) deficiency induces processes leading to increased Fe solubilization in the rhizosphere, including reduction by ferric reductases and active proton extrusion. These processes require active respiration to function. In this work we investigated the effect of Fe deficiency on respiratory activities of cucumber (Cucumis sativus) roots.

• We compared oxygen consumption rate and the activities of the respiratory chain complexes on purified mitochondria from roots grown in the presence or absence of Fe using biochemical and molecular approaches.

• Oxygen consumption rate in apex roots was increased under Fe deficiency that was mostly resistant to KCN and salycilichydroxamic acid (SHAM) inhibitors, indicating other oxygen-consuming reactions could be present. Indeed, enzyme assays revealed that lack of Fe induced a decrease in the activities of respiratory complexes that was proportional to the number of Fe atoms in each complex. A decrease of cyt c, Rieske and NAD9 proteins was also observed. Transmission electron microscopy (TEM) analysis showed that mitochondria undergo structural changes under Fe deficiency.

• Our data show that mitochondria and the electron transport chain are an important target of Fe limitation and that mitochondria modify their function to meet higher demands for organic acids while restricting the activity of enzymes with Fe cofactors.

Useful Links