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Northern peatlands form a major soil carbon (C) stock. With climate change, peatland C mineralization is expected to increase, which in turn would accelerate climate change. A particularity of peatlands is the importance of soil aeration, which regulates peatland functioning and likely modulates the responses to warming climate. Our aim is to assess the impacts of warming on a southern boreal and a sub-arctic sedge fen carbon dioxide (CO2) exchange under two plausible water table regimes: wet and moderately dry. We focused this study on minerotrophic treeless sedge fens, as they are common peatland types at boreal and (sub)arctic areas, which are expected to face the highest rates of climate warming. In addition, fens are expected to respond to environmental changes faster than the nutrient poor bogs. Our study confirmed that CO2 exchange is more strongly affected by drying than warming. Experimental water level draw-down (WLD) significantly increased gross photosynthesis and ecosystem respiration. Warming alone had insignificant impacts on the CO2 exchange components, but when combined with WLD it further increased ecosystem respiration. In the southern fen, CO2 uptake decreased due to WLD, which was amplified by warming, while at northern fen it remained stable. As a conclusion, our results suggest that a very small difference in the WLD may be decisive, whether the C sink of a fen decreases, or whether the system is able to adapt within its regime and maintain its functions. Moreover, the water table has a role in determining how much the increased temperature impacts the CO2 exchange. This article is protected by copyright. All rights reserved.

The ratio of light-driven O2 consumption to gross photosynthetic O2 evolution decreased significantly with increasing CO2, which is probably due to a reduced cost of operating the carbon-concentrating mechanism., As atmospheric CO2 concentrations increase, so too does the dissolved CO2 and HCO3– concentrations in the world’s oceans. There are still many uncertainties regarding the biological response of key groups of organisms to these changing conditions, which is crucial for predicting future species distributions, primary productivity rates, and biogeochemical cycling. In this study, we established the relationship between gross photosynthetic O2 evolution and light-dependent O2 consumption in Trichodesmium erythraeum IMS101 acclimated to three targeted pCO2 concentrations (180 µmol mol–1=low-CO2, 380 µmol mol–1=mid-CO2, and 720 µmol mol–1=high-CO2). We found that biomass- (carbon) specific, light-saturated maximum net O2 evolution rates (PnC,max) and acclimated growth rates increased from low- to mid-CO2, but did not differ significantly between mid- and high-CO2. Dark respiration rates were five times higher than required to maintain cellular metabolism, suggesting that respiration provides a substantial proportion of the ATP and reductant for N2 fixation. Oxygen uptake increased linearly with gross O2 evolution across light intensities ranging from darkness to 1100 µmol photons m–2 s–1. The slope of this relationship decreased with increasing CO2, which we attribute to the increased energetic cost of operating the carbon-concentrating mechanism at lower CO2 concentrations. Our results indicate that net photosynthesis and growth of T. erythraeum IMS101 would have been severely CO2 limited at the last glacial maximum, but that the direct effect of future increases of CO2 may only cause marginal increases in growth.

Photosynthetic rates in the cyanobacterium Trichodesmium erythraeum appear to be a function of CO2, although numerical simulations of the carbon-concentrating mechanism show carboxylation to be mediated as a function of pH and HCO3–., Increasing atmospheric CO2 concentrations are leading to increases in dissolved CO2 and HCO3– concentrations and decreases in pH and CO32– in the world’s oceans. There remain many uncertainties as to the magnitude of biological responses of key organisms to these chemical changes. In this study, we established the relationship between photosynthetic carbon fixation rates and pH, CO2, and HCO3– concentrations in the diazotroph, Trichodesmium erythraeum IMS101. Inorganic 14C-assimilation was measured in TRIS-buffered artificial seawater medium where the absolute and relative concentrations of CO2, pH, and HCO3– were manipulated. First, we varied the total dissolved inorganic carbon concentration (TIC) (

Recent climatic projections predict a decline in rainfall mainly during the summer period and an increase in air temperature for the Mediterranean basin, resulting in extended periods of soil water deficit. Mediterranean evergreen species attain drought resistance through different traits or combination of traits. The main objective of this research is to analyze the response of the evergreen species co-occurring in the Mediterranean maquis to variations in water availability and air temperature during the year. The results show that leaf structural traits significantly affect physiological traits as confirmed by the Partial Least Squares Regression analysis (PLS). In particular, the considered species have a similar leaf respiration (RL) trend during the year with the lowest rates in winter (mean 0.95 ± 0.44 µmol m-2 s-1) and the highest in drought (mean 3.05 ± 0.96 µmol m-2 s-1). Nevertheless, a different RL effect on gross photosynthesis (PG) during drought was observed. C. incanus, E. multiflora, R. officinalis and S. aspera have the highest RL/PG ratio (mean 0.54 ± 0.08), while Q. ilex, P. latifolia, P. lentiscus, A. unedo and E. arborea have the lowest (mean 0.22 ± 0.07). RL/PG ratio variations depend on the sensitivity of both the two parameters to drought. Considering the increase of the length and intensity of drought in the Mediterranean basin, and that the photosynthesis of Mediterranean evergreen species is frequently limited by sub-optimal conditions (i.e., water deficit, high light intensity and high air temperature), it is important to improve knowledge on RL, since it has a critical function in modulating carbon balance of Mediterranean species.

8 pages, figures, and tables statistics., This study has two main objectives, the first being the determination of net phytoplankton primary production to explain the phytoplankton’s function in a wetland carbon cycle, while the second objective is to relate this function with the phytoplankton assemblage composition. The annual variation in the phytoplankton production was monitored monthly for more than a year (2007–2008) in the semiarid eutrophic, hydrologically-perturbed ‘‘Tablas de Daimiel’’ National Park wetland. The phytoplankton fraction considered in this study comprised all organisms between the size 3 and 100 lm. The total biomass of phytoplankton was obtained by counting algae and calculating their volume, while net primary production and respiration were quantified by in situ incubations with the Winkler method. The respiration ranged from undetectable to 0.07mgO2 l-1 h-1; net photosynthesis reached 0.20 mgO2 l-1 h-1. Net primary production was maximum at the end of the warm period (October 2007), and other peaks occurred at the start of summer (July 2007) or spring (March 2008). When maximum production took place, phytoplankton was mainly composed of small fast-growing chlorophytes (Tetraselmis cf. fontiana or Chlamydomonas sp.), in addition to some of the large, S-strategist algae (Peridinium umbonatum, Microcystis flos-aquae, Euglena sp.). The phytoplankton metabolism in ‘‘Tablas de Daimiel’’ was autotrophic as a whole due to changing contributions of algal groups. Only chlorophyte biomass was statistically related to net primary production. The conclusion reached is that this shallow eutrophic semiarid wetland possessed an annual net autotrophic production of phytoplankton fraction resulting from the small, fast-growing algae enhanced by hydrological perturbations that interrupted the autogenic course of S strategists.

Single polyps of Galaxea fascicularis were fixed to glass vials with underwater epoxy resin. After regeneration into microcolonies they were used for microsensor measurements of photosynthesis and calcification under different incubating temperatures. Gross photosynthesis was found highest at temperatures of 23 and 26°C (ca. 0.022 mole O2 m-3 s–1), close to the ambient temperature (i.e. 26°C). At 35°C, gross photosynthesis was irreversibly inhibited as the microcolonies bleached. The net photosynthesis rapidly decreased with temperature and became negative at temperatures higher than 29°C. Profiles of O2 and Ca2+ showed a strong effect of temperature on them. The concentrations of Ca2+ measured on the polyp surface also showed temperature dependence of Ca2+ uptake. In the dark and below 29°C, the surface Ca2+ concentration was temperature independent. During illumination, the surface Ca2+ concentration showed a dip at 26°C (ca. 8.7 mM), indicating maximum uptake rates at ambient temperature. However, at 32°C and higher, Ca2+ was slightly higher at the tissue surface than in the seawater, in both light and dark, resulting from calcium dissolution. The surface pH in light increased gradually from 8.3 to 8.6 with increasing temperature to 23°C, and thereafter remained constant to 29°C. At 32°C, the pH became slightly acidic compared with the water phase, probably due to a decrease in the uptake of CO2 by photosynthesis. The largest difference in pH between light and dark incubations was at temperatures between 23 and 29°C (7.5-7.7 in dark versus 8.6-8.7 in light), which indicate high rates of photosynthesis and respiration in this temperature range. It is concluded that photosynthetic activity in the coral is maintained up to rather high temperatures (32°C), but corals at super-optimum temperatures (above 26°C) consume more O2 than they produce, decalcify and produce CO2 Se fijaron pólipos de Galaxea fascicularis sobre viales de cristal con resina epoxy. Una vez generaron pequeñas colonias se utilizaron como sensores para medir los cambios en la fotosíntesis y calsificación a diferentes temperaturas. Los valores de fotosíntesis total (bruta) fueron más elevados a temperaturas entre 23 y 26°C (ca. 0,022 mole O2 m-3 s-1), similares a los del ambiente (26°C). A valores de 35°C, la fotosíntesis total se inhibió irreversiblemente y las pequeñas colonias se blanquearon. La fotosíntesis neta disminuyó rápidamente con la temperatura hasta llegar a valores negativos en temperaturas mayores de 29°C. Los perfiles de O2 y Ca2+ mostraron un elevado efecto de la temperatura. Las concentraciones de Ca2+ medidas en la superficie de los pólipos también mostraron una influencia en la incorporación de Ca2+. En condiciones de oscuridad y temperatura por debajo de 29°C, la concentración de Ca2+ era dependiente de la temperatura. En periodos iluminados, el Ca2+ concentración mostró un pico 26°C (ca. 8,7 mM) hecho que indicaba una tasa de incorporación a temperatura ambiente. hecho que indica que las máximas incorporaciones se efectuaron a temperatura ambiente. Sin embargo, a 32°C o más, los valores de Ca2+ fueren ligeramente altos en la superficie del tejido que en agua de mar, en ambas situaciones de iluminación y oscuridad, resultado de la disolución de la disolución de Calcio. El pH en periodos iluminados se incrementó ligeramente de 8.3 a 8.6, incrementándose la temperatura se y permaneció constante hasta 23°C aunque permenecía constante hasta los 29°C. A 23°C el pH se transformó en un pH ligeramente ácido, probablemente debido a la disminución de en la tasa de retención de CO2 mediante la fotosíntesis. Las mayores diferencias en pH en peiodos iluminados y oscuros fue de 23-29°C (7.5-7.7 en oscuridad versus 8.6-8.7) lo que infica un alta tasa de fotosíntesis y respiración a estos datos en este margen de temperaturas. La conclusión del trabajo es que, la actividad fotosintética en el coral es claramente elevada y se mantiene alta a temperaturas hasta alcanzar los 32°C, pero los corales, en el periodo óptimo de temperaturas de verano (por encima de 26°C) consume mas O2 que el que produce, se descalcifica y produce CO2

The CO2 mass transfer problem of the assimilation cell phase of the crop leaf in the gross photosynthesis process was solved by the use of analytical procedures for net photosynthesis in the previous investigation (Komori and Ikemoto, 1999). The solutions were applied to evaluate the CO2 gross mass transfer coefficient kL0, the gross photosynthetic reaction rate constant k10 and the CO2 concentration profile CA(z, t) in the assimilation cell phase with a constant respiration rate k0 for the case of rice. The summary is as follows: 1) Exact solutions for CA(z, t), the CO2 flux NA0, kL0 and the gross photosynthetic rate RAT0 are simplified to Eq. (13) through Eq. (16). These approximate solutions are available to obtain the relation of the CO2 mass transfer mechanism between the gross and the net photosynthesis in the assimilation celll phase. 2) Equation (22) or Eq. (39) gives the correlation of the gross and the net photosynthesis with the CO2 mass transfer rate. Equation (22) suggests that k0 has no influence on the gas phase CO2 mass transfer coefficient kG and for the over-all CO2 mass transfer coefficient, Eq. (39) provides Eq. (40). Moreover, Eqs. (22) and (39) indicate that the graphical method (Komori and Ikemoto, 1999) is appropriate for estimation of kL and kG. 3) Figure 3, generated from Eq. (22) or Eq. (39), shows the relationship between k10 and the net photosynthetic reaction rate constant k1, and is also the graphical method to estimate k10 from the net photosynthetic rate RAT and k0. Following the analytical discussion of Eq. (21) through Eq. (29) the k10-RAT curve in Fig. 3, shows that for assimilation of the crop leaf, the practical gross photosynthesis is biophysically different from the substantial net photosynthesis. 4) In order to quantitatively evaluate the characteristics of the photosynthetic reaction, the assimilation cell effectiveness factor Ef0 (Bird et al., 1960; Ohtake, 1963), defined by Eq. (50), was introduced. The Ef0 curve in Fig. 9 indicates the equilibrium point, kGb=kGs, the transition point, kL=HkG for the CO2 mass transfer resistance and the terminal point of RATmax at the maximum RAT in the region of 0≤RAT≤RATmax. In addition, Ef0 suggests that the photosynthetic reaction is very fast and can be performed near the surface of the assimilation cell phase.

The theoretical basis for the link between the leaf exchange of carbonyl sulfide (COS), carbon dioxide (CO2) and water vapour (H2O) and the assumptions that need to be made in order to use COS as a tracer for canopy net photosynthesis, transpiration and stomatal conductance, are reviewed. The ratios of COS to CO2 and H2O deposition velocities used to this end are shown to vary with the ratio of the internal to ambient CO2 and H2O mole fractions and the relative limitations by boundary layer, stomatal and internal conductance for COS. It is suggested that these deposition velocity ratios exhibit considerable variability, a finding that challenges current parameterizations, which treat these as vegetation-specific constants. COS is shown to represent a better tracer for CO2 than H2O. Using COS as a tracer for stomatal conductance is hampered by our present poor understanding of the leaf internal conductance to COS. Estimating canopy level CO2 and H2O fluxes requires disentangling leaf COS exchange from other ecosystem sources/sinks of COS. We conclude that future priorities for COS research should be to improve the quantitative understanding of the variability in the ratios of COS to CO2 and H2O deposition velocities and the controlling factors, and to develop operational methods for disentangling ecosystem COS exchange into contributions by leaves and other sources/sinks. To this end, integrated studies, which concurrently quantify the ecosystem-scale CO2, H2O and COS exchange and the corresponding component fluxes, are urgently needed. We investigate the potential of carbonyl sulfide (COS) for being used as a tracer for canopy net photosynthesis, transpiration and stomatal conductance by examining the theoretical basis of the link between leaf COS, carbon dioxide (CO2) and water vapour (H2O) exchange. Our analysis identifies several limitations that need to be overcome to this end, however at present we lack appropriate ecosystem-scale field measurements for assessing their practical significance. It however appears that COS represents a better tracer for CO2 than H2O. Concurrent measurements of ecosystem scale COS, CO2 and H2O exchange are advocated.

Microbial mats are characterized by high primary production but low growth rates, pointing to a limitation of growth by the lack of nutrients or substrates. We identified compounds that instantaneously stimulated photosynthesis rates and oxygen consumption rates in a hypersaline microbial mat by following the short-term response (c. 6 h) of these processes to addition of nutrients, organic and inorganic carbon compounds, using microsensors. Net photosynthesis rates were not stimulated by compound additions. However, both gross photosynthesis and oxygen consumption were substantially stimulated (by a minimum of 25%) by alanine (1 mM) and glutamate (3.5 mM) as well as by phosphate (0.1 mM). A low concentration of ammonium (0.1 mM) did not affect photosynthesis and oxygen consumption, whereas a higher concentration (3.5 mM) decreased both process rates. High concentrations of glycolate (5 mM) and phosphate (1 mM) inhibited gross photosynthesis but not oxygen consumption, leading to a decrease of net photosynthesis. Photosynthesis was not stimulated by addition of inorganic carbon, nor was oxygen consumption stimulated by organic compounds like glycolate (5 mM) or glucose (5 mM), indicating that carbon was efficiently cycled within the mat. Photosynthesis and oxygen consumption were apparently tightly coupled, because stimulations always affected both processes to the same extent, which resulted in unchanged net photosynthesis rates. These findings illustrate that microsensor techniques, due to their ability to quantify all three processes, can clarify community responses to nutrient enrichment studies much better than techniques that solely monitor net fluxes.

Single polyps of Galaxea fascicularis were fixed to glass vials with underwater epoxy resin. After regeneration into microcolonies they were used for microsensor measurements of photosynthesis and calcification under different incubating temperatures. Gross photosynthesis was found highest at temperatures of 23 and 26°C (ca. 0.022 mole O2 m-3 s–1), close to the ambient temperature (i.e. 26°C). At 35°C, gross photosynthesis was irreversibly inhibited as the microcolonies bleached. The net photosynthesis rapidly decreased with temperature and became negative at temperatures higher than 29°C. Profiles of O2 and Ca2+ showed a strong effect of temperature on them. The concentrations of Ca2+ measured on the polyp surface also showed temperature dependence of Ca2+ uptake. In the dark and below 29°C, the surface Ca2+ concentration was temperature independent. During illumination, the surface Ca2+ concentration showed a dip at 26°C (ca. 8.7 mM), indicating maximum uptake rates at ambient temperature. However, at 32°C and higher, Ca2+ was slightly higher at the tissue surface than in the seawater, in both light and dark, resulting from calcium dissolution. The surface pH in light increased gradually from 8.3 to 8.6 with increasing temperature to 23°C, and thereafter remained constant to 29°C. At 32°C, the pH became slightly acidic compared with the water phase, probably due to a decrease in the uptake of CO2 by photosynthesis. The largest difference in pH between light and dark incubations was at temperatures between 23 and 29°C (7.5-7.7 in dark versus 8.6-8.7 in light), which indicate high rates of photosynthesis and respiration in this temperature range. It is concluded that photosynthetic activity in the coral is maintained up to rather high temperatures (32°C), but corals at super-optimum temperatures (above 26°C) consume more O2 than they produce, decalcify and produce CO2, Se fijaron pólipos de Galaxea fascicularis sobre viales de cristal con resina epoxy. Una vez generaron pequeñas colonias se utilizaron como sensores para medir los cambios en la fotosíntesis y calsificación a diferentes temperaturas. Los valores de fotosíntesis total (bruta) fueron más elevados a temperaturas entre 23 y 26°C (ca. 0,022 mole O2 m-3 s-1), similares a los del ambiente (26°C). A valores de 35°C, la fotosíntesis total se inhibió irreversiblemente y las pequeñas colonias se blanquearon. La fotosíntesis neta disminuyó rápidamente con la temperatura hasta llegar a valores negativos en temperaturas mayores de 29°C. Los perfiles de O2 y Ca2+ mostraron un elevado efecto de la temperatura. Las concentraciones de Ca2+ medidas en la superficie de los pólipos también mostraron una influencia en la incorporación de Ca2+. En condiciones de oscuridad y temperatura por debajo de 29°C, la concentración de Ca2+ era dependiente de la temperatura. En periodos iluminados, el Ca2+ concentración mostró un pico 26°C (ca. 8,7 mM) hecho que indicaba una tasa de incorporación a temperatura ambiente. hecho que indica que las máximas incorporaciones se efectuaron a temperatura ambiente. Sin embargo, a 32°C o más, los valores de Ca2+ fueren ligeramente altos en la superficie del tejido que en agua de mar, en ambas situaciones de iluminación y oscuridad, resultado de la disolución de la disolución de Calcio. El pH en periodos iluminados se incrementó ligeramente de 8.3 a 8.6, incrementándose la temperatura se y permaneció constante hasta 23°C aunque permenecía constante hasta los 29°C. A 23°C el pH se transformó en un pH ligeramente ácido, probablemente debido a la disminución de en la tasa de retención de CO2 mediante la fotosíntesis. Las mayores diferencias en pH en peiodos iluminados y oscuros fue de 23-29°C (7.5-7.7 en oscuridad versus 8.6-8.7) lo que infica un alta tasa de fotosíntesis y respiración a estos datos en este margen de temperaturas. La conclusión del trabajo es que, la actividad fotosintética en el coral es claramente elevada y se mantiene alta a temperaturas hasta alcanzar los 32°C, pero los corales, en el periodo óptimo de temperaturas de verano (por encima de 26°C) consume mas O2 que el que produce, se descalcifica y produce CO2