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During the past decades, and notably after the Chernobyl accident, radioecology lost the vision and skills of its founders who were much inspired and involved in ecology and ecosystem science (Rhod...

International audience; In the Fall of 2016 a workshop was held which brought together over 50 scientists from the ecological and radio- logical fields to discuss feasibility and challenges of reintegrating ecosystem science into radioecology. There is a growing desire to incorporate attributes of ecosystem science into radiological risk assessment and radioecological research more generally, fueled by recent advances in quantification of emergent ecosystem at- tributes and the desire to accurately reflect impacts of radiological stressors upon ecosystem function. This paper is a synthesis of the discussions and consensus of the workshop participant's responses to three primary questions, which were: 1) How can ecosystem science support radiological risk assessment? 2) What ecosystem level endpoints potentially could be used for radiological risk assessment? and 3) What inference strategies and associated methods would be most appropriate to assess the effects of radionuclides on ecosystem structure and function? The consensus of the participants was that ecosystem science can and should support radiological risk assessment through the incorporation of quantitative metrics that reflect ecosystem functions which are sensi- tive to radiological contaminants. The participants also agreed that many such endpoints exit or are thought to exit and while many are used in ecological risk assessment currently, additional data need to be collected that link the causal mechanisms of radiological exposure to these endpoints. Finally, the participants agreed that ra- diological risk assessments must be designed and informed by rigorous statistical frameworks capable of reveal- ing the causal inference tying radiological exposure to the endpoints selected for measurement.

International audience; This consensus paper presents the results of a workshop held in Essen, Germany in September 2017, called to examine critically the current approach to radiological environmental protection. The meeting brought together participants from the field of low dose radiobiology and those working in radioecology. Both groups have a common aim of identifying radiation exposures and protecting populations and individuals from harmful effects of ionising radiation exposure, but rarely work closely together. A key question in radiobiology is to understand mechanisms triggered by low doses or dose rates, leading to adverse outcomes of individuals while in radioecology a key objective is to recognise when harm is occurring at the level of the ecosystem. The discussion provided a total of six strategic recommendations which would help to address these questions. © 2018 The Authors

This article presents the results of a workshop held in Stirling, Scotland in June 2018, called to examine critically the effects of low-dose ionising radiation on the ecosphere. The meeting brought together participants from the fields of low- and high-dose radiobiology and those working in radioecology to discuss the effects that low doses of radiation have on non-human biota. In particular, the shape of the low-dose response relationship and the extent to which the effects of low-dose and chronic exposure may be predicted from high dose rate exposures were discussed. It was concluded that high dose effects were not predictive of low dose effects. It followed that the tools presently available were deemed insufficient to reliably predict risk of low dose exposures in ecosystems. The workshop participants agreed on three major recommendations for a path forward. First, as treating radiation as a single or unique stressor was considered insufficient, the development of a multidisciplinary approach is suggested to address key concerns about multiple stressors in the ecosphere. Second, agreed definitions are needed to deal with the multiplicity of factors determining outcome to low dose exposures as a term can have different meanings in different disciplines. Third, appropriate tools need to be developed to deal with the different time, space and organisation level scales. These recommendations permit a more accurate picture of prospective risks. © 2018 The Author(s)

Despite the fact that the Chernobyl and Fukushima accidents have both stimulated research on the environmental impact of radiation, interpretations about the occurrence of ecological effects in the contaminated areas still do not converge. In an effort to improve the situation and progress toward better general scientific understanding of ecological impacts of radiation, reasons that may explain the disagreements and discrepancies are explored. The divergence in interpretations of the impacts from both nuclear accidents arises from differences in methodological and conceptual inference strategies (a cultural issue) more so than fundamental differences in the processes governing ecological harm. Improved integration of scientific communities that use different study approaches should be encouraged to better understand and monitor the determination of the ecological impacts of radiation. Integr Environ Assess Manag 2016;12:673-676. © 2016 SETAC.

SARNET (Severe Accident Research Network) was set up under the aegis of the Framework Programmes of the European Commission from 2004 to 2013 and coordinated by IRSN to perform R&D on severe accidents in water-cooled nuclear power plants. The network self-sustainability was achieved through integration mid-2013 in the NUGENIA European association devoted to R&D on fission technology of Generation II and III. The SARNET activities continue in the technical area “Severe accidents” through technical workshops, ranking of R&D priorities, improvements of severe accident codes, ERMSAR international conferences, and education and training courses. Six technical domains are addressed in this technical area: in-vessel corium/debris coolability, ex-vessel corium interactions and coolability, containment behaviour including hydrogen risk, source term released to the environment, impact of severe accidents on the environment and emergency management, and severe accident scenarios. The ranking of research priorities in the NUGENIA R&D roadmap that was published in 2015 underlined the need to focus efforts in the next years on the improvement of prevention of severe accidents and on the mitigation of their consequences, as highlighted by the Fukushima Dai-ichi accidents. Several current projects on mitigation of severe accident consequences in Euratom or NUGENIA frame are shortly described in this paper.

International audience; Radiation protection goals for ecological resources are focussed on ecological structures and functions at population-, community-, and ecosystem-levels. The current approach to radiation safety for non-human biota relies on organism-level endpoints, and as such is not aligned with the stated overarching protection goals of international agencies. Exposure to stressors can trigger non-linear changes in ecosystem structure and function that cannot be predicted from effects on individual organisms. From the ecological sciences, we know that important interactive dynamics related to such emergent properties determine the flows of goods and services in ecological systems that human societies rely upon. A previous Task Group of the IUR (International Union of Radioecology) has presented the rationale for adding an Ecosystem Approach to the suite of tools available to manage radiation safety. In this paper, we summarize the arguments for an Ecosystem Approach and identify next steps and challenges ahead pertaining to developing and implementing a practical Ecosystem Approach to complement organism-level endpoints currently used in radiation safety. © 2014 Elsevier Ltd.

International audience; [No abstract available]

International audience; During the past decades, many specialised networks have formed to meet specific radioecological objectives, whether regional or sectorial (purpose-oriented). Regional networks deal with an array of radioecological issues related to their territories. Examples include the South Pacific network of radioecologists, and the European network of excellence in radioecology. The latter is now part of the European platform for radiation protection. Sectorial networks are more problem-oriented, often with wider international representativeness, but restricted to one specific issue, (e.g. radioactive waste, low-level atmospheric contamination, modelling). All such networks, while often working in relative isolation, contribute to a flow of scientific information which, through United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR's) efforts of synthesis, feeds into the radiation protection frameworks of protecting humans and the environment. The IUR has therefore prompted a co-construction process aimed at improving worldwide harmonisation of radioecology networks. An initiative based on an initial set of 15 networks, now called the IUR FORUM, was launched in June 2014. The IUR Forum agreed to build a framework for improved coordination of scientific knowledge, integration and consensus development relative to environmental radioactivity. Three objectives have been collectively assigned to the IUR FORUM: (1) coordination, (2) global integration and construction of consensus and (3) maintenance of expertise. One particular achievement of the FORUM was an improved description and common understanding of the respective roles and functions of the various networks within the overall scene of radioecology R&D. It clarifies how the various networks assembled within the IUR FORUM interface with UNSCEAR and other international regulatory bodies (IAEA, ICRP), and how consensus on the assessment of risk is constructed. All these agencies interact with regional networks covering different geographical areas, and with other networks which address specific topics within radiation protection. After holding its first Consensus Symposium in 2015, examining the possible ecological impact of radiation from environmental contamination, the IUR FORUM continues its work towards improved radiation protection of humans and the environment. We welcome new members. © The Author 2016.

In order to be fully adequate, efficient, pertinent and demonstrative with respect to ecological risk, a system for environment protection against radiation requires an ecosystem approach. Starting from an historical analysis of the cultural context within which environment protection has evolved in the radiation protection community, and taking stock of the IAEA member states’ reluctance to implement it in international regulation, we revisit the strategic justification expressed at the origin and observe that the scoping was weak due to aiming at “filling a conceptual gap” and a “demonstration goal” rather than simply assessing/preventing ecological detriment per se. The system framework best currently achieved is biocentric and dominated by high levels of reductionism because recent compilations of literature upon which the operational methodology is constructed are largely restricted to biological effects of radiation observed at organism level. As such, this first methodology misses to address also ecological risk, the actual goal of environment protection that all now acknowledge. It is stressed that addressing ecological risk cannot be extrapolated or simply derived from this first methodology, and requires designing an ecosystem approach in addition. Several results and findings recently published corroborate this view towards a more ecocentric vision. The ecosystem approach provides a conceptual vision which integrates humans within the environment. It therefore brings a suitable basis to build on for addressing ecological risk, assessing how, and to which extent, the human and environment radiation protection systems could be integrated together, and relating ecological detriment to potential loss of ecosystem services.

After a period of scepticism about the future of radioecology due to post Chernobyl political trends and decisions, recent events (worldwide nuclear renaissance, Fukushima accident) demonstrate that the discipline is not only still alive but definitely needed, perhaps more than ever. However, given its long standing anthropocentric view over the environment, it has for a long time been bound exclusively to human radioprotection needs. It is argued that moving toward a more integrated eco-centric view over the environment is the clue for radioecology to reach full maturity as a stand-alone discipline, a movement which does not prevent continuing its contribution to feed human radioprotection.

Uptake of 137 Cs was measured in different agricultural plant species (beans, lettuce, barley and ryegrass) grown in 5 undisturbed soil monoliths covering major European soil types. The first cultivation was made three years after soil contamination and plants were grown during 3 successive years. The plant–soil 137 Cs transfer factors varied maximally 12-fold among soils and 35-fold among species when grown on the same soil. Single correlations between transfer factors and soil properties were found, but they varied widely with plant type and can hardly be used as a predictive tool because of the few soils used. The variation of 137 Cs concentrations in plants among soils was related to differences in soil solution 137 Cs and K concentrations, consistent with previous observations in hydroponics and pot trials. Absolute values of transfer factors could not be predicted based on a model validated for pot trials. The 137 Cs activity concentration in soil solution decreased significantly (11- to 250-fold) for most soils in the 1997–1999 period and is partly explained by decreasing K in soil solution. Transfer factors of lettuce showed both increasing and decreasing trends between 2 consecutive years depending on soil type. The trends could be explained by the variation in 137 Cs and K concentrations in soil solution. It is concluded that differences in 137 Cs transfer factors among soils and trends in transfer factors as a function of time can be explained from soil solution composition, as shown previously for pot trials, although absolute values of transfer factors could not be predicted.

International audience; The paper recently published by Mothersill and Seymour (Radiat Environ Biophys 2013, doi 10.1007/s00411-013-0472-y) is commented upon by emphasizing on the recommendation not to confound the fields of radiation protection and radiobiological science as a source of controversy. Instead, these authors are proposing a new vision which suggests novel lines of scientific investigations to be addressed. At the moment, these include moving beyond the conceptual approach of DNA alteration through energy deposition in cells, and exploring the striking parallel currently existing between the ongoing individual/population debate in radioecology and that for cells/tissues in radiobiology. These interesting issues are briefly discussed and supported. © 2013 Springer-Verlag Berlin Heidelberg.

Les activites industrielles et economiques font l'experience d'impacts qui s'averent nefastes, et qui parfois se revelent tardivement, rendant difficile ou illusoire la mise en oeuvre de mesures correctrices. On vise desormais une meilleure capacite d'anticipation dans le but de promouvoir un developpement qui soit "durable", c'est-a-dire s'attachant a equilibrer l'innovation technologique et la maitrise des risques afferents. Ainsi, on realise aujourd'hui toute la portee des relations que l'homme entretient, a toujours entretenu, et devra encore entretenir avec l'environnement dans lequel son espece evolue, et a quel point sa sante se trouve liee a celle de l'environnement. C'est ce contexte general qui sollicite aujourd'hui la radioprotection vers une prise en compte explicite des especes vivantes non humaines. La Commission Internationale de Protection Radiologique entreprend donc une reevaluation de sa position anterieure selon laquelle proteger l'homme assurait implicitement une protection adequate des populations d'autres etres vivants.

Plant uptake of radiocaesium from soil is an important pathway for the entry of this pollutant into the human food chain and so contributes to any assessment of the radiation dose following contamination. Large differences in soil–plant transfer factors have been reported for plant species grown on the same soils. Few studies have attempted to distinguish between differences in root uptake and root-to-shoot translocation. We have investigated the root uptake of radiocaesium from artificially contaminated soils and the subsequent translocation to shoots for various plant species grown on three agricultural soils. The effects of short contact times and potassium starvation or enrichment have been studied. The Cs adsorption properties of rhizosphere soils have been compared with those of the initial soils. The proportion of activity removed from soil is largely soil dependent. Root uptake properties have less effect, but appear to be species determined, and not influenced by soil properties. Differences in soil-to-shoot transfer factor arise from species-dependent differences in root-to-shoot translocation. Root-to-shoot activity ratios are not soil dependent. There was little effect of soil potassium status. Root action slightly enhanced Cs adsorption on one soil, probably due to mineral weathering associated with the release of nonexchangeable potassium.

After the release of radionuclides into the environment it is important to be able to readily identify major routes of radiation exposure, the most highly exposed individuals or populations and the geographical areas of most concern. There have been significant recent improvements in our capability to estimate spatial variation in the environmental behaviour of radionuclides through better understanding of the underlying processes and an ability to spatially apply this knowledge by integrating relevant spatial information in the form of digital data sets using geographical information systems. Thus, it is now possible to refine the estimation of spatial variation in radiation exposure, both for routine releases and in accident situations. Within a recent EC-funded concerted action (the Radioecological Sensitivity Forum), there has been a renewed consideration of the concept of radioecological sensitivity with a particular focus on identifying sensitive areas as well as processes and communities. The concept should be relevant for both terrestrial and aquatic ecosystems, and might even be applied for consideration of doses to biota, although the current focus has been restricted to a consideration of human exposure. The conclusions of the action are outlined, considering the potential usefulness of the concept, and methods by which it can be applied. A framework for the estimation of radioecological sensitivity is proposed and the various measures by which it can be considered, including (i) aggregated transfer coefficients, (ii) action loads, (iii) fluxes and (iv) individual exposure of humans are discussed. The importance of spatial and temporal consideration of each of these outputs is emphasized.

There is a present consensus in that environment radioprotection is essentially to deal with chronic multiple exposures to low dose rates. In terms of protection, man and the environment are not similar in nature in that the environment is not equivalent to a single species community to be protected. The immediate question which arises therefore is : what do we want to protect, or what do we mean by the environment ? It is proposed that the keyword here is the "ecosystem", i.e. a complex-organized self-sustaining living entity to which man survival is fully subordinated. This leads to a new conceptual approach which also evolves from the growing public "feeling" (not yet appropriately substantiated in scientific terms, however) that if the environment is properly protected, then man would not be harmed. Along this line, the position of man with respect to the environment is to be reconsidered. As an inherent part of it, he is both capable of promoting substantial change of its structure and function, but also remains fully subordinated to the life support function that it hosts. In line with this conceptual view, this paper suggests an innovative approach designed around closed artificial ecosystems, as simplified reference models prone to support experimental investigations on chronic low-dose effects in controlled conditions.

There is currently a revitalized concern about the potential impact of ionizing radiation on the environment that calls for the construction of a system ensunng an adequate radioprotection of the non-human biota and their associated biotopes. This paper first sets the context of the problem hoth, with respect to the general phuosophy of environmental protection as a whole, but also with respect to the consideration of the environment achieved so far in the purpose of human radioprotection. The current accumulated knowledge on the effects of ionizing radiation to biota (fauna and flora) is then briefly reviewed, encompassing effects at individual and community/ecosystem level, situations of acute and chronic exposure to high and low doses, finally leading to the identification of the mosi critical gaps in scientific knowledge: effects of mixed low dose rates in chronic exposure to communities and ecosystems. The most significant current international efforts towards the identification of environmental radioprotection critena and standards are finally presented along with some relevant national examples.

In order to draw the attention of EEIU and IUR members, as well as others interested in the ecological/envi- ronmental aspects of radioactivity as related to ethics, science and politics, ESEP presents the key IUR Statement Protection of the environment in the 21st century: radiation protection of the biosphere including humankind (Brechignac et al. 2003), which is currently in press with the Journal of Environmental Radioactivity. More information about the IUR is available at www.iur-uir.org.

The incident at the Fukushima Daiichi nuclear power plant, resulting from the powerful earthquake and tsunami that struck the northeastern coast of Japan in March 2011, reminds humankind of the powerful natural forces that shape our world. This article calls for a new ecocentric approach to human interaction with the environment, with particular reference to the environmental consequences of radiation. Integr Environ Assess Manag 2011;7:409–410. © 2011 SETAC

This brief commentary summarizes the views of a working group assembled by the International Union of Radioecology to advance the approaches used to evaluate effects of radioactive materials in the environment. The key message in both the research needs and the recommendations for management of radioactive materials centers around the need to adopt an ecocentric approach that recognizes the interconnectedness of biota, including humans, and ecological processes. © 2011 SETAC.

The system of radiological protection of the environment that is currently under development is one contribution to the general need to adequately protect the environment against stress. Dominated by operational goals, it emphasizes conceptual and methodological approaches that are readily accessible today: reference organisms supported by individual-based traditional ecotoxicological data. Whilst there are immediate advantages to this approach (pragmatism, consistency with other approaches in use for man and biota), there are also clear limitations, especially in a longer run perspective, that need to be acknowledged and further considered. One can mention a few: uncertainties generated by the need for various extrapolations (from lower to higher levels of biological organisation, ...), various features missed such as potential ecological impact through impairment of ecosystem processes, trans-generational impacts as mediated through genomic instability, indirect effects mediated through trophic interactions or disruption of ecological balances,... Such limitations have already been faced in other fields of environmental protection against other stressors, pushing a number of environment professionals to assign stronger emphasis on more systemic approaches. This review discusses the advantages and limitations of the current approach designed for the radiological protection of non-human biota in the broader context of environment protection as a whole, with especial reference to upcoming trends and evolutions. This leads in particular to advocating the need to boost scientific and methodological approaches featuring the ecosystem concept as a mean to access a unified goal of protection: preserving life sustainability through protection of ecosystem structure and functioning. © 2009 Elsevier Ltd. All rights reserved.

Born in the fifties together with the emergence of the nuclear technologies, radioecology is a scientific discipline that primarily addresses environmental issues relevant to radioprotection. With a current membership of nearly 600 worldwide, the International Union of Radioecology was founded in the seventies as a non-governmental knowing society dedicated to the development and the promotion of this discipline. The scientific directions taken in Radioecology have been drastically influenced in the past by the Chernobyl accident, which forced a focus on environmental transfers through the environment to feed human radioprotection needs. Currently, a profound evolution is underway towards more ecological effects research and studies, under the driving pressure of the raise of society's concern on environmental issues and the concomitant re-boost of nuclear industry to face global warming and the future energetic demands. The IUR plays a central role within this evolution which is described here in more details along a description of its four major tools of action: dedicated task groups; workshops, seminars and conferences; training courses; web site tool for information and communication. Finally, together with the recent election of a new Board of Council to manage the Union, the main lines of the new strategic plan for the coming years are given. © 2008 EDP Sciences.

Stimulated by the apparition of large-scale environmental problems, the protection of the environment is becoming increasingly prominent within current concerns of human societies. Industrial and economical activities are experiencing detrimental impacts, which sometimes only become apparent after some delay, making it difficult or illusory to set corrective measures. Hence, a better capacity for anticipation needs to be targeted with a concomitant emphasis on regulation efforts to promote “sustainable development”, where there is a balance achieved between technological innovation and the potential for mastering the associated environmental risk.Since 2000, the ICRP has therefore worked at constructing a general framework for the radiological protection of non-human biota which is currently based on 4 main elements: 1) an approach channelled through the definition of “reference organisms” to circumvent the difficulty of tackling the overall biodiversity of life forms, and the variety of their life spans, habitats, and metabolisms, 2) units and reference dosimetry models scaled to these reference organisms to be able to estimate radiation doses received by various biota, 3) a set of endpoints that would both ensure fulfilling the protection goals, and be accessible to quantification, and 4) a scale of risk based on the best interpretation of the information available on dose-effects relationships at the level of individuals. These concepts will be reviewed and discussed.

This paper discusses the current approaches to environmental protection from ionising radiation from an ecological perspective, highlighting the need to understand fully what we are trying to protect. Ecologically relevant endpoints for environmental protection are discussed along with the need to integrate protection from ionising radiation with the approaches adopted for non-radioactive contaminants. A possible integrated assessment approach is outlined.

The development of a system capable of ensuring adequate protection of the environment from the harmful effects of ionising radiation is at present particularly debated. This need comes both from a restrictive consideration of the environment in the so far existing system for human radioprotection, and the planetary-wide growing concerns about man's technogenic influence on his environment which have yielded 'sustainability' and 'precaution' as guiding principles for environmental protection. Whilst evolving from the field of human radioprotection, the radioprotection of the environment needs to be discussed in a wider perspective, with particular emphasis on the most advanced concepts which emerge from the efforts to deriving improved approaches to Ecological Risk Assessment. For the sake of protection, the environment is traditionally addressed through its biota since these are the sensitive components of ecosystems. Similarities between man and biotas reflect the ubiquitous mechanistic effects of radiation on life which disrupt molecules. However, important differences also arise in a number of perspectives, from the large spectrum of different species of biotas to their hierarchical self-organisation as interacting populations within ecosystems. Altogether, these aspects are prone to promote complex arrays of different responses to stress which lie beyond the scope of human radioprotection due to its focus on individuals of a single species. By means of selected illustrations, this paper reviews and discusses the current challenges faced in proper identification of measurable effect endpoints (stochastic/deterministic, individual/population- or ecosystem-relevant), dose limits in chronic exposure (or levels of concern), and their consideration according to radiation type (RBE) and interactions with other contaminants (synergies/antagonisms) which represent critical gaps in knowledge. The system of human radioprotection has conceptually been targeted at limiting cancer induction (stochastic) in human individuals, whereas the current approach in radioprotection of biota targets reproductive success (deterministic) and cytogenetic effects, thought to have the highest significance at population and ecosystem levels. The focus on individuals in a bottom-up approach, due to the ease with which it may be quantified, has prompted the development of current ecotoxicological methods as a scientific foundation for environmental protection regulation. However, the most recent ecological theories, which emphasise on complex systems as a key to modern ecological understanding, call for the additional consideration of more holistic, top-down, approaches. Critically, dose-effect relationships of the subsystem components may lose their predictive ability at the system level.

Chemical availability of 137Cs and 90Sr was determined in four undisturbed soils in a lysimeter study three and four years after deposition to the soil surface. The study was part of a larger project on radionuclide soil-plant interactions under well-defined conditions. The soil types were loam, silt loam, sandy loam and loamy sand, and were representatives of important European soil and climatic conditions. The lysimeters were installed in greenhouses with climatic and hydrological control, and were contaminated with 137Cs and 90Sr in an aerosol mixture simulating fallout from a nuclear accident. Soil samples were taken from several depths in each soil in 1997 and 1998 and the samples were sequentially extracted with H2O, NH4Ac, NH2OH.HCl, H2O2 and HNO3. Extractability of 137Cs decreased in the order: HNO3 > R-esidual > or = NH4Ac > H2O2 > or = NH2OH.HCl > or = H2O. More than 80% was found in the acid digestible or residual fractions, and 11-17% in labile fractions. Soil type differences were small. Extractability of 90Sr decreased in the order: NH4Ac > NH2OH.HCl > HNO3 > H2O2 approximately H2O. 31-58% was found in easily available fractions. Differences between soil types were quite small. The results suggest that availability of 137Cs for plant uptake and migration is low, whereas availability of 90Sr is rather high.

With an experimental system using mass spectrometry techniques and infra-red gas analysis of CO2 developed for aquatic plants, we studied the responses to various light intensities and CO2 concentrations of photosynthesis and O2 uptake of the red macroalga Chondrus crispus S. The CO2 exchange resistance at air-water interface which could limit the photosynthesis was experimentally measured. It allowed the calculation of the free dissolved CO2 concentration. The response to light showed a small O2 uptake (37% of net photosynthesis in standard conditions) compared to C3 plants; it was always higher than dark respiration and probably included a photoindependent part. The response to CO2 showed: (a) an O2 uptake relatively insensitive to CO2 concentration and not completely inhibited with high CO2, (b) a general inhibition of gas exchanges below 130 microliters CO2 per liter (gas phase), (c) an absence of an inverse relationship between O2 and CO2 uptakes, and (d) a low apparent Km of photosynthesis for free CO2 (1 micromolar). These results suggest that O2 uptake in the light is the sum of different oxidation processes such as the glycolate pathway, the Mehler reaction, and mitochondrial respiration. The high affinity for CO2 is discussed in relation to the use of HCO3− and/or the internal CO2 accumulation.

With an experimental system using mass spectrometry techniques and infra-red gas analysis of CO 2 developed for aquatic plants, we studied the responses to various light intensities and CO 2 concentrations of photosynthesis and O 2 uptake of the red macroalga Chondrus crispus S. The CO 2 exchange resistance at air-water interface which could limit the photosynthesis was experimentally measured. It allowed the calculation of the free dissolved CO 2 concentration. The response to light showed a small O 2 uptake (37% of net photosynthesis in standard conditions) compared to C 3 plants; it was always higher than dark respiration and probably included a photoindependent part. The response to CO 2 showed: (a) an O 2 uptake relatively insensitive to CO 2 concentration and not completely inhibited with high CO 2 , (b) a general inhibition of gas exchanges below 130 microliters CO 2 per liter (gas phase), (c) an absence of an inverse relationship between O 2 and CO 2 uptakes, and (d) a low apparent K m of photosynthesis for free CO 2 (1 micromolar). These results suggest that O 2 uptake in the light is the sum of different oxidation processes such as the glycolate pathway, the Mehler reaction, and mitochondrial respiration. The high affinity for CO 2 is discussed in relation to the use of HCO 3 − and/or the internal CO 2 accumulation.

The rate of HCO(3) (-) uptake by the red macroalga Chondrus crispus has been investigated. Unbalanced concentrations of free CO(2) and HCO(3) (-), generated by the photosynthetic activity, were detected in steady state conditions by using an exchange column apparatus linked to an assimilation chamber. Observing the variations of this gradient as influenced by the time of seawater transit from the assimilation chamber towards the column allowed an experimental determination of: (a) the actual gradient created by the photosynthetic activity, (b) the rate constant of the chemical conversion of free CO(2) to HCO(3) (-). With a value of 0.115 per second at pH 8.92, this rate constant was in good agreement with a previous estimation. By using a simple model, we show that the photosynthetic rate of HCO(3) (-) consumption can be estimated by the product of the actual gradient and the rate constant. In the conditions of the experiments reported here, this rate represented more than 90% of the whole photosynthetic flux.

An experimental system consisting of a gas exchange column linked to an assimilation chamber has been developed to record continuously the free dissolved CO(2) concentration in seawater containing marine plants. From experiments performed on the red macroalga Chondrus crispus (Rhodophyta, Gigartinales), this measurement is in agreement with the free CO(2) concentration calculated from the resistance to CO(2) exchanges in a biphasic system (gas and liquid) as earlier reported. The response time of this apparatus is short enough to detect, in conditions of constant pH, a photosynthesis-caused gradient between free CO(2) and HCO(3) (-) pools which half-equilibrates in 25 seconds. Abolished by carbonic anhydrase, the magnitude of this gradient increases with decreasing time of seawater transit from the chamber to the column apparatus. But its maximum magnitude (0.35 micromolar CO(2)) is negligible compared to the difference between air and free CO(2) (11.4 micromolar CO(2)). This illustrates the extent of the physical limiting-step occurring at the air-water interface when inorganic carbon consumption in seawater is balanced by dissolving gaseous CO(2). The direction of this small free CO(2)/HCO(3) (-) gradient indicates that HCO(3) (-) is consumed during photosynthesis.

An O(2) electrode system with a specially designed chamber for ;whorl' cell complexes of Chara corallina was used to study the combined effects of inorganic carbon and O(2) concentrations on photosynthetic O(2) evolution. At pH = 5.5 and 20% O(2), cells grown in HCO(3) (-) medium (low CO(2), pH >/= 9.0) exhibited a higher affinity for external CO(2) (K((1/2))(CO(2)) = 40 +/- 6 micromolar) than the cells grown for at least 24 hours in high-CO(2) medium (pH = 6.5), (K((1/2))(CO(2)) = 94 +/- 16 micromolar). With O(2)

Whether photorespiration occurs in marine algae is still very controversial for two main reasons. First, the methods used for its detection are often indirect (O2 sensitivity of photosynthesis), or known to underestimate the process (14CO2 method). In addition, the nature of the external carbon form acquired for photosynthesis (CO2 and/or HCO 3 - ) is still thought to be quite variable among marine species, and is strongly dependent upon the experimental conditions. Since I) the HCO 3 - concentration in seawater is about 200 times greater than the free CO2 concentration, 2) its uptake might drive putative internal DIC accumulation, and 3) the O2 and CO2 substrates interact on Rubisco in a competitive manner, it appears essential to know which DIC form is absorbed in order to understand the photorespiratory phenomenon in these organisms.