Diurnal carbon restrictions on the photosynthesis of dense stands of Elodea nuttallii (Planch.) St. John

In slow-moving and static eutrophic waters, submerged macrophytes growing in dense stands produce a highly structured environment, with reduced internal water flow. An afternoon lull in the net photosynthesis of such stands has been reported from a number of previous studies. This has been attributed to increased photorespiration caused by an accumulation of photosynthetically-derived, dissolved oxygen in the surrounding water. Results here demonstrate that even in a water quite rich in dissolved inorganic carbon (2.5 mmol l^–1), limitations on the supply of inorganic carbon will normally be more important in curtailing photosynthesis, with photorespiration playing only a minor role.     

On the requirement of minimum number of four versus eight quanta of light for the evolution of one molecule of oxygen in photosynthesis: A historical note

A bitter controversy had existed as to the minimum number of quanta required for the evolution of one molecule of oxygen in photosynthesis: Otto Warburg had insisted since 1923 that this value was 3–4, whereas Robert Emerson and others continued to obtain a value of 8–12 since the 1940s. It is shown in this letter that the 1931 Nobel-laureate of Physiology & Medicine Otto Warburg published, in his last and final paper, just before his death in 1970, a measured minimum quantum requirement of oxygen evolution of 12 at the lowest intensities of light he used. Although using his theory on photolyte, Warburg calculated a value of 3–4 for the quantum requirement, this is the first confirmation by Warburg of the higher measured quantum requirement. However, it has remained unknown to most investigators. It is expected that this information will be of general interest not only to those interested in the history and research on photosynthesis, but to the entire sci entific community, especially the writers of text books in biology, biochemistry and biophysics.     

Relationships between plant photosynthesis,radial oxygen loss and nutrient removal in constructed wetland microcosms

The objective of this study was to investigate the relationships between root radial oxygen loss (ROL), photosynthesis, and nutrient removal, based on the hypothesis that ROL is primarily an active process which is affected positively by photosynthesis, and is correlated positively with nutrient removal. Four common wetland plants were studied in small-scale monoculture wetlands. Higher ROL coincided with faster growth among the four monocultures. Significant correlation between ROL and photosynthetic rate existed in Cyperus flabelliformis wetland (P < 0.01). Both ROL and photosynthesis represented close correlations with nutrient removal rates in all four monocultures. Significant differences in ROL, photosynthetic rate, removal rates of NH₄⁺, and soluble reactive phosphorus (SRP) were found among the four species. ROL and photosynthetic rates showed single-peak daily and seasonal patterns, with maximum daily values around noon, and with maximum yearly values in summer or autumn for the four monocultures. The results suggest that the ROL of wetland plants is related to active physiological processes. Both ROL and photosynthetic rate are indices which can be used to identify wetland plants with a higher nutrient removal capacity.     

Regulation of photosynthesis and oxygen consumption in a hypersaline cyanobacterial mat (Camargue, France) by irradiance, temperature and salinity

Short-term effects of irradiance (0-1560 micromol photons m(-2) s(-1)), temperature (10-25 degrees C), and salinity (40-160) on oxygenic photosynthesis and oxygen consumption in a hypersaline mat (Salin-de-Giraud, France) were investigated with microsensors under controlled laboratory conditions. Dark O(2) consumption rates were mainly regulated by the mass transfer limitations imposed by the diffusive boundary layer. Areal rates of net photosynthesis increased with irradiance and saturated at irradiances >400 micromol photons m(-2) s(-1). At low irradiances, oxygen consumption increased more strongly with temperature than photosynthesis, whereas the opposite was observed at saturating irradiances. Net photosynthesis vs. irradiance curves were almost unaffected by decreasing salinity (100 to 40), whereas increasing salinities (100 to 160) led to a decrease of net photosynthesis at each irradiance. Dark O(2) consumption rates, maximal gross and net photosynthesis at light saturation were relatively constant over a broad salinity range (60-100) and decreased at salinities above the in situ salinity of 100. Within the range of natural variation, temperature was more important than salinity in regulating photosynthesis and oxygen consumption. At higher salinities the inhibitory impact of salinity on these processes and therefore the importance of salinity as a regulating environmental parameter increased, indicating that in more hypersaline systems, salinity has a stronger limiting effect on microbial activity.     

Regulation of nitrogenase activity by light in the azolla-anabaena symbiosis

Nitrogenase activity and the rate of photosynthesis were measured simultaneously in Azolla by a continuous gas flow system. The mode of interaction between light, photosynthesis and nitrogenase activity was analysed.Nitrogenase activity dropped off when either Azolla plants or the cyanobiont Anabaena were transferred from light to dark. This decline was immediate and was independent of length or intensity of the prior light phase. Reillumination restored nitrogenase activity.Nitrogenase activity did not depend on the rate of photosynthesis at light intensities below 10 μE m⁻² s⁻¹. Its activity was saturated at 200 μE m⁻² s⁻¹ while CO₂ fixation was saturated at a light intensity of 850 μE m⁻² s⁻¹. Azolla photosynthetic activity followed the absorption spectrum of chlorophyll a, while nitrogenase activity markedly increased between 690 and 710 nm. Inhibition of photosynthesis by DCMU was accompanied by an increase in nitrogenase activity. These results suggest direct light regulation of nitrogenase activity in Azolla independent of CO₂ fixation, and a possible inhibition of nitrogenase activity by the oxygen produced in photosynthesis.     

Contributions of Theodor Wilhelm Engelmann on phototaxis,chemotaxis, and photosynthesis

Theodor Wilhelm Engelmann (1843–1909), who had a creative life in music, muscle physiology, and microbiology, developed a sensitive method for tracing the photosynthetic oxygen production of unicellular plants by means of bacterial aerotaxis (chemotaxis). He discovered the absorption spectrum of bacteriopurpurin (bacteriochlorophyll a) and the scotophobic response, photokinesis, and photosynthesis of purple bacteria.     

The oxygen evolution methodology affects photosynthetic rate measurements of microalgae in well‐defined light regimes

Designing photobioreactors correctly is a must for the success of microalgal mass production. Optimal photobioreactor design requires a precise knowledge of photosynthesis dynamics in fluctuating light conditions and hence a method for the measurement of photosynthetic rates in specific light regimes. However, it is not uncommon in literature that experimental protocols used to obtain oxygen generation rates are described ambiguously and the reported rates of photosynthesis vary widely depending on the methodology. Additionally, quite a number of methods overlook certain aspects that can affect the estimated rates significantly, and can therefore affect photobioreactor design. We have developed a method based on oxygen evolution measurements that accurately determines photosynthetic rates under well‐defined light regimes. Our experimental protocol takes into account most of the issues that can affect the rates of oxygen generation, such as depletion of nutrients during the measurements and precision of the measurements. We have focused on the basic applications in photobioreactor design and used a dynamic model of photosynthesis to analyze our results and compare them with available published data. The results suggest that our oxygen evolution method is consistent. Biotechnol. Bioeng. 2010;106: 228–237. © 2010 Wiley Periodicals, Inc.     

Modulation of the Photosynthetic Source:Sink Relationship in Cultures of the Cyanobacterium Nostoc Rivulare

Nostoc rivulare was grown in batch cultures under controlled CO₂ and NO₃ ^– concentrations to modulate the photosynthetic source:sink relationship. Increasing CO₂ supply accelerated the accumulation of chlorophyll (Chl) a, i.e., supplemental CO₂ combined with double concentrations of NO₃ ^– more than doubled the amounts of Chl a relative to those of the original medium. Photosynthetic oxygen evolution and respiratory oxygen uptake were both enhanced by elevated CO₂ and NO₃ ^–. Contents of soluble sugars and starch (total non-structural saccharides) as well as insoluble saccharides (structural fraction) were affected by altering CO₂-NO₃ ^– combinations. Uptake as well as reduction of either NO₃ ^– or NO₂ ^– was inhibited by CO₂ deprivation. Expanding the sink size via increasing NO₃ ^– supply enhanced photosynthesis and thus the sink (NO₃ ^–) acted as a feed forward stimulator of the source (photosynthesis). The regulatory role of nitrate on photosynthesis was most influential in CO₂-deprived cultures since it could enhance photosynthesis to higher levels than CO₂-supplemented, nitrate-free cultures.     

Limitation of oxygenic photosynthesis and oxygen consumption by phosphate and organic nitrogen in a hypersaline microbial mat: a microsensor study

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.     

基于GIS的关中-天水经济区土地生态系统固碳释氧价值评价

气体调节服务功能是生态服务功能的重要的一部分,生态系统的固碳释氧功能,对于人类社会和整个动物界以及全球气候平衡,都具有重要意义.采用光合作用方程式,利用遥感估算模型,基于植被NPP(第一性生产力)物质量测算结果,测算关中-天水天经济区绿色植物固碳释氧物质量,以此为基础,分别采用造林成本法和工业制氧法测算其价值量,探讨关天经济区生态系统固碳释氧价值的时间变化、空间分布.结果表明:1)1998-2007年关天水经济区年固定CO2的价值量为226.35亿元/a.10a间2005年固定CO2的价值量最高,为301.73亿元/a,2002年最低,为159.06元/a.释放O2价值量取两种测评方法的平均值,年平均价值量为240.45亿元/a,比固定CO2的年均值多14.1亿元/a.2)从各土地利用类型来看,1998年和2007年平均固碳释氧价值排序为:林地＞草地＞耕地＞其他类型.耕地向林地、草地转变时,平均固碳释氧价值分别增加了1614.29、1960.67元·hm-2·a-1,林地、草地向耕地转变时平均固碳释氧价值分别减少了1081.37、1706.60元·hm-2·a-1.3)从空间分布上来看,南部各县的单位面积固定CO2和释放O2价值普遍高于北部各县,总体上分布沿南部向北部逐渐降低.     

A photoacoustic method for rapid assessment of temperature effects on photosynthesis

The photosynthetic and photoacoustic properties of leaf samples were studied using a photoacoustic system modified for precise temperature control. Data were collected over a temperature range of −10 °C to +60 °C. A distinct acoustic noise transient marked the freezing temperature of the samples. A positive absorption transient and a brief period of oxygen uptake marked the thermal denaturing temperature of the samples. Between these extremes, the effects of temperature on light absorption, oxygen evolution, and photochemical energy storage were quantified quickly and easily. Oxygen evolution could be measured as low as −5 °C and showed a broad temperature peak that was 10 °C lower under limiting light intensity than under saturating light intensity. Photochemical energy storage showed a narrower temperature peak that was only slightly lower for limiting light intensities than for saturating light intensities. In a survey of diverse plants, temperature response curves for oxygen evolution were determined readily for a variety of leaf types, including ferns and conifer needles. These results demonstrate that temperature-controlled photoacoustics can be useful for rapid assessment of temperature effects on photosynthesis and other leaf properties.     

Oxygen exchange during growth of photomixotrophic cell suspensions of Euphorbia characias L.

Growth of photomixotrophic cell culture of Euphorbia characias L. is described; oxygen exchange rates were measured along this growth cycle using a mass-spectrometric technique. During the exponential and mid-stationary phases, photosynthesis was strongly increasing, the major part of oxygen uptake in the light was due to mitochondrial respiration. In the late stationary phase, gross photosynthesis was decreasing; this could not be explained by an alteration of Rubisco because photorespiratory process could be observed; in addition the Mehler reaction must be called upon to explain whole oxygen uptake in the light.     

Cyclic variations of photosynthetic activity under nitrogen fixing conditions in Synchococcus RF-1

When nitrogen fixing cell cultures of Synechococcus RF-1 were subjected to an alternating lightdark regime (12 h:12 h), a cyclic decrease in the photosynthetic oxygen evolution potential was observed during the dark periods. This rhythm of net photosynthesis rate was maintained for at least two days after transition to continuous light. The decrease in net photosynthesis was accompanied by a stimulation of dark respiration. However, the magnitude of oxygen uptake was considerably smaller than the observed decrease in oxygen evolution. The photosynthetic activity of cells taken from the dark period was characterized by (i) a significantly lower quantum yield and (ii) a strong reduction in the light-saturated rate of photosynthesis. Growing the cultures on nitrate or under continuous light completely suppressed this rhythm. Protein synthesis was not necessary for the recovery of the light-saturated rate of photosynthesis during the light period. The cellular content of chlorophyll a and of phycobiliproteins did not vary between light and dark period, indicating that quantitative changes in the composition of the photosynthetic apparatus are not the basis for the observed oscillations. Regulatory modifications of the photosynthetic efficiency are proposed as an adaptation mechanism to adjust the intracellular oxygen concentration to the needs for nitrogenase activity.Abbreviation Chl chlorophyll     

Application of photorespiration concepts to whole stream productivity

We conducted two-station diel surveys of dissolved oxygen content to estimate whole-stream productivity in the experimental streams of the Monticello Ecological Research Station for two years following channel reconstruction. Community productivity measurements compare well to previous measurements in these streams, but apparent hysteresis in the P/I relation was measured in over two-thirds of the diel surveys. Apparent hysteresis in photosynthesis with solar irradiance is a characteristic of photorespiration, and modeling the effect of light on whole-stream respiratory rates reduced the magnitude of P/I curve hysteresis and improved the predictions of dissolved oxygen content (DO) in the stream. Stream productivity models normally assume respiratory rates measured at night are constant throughout the day, but when this assumption yields apparent hysteresis in the P/I curve, the inclusion of a photorespiration model in the analyses of whole-stream productivity facilitates the comparison of photosynthesis and respiratory rates between different streams. The computed total daily consumption of oxygen by photorespiratory processes is proportional to the total daily photosynthetic production of oxygen in the streams. We also found that the diel DO curves occurring in the experimental streams are best described by a photorespiration model that utilizes a four hour moving average of irradiance. Accounting for photorespiration in the streams increases the apparent efficiency of photosynthesis, improves the accuracy of DO predictions, and reduces uncertainty in photosynthesis and respiratory rate estimates. This revised version was published online in July 2006 with corrections to the Cover Date.     

A biographical sketch of Charles F. Yocum: “It's the biochemistry, stupid”

Charles F. Yocum has been a leader in the applications of biochemical techniques to the resolution and reconstitution of Photosystem II. His formal science education began as an undergraduate in biochemistry at Iowa State University and continued with graduate work in photosynthesis, first at the Illinois Institute of Technology and later at Indiana University. Following postdoctoral work at Cornell University, he joined the faculty of the University of Michigan where he has remained throughout his academic career. Charlie's contributions to a biochemical understanding of photosynthesis, particularly Photosystem II have been considerable, but most notably include his initial isolation of the first highly active oxygen-evolving particle from higher plant chloroplasts, the well-known and widely utilized `BBY particles'. In the aftermath of that isolation, Charlie's research further resolved these particles into ever finer and simpler, but active, Photosystem II complexes. In addition, Charlie's research has provided significant insight into the roles of both Cl⁻ and Ca²⁺ as required cofactors in photosynthetic oxygen evolution. This revised version was published online in June 2006 with corrections to the Cover Date.     

The Light Meter: A Powerful Tool in Physical Science

Photosynthesis and cellular respiration are two processes that transform energy and affect concentrations of carbon dioxide and oxygen in air and water. In this lesson, middle school students use graphing calculators and calculator-based laboratory units to measure dissolved oxygen in water and graph their results to gain an under-standing of the relationship between photosynthesis and cellular respiration.     

温度变化对藻类光合电子传递与光合放氧关系的影响

由于直接测定藻类的光合速率耗时且不方便,研究者们常通过测定藻类光合电子传递速率的方式来间接反映其光合速率,理论上,以氧气产生来度量的总光合速率（PGross）与电子传递速率(ETR)之间应该存在很好的线性关系。然而,由于温度的变化会影响藻类的光呼吸等耗氧的生理过程从而影响光合作用中的氧气释放,因此温度可能会对PGross与ETR之间的线性关系产生影响。研究了温度变化对蛋白核小球藻（Cholorella pyrenoidosa）、菱形藻（Nitzschia sp.）和水生集胞藻（Synechocystis aquetilis Sauv.）的总光合放氧速率（PGross）与电子传递速率(ETR)之间比率的影响,结果表明PGross/ETR随温度的升高而降低,低温条件下PGross/ETR比值较高,说明在相同的电子传递速率的情况下水的光裂解产生的氧有更多的可以释放出来;在高温条件下PGross/ETR比值相对较低,说明高温条件下可能有相对更多的水光裂解产生的氧被用于耗氧的生理过程而没有释放出来。研究表明当温度发生变化时,光合放氧与电子传递之间并不呈线性关系,这说明将ETR作为实际光合生产的评价指标时要谨慎,不能不加分析地直接应用。     

Experimental and theoretical studies on the excess capacity of Photosystem II

It has been recently suggested that compensatory changes in Photosystem II (PS II) electron turnover rates can protect photosynthesis from photoinhibition [Behrenfeld et al. (1998) Photosynth Res 58: 259–268]. We have further explored this feature of PS II using a rate electrode for simultaneous measurements of the steady-state rate of oxygen evolution and the oxygen flash yield depending on the background irradiance in both control and photoinhibited algal cells of Chlorella Böhm. Theoretical simulations based on the two-electron gate model agree qualitatively with experimental data if we assume an increase of the electron turnover rate in the remaining functional PS II centers of the photoinhibited sample. Our results confirm the hypothesis that the compensatory effect enables cells to maintain the maximal rates of photosynthesis even in the presence of moderate photoinhibition (decrease of up to 50% in the number of functional centers) and that the effect originates from the inner capacity of electron transport through PS II. The origin of the compensatory effect is briefly discussed.     

Environmental factors regulating the radial oxygen loss from roots of Myriophyllum spicatum and Potamogeton crispus

Myriophyllum spicatum and Potamogeton crispus are common species of shallow eutrophic lakes in north-eastern Germany, where a slow recovery of the submersed aquatic vegetation was observed. Thus, the characterisation of the root oxygen release (ROL) as well as its implication for geochemical processes in the sediment are of particular interest. A combination of microelectrode measurements, methylene blue agar and a titanium(III) redox buffer was used to investigate the influence of the oxygen content in the water column on ROL, diel ROL dynamics as well as the impact of sediment milieu. Oxygen gradients around the roots revealed a maximum oxygen diffusion zone of up to 250 μm. During a sequence with a light/dark cycle as well as alternating aeration of the water column, maximum ROL with up to 35% oxygen saturation at the root surface occurred under light/O₂-saturated conditions. A decrease to about 30% was observed under dark/O₂-saturated conditions, no ROL was detected at dark/O₂-depleted conditions and only a weak ROL with 5–10% oxygen saturation at the root surface was measured under light but O₂-depleted water column. These results indicate, that during darkness, ROL is supplied by oxygen from the water column and even during illumination and active photosynthesis production, ROL is modified by the oxygen content in the water column. Visualisation of ROL patterns revealed an enhanced ROL for plants which were grown in sulfidic littoral sediment in comparison to plants grown in pure quartz sand. For both plant species grown in sulfidic littoral sediment, a ROL rate of 3–4 μmol O₂ h⁻¹ plant⁻¹ was determined with the Ti(III) redox buffer. For plants grown in pure quartz sand, the ROL rate decreased to 1–2 μmol O₂ h⁻¹ plant⁻¹. Hence, aside from the oxygen content in the water column, the redox conditions and microbial oxygen demand in the sediment has to be considered as a further major determinant of ROL.     

Acclimation of a terrestrial plant to submergence facilitates gas exchange under water

Flooding imposes stress upon terrestrial plants since it severely hampers gas exchange rates between the shoot and the environment. The resulting oxygen deficiency is considered to be the major problem for submerged plants. Oxygen microelectrode studies have, however, shown that aquatic plants maintain relatively high internal oxygen pressures under water, and even may release oxygen via the roots into the sediment, also in dark. Based on these results, we challenge the dogma that oxygen pressures in submerged terrestrial plants immediately drop to levels at which aerobic respiration is impaired. The present study demonstrates that the internal oxygen pressure in the petioles of Rumex palustris plants under water is indeed well above the critical oxygen pressure for aerobic respiration, provided that the air‐saturated water is not completely stagnant. The beneficial effect of shoot acclimation of this terrestrial plant species to submergence for gas exchange capacity is also shown. Shoot acclimation to submergence involved a reduction of the diffusion resistance to gases, which was not only functional by increasing diffusion of oxygen into the plant, but also by increasing influx of CO₂, which enhances underwater photosynthesis.