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.     

Global patterns of the responses of leaf-level photosynthesis and respiration in terrestrial plants to experimental warming

Aims The balance between leaf photosynthesis and respiration of terrestrial plants determines the net carbon (C) gain by vegetation and consequently is important to climate–C cycle feedback. This study is to reveal the global patterns of the responses of leaf-level net photosynthesis and dark respiration to elevated temperature.Methods Data for leaf-level net photosynthesis rate (P n) and dark respiration rate (R d) in natural terrestrial plant species with standard deviation (or standard error or confidence interval) and sample size were collected from searched literatures on Web of Science. Then a meta-analysis was conducted to estimate the effects of experimental warming on leaf-level P n and R d of terrestrial plants.Important findings Across all the plants included in the analysis, warming enhanced P n and R d significantly by 6.13 and 33.14%, respectively. However, the responses were plant functional type (PFT) specific. Specifically, photosynthesis of C₄ herbs responded to experimental warming positively but that of C₃ herbs did not, whereas their respiratory responses were similar, suggesting C₄ plants would benefit more from warming. The photosynthetic response declined linearly with increasing ambient temperature. The respiratory responses linearly enhanced with the increase in warming magnitude. In addition, a thermal acclimation of R d, instead of P n, was observed. Although greater proportion of fixed C was consumed (greater R d / P n ratio), warming significantly enhanced the daily net C balance at the leaf level. This provides an important mechanism for the positive responses of plant biomass and net primary productivity to warming. Overall, the findings, including the contrastive responses of different PFTs and the enhancement in daily leaf net C balance, are important for improving model projection of the climate–C cycle feedback.     

An automatic system to study the responses of respiration and photosynthesis by submerged macrophytes to environmental variables

An apparatus to measure the rates of respiration and photosynthesis of aquatic plants in water at velocities of up to 200 mm s^–1 in a closed water-flow system with partial recirculation, is described. The temperature, the light regime and the concentration of dissolved oxygen are controlled automatically. Typical results are given for Ranunculus penicillatus var. calcareus which were repeatable between the same season in different years and compared with published data.     

Oxygen diffusion and dark respiration in aquatic macrophytes

Abstract. The supply of oxygen to respiring shoot tissue was investigated for three submerged macrophytes (Potamogeton crispus L., Egeria densa Planch, and Myriophyllum triphyllum Orchard). For all species, the response of oxygen uptake rates to the external O₂ concentration was a rectangular hyperbola over the range 0–5.0 × 10^?3m³ m^?3. However, the response pattern for material with water-infiltrated lacunar airspaces was non-hyperbolic over this range. The change in response was interpreted as an increased substrate (O₂) limitation, resulting from lower radial diffusion rates within the infiltrated material. Neither the uninfiltrated nor the infiltrated responses obeyed the linear and logarithmic formulae of the type observed for submerged macrophytes by earlier authors. These results suggest that the responses observed are affected by factors such as water velocity, internal restrictions to diffusion and the range of oxygen tensions investigated. Therefore, it is unlikely that one response formula can adequately account for the effects of oxygen concentration on submerged macrophyte oxygen uptake. The lacunar airspaces also represent a possible oxygen source for dark respiration. The consumption of oxygen from the airspaces was investigated by displacing the gas from the lacunae and measuring the subsequent increase in the rate of oxygen assimilation from the external liquid. Approximately 30% of the oxygen consumed by E. densa and P. crispus, and more than 40% of that consumed by M. triphyllum, was derived from the lacunar system. This O₂ supply is a consequence of the higher oxygen concentration in the lacunae than in the external medium, due to the low solubility of oxygen in water. Storage of photosynthetically-produced oxygen in the lacunae could not be identified during a light/dark transient, due to rate changes caused by the effects of light on the respiratory metabolism. However, O₂ partial pressure gradients artificially set up between the lacunae and water equilibrated within an hour, suggesting that excess oxygen would be lost to the water within this time.     

光照下菜豆叶片抗氰呼吸与光合作用关系的分析北大核心CSCD

为了进一步了解光照下植物呼吸作用的内在机理以及呼吸作用和光合作用的关系,该文研究了在光照下菜豆(Phaseolus vulgaris)叶片抗氰呼吸与光合作用的关系。研究发现,将黑暗下生长的菜豆幼苗叶片转到光照下10 h,总呼吸、抗氰呼吸以及抗氰呼吸在总呼吸中的比例均逐步上升;光照也导致了叶片叶绿体光合放氧和CO2固定的出现及其速率的增加,但光合放氧和CO2固定速率的增加均滞后于抗氰呼吸的增加。将黑暗下生长的叶片转到光照下之前用抗氰呼吸的抑制剂水杨基氧肟酸(SHAM)处理叶片,发现用SHAM处理并没有导致叶片在光照下光合放氧和CO2固定速率的明显变化,这也提示了黑暗下生长的叶片转至光照的过程中,抗氰呼吸和光合作用没有产生偶联。进一步研究发现,在黑暗中对叶片施加短时间的光照能够增加抗氰呼吸在总呼吸中的比例,但短时间的光照对叶片光合CO2固定速率没有影响。这些结果表明了光照对抗氰呼吸的诱导可以不依赖于光合作用,光照可能是作为一种直接的信号去诱导抗氰呼吸。     

光照下菜豆叶片抗氰呼吸与光合作用关系的分析

为了进一步了解光照下植物呼吸作用的内在机理以及呼吸作用和光合作用的关系, 该文研究了在光照下菜豆(Phaseolus vulgaris)叶片抗氰呼吸与光合作用的关系。研究发现, 将黑暗下生长的菜豆幼苗叶片转到光照下10 h, 总呼吸、抗氰呼吸以及抗氰呼吸在总呼吸中的比例均逐步上升; 光照也导致了叶片叶绿体光合放氧和CO₂固定的出现及其速率的增加, 但光合放氧和CO₂固定速率的增加均滞后于抗氰呼吸的增加。将黑暗下生长的叶片转到光照下之前用抗氰呼吸的抑制剂水杨基氧肟酸(SHAM)处理叶片, 发现用SHAM处理并没有导致叶片在光照下光合放氧和CO₂固定速率的明显变化, 这也提示了黑暗下生长的叶片转至光照的过程中, 抗氰呼吸和光合作用没有产生偶联。进一步研究发现, 在黑暗中对叶片施加短时间的光照能够增加抗氰呼吸在总呼吸中的比例, 但短时间的光照对叶片光合CO₂固定速率没有影响。这些结果表明了光照对抗氰呼吸的诱导可以不依赖于光合作用, 光照可能是作为一种直接的信号去诱导抗氰呼吸。     

Crayfish as geomorphic agents and ecosystem engineers: effect of a biomass gradient on baseflow and flood-induced transport of gravel and sand in experimental streams

SUMMARY 1. Using experimental streams, we studied the impact of the crayfish Orconectes limosus on (i) the transport of gravel and sand at baseflow; (ii) the sediment surface (bedform, particle consolidation, proportion of sand, algal and gravel cover); and (iii) the critical shear stress (τ_C) causing incipient gravel and sand motion during simulated floods. We examined (i) and (ii) in experimental outdoor flumes that replicated riffle‐pool sequences and (iii) in a larger laboratory flume, in which we exposed sediments retrieved from the outdoor flumes to a progressively increasing discharge. 2. Habitat changes induced by crayfish, such as bedform alterations in riffles (downstream displacement of riffle heads) and the increase of gravel on sand dunes in pools, had major impacts on the spatial and temporal patterns of the baseflow transport of gravel and sand. 3. In addition to their impact on bedform in riffles and on gravel cover in pools, crayfish prevented the physical consolidation of particles in riffles and reduced the algal cover and the proportion of sand in the surface layer in both riffles and pools. These crayfish impacts on sediment surface variables had complex, interacting effects on the mobilisation of gravel and sand during subsequent flood simulations. For sand, crayfish progressively decreased the τ_C (i.e. the sum of bedform drag and skin friction) by about 50% along the entire biomass gradient in pools, whereas the presence of crayfish abruptly decreased the τ_C by about 75% in riffles. For gravel, the discharge causing motion in riffles produced a shear stress (in terms of skin friction) on an even bedform that was about 75% lower in all flumes with crayfish compared with the flumes without crayfish. Crayfish had no impact on τ_C for gravel in pools. 4. Scaling‐up these experimental results to real streams suggests that crayfish could affect the patch dynamics of major sediment transport events and habitat suitability for other organisms that, at larger spatial scales, could increase the overall spatio‐temporal habitat diversity and thus the overall structural and functional biodiversity of lotic communities.     

Influence of medium frequency light/dark cycles of equal duration on the photosynthesis and respiration of Chlorella pyrenoidosa

Chlorella pyrenoidosa was grown in three continuous cultures each receiving a different light regime during the light period of a diurnal cycle. Hourly samples taken during the light period were subjected to medium frequency light/dark oscillations of equal duration, ranging from 3 to 240 seconds. The oxygen consumption and production of each sample were measured with an oxygen electrode in a small oxygen chamber. Although the light/dark cycles had little overall influence on photosynthetic activity, the microalgae appeared to adapt to the light regime to which they were subjected. Large differences were found between the maximum chlorophyll-specific production rates (P _infmax ^supB ), the chlorophyll-specific production rates (P^B) and the respiration rates between the cultures and treated subsamples. Respiration rates increased during the light period, whilst P^B either increased, or had a mid light period minimum or maximum. The culture which received an hourly light oscillation during the light period had the highest P _infmax ^supB and lowest respiration rates, and it is suggested that these algae react as in nature, whereas either a sinusoidal or a block light pattern is unnatural. The latter light regime is commonly used in laboratory studies.     

Role of dark respiration in photoinhibition of photosynthesis and its reactivation in the cyanobacterium Anacystis nidulans

Photoinhibition of photosynthesis and its reactivation was studied in the cyanobaterium A. nidulans in the presence of the respiratory inhibitor sodium azide, the uncouplers carbonyl cyanide p -(trifluoromethoxy)-phenylhydrazone (FCCP) and carbonyl cyanide m -chlorophenylhydrazone (CCCP) and the photosystem I elicitor phenazine methosulphate (PMS). Inhibition of dark respiration by azide increased the susceptibility of the cyanobacterium to photoinhibition. Both FCCP and CCCP also remarkably affected the process of photoinhibition in A. nidulans. The PMS at lower photoinhibitory light intensity partially protected A. nidulans from photoinhibition. The recovery from photoinhibition in the presence of azide or FCCP was slow and normal photosynthesis could not be resumed even after a longer period of incubation under suitable reactivating condition. Thus dark respiration has a key function in the process of photoinhibition of photosynthesis and its reactivation in the cyanobacterium A. nidulans.     

The seasonal temperature dependency of photosynthesis and respiration in two deciduous forests

Novel nonstationary and nonlinear dynamic time series analysis tools are applied to multiyear eddy covariance CO₂ flux and micrometeorological data from the Harvard Forest and University of Michigan Biological Station field study sites. Firstly, the utility of these tools for partitioning the gross photosynthesis and bulk respiration signals within these series is demonstrated when employed within a simple model framework. This same framework offers a promising new method for gap filling missing CO₂ flux data. Analysing the dominant seasonal components extracted from the CO₂ flux data using these tools, models are inferred for daily gross photosynthesis and bulk respiration. Despite their simplicity, these models fit the data well and yet are characterized by well‐defined parameter estimates when the models are optimized against calibration data. Predictive validation of the models also demonstrates faithful forecasts of annual net cumulative CO₂ fluxes for these sites.     

Seasonal changes in temperature and nutrient control of photosynthesis, respiration and growth of natural phytoplankton communities

1. To investigate the influence of elevated temperatures and nutrients on photosynthesis, respiration and growth of natural phytoplankton assemblages, water was collected from a eutrophic lake in spring, summer, autumn, winter and the following spring and exposed to ambient temperature and ambient +2, +4 and +6 °C for 2 weeks with and without addition of extra inorganic nutrients. 2. Rates of photosynthesis, respiration and growth generally increased with temperature, but this effect was strongly enhanced by high nutrient availability, and therefore was most evident for nutrient amended cultures in seasons of low ambient nutrient availability. 3. Temperature stimulation of growth and metabolism was higher at low than high ambient temperature showing that long‐term temperature acclimation of the phytoplankton community before the experiments was of great importance for the measured rates. 4. Although we found distinct responses to relatively small temperature increases, the interaction between nutrient availability, time of the year and, thus, ambient temperature was responsible for most of the observed variability in phytoplankton growth, photosynthesis and respiration. 5. Although an increase in global temperature will influence production and degradation of organic material in lakes, the documented importance of ambient temperatures and nutrient conditions suggests that effects will be most pronounced during winter and early spring, while the remaining part of the growth season will be practically unaffected by increasing temperatures.     

Plastoquinone as a common link between photosynthesis and respiration in a blue-green alga

The role of plastoquinone in a thermophilic blue-green alga, Shynechococcus sp., was studied by measuring reduction kinetics of cytochrome 553 which was oxidized with red flash preferentially exciting photosystem I. Sensitivity of the cytochrome reduction to DBMIB indicates that cytochrome 553 accepts electrons from reduced plastoquinone. Plastoquinone is in turn reduced in cells without electrons from photosystem II, since DCMU, which inhibited methyl viologen photoreduction more strongly than DBMIB, failed to affect the cytochrome reduction. Participation of cyclic electron transport around photosystem I in cytochrome reduction in the presence of DCMU was excluded, because methyl viologen and antimycin A had no effect on the cytochrome kinetics. On the other hand, electron donation from endogenous substrates to plastoquinone was suggested from decreases in rate of the cytochrome reduction by dark starvation of cells and also from restoration of fast reduction kinetics by the addition of exogenous substrates to or by reillumination of starved cells.KCN, which completely suppressed respiratory O₂-uptake, induced a marked acceleration of the cytochrome reduction in starved cells. The poison was less or not effective in stimulating the cytochrome reduction in more extensively starved or reilluminated cells.Results indicate that plastoquinone is functioning not only in the photosynthetic but also in the respiratory electron transport chain, thereby forming a common link between the two energy conservation systems of the blue-green alga.

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Acclimation of the respiration/photosynthesis ratio to temperature: insights from a model

Based on short-term experiments, many plant growth models – including those used in global change research – assume that an increase in temperature stimulates plant respiration (R) more than photosynthesis (P), leading to an increase in the R/P ratio. Longer-term experiments, however, have demonstrated that R/P is relatively insensitive to growth temperature. We show that both types of temperature response may be reconciled within a simple substrate-based model of plant acclimation to temperature, in which respiration is effectively limited by the supply of carbohydrates fixed through photosynthesis. The short-term, positive temperature response of R/P reflects the transient dynamics of the nonstructural carbohydrate and protein pools; the insensitivity of R/P to temperature on longer time-scales reflects the steady-state behaviour of these pools. Thus the substrate approach may provide a basis for predicting plant respiration responses to temperature that is more robust than the current modelling paradigm based on the extrapolation of results from short-term experiments. The present model predicts that the acclimated R/P depends mainly on the internal allocation of carbohydrates to protein synthesis, a better understanding of which is therefore required to underpin the wider use of a constant R/P as an alternative modelling paradigm in global change research.     

Epilithic chlorophyll a,photosynthesis, and respiration in control and fertilized reaches of a tundra stream

Photosynthesis and respiration by the epilithic community on cobble in an arctic tundra stream, were estimated from oxygen production and consumption in short-term (4–12 h), light and dark, chamber incubations. Chlorophyll a was estimated at the end of each incubation by quantitatively removing the epilithon from the cobble. Fertilization of the river with phosphate alone moderately increased epilithic chlorophyll a, photosynthesis, and respiration. Fertilization with ammonium sulfate and phosphate, together, greatly increased each of these variables. Generally, under both control and fertilized conditions, epilithic chlorophyll a concentrations (mg m⁻²), photosynthesis, and respiration (mg O₂ m⁻², h⁻¹) were higher in pools than in riffles. Under all conditions, the P/R ratio was consistent at ∼ 1.8 to 2.0. The vigor of epilithic algae in riffles, estimated from assimilation coefficients (mg O₂ [mg Chl a]⁻¹ h⁻¹) was greater than the vigor of epilithic algae in pools. However, due to the greater accumulation of epilithic chlorophyll a in pools, total production (and respiration) in pools exceeded that in riffles. The epilithic community removed both ammonium and nitrate from water in chambers. Epilithic material, scoured by high discharge in response to storm events and suspended in the water column, removed ammonium and may have increased nitrate concentrations in bulk river water. However, these changes were small compared to the changes exerted by attached epilithon.     

Grazing alters warming effects on leaf photosynthesis and respiration in Gentiana straminea,an alpine forb species

Aims Vast grasslands on the Tibetan Plateau are almost all under livestock grazing. It is unclear, however, what is the role that the grazing will play in carbon cycle of the grassland under future climate warming. We found in our previous study that experimental warming can shift the optimum temperature of saturated photosynthetic rate into higher temperature in alpine plants. In this study, we proposed and tested the hypothesis that livestock grazing would alter the warming effect on photosynthetic and respiration through changing physical environments of grassland plants.Methods Experimental warming was carried by using an infrared heating system to increase the air temperature by 1.2 and 1.7°C during the day and night, respectively. The warming and ambient temperature treatments were crossed over to the two grazing treatments, grazing and un-grazed treatments, respectively. To assess the effects of grazing and warming, we examined photosynthesis, dark respiration, maximum rates of the photosynthetic electron transport (J max), RuBP carboxylation (V cmax) and temperature sensitivity of respiration Q 10 in Gentiana straminea, an alpine species widely distributed on the Tibetan grassland. Leaf morphological and chemical properties were also examined to understand the physiological responses.Important findings 1) Light-saturated photosynthetic rate (A max) of G. straminea showed similar temperature optimum at around 16°C in plants from all experimental conditions. Experimental warming increased A max at all measuring temperatures from 10 to 25°C, but the positive effect of the warming occurred only in plants grown under the un-grazed conditions. Under the same measuring temperature, A max was significantly higher in plants from the grazed than the un-grazed condition. 2) There was significant crossing effect of warming and grazing on the temperature sensitivity (Q 10) of leaf dark respiration. Under the un-grazed condition, plants from the warming treatment showed lower respiration rate but similar Q 10 in comparison with plants from the ambient temperature treatment. However, under the grazed condition Q 10 was significantly lower in plants from the warming than the ambient treatment. 3) The results indicate that livestock grazing can alter the warming effects on leaf photosynthesis and temperature sensitivity of leaf dark respiration through changing physical environment of the grassland plants. The study suggests for the first time that grazing effects should be taken into account in predicting global warming effects on photosynthesis and respiration of plants in those grasslands with livestock grazing.     

Effects of water velocity on photosynthesis and dark respiration in submerged stream macrophytes

The effects of flow velocities on dark respiration and net photosynthesis of eight submerged stream macrophytes were examined in a laboratory oxygen chamber. The shoots/leaves were exposed to saturating free-CO₂ concentrations and were attached basally so that they could move in the flowing water. Net photosynthesis declined by 34–61% as flow velocity increased from 1 to 8.6cm s^?1, while dark respiration increased 2.4-fold over the same range. The increase in dark respiration could only account for between 19 and 67% of the decrease in net photosynthesis. The relationship between flow velocity (U) and net photosynthesis (P) was described by: P=b×U^a. The exponent, a, varied from -0.20 to –0.48 and showed a negative correlation to the surface: volume (SA: V) ratio of the plants, i.e. species with high SA: V ratio were more sensitive to flow. In contrast, net photosynthesis of plants firmly attached to a supporting frame was not significantly affected by increasing flow velocity. This result indicates that the physical stress imposed on the plants by agitation or stretching in the flowing water is a key factor for the observed response.     

Scaling up calcification,respiration, and photosynthesis rates of six prominent coral taxa

Coral reefs provide a range of important services to humanity, which are underpinned by community‐level ecological processes such as coral calcification. Estimating these processes relies on our knowledge of individual physiological rates and species‐specific abundances in the field. For colonial animals such as reef‐building corals, abundance is frequently expressed as the relative surface cover of coral colonies, a metric that does not account for demographic parameters such as coral size. This may be problematic because many physiological rates are directly related to organism size, and failure to account for linear scaling patterns may skew estimates of ecosystem functioning. In the present study, we characterize the scaling of three physiological rates — calcification, respiration, and photosynthesis — considering the colony size for six prominent, reef‐building coral taxa in Mo''orea, French Polynesia. After a seven‐day acclimation period in the laboratory, we quantified coral physiological rates for three hours during daylight (i.e., calcification and gross photosynthesis) and one hour during night light conditions (i.e., dark respiration). Our results indicate that area‐specific calcification rates are higher for smaller colonies across all taxa. However, photosynthesis and respiration rates remain constant over the colony‐size gradient. Furthermore, we revealed a correlation between the demographic dynamics of coral genera and the ratio between net primary production and calcification rates. Therefore, intraspecific scaling of reef‐building coral physiology not only improves our understanding of community‐level coral reef functioning but it may also explain species‐specific responses to disturbances.     

Beneficial interaction between photosynthesis and respiration in mesophyll protoplasts of pea during short light-dark cycles

The respiratory uptake or photosynthetic evolution of oxygen by mesophyll protoplasts of pea ( Pisum sativum L. cv. Arkel) were monitored during successive short. (3–5 min) cycles of darkness and illumination. The rate of respiration was nearly doubled after 3–4 short periods of illumination while there was a 15–20% enhancement in photosynthesis with cycles of illumination and darkness preceding illumination. Such interaction between photosynthesis and respiration was statistically significant when bicarbonate was present in the reaction medium. The inhibitors of photosynthesis [3(3,4–dichlorophenyl)-l,l-dimethylurea (DCMU), glyceraldehyde] decreased respiration after periods of illumination, whereas inhibitors of respiratory electron transport (Rotenone, antimycin A, NaN₃) suppressed photosynthesis, as well. We suggest that a rapid beneficial interaction exists between photosynthesis and respiration in protoplasts, even during short cycles of light and darkness.