Ratio Of Gross Photosynthesis Research Articles

Effects of iron limitation on carbon balance and photophysiology of the Antarctic diatom Chaetoceros cf. simplex

In the Southern Ocean (SO), iron (Fe) limitation strongly inhibits phytoplankton growth and generally decreases their primary productivity. Diatoms are a key component in the carbon (C) cycle, by taking up large amounts of anthropogenic CO2 through the biological carbon pump. In this study, we investigated the effects of Fe availability (no Fe and 4 nM FeCl3 addition) on the physiology of Chaetoceros cf. simplex, an ecologically relevant SO diatom. Our results are the first combining oxygen evolution and uptake rates with particulate organic carbon (POC) build up, pigments, photophysiological parameters and intracellular trace metal (TM) quotas in an Fe-deficient Antarctic diatom. Decreases in both oxygen evolution (through photosynthesis, P) and uptake (respiration, R) coincided with a lowered growth rate of Fe-deficient cells. In addition, cells displayed reduced electron transport rates (ETR) and chlorophyll a (Chla) content, resulting in reduced cellular POC formation. Interestingly, no differences were observed in non-photochemical quenching (NPQ) or in the ratio of gross photosynthesis to respiration (GP:R). Furthermore, TM quotas were measured, which represent an important and rarely quantified parameter in previous studies. Cellular quotas of manganese, zinc, cobalt and copper remained unchanged while Fe quotas of Fe-deficient cells were reduced by 60% compared with High Fe cells. Based on our data, Fe-deficient Chaetoceros cf. simplex cells were able to efficiently acclimate to low Fe conditions, reducing their intracellular Fe concentrations, the number of functional reaction centers of photosystem II (RCII) and photosynthetic rates, thus avoiding light absorption rather than dissipating the energy through NPQ. Our results demonstrate how Chaetoceros cf. simplex can adapt their physiology to lowered assimilatory metabolism by decreasing respiratory losses.

Effects of temperature and salinity on respiratory losses and the ratio of photosynthesis to respiration in representative Antarctic phytoplankton species.

The Southern Ocean (SO) is a net sink for atmospheric CO2 whereby the photosynthetic activity of phytoplankton and sequestration of organic carbon (biological pump) plays an important role. Global climate change will tremendously influence the dynamics of environmental conditions for the phytoplankton community, and the phytoplankton will have to acclimate to a combination of changes of e.g. water temperature, salinity, pH, and nutrient supply. The efficiency of the biological pump is not only determined by the photosynthetic activity but also by the extent of respiratory carbon losses of phytoplankton cells. Thus, the present study investigated the effect of different temperature and salinity combinations on the ratio of gross photosynthesis to respiration (rGP/R) in two representative phytoplankton species of the SO. In the comparison of phytoplankton grown at 1 and 4°C the rGP/R decreased from 11.5 to 7.7 in Chaetoceros sp., from 9.1 to 3.2 in Phaeocystis antarctica strain 109, and from 12.4 to 7.0 in P. antarctica strain 764, respectively. The decrease of rGP/R was primarily dependent on temperature whereas salinity was only of minor importance. Moreover, the different rGP/R at 1 and 4°C were caused by changes of temperature-dependent respiration rates but were independent of changes of photosynthetic rates. For further interpretation, net primary production (NPP) was calculated for different seasonal conditions in the SO with specific combinations of irradiance, temperature, and salinity. Whereas, maximum photosynthetic rates significantly correlated with calculated NPP under experimental ‘Spring’, ‘Summer’, and ‘Autumn’ conditions, there was no correlation between rGP/R and the respective values of NPP. The study revealed species-specific differences in the acclimation to temperature and salinity changes that could be linked to their different original habitats.

Photosynthetic characteristics and their spatial variance on biological soil crusts covering initial soils of post-mining sites in Lower Lusatia, NE Germany

Following surface disturbance, quaternary sands are the basic substrate for soil development in the Lusatian reclamation area. These substrates mostly contain few organic matter and, hence, are nutrient poor. Accumulation of soil carbon is an important factor for ecosystem development, where biological soil crusts initially influence soil processes and promote ecosystem succession. The compositional structures of biological soil crusts at various developmental stages and their photosynthetic properties were investigated on two former open-cast lignite sites, currently under reclamation, an artificial sand dune in Welzow Süd, and a forest plantation in Schlabendorf Süd (Brandenburg, Germany). As development of biological soil crusts progressed, their contents of organic carbon and total chlorophyll increased. The ratio of these parameters, however, varied with the relative contribution of lichens and mosses in particular. Also maximum photochemical efficiency, net photosynthesis and respiration increased with crustal development. An additional evaluation of NDVI and chlorophyll fluorescence images showed that especially moss-dominated biocrusts had higher photosynthetic capacity compared to green algae-dominated biocrusts or soil lichens, so the photosynthetic capacity showed to be highly species-specific. The ratio of gross photosynthesis to respiration indicated a higher ecological efficiency of biocrusts dominated by green algae than of lichen-dominated biocrusts. The occurrence of soil lichens reduced net CO2 fixation and increased CO2 release due to the enhanced mycobiontic respiration. During crustal succession, the rise of photosynthesis-related parameters is not necessarily linear as a result of the highly heterogenic distribution of the different crustal organisms between biocrusts of similar developmental stages as well as between those growing at the two study sites. Therefore, the evaluation of relevant ecophysiological parameters highlighted that not all biocrust-forming organisms similarly contribute to the ecophysiological behavior of biological soil crusts. Nevertheless, the occurrence of the biological soil crusts promoted soil formation and accumulation of soil carbon in initial soils.

Photosynthetic contribution of UV-A to carbon fixation by macroalgae

:Previous studies showed that energy of ultraviolet light A (UV-A) (315–400 nm) could be used for photosynthesis by some macroalgae; however, little has been documented on the extent of such photosynthetic contribution among different macroalgal taxa. We selected 11 macroalgal species, representing red, brown and green phyla, and investigated their ability to utilize UV-A for photosynthesis. Our results showed that, in the absence of photosynthetically active radiation (PAR), UV-A alone triggered photosynthetic carbon fixation rates in all the selected species. The gross photosynthetic rates of the tested macroalgae when exposed to UV-A ranged from 6.5 ± 0.3 to 52.3 ± 1.8 μmol C g (fresh weight)−1 h−1, with the highest rate found in the green alga Ulva lactuca Linnaeus. The ratio of gross photosynthesis driven by UV-A alone to that by saturating PAR varied from 14% to 22%. The present work demonstrated that macroalgae are capable of utilizing UV-A irradiance to drive photosynthetic carbon fixation, and this was consistent for all the species tested across green, red and brown algae.

Non steady-state dynamics of stable oxygen isotopes for estimates of metabolic balance in large lakes

Abstract The ratio of gross photosynthesis to community respiration ( P : R ) is a vital characteristic of ecosystem function but is poorly defined in large lakes because traditional methods are impractical for measuring P and R on appropriate time and space scales. The new steady state in situ 18 O method has a great power to assess metabolic patterns in large lakes. However it could be confounded by seasonal and/or episodic temperature changes, which can violate the steady-state assumptions by altering the saturation level of dissolved O 2 without actual gain or loss of O 2 when air–water gas exchange is too slow to compensate for the altered solubility. We estimated P , R and P : R at three coastal sites of varied depth, productivity and physical exposure in the Laurentian Great Lakes by both the 18 O method and experimental incubations. At two shallow sites with low and moderate exposure to open lake forces, the 18 O and incubation methods returned similar estimates for P , R and P : R . The deepest site experienced large and frequent upwelling episodes and the 18 O method was unreliable, with P and R estimates usually negative. We define an O 2 saturation ratio ( γ ) that determines the applicability of the 18 O method to any given system. Estimates obtained using observed O 2 saturation above this threshold are invalid. The γ ratio increases with lake productivity. Higher productivity and/or shallower lakes appear good candidates for use of the 18 O method, but applications in deeper, physically-driven lakes will likely need explicit attention to temperature-driven non-steady state effects.

Peculiarities of CO<sub>2</sub> exchange in soybean genotypes contrasting in grain yield

The peculiarities of leaf carbon dioxide gas exchange in soybean genotypes grown in field over a large area and contrasting in duration of vegetation, photosynthetic traits and productivity were studied. Varietal differences in the daily and ontogenetic changes in photosynthesis and photorespiration were identified. It was established that the period of the high activity of photosynthetic apparatus in high productive soybean genotypes lasts for a longer time. The photosynthetic rate and the rate of CO2 release in light due to photorespiration are higher in high productive genotypes. A value of photorespiration in contrasting soybean genotypes constitutes about 28% - 35% of photosynthetic rate. The ratio of gross photosynthesis to photorespiration in genotypes with different productivity is constant enough during ontogenesis, indicating a direct positive correlation between gross photosynthesis and photorespiration. Therefore, contrary to conception arisen during many years on the waste-fulness of photorespiration, taking into account the versatile investigations on different aspects of photo-respiration, it was proved that photorespiration is one of the evolutionarily developed vital metabolic processes in plants and the attempts to reduce this process with the purpose of increasing the crop productivity are inconsistent.

INTERPRETING WOODY PLANT RICHNESS FROM SEASONAL RATIOS OF PHOTOSYNTHESIS

In forested portions of Oregon, species richness of woody plants on plots 400-500 m 2 ranged from 1 to .20. We investigated what might account for this variation using a satellite-driven process model that predicts gross photosynthesis and establishes, on a monthly time step, the most constraining environmental variable. Independent satellite and ground-based data confirmed that the highest species richness occurs on sites of in- termediate productivity, where 60-70% of the light is intercepted by vegetation. We dem- onstrated that most photosynthesis takes place during the spring and summer months for both evergreen and deciduous species. We estimated that the spring to summer ratio of gross photosynthesis (DPG) varies from , 1t o.5 across the state. Both the most productive coastal rainforests and least productive arid woodlands exhibited the lowest values of DPG near 1, and had lowest species richness. Plots with highest species richness were located in areas with mild, moist, spring weather conditions, followed by a summer drought, with DPG averaging above 3. Satellite-derived estimates of gross photosynthesis are available for more extensive analysis.

Seasonal courses of CO(2) exchange and carbon balance in fruits of Cinnamomum camphora.

Carbon dioxide exchange in fruits of Cinnamomum camphora Sieb. was followed over a growing season from July to December 1992. Dark respiration was exponentially related to temperature, with a Q(10) value near 2. Light dependence of photosynthetic CO(2) refixation, i.e., the ratio of gross photosynthesis to dark respiration, was approximated by a hyperbolic function. Seasonal variation in maximum CO(2) refixation capacity ranged between 52 and 174%, reaching a maximum in early August. Daily photosynthetic CO(2) refixation ranged between 17 and 51% over the growth period. We evaluated seasonal variation in translocation rate to the fruit on the basis of the seasonal rates of gross photosynthesis, dark respiration and increase in fruit dry weight, and used the results to develop a simple carbon flow model of fruit development. Seasonal changes in translocation rate paralleled those in fruit growth rate, with two peaks during the periods before and after September. Seed formation took place in the period between the two peaks. The relationship between fruit growth rate and translocation rate was approximated by a linear function. The carbon flow model estimated that, over the reproductive period, the amount of assimilate translocated to each fruit was 377.2 mg dry weight, of which 58.5% was accounted for by weight growth and 41.5% was consumed by net respiration. Carbon dioxide refixation accounted for 22.9% of the carbon balance of the fruit.

Biomass and oxygen dynamics of the epiphyte community in a Danish lowland stream

SUMMARY. 1. We examined the abundance and oxygen metabolism of epiphytic organisms on the dominant macrophyte, Potamogeton pectinatus, in headwaters of the eutrophic River Suså. Microbenthic algae were abundant in the stream during spring and macrophytes during summer.2. The low macrophyte biomass in spring supported a dense epiphyte cover whereas the high macrophyte biomass during summer had a thin epiphyte cover of 10–100‐fold lower abundance per unit area of macrophyte surface. The epiphyte community was dominated by microalgae in spring and by heterotrophs, probably bacteria, during summer. This seasonal shift was shown by pronounced reductions of the chlorophyll a content (from 2–3% to 0.1–0.7% of organic DW), the gross photosynthetic rate (from 20–85 to 3–15 mg O2, g‐1 organic DW h−1) and the ratio of gross photosynthesis to dark respiration in the epiphyte community (from 5–18 to 1). The reduced contributions of epiphytic microalgae correlated with reduced light availability during summer.3. Both the density and the photosynthetic activity of epiphytic algae were low on a stream area basis relative to those of microbenthic algae and macrophytes. Rapid variations in water velocity and extensive light attenuation in water and macrophyte stands probably constrained the development of epiphytic algae. The epiphyte community was more important in overall stream respiration, contributing c. 10% to total summer respiration and c. 20% to summer respiration within the predominantly heterotrophic microbial communities on sediments and macrophyte surfaces.

Glycerol translocation in Condylactis gigantea

Sodium cyanide (NaCN) was used to partially uncouple respiration and photosynthesis in the symbiotic sea anemone Condylactis gigantea. NaCN significantly increased the ratio of gross photosynthesis to respiration in both intact tentacles and isolated zooxanthellae (Symbiodinium microadriaticum), increased carbon translocation from 17.7±3.5% of total fixed in controls to 43.5±5.8%, and doubled the amount of photosynthetically fixed carbon accumulating in the coelenterate host over that in controls. Only 2% of the non-particulate radioactivity recovered in the host tissue was 14C-glycerol when uninhibited symbiotic tentacles were incubated in 14C-bicarbonate for 1 h. At 10-5M NaCN, approximately 25% of the host nonparticulate radioactivity was recovered as 14C-glycerol, the absolute concentration of glycerol in the host tissue was three times higher than in controls, and 14C-glycerol was found in the medium. While glycerol has been proposed to play a major role in the translocation of photosynthetically fixed carbon from zooxanthellae to their coelenterate hosts, its concentration has never been measured in the animal and algal components of the symbiosis. The isolated zooxanthellae contained 3.62±0.33 mM glycerol, 26x the 0.141±0.02 mM found in the anemone. Aposymbiotic anemone tissue contained 0.169±0.06 mM glycerol. The rate of glycerol mineralization was not saturated even when exogenous glycerol levels were 70x internal concentrations. These data show that respiration and photosynthesis in symbiotic associations may be partially uncoupled by NaCN, and that this uncoupling allows the verification of the translocation and rapid catabolism of glycerol within the host.

Relationships between respiratory rate of root and temperature modulated photosynthesis in rice plant and the factors concerning the respiratory rate of root.

Two cultivars of potted rice plants were given various treatments, such as, 10 cm depth inundation, high water parcolation (30 mm/day) and excision of lower leaves below top three leaves, in order to change the respiratoy rate of roots. Photosynthesis and dark respiration were measured by the assimilation chamber method under the given conditions of temperature range from 20°C to 40°C during 4 hours at the time of young panicle formation, heading and mid-period of ripening. Immediately after this measurement, the roots were sampled with thoroughly washing out soil and the root respiration in normal air was measured by chamber method. At the time of young panicle formation, the respiratory rate of younger roots from upper three nodes at the base of stem showed much higher activity than that of older roots on lower nodes, however, such diflbrences were not noticed during the period after heading. The ratio of gross photosynthesis of 30°C to 40°C showed a high positive correlation to the respiratory rate of root ; the plants with lower rate of respiration exhibited strongly depressed photosynthesis at high temperature of 40°C perhaps due to thermoactivc closure of stomata. The depression observed at high temperature appears to be caused by water deficit in leaves due to inferior water absorption, since the transpiration efticiency at 30°C was quite dependent on the respiratory rate of roots. Multiple regression analysis of root respiration, nitrogen and sugar content in root revealed that the respiratory rate of root had high positive correlation with the nitrogen as well as the sugar content of the roots. The nitrogen content in root was swayed by nitrogen concentration at the top whereas the sugar content was parallel to net photosynthetic, activity of the plant which in turn is capable of expressing by nitrogen content in leaves of the plant.

A culture system enabling in situ determination of net and gross photosynthesis, O2 evolution, N assimilation, and C2H2 reduction in cyanobacteria

A chemostat culture system is described in which measurements of rates associated with carbon and nitrogen assimilation may be made in in situ steady-state cultures of N2-fixing cyanobacteria. Net C and N assimilations were determined from the steady-state cellular carbon and nitrogen contents and the steady-state growth rate of the cultures. O2 evolution in the light and short-term 14C assimilation were measured simultaneously in unperturbed culture cuvettes. 14C assimilation was linear with time through the origin over the 20-min sampling period, thereby providing a measure of gross photosynthesis. C2H2 reduction was measured within the culture cuvette using an open gas analysis system. Steady-state rates of C2H2 reduction were obtained within 10 min and remained constant for up to 1 h. Preliminary results showed that at similar growth rates (0.018–0.019 h−1) cultures grown on [Formula: see text] and N2 contained heterocysts, were smaller, and had higher chlorophyll contents than cells grown on NH3. Corresponding gross photosynthesis was 1.6 to 1.8 times higher than net photosynthesis in [Formula: see text] and N2-grown cells; however, for NH3-grown cells the ratio of gross photosynthesis:net photosynthesis was close to unity. These results are discussed with reference to the energetic costs associated with N assimilation in cyanobacteria.

Photosynthetic Rate Control in Cotton

The purpose of this research was to determine the magnitude of photorespiration in field-grown cotton (Gossypium hirsutum L.) as a function of environmental and plant-related factors. Photorespiration rates were estimated as the difference between measured gross and net photosynthetic rates.A linear increase in photorespiration was observed as air temperature increased from 22 to 40 degrees C at saturating photon flux density. At 22 degrees C, photorespiration was less than 15 per cent of net photosynthesis and very comparable to the dark respiration rate. At 40 degrees C, photorespiration represented about 50 per cent of net photosynthesis. Gross photosynthesis had a temperature optimum of 32 to 34 degrees C. Water stress, as indicated by Psi(L), did not alter the ratio of gross photosynthesis to net photosynthesis when the confounding effects of leaf temperature differences were accounted for in the data analyses. A reduction in both gross and net photosynthesis was apparent as Psi(L) declined from -2.0 megapascals indicating direct effects of water stress on the photosynthetic process. Photorespiration expressed as a proportion of net photosynthesis increased as water stress intensified.Cotton cultivars possessing a fruit load had significantly higher gross and net photosynthetic rates and lower photorespiration rates than did photoperiod-sensitive cotton strains without a fruit load. Within the fruiting types, which were genetically very similar, only minor differences were observed in the photorespiration:net photosynthesis ratios. However, in the photoperiod-sensitive strains, considerable genetic variability existed when photorespiration was expressed as a proportion of net photosynthesis. These results suggest that the kinetics of ribulose-1,5-bisphosphate carboxylase:oxygenase may be different and, thus, the possibility of genetically reducing photorespiration exists.