Photosynthetic acclimation and photosynthate partitioning in soybean leaves in response to carbon dioxide enrichment

Photosynthetic rates and photosynthate partitioning were studied in three-week-old soybean [Glycine max (L.) Merr. cv. Williams] plants exposed to either ambient (35 Pa) or elevated (70 Pa) CO₂ in controlled environment chambers. Ambient CO₂-grown plants also were given a single 24 h treatment with 70 Pa CO₂ 1 d prior to sampling. Photosynthetic rates of ambient CO₂-grown plants initially increased 36% when the measurement CO₂ was doubled from 35 to 70 Pa. Photosynthetic rates of the third trifoliolate leaf, both after 1 and 21 d of elevated CO₂ treatment, were 30 to 45% below those of ambient CO₂-grown plants when measured at 35 Pa CO₂. These reduced photosynthetic rates were not due to increased stomatal resistance and were observed for 2 to 8 h after plants given 1 d of CO₂ enrichment were returned to ambient CO₂. Initial and total ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) activities, percent activation, Rubisco protein, soluble protein and leaf chlorophyll content were similar in all CO₂ treatments. Quantum yields of photosynthesis, determined at limiting irradiances and at 35 Pa CO₂, were 0.049±0.003 and 0.038±0.005 mol CO₂ fixed per mol quanta for ambient and elevated CO₂-grown plants, respectively (p<0.05). Leaf starch and sucrose levels were greater in plants grown at 70 than at 35 Pa CO₂. Starch accumulation rates during the day were greater in ambient CO₂-grown plants than in plants exposed to elevated CO₂ for either 1 or 21 d. However, the percentage of C partitioned to starch relative to total C fixed was unaffected by 1 d of CO₂ enrichment. The above results showed that both photosynthetic and starch accumulation rates of soybean leaflets measured at 35 Pa CO₂ were temporarily reduced after 1 and 21 d of CO₂ enrichment. The biochemical mechanism affecting these responses was not identified.Abbreviations SLW- specific leaf weight (g m^–2) - Rubisco- ribulose 1,5-bisphosphate carboxylase/oxygenase - Rul- 5bisP, ribulose 1,5 bisphosphate - DAP- days after planting - SAR- starch accumulation rate - C_i- intercellular CO₂ concentration     

Production of dissolved organic carbon and low-molecular weight organic acids in soil solution driven by recent tree photosynthate

Dissolved organic carbon (DOC) is an important component in the terrestrial carbon cycle. Yet, the relative importance of different inputs of DOC to the soil solution remains uncertain. Here, we used a large-scale forest girdling experiment to examine how the supply of recent photosynthate to tree roots and their mycorrhizal fungi affects DOC, in particular low-molecular weight organic acids (LMWOA). We also studied effects of tree girdling on non-structural carbohydrates in microorganism, and examined the effects of freezing of soil and the presence of roots in the soil samples on soil solution DOC and LMWOA in this experiment. The concentration of DOC was reduced by 40%, while citrate was reduced by up to 90% in the soil solution by the girdling treatment. Other LMWOA such as oxalate, succinate, formate and propionate were unaffected by the girdling. We also found that girdling reduced the concentrations of trehalose (by 50%), a typical fungal sugar, and of monosaccharides (by 40%) in microorganisms in root-free soil. The effect of freezing on DOC concentrations was marked in samples from control plots, but insignificant in samples from girdled plots. Release of DOC from cell lysis after freezing was attributed equally to roots and to microorganisms. Our observations suggest a direct link from tree photosynthesis through roots and their mycorrhizal fungi to soil solution chemistry. This direct link should impact solute transport and speciation, mineral weathering and C dynamics in the soil compartment. Importantly, our finding of a substantial photosynthate driven production of DOC challenges the paradigm that DOC is mainly the result of decomposition of organic matter.     

The role of sink demand in carbon partitioning and photosynthetic reinvigoration following shoot decapitation

Photosynthesis, growth, and carbon partitioning of vigorous coppice shoots were compared with the slower growing intact shoots of Populus maximowiczii × nigra L. MN9 to determine the relationship between carbon partitioning and photosynthetic rate. Relative height growth rate of coppice shoots was 2.2 times that of intact shoots with net photosynthetic rate 1.9 times that of intact shoots. Coppice leaves exported a larger proportion of newly-fixed assimilate (11% compared with 6%) after a 4-h chase. The greater export from coppice leaves was correlated with a greater proportion of [¹⁴C]-labelled photosynthate deposited as starch in stems 4 cm below the point of label application. Coppice leaf assimilate levels were reduced to 15% that of leaves on intact plants, but coppice leaves had twice the concentration of labelled sucrose. Carbohydrates constituted 55% of the water-soluble [¹⁴C]-labelled photosynthate in leaves of coppice shoots compared with 40% in intact shoots. The results suggest that carbon allocation and partitioning in coppice shoots were altered towards production and export of new assimilate, and support the hypothesis that photosynthetic rate is responsive to sink demand for assimilates.     

Crop responses to ozone: uptake, modes of action, carbon assimilation and partitioning

The inhibitory effects of tropospheric O₃ on crop photosynthesis, growth, and yield have been documented in numerous studies over the past 35 years. In large part, the results of this research supported governmental regulations designed to limit tropospheric O₃ levels to concentrations that affected crop production at economically acceptable levels. Recent studies have brought into question the efficacy of these concentration-based O₃ standards compared with flux-based approaches that incorporate O₃ uptake along with environmental and biotic factors that influence plant responses. In addition, recent studies provide insight into the biochemical mechanisms of O₃ injury to plants. Current interpretations suggest that upon entry into the leaf intercellular space O₃ rapidly reacts with components of the leaf apoplast to initiate a complex set of responses involving the formation of toxic metabolites and generation of plant defence responses that constitute variably effective countermeasures. Plant species and cultivars exhibit a range of sensitivity to O₃, evident as heritable characteristics, that must reflect identifiable biochemical and molecular processes that affect sensitivity to O₃ injury, although their exact makeup remains unclear. Ozone clearly impairs photosynthetic processes, which might include the effects on electron transport and guard cell homeostasis as well as the better-documented effects on carbon fixation via decreased Rubisco activity. Translocation of photosynthate could be inhibited by O₃ exposure as well. Further, the influence of tropospheric O₃ needs to be considered when assessing potential effects of rising concentrations of atmospheric CO₂ on crop production. Advances in O₃ flux modelling and improved understanding of biochemical and molecular effects of O₃ on photosynthetic gas exchange and plant defence processes are leading to more complete, integrated assessments of O₃ impacts on crop physiology that continue to support the rationale for maintaining or improving current O₃ air quality standards as well as providing a basis for development of more O₃-tolerant crop lines.     

The effect of leaf size on mutual shading and cultivar differences in soybean leaf photosynthetic capacity

This study investigated the basis of the negative relationship between leaf size and photosynthetic rate per unit of area among five cultivars of soybeans. Exposure of developing mainstem leaves to light, and sizes and light saturated photosynthesis rates of those leaves at maturity were compared in cultivars grown in field plots for two years at Beltsville, Maryland, USA. Plants were grown both in stands at 2.5 cm by 1 m spacing and as isolated plants. While cultivar differences in leaf size were large and consistent in both planting arrangements, significant cultivar differences in light saturated photosynthetic rates were found only in plants grown in stands. Similarly, leaf size was significantly correlated with specific leaf weight only for plants grown in stands. The mainstem apex and developing mainstem leaves experienced more severe shading in large-leaved cultivars than in small-leaved cultivars when plants were grown in stands. Thus, cultivar differences in photosynthetic capacity were probably a consequence of differences in the exposure of developing leaves to light.     

赤峰市敖汉旗土壤有机碳含量的垂直分布及其影响因素

选取内蒙古赤峰市敖汉旗为研究对象,运用广义相加模型—分析敖汉旗0—100 cm深度土壤有机碳含量的空间变异特征,分析影响土壤有机碳空间变异的主导因素。结果表明,0—100 cm深度土壤有机碳含量的变化范围为0.23—20.71 g/kg,且随着土壤深度的增加有机碳含量逐渐降低。广义相加模型可以较为准确地解释土壤有机碳含量与环境因素之间的关系。植被因素的变化是影响表层土壤有机碳含量最重要的因素;在深层土壤中,含水率的变化是影响有机碳含量的主要因素。影响土壤有机碳空间变异的主导因素随着土壤深度的变化也表现出较大的差异。     

Interactions of blue light and inorganic carbon supply in the control of light-saturated photosynthesis in brown algae

Photosynthetic capacities of five species of brown algae in red light were found to be strongly limited by the inorganic carbon supply of natural sea water. Under these conditions, pH 8·2 and dissolved inorganic carbon concentration (DIG) of 2·1 mol m^?3, a short pulse of blue light was found to increase the subsequent rate of photosynthesis in saturating red light. The degree of blue light stimulation varied between species, ranging from an increase of over 200% of the original rate in Colpomenia peregrins to only 10% in Dictyota dichotoma. Increasing the DIG concentration of sea water by bicarbonate addition resulted in carbon saturation of photosynthesis in all five species. Blue light stimulation was greatly reduced at these higher DIG concentrations. The response in Laminaria digitata was examined in more detail by manipulation of pH and DIG to produce solutions with different concentrations of dissolved CO₂. At a CO₂ concentration typical of normal sea water (12·4 mmol m^?3), blue light treatment increased photosynthetic rate by approximately 50%. Blue light stimulation was increased to over 150% at CO₂ concentrations below that of sea water, whereas at concentrations above that of sea water, the effect was diminished. Therefore, the effect of blue light on photosynthetic capacity appears to involve an increase in the rate of supply of carbon dioxide to the plant.     

The effect of wind exposure and filamentous algae on the distribution of surf zone macroinvertebrates in Lake Esrom,Denmark

Distribution and composition of the epilithic macroinvertebrate fauna was studied on 21 different sites situated in the surf zone of Lake Esrom. A relative degree-of-exposure (windinduced wave activity) was calculated for each station from the specific number of wind days, wind velocity and a measured wind fetch. Macroinvertebrate abundance averaged 20 200 ind. m^–2 stone bottom, and was composed primarily of six taxa (70% of the mean densities). The distribution patterns of the 48 most common taxa were compared to exposure, the amount of filamentous algae and shore slope, by regression, cluster analysis and ordination analysis (PCA and RDA). The abundance of 25 taxa was significantly correlated to the amount of filamentous algae, and a protectional effect of algae growth was suggested for the exposed sites. Seventeen taxa showed significant difference in abundance between sheltered western stations and exposed eastern stations. Stations with a gentle slope were characterised by sand covered stones and a fauna that qualitatively was similar to the fauna at greater depth in the littoral. Redundancy analysis (RDA) showed filamentous algae and slope to be the most important factors controlling the species distribution, whereas the gradient of exposure in Lake Esrom was too short to explain the species tolerance range.     

Sources of organic carbon in the littoral of Lake Gooimeer as indicated by stable carbon isotope and carbohydrate compositions

The relative importance of potential carbon sources in the littoral of Lake Gooimeer, a lake in the centre of the Netherlands, was studied using a combination of ¹³C/¹²C-ratio analysis and carbohydrate composition analysis. The littoral is covered on the land side by a 80 m wide Phragmites australis bed. Potential carbon sources were macrophyte litter, seston and benthic algae. Samples of potential carbon sources, sediments and benthic macrofauna from inside and outside the bed were analyzed for their¹³C/¹²C-ratio and some for their carbohydrate composition. Results indicate that inside the bed, macrophyte litter was the main source of carbon for both the sediment organic matter and the benthic macrofauna, and that algal material was of minor importance. Outside the bed, production by benthic algae was the main carbon source, with seston as a second source. No macrophyte derived material could be detected outside the reed bed.Abbreviations DOC (Dissolved Organic Carbon) - SOM (Sediment Organic Matter)     

The importance and place of the photosynthetic carbon sequestration in the organic branch of its global cycle

Results of comparative analysis of turnover times and the capacity of major global pools of organic carbon are presented; the place of photosynthetic carbon sequestration is defined; concept of its catalytic role in the regulation of the organic branch of the global carbon cycle is ground. Concept of reservoir-flux model of photosynthetic carbon sequestration and of the net photosynthetic production at the territory of Northern Eurasia is suggested.Translated from Fiziologiya Rastenii, Vol. 52, No. 1, 2005, pp. 81–89.Original Russian Text Copyright © 2005 by Voronin, Black.     

Influence of carbon supply on the stimulation of light-saturated photosynthesis by blue light in Laminaria saccharina: implications for the mechanism of carbon acquisition in higher brown algae

In saturating irradiances of red light, photosynthesis of Laminaria saccharina (L.) Lamouroux was stimulated by low irradiances of continuous blue light only when the supply of dissolved inorganic carbon (DIC) was limiting. The degree of this stimulation was inversely proportional to the logarithm of the concentration of free CO₂, whether this was adjusted by varying the total DIC or the pH at a given DIC concentration. The final pH reached in a closed system was higher in blue light than in red light. Both acetazolamide and ethoxyzolamide suppressed the responses to blue light almost completely, but reduced photosynthesis in red light by only 30%. Buffering the pH of the seawater also suppressed the stimulation of photosynthesis by blue light without affecting the photosynthetic rate in red light. The transient stimulation of O₂ evolution by a blue light pulse was not accompanied by a corresponding increase in CO₂ consumption. These observations could be explained if, in analogy to the mechanism proposed for Ectocarpus (Schmid, Mills & Dring 1996, Plant Cell and Environment 19,373–382, this issue, accompanying paper), photosynthesis was supported by a blue-light-activated release of CO₂ from an internal store. We suggest that the store is located in the vacuoles of the cortical tissue of the blades. The main photosynthetic tissue, however, is in the overlying meristoderm, and blue-light-activated mobilization of the store could stimulate O₂ evolution only if periplasmic carbonic anhydrase was available to facilitate CO₂ uptake from the cortex.     

Use of lakes by black duck broods in relation to biological,chemical, and physical features

Characteristics of 32 freshwater lakes in central and western Nova Scotia were quantified to determine the relative influence of various biological, chemical, and physical factors on habitat selection by black ducks (Anas rubripes Brewster) during brood-rearing. Acidity and trophic status varied greatly among the waterbodies, of which 20 were used by black ducks for rearing their young. Duck brood density was positively related to lake trophic status. The highest brood densities occurred on hypertrophic waterbodies with a large anthropogenic input of nutrients.Lakes with black duck broods had significantly higher concentrations of phosphorus and nitrogen, darker water with more dissolved organic carbon, and within the littoral zone, greater macrophyte cover, greater density and biomass of pelagic invertebrates, gentler slopes, and a softer, more organic substrate. Similar trends were observed within a subset of 17 acidic lakes (pH 5.5), 8 of which supported black ducks.The density of black duck broods was significantly correlated with 17 of 20 variables, most notably total phosphorus (r= + 0.81). Partial correlation (removing the effect of total phosphorus) revealed that brood density was significantly correlated with the abundances of pelagic (r= + 0.77) and benthic (r= + 0.68) invertebrates, macrophyte cover (r= + 0.52), and substrate score (r= + 0.57), but not with other chemical variables, including pH.Our results suggest that quality brood-rearing habitat is distinguished by a combination of factors, especially available nutrients, macrophyte cover, and invertebrates, subject to constraints imposed by physical characteristics of the littoral zone of the lake. The abundance of invertebrates, the primary food of young black ducks, emerged as the most important biological factor influencing the density of black duck broods.     

Relationship between banding and photosynthetic activity in Chara corallina as studied by the spatially different induction curves of chlorophyll fluorescence observed by an image analysis system

Image analysis was applied for studying the kinetics of chlorophyll fluorescence in the alkaline and acid zones of internodal cells of Chara corallina Klein ex Willd., in order to test the hypothesis that in the acid bands an outward proton current yields a conversion of HCO₃⁻ ions to CO₂, thus facilitating inward diffusion of CO₂.
The analysis of the responses of chlorophyll fluorescence induced by changes in light intensity from 0.15 W m⁻² to 2.0 W m⁻² (λ <580 nm) revealed different kinetic behaviour. In the alkaline zones, the amplitude of the variable components of fluorescence was smaller than in the acid zones. Curve fitting by a sum of exponentials showed that the 4 time constants of about 2, 22, 48 and 140 s were not significantly different between the alkaline and acid zones. In contrast the related amplitude factors were smaller in the alkaline zones. by a factor of about 1.6 to 2.0 in old calcified cells and by a factor of about 1.2 in young cells without acrustations.
The interpretation of these results in terms of a better supply of carbon dioxide in the acid zones was supported by investigations on leaves of tobacco. Lowering the CO₂ concentration of an artificial atmosphere below 20 ppm resulted in a similar reduction of the variable component of chlorophyll fluorescence as found in the alkaline zones of Chara .     

Influence of carbon supply on the circadian rhythmicity of photosynthesis and its stimulation by blue light in Ectocarpus siliculosus: clues to the mechanism of inorganic carbon acquisition in lower brown algae

Stimulation or light-saturated rates of photosynthesis in Ectocarpus siliculosus (Dillwyn) Lyngb. by blue light was eliminated by increasing dissolved inorganic carbon (DIC) or by lowering pH in natural seawater. The amplitude of the circadian rhythm of photosynthesis was also diminished under these conditions, and the pH compensation points in a closed system were higher in the presence of blue light and during the circadian day. These observations suggest that blue light and the circadian clock regulate the activity of a carbon acquisition system in these plants. The inhibitor of external carbonic anhydrase, acetazolamide, reduced overall rates of photosynthesis by only about 30%, but ethoxyzolamide suppressed the circadian rhythm of photosynthesis almost completely and markedly reduced the duration of responses to blue light pulses. Similar patterns were obtained when photosynthesis was measured in strongly limiting DIC concentrations (0–0.5 mol m^?3). Since blue light stimulated photosynthesis under these conditions of strong carbon limitation, we suggest that blue light activates the release of CO₂ from an internal CO₂ store. We propose a metabolic pathway with similarities to that of CAM plants. Non-photosynthetic fixation leads to the accumulation of a storage metabolite. The circadian clock and blue light control the mobilization of CO₂ at the site of decarboxylation of this metabolite. In the presence of continuous blue light the pathway is proposed to cycle and act as a pump for CO₂ into the chloroplasts. This hypothesis helps to explain a number of previously reported peculiarities of brown algal photosynthesis.     

Light response curves for Gelidium sesquipedale from different depths, determined by two methods: O2 evolution and chlorophyll fluorescence

Photosynthesis-light response curves of Gelidium sesquipedale from the west coast of Portugal (Cape Espichel) were determined at four different depths, 3, 10, 15 and 22 m. Data acquisition using chlorophyll a fluorescence methodology and oxygen electrode measurements were compared. Response curves were determined over an increasing range of irradiance values (I), from darkness to 900 μmol photon m-2 s-1 PAR. In general, light response curves obtained for G. sesquipedale showed a similar pattern whether determined by the chlorophyll fluorescence method or by oxygen evolution. The photosynthetic capacity of G. sesquipedale decreased with depth, as expected, revealing a ‘sun’ and ‘shade’ acclimation pattern, between shallow and deeper waters. This revised version was published online in June 2006 with corrections to the Cover Date.     

Induction of exocytosis in characean internodal cells by locally restricted application of chlortetracycline and the effect of cytochalasin B,depolarizing and hyperpolarizing agents*

Abstract. Local exocytosis with concomitant deposition of cell wall material (plugs) was induced in mature characean internodal cells by application of Sephadex beads loaded with a chlortetracycline (CTC)/CaCl₂ solution. Plugs can be formed anywhere on the cells independently of structural and/or functional plasma membrane domains, provided that the pH of the CTC/CaCl₂ solution is above 5.5. Plug formation is inhibited by cytochalasin B and membrane depolarizing agents. Treatment with fusicoccin enhances exocytosis. The results suggest that actin filaments are involved in the transport of vesicles and endoplasmic reticulum cisternae towards the cell membrane, and that the membrane potential determines the extent of CTC mediated Ca²⁺ influx.     

Plankton photosynthesis, extracellular release and bacterial utilization of released dissolved organic carbon (RDOC) in lakes of different trophy

The major objective of these studies was to assess the extent of the flow of released dissolved organic carbon (RDOC) from phytoplankton to heterotrophic bacteria. The second aim was to test Nalewajko and Schindler's (1976) hypothesis that the percentage of extracellular release (PER) of RDOC by phytoplankton is higher in oligotrophic than eutrophic waters. The studies on the relationship between the bacterial assimilation of RDOC and productivity of phytoplankton in the lakes of different trophy have shown a direct correlation. It was observed that higher utilization rate of phytoplankton RDOC occurred in lakes with higher primary production. The inverse relationship between productivity of lakes, i.e. trophy of waters, and amount of RDOC or PER is closely dependent on the heterotrophic activity of bacteria in waters.     

Metabolism of dissolved organic carbon by planktonic bacteria and mixotrophic algae in lake neutralisation experiments

1. Lakes formed in mining pits often contain high concentrations of dissolved ferric iron and sulphate (e.g. 2 and 16 mmol L^?1, respectively) and the pH is buffered between 2.5 and 3.5. Efforts to neutralise their water are based on the stimulation of lake internal, bacterial iron‐ and sulphate reduction. Electron donors may be supplied by organic carbon compounds or indirectly by enhancement of primary production. Here, we investigated the function of mixotrophic algae, which can potentially supplement or deplete the organic carbon pool, in the carbon metabolism and alkalinity budget of an acidic mining lake. 2. Two weeks after organic substrates had been added in a large in situ mesocosm of 30 m diameter, a bloom of Chlamydomonas occurred, reaching a biovolume of 80 mm³ L^?1. Growth experiments using filtered lake water showed that the alga reduced the overall dissolved organic carbon (DOC) concentration despite significant photosynthetic activity. However, when Chlamydomonas were grown together with natural bacterioplankton, net DOC consumption did not increase. 3. Uptake experiments using [¹⁴C]‐glucose indicated that bacteria dominated glucose uptake and remineralisation. Therefore, the DOC leached in the water column was processed mainly by planktonic bacteria. Leached DOC must be regarded as loss, not transferred by larger organisms to the sediment, where reduction processes take place. 4. From phytoplankton biomass and production 2 years after fertilisation we estimated that pelagic photosynthesis does not supply an electron donor capacity capable of reducing more than 2% of actual stock of acidity per year. We estimated that only the benthic primary production was in a range to compensate for ongoing inputs of iron and sulphate.