Interactions mitochondries / chloroplastes au cours de la photosynthèse et de la réponse aux stress chez Nicotiana sylvestris.

The acclimation of photosynthesis to growth light intensity and abiotic stress responses were investigated in a complex I deficient mitochondrial mutant of Nicotiana sylvestris (CMSII) cultivated at 80 (LL) and 350 (HL) µmol PAR m-2 s-1. Under different light levels, 380 ppm CO2 and 21% O2, HL grown CMSII leaves showed lower photosynthetic activity and lower initial Rubisco and SPS activities as compared to HL grown WT leaves. These differences disappear after an exposure to an atmosphere either enriched in CO2 and/or depleted in O2, or when plants are grown under low-light growth condition. Our results showed a lower leaf internal conductance for CO2 which limits CO2 supply to the carboxylase activity of Rubisco. This could explain the lower net CO2 assimilation rates, the lower initial Rubisco activity and higher rates of photorespiration in HL grown CMSII compared to WT. Gas exchanges, chlorophyll fluorescence, chlorophyll content and conductivity measurements indicated a lower sensitivity of CMSII leaves to MV compared to WT leaves grown in the same conditions, in particular for LL grown plants. This higher tolerance may be caused by an higher efficiency of antioxidative protection (as indicated by SOD and CAT activities), a lower uptake of the MV and an higher cyclic electron transport around PS I in CMSII leaves. Connections between CMSII mutation and its effects on internal CO2 conductance and antioxidative protection are briefly discussed.L'acclimatation de la photosynthèse à différentes intensités lumineuses de croissance ainsi que les réponses à différents stress abiotiques ont été étudiées chez un mutant CMS de Nicotiana sylvestris dépourvu de complexe I de la chaîne mitochondriale de transport des électrons et cultivé sous deux intensités lumineuses : 80 (CMS 80) et 350 µmoles PAR m-2 s-1 (CMS 350). Les plantes CMS 350 présentent, sous différentes intensités lumineuses, 380 ppm de CO2 et 21% d'O2, une plus faible assimilation nette de CO2, de plus faibles activiteés initiales Rubisco et Saccharose phosphate synthase par rapport aux plantes WT cultivées dans les mêmes conditions. Ces différences disparaissent soit lorsque les plantes sont soumises à de fortes concentrations en CO2 et/ou une atmosphère appauvrie en O2, soit lorsqu'elles sont cultivées sous faible éclairement. Nos résultats ont montré une conductance interne plus faible chez les plantes CMS 350 par rapport aux plantes WT 350, limitant l'apport de CO2 pour l'activité carboxylase de la Rubisco. Ceci pourrait expliquer le défaut d'assimilation nette de CO2, les plus faibles niveaux d'activation de l'enzyme et une photorespiration accrue chez ces plantes CMS 350 par rapport aux plantes WT. Les mesures d'échanges gazeux, de fluorescence chlorophyllienne, de contenu en chlorophylles, de destruction des membranes cellulaires ont indiqué une plus faible sensibilité des plantes CMSII par rapport aux plantes WT, ceci de façon plus marquée lorsque les plantes sont cultivées sous faible éclairement. Cette plus forte tolérance des plantes CMSII par rapport aux plantes WT a pu être associée à la combinaison d'un système de protection plus efficace, d'une plus faible diffusion du méthylviologène à l'intérieur des feuilles voire d'un transport cyclique accru autour du photosystème I. Les rapports entre la mutation et les effets sur la conductance interne vis-à-vis de la diffusion du CO2 ou la protection antioxydante sont brièvement discutés

Interactions mitochondries / chloroplastes au cours de la photosynthèse et de la réponse aux stress chez Nicotiana sylvestris

L'acclimatation de la photosynthèse à différentes intensités lumineuses de croissance ainsi que les réponses à différents stress abiotiques ont été étudiées chez un mutant CMS de Nicotiana sylvestris dépourvu de complexe I de la chaîne mitochondriale de transport des électrons et cultivé sous deux intensités lumineuses : 80 (CMS 80) et 350 moles PAR m-2 s-1 (CMS 350). Les plantes CMS 350 présentent, sous différentes intensités lumineuses, 380 ppm de CO2 et 21% d'O2, une plus faible assimilation nette de CO2, de plus faibles activités initiales Rubisco et Saccharose phosphate synthase par rapport aux plantes WT cultivées dans les mêmes conditions. Ces différences disparaissent soit lorsque les plantes sont soumises à de fortes concentrations en CO2 et/ou une atmosphère appauvrie en O2, soit lorsqu'elles sont cultivées sous faible éclairement. Nos résultats ont montré une conductance interne plus faible chez les plantes CMS 350 par rapport aux plantes WT 350, limitant l'apport de CO2 pour l'activité carboxylase de la Rubisco. Ceci pourrait expliquer le défaut d'assimilation nette de CO2, les plus faibles niveaux d'activation de l'enzyme et une photorespiration accrue chez ces plantes CMS 350 par rapport aux plantes WT.Les mesures d'échanges gazeux, de fluorescence chlorophyllienne, de contenu en chlorophylles, de destruction des membranes cellulaires ont indiqué une plus faible sensibilité des plantes CMSII par rapport aux plantes WT, ceci de façon plus marquée lorsque les plantes sont cultivées sous faible éclairement. Cette plus forte tolérance des plantes CMSII par rapport aux plantes WT a pu être associée à la combinaison d'un système de protection plus efficace, d'une plus faible diffusion du méthylviologène à l'intérieur des feuilles voire d'un transport cyclique accru autour du photosystème I.Les rapports entre la mutation et les effets sur la conductance interne vis-à-vis de la diffusion du CO2 ou la protection antioxydante sont brièvement discutés.The acclimation of photosynthesis to growth light intensity and abiotic stress responses were investigated in a complex I deficient mitochondrial mutant of Nicotiana sylvestris (CMSII) cultivated at 80 (LL) and 350 (HL) mol PAR m-2 s-1. Under different light levels, 380 ppm CO2 and 21% O2, HL grown CMSII leaves showed lower photosynthetic activity and lower initial Rubisco and SPS activities as compared to HL grown WT leaves. These differences disappear after an exposure to an atmosphere either enriched in CO2 and/or depleted in O2, or when plants are grown under low-light growth condition. Our results showed a lower leaf internal conductance for CO2 which limits CO2 supply to the carboxylase activity of Rubisco. This could explain the lower net CO2 assimilation rates, the lower initial Rubisco activity and higher rates of photorespiration in HL grown CMSII compared to WT. Gas exchanges, chlorophyll fluorescence, chlorophyll content and conductivity measurements indicated a lower sensitivity of CMSII leaves to MV compared to WT leaves grown in the same conditions, in particular for LL grown plants. This higher tolerance may be caused by an higher efficiency of antioxidative protection (as indicated by SOD and CAT activities), a lower uptake of the MV and an higher cyclic electron transport around PS I in CMSII leaves.Connections between CMSII mutation and its effects on internal CO2 conductance and antioxidative protection are briefly discussed.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Mitochondria – Chloroplast interactions : Acclimation of a Nicotiana sylvestris mitochondrial mutant to growth light intensity.

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Phénologie des bourgeons de l’Aulne et du Peuplier en plantations mélangées forestière et agroforestière

La durée de la saison de végétation est importante à considérer puisqu’elle va directement impacter l’absorption photosynthétique saisonnière qui va conditionner la croissance des arbres. Cette étude avait pour objectifs de proposer une échelle de notation visuelle pour les processus de débourrement et d’entrée en dormance chez l’aulne glutineux et de déterminer l’effet de l’association de l’aulne avec le peuplier hybride, entre eux et avec des cultures herbacées, sur la durée de la saison de végétation des espèces ligneuses, comparativement à leurs monocultures respectives. Bien que la durée de la saison de végétation n’était pas significativement différente entre les arbres en mélange et leurs monocultures respectives, les aulnes agroforestiers ont eu tendance à débourrer plus tard et à entrer en dormance plus tôt, tandis que le contraire a été observé pour les peupliers agroforestiers. Messages clés • Le mélange d’espèces n’a pas eu d’influence sur la phénologie du bourgeon de l’Aulne et du Peuplier. • Les Aulnes agroforestiers ont eu tendance à débourrer plus tard et à entrer en dormance plus tôt par rapport à leur monoculture. • Les Peupliers agroforestiers ont eu tendance à débourrer plus tôt et à entrer en dormance plus tard par rapport à leur monoculture

Sphagnum physiological responses to elevated temperature, nitrogen, CO2 and low moisture in laboratory and in situ microhabitats: a review

International audienceSphagnum mosses are considered peatland engineers because of their ability to create conditions inducing carbon accumulation. Here, we report on a review of the effects of four environmental variables (elevated temperature, N and CO2 and reduced moisture) on the capitulum biomass, length increment, respiration, photosynthetic capability, N and P exchange and content of the 3 most studied Sphagnum subgenera (Acutifolia, Cuspidata, Sphagnum). Overall, we observe that, when compared to in situ experiments, laboratory experiments tend to exacerbate length increments and underestimate maximum photosynthesis in most of the studies inventoried. This review underscores some differences among results that can be associated with the used of different protocols (e.g. exposure time, instrumental analysis). Studies that investigated the impact of elevated temperature (2-5 degrees C) on Sphagnum reveal an increase in length, respiration and photosynthesis regardless of the experimental conditions and subgenus. Elevated N (3-23 g Nm(-2)y(-1)) on the other hand appears to reduce the length increment but had contrasting effects on photosynthesis. Some divergent responses are found with Cuspidata species because of their tolerance to high doses of N. Low moisture reduces the length increment and photosynthesis of species of the Cuspidata and Sphagnum subgenera but has different effects on species of the Acutifolia subgenus, which are relatively tolerant to water fluctuations. Responses to elevated CO2 have no clear trends reported. Allelochemical interactions between Sphagnum, their microbiome or surrounding mosses or other plants were found to be determinant to Sphagnum responses under those variables and reinforce the interest of such investigations

Allocation of recently assimilated carbon in Beech leaves

Investigating the short-term dynamics of trees’ carbon allocation is critical for understandingthe mechanisms underlying annual patterns of carbon allocation in forest ecosystems, influenced bytree phenology and environmental conditions. Pulse-labelling with stable carbon isotope (13C) enablesto trace the fate of labelled carbon into tree and its release to the atmosphere by respiration. This studyaimed at characterizing the short-term allocation pattern of the recently assimilated carbon in beechleaves, from its assimilation to its partitioning among the several carbon-containing metabolic pools,and its evolution across seasons.In situ whole-tree crown 13CO2-pulse labelling experiments were performed on 10 adultbeeches (20-year-old Fagus sylvatica L.) in a natural regeneration mixed stand located in the stateforest of Hesse in Northeastern France. Pulse-labelling campaigns were conducted four times duringthe growing season, in May, July, August, and September, in order to cover the different beechgrowing phases. For each labelled tree, leaf samples were harvested over a 6-day chase period.Purification and quantification of C-containing metabolic pools - including the isolation of solublecarbohydrates (including soluble sugars, amino and organic acids), starch and structural compounds -were performed. Total leaf organic matter (bulk) and metabolic pools δ13C were determined by IRMS.In addition, the isotope composition of leaf CO2 efflux was monitored by incubating leaves andanalysing respired CO2 by IRMS.The labelled 13C was rapidly assimilated in leaves of each tree and recovered in starch, solublecarbohydrates, structural compounds, and in leaf CO2 efflux. Variations among the different labellingperiods were observed and the implication of season vs environmental factors will be discussed.Finally, these results will also be used for feeding a leaf-scale compartmental model, which describesthe fate of the recently-assimilated carbon among leaf respiration, growth, storage and export, givingthe opportunity to isolates kinetics parameters of carbon allocation in leaves

Prevalence of interspecific competition in a mixed poplar/black locust plantation under adverse climate conditions

Key message : In a mixed poplar/black locust plantation in central France, adverse conditions have led to a prevalence of interspecific competition, resulting in a poorer performance than monocultures.Context : In mixed tree plantations, the presence of woody N-2-fixing species is thought to reduce N needs by fertilization. However, benefits associated to soil nitrogen enrichment have to outweigh the negative effects of interspecific competition. To do so, co-occurring tree species have to be chosen carefully to promote niche sharing between species and reduce competition. Black locust and poplar mixtures therefore seem promising since both species are fast growing and have potentially complementary crown shapes.Aims : Our objective was to evaluate the impact of the poplar/black locust mixture on the growth, above-and belowground biomass production, and nitrogen allocation of the two species, as compared to their respective monocultures.Methods : An experimental plantation mixing poplar and black locust was set up in central France. For five growing seasons, growth, nitrogen allocation, and carbon allocation were monitored for the two species growing either in mixture or in monoculture.Results : After a couple of promising growing seasons, black locust growth and survival slowly declined, mainly in the mixture. At the stand level, biomass production in the mixed plots was nearly 50% below the most productive monoculture (poplar) by age 5 years.Conclusion : Under adverse conditions, interspecific competition in the mixture was the preponderant interaction, resulting in higher mortality and lower biomass production than the two monocultures

Growth dynamics of fast-growing tree species in mixed forestry and agroforestry plantations

International audienceIn recent years, plantations of fast-growing tree species have emerged as a possible way to meet the increasing demand for biomass for renewable energy in Europe. Agroforestry plantations including fast-growing tree species could be an attractive option because they reduce land competition for biomass and food production while providing forest benefits. Today, the species interactions that determine whether a given mixture will be more productive than the corresponding monocultures are still poorly understood. Our objective was to assess the performance of fast-growing trees, i.e. poplar (Populus nigra × P. deltoides) and alder (Alnus glutinosa), in association with herbaceous species either N 2-fixing species (succession alfalfa (Medicago sativa) and clover (Trifolium pratense)) or graminoids (succession of wheat (Triticum aestivum)-triticale (Triticosecale)-temporary grassland consisting of mixtures of perennial ryegrass (Lolium perenne) and fescue (Festuca ovina)), respectively, and in association together. We compared tree growth in mixed stands to growth in the respective tree monocultures. An experimental plantation composed of three blocks including the different treatments was set up in 2014 in northeastern France. In the forest mixture, poplar and alder were planted in alternating rows, and in the agro-forestry plots, every second line of trees was replaced by the crops. No fertilizers (of any kind) were used during the experiments. During six growing seasons, tree growth (height and diameter at breast height) was monitored monthly in the agroforestry stands, the forest mixture stand and the two tree monocultures. By the end of 2019, poplar stem height in association with N 2-fixing crops (alfalfa, then clover) was higher than in the forest mixture and the monoculture. During the warmest growing season with a marked dry period in June-July (2018), poplar height growth rate in the agroforestry treatment was between three and five times higher than for the poplars in the monoculture and the forest mixture. A facilitation process in the agroforestry plantations could explain this result due to a significant enrichment of the soil in nitrogen by the N 2-fixing crops. This result only appeared several years after tree planting, and management actions were necessary in order to control the strong competition between crops and trees during the early stages. In the forest mixture, poplars associated with alders were smaller than in their monoculture, in spite of a stratification of the canopies of the two species. For alders, tree growth did not appear to be affected by either an association with graminoids or with poplar