Open Gas Exchange System Research Articles

ИЗМЕРЕНИЕ ПОТОКОВ CO2 И H2O МЕЖДУ СРЕДОЙ И РАСТЕНИЯМИ ИНФРАКРАСНЫМ ГАЗОАНАЛИЗАТОРОМ НА ОСНОВЕ ОТКРЫТОЙ СИСТЕМЫ ГАЗООБМЕНА С УЧЕТОМ ИНСТРУМЕНТАЛЬНОЙ ОШИБКИ

Currently, the study of gas exchange in leaves and even entire plants is not difficult. Measurement of gas exchange parameters is, as a rule, carried out using infrared gas analyzers integrated with open gas exchange systems. The measured parameter values are used to evaluate and calculate the physiological processes of interest to the investigator, such as, for example, the rate of absorption of carbon dioxide by the plant during photosynthesis or the rate of release of water vapors during transpiration. In the scientific literature on plant physiology, the error of the result of measuring physiological parameters is given without taking into account the instrumental error, the contribution of which to the total error can be significant, since the physiological parameters of interest to the researcher are mostly indirectly measurable values. This work is devoted to the study of the influence of the error of measuring the parameters of gas exchange of plants obtained using open gas exchange systems on the error of the estimated physiological parameters. The work analyzes equations that are used to estimate the rate of absorption of carbon dioxide and the release of water vapors based on the gas exchange parameters of the plant and are actually standard for open gas exchange systems; issues related to the release of carbon dioxide from the plant in the form of gas during respiratory processes in the light are also considered. An evaluation of instrumental error of carbon dioxide absorption rate measurement during photosynthesis for open gas exchange systems is given.

MIC-100, a new system for high-throughput phenotyping of instantaneous leaf photosynthetic rate in the field.

Photosynthesis occurs mainly in plant leaves and is a fundamental process in the global carbon cycle and in crop production. The exploitation of natural genetic variation in leaf photosynthetic capacity is a promising strategy to meet the increasing demand for crops. The present study reports the newly developed photosynthesis measurement system 'MIC-100,' with a higher throughput for measuring instantaneous photosynthetic rate in the field. MIC-100 is established based on the closed system and directly detects the CO2 absorption in the leaf chamber. The reproducibility, accuracy, and measurement throughput of MIC-100 were tested using soybean (Glycine max L. (Merr.)) and rice (Oryza sativa L.) grown under field conditions. In most cases, the coefficient of variance (CV) for repeated-measurements of the same leaf was less than 0.1. The photosynthetic rates measured with the MIC-100 model showed a significant correlation (R2 = 0.93-0.95) with rates measured by a widely used gas-exchange system. The measurement throughput of the MIC-100 is significantly greater than that of conventional open gas-exchange systems under field conditions. Although MIC-100 solely detects the instantaneous photosynthetic rate under a given environment, this study demonstrated that the MIC-100 enables the rough evaluation of leaf photosynthesis within the large-scale plant populations grown in the field.

Nitrogen Loading Enhances Stress Impact of Drought on a Semi-natural Temperate Grassland.

Two important threats to the sustainable functioning of seminatural grasslands in temperate zones are (1) nutrient loading due to agricultural fertilization and pollution, and (2) the increase of extreme drought events due to climate change. These threats may cause substantial shifts in species diversity and abundance and considerably affect the carbon and water balance of ecosystems. The synergistic effects between those two threats, however, can be complex and are poorly understood. Here, we experimentally investigated the effects of nitrogen addition and extreme drought (separately and in combination) on a seminatural temperate grassland, located in Freiburg (South Germany). To study the grassland response, we combined eddy-covariance techniques with open gas exchange systems. Open gas exchange chambers were connected to an infrared gas analyzer and water isotope spectrometer, which allowed the partitioning of net ecosystem exchange and evapotranspiration. Vegetation parameters were described by species richness, species abundance, and leaf area index. Our results suggest that grassland communities, strongly weakened in their stress response by nitrogen loading, can substantially lose their carbon sink function during drought. While nitrogen addition caused a significant loss in forb species (−25%), precipitation reduction promoted a strong dominance of grass species at season start. Consequently, the grass-dominated and species-poor community suffered from a strong above-ground dieback during the dry summer months, likely caused by lower water use efficiency and weaker drought adaptations of the species community. Over the growing season (April-September), the carbon sequestration of the studied grassland was reduced by more than 60% as a consequence of nitrogen addition. Nitrogen addition in combination with precipitation reduction decreased carbon sequestration by 73%. Eutrophication can severely threaten the resilient functioning of grasslands, in particular when drought periods will increase as predicted by future climate scenarios. Our findings emphasize the importance of preserving high diversity of grasslands to strengthen their resistance against extreme events such as droughts.

Diurnal changes and effect of elevated CO2 on gas exchange under individual and interactive salt and water stress in wheat (Triticum aestivum)

To evaluate the individual and interactive effects of drought and salt stress on diurnal stomatal behaviour and gas exchange parameters, two salt tolerant (Kharchia 65, KRL 210) and two salt sensitive (HD 2851, HD 2009) wheat (Triticum aestivum L.) varieties were subjected to drought (25% and 50% water deficit) and salt (50 mM and 100 mM NaCl) stresses, imposed separately and in combination. Diurnal changes in photosynthetic rate (Pn), stomatal conductance (gS) and transpiration rates (E) of wheat leaves were measured at 4 h intervals under field conditions, using an infrared open gas exchange system. Photosynthetic rate was also measured across a range of variable intercellular CO2 concentrations (50 – 800 ppm). Kharchia 65 (salt tolerant) and KRL 210 (moderately salt tolerant) wheat varieties showed photosynthetic rate of 19.74 and 9.19 μmol/m2/s, while HD 2009 and HD 2851 (salt sensitive) showed photosynthetic rate of -27.65 and -17.65 μmol/m2/s at 50 ppm intercellular CO2 concentration which increased with increasing CO2 concentration. Up to 200 ppm intercellular CO2 concentration, these sensitive varieties showed negative Pn values. Diurnal photosynthetic activities of wheat varieties significantly differed under stressful environment but these differences could not be expressed in control conditions. Pn was low in the early morning, increasing with time and reached maximum (μmol/m2/s) between 10:00 AM to 2:00 PM, thereafter, Pn decreased. Similar trends of increase and decrease were observed for gS and E.

Effectiveness of Plant Species for Removing Atmospheric Ammonia

Effectiveness of Plant Species for Removing Atmospheric Ammonia Marife B. Anunciado, M. S; Sheryll B. Jerez, Ph.D; Hans Williams, Ph.D; Joey Bray, Ph.D; Dean Coble, Ph.D; Rena Saito, Ph.D. Abstract Six plant species of Yaupon, Eastern red cedar, American holly, Arizona cypress, Arborvitae and Roughleaf dogwood were utilized to determine their effectiveness in the removal of atmospheric ammonia. All species were exposed to three ammonia levels (1, 5 and 10 ppm) in an environmental chamber. Foliar ammonia content was quantified using an enzymatic technique. The effects of exposure to ammonia on the physiological responses (e.g. photosynthetic activity, stomatal conductance, and transpiration rate) of plants in ambient condition were also determined using an open design photosynthetic gas exchange system. Foliar ammonia content was significantly different among the six plant species (p<0.0001) with Eastern red cedar exhibiting the highest content. The physiological responses differed significantly depending on the plant species and the ammonia treatment level. The photosynthetic response of plants to the presence of ammonia was mixed. At low exposure level, all species except Arborvitae had decreased photosynthetic activity, reducing by as much as 44.5% for Yaupon. At the highest concentration, however, Yaupon’s photosynthetic activity improved by about 10%. Exposure to ammonia caused increased stomatal conductance and transpiration rate on American holly and Arizona cypress, making them more susceptible to water loss. Full Text: PDF DOI: 10.15640/jaes.v8n1a1

A practical approach to estimate diffusional leakages of leaf chamber of open gas exchange systems using intact leaves.

We propose a novel approach to determine the coefficient of CO2 diffusional leakage (k_CO2 ) in the chamber of a portable open gas exchange system (Li-6400, Li-Cor Inc., NE, USA) using intact leaves. Assuming that dark respiration rate (Rn ) is constant at various CO2 concentrations, at least in a short term, k_CO2 should be the value that makes the leak-corrected Rn constant. We used 2 representative tree species native to northern Japan, Japanese white birch (Betula platyphylla var. japonica) and Japanese oak (Quercus mongolica var. crispula), to determine k_CO2 , by measuring Rn at various CO2 concentrations. Irrespective of the species, k_CO2 estimated by the present approach was well correlated with the diffusional leak coefficient (k_flow ) estimated by the generally used approach that utilizes CO2 concentrations inside and outside the chamber based on thermally killed leaves at various flow rates. Furthermore, the present approach does not require the ambient CO2 concentration outside the chamber (Ca ) if Ca in the laboratory is stable, which provides a feasible way to correct the photosynthetic rate, taking diffusional leakage into account.

Parameter Estimation of the Farquhar—von Caemmerer—Berry Biochemical Model from Photosynthetic Carbon Dioxide Response Curves

The Farquhar—von Caemmerer—Berry (FvCB) biochemical model of photosynthesis, commonly used to estimate CO2 assimilation at various spatial scales from leaf to global, has been used to assess the impacts of climate change on crop and ecosystem productivities. However, it is widely known that the parameters in the FvCB model are difficult to accurately estimate. The objective of this study was to assess the methods of Sharkey et al. and Gu et al., which are often used to estimate the parameters of the FvCB model. We generated An/Ci datasets with different data accuracies, numbers of data points, and data point distributions. The results showed that neither method accurately estimated the parameters; however, Gu et al.’s approach provided slightly better estimates. Using Gu et al.’s approach and datasets with measurement errors and the same accuracy as a typical open gas exchange system (i.e., Li-6400), the majority of the estimated parameters—Vcmax (maximal Rubisco carboxylation rate), Kco (effective Michaelis-Menten coefficient for CO2), gm (internal (mesophyll) conductance to CO2 transport) and Γ* (chloroplastic CO2 photocompensation point)—were underestimated, while the majority of Rd (day respiration) and α (the non-returned fraction of the glycolate carbon recycled in the photorespiratory cycle) were overestimated. The distributions of Tp (the rate of triose phosphate export from the chloroplast) were evenly dispersed around the 1:1 line using both approaches. This study revealed that a high accuracy of leaf gas exchange measurements and sufficient data points are required to correctly estimate the parameters for the biochemical model. The accurate estimation of these parameters can contribute to the enhancement of food security under climate change through accurate predictions of crop and ecosystem productivities. A further study is recommended to address the question of how the measurement accuracies can be improved.

Cuticle Affects Calculations of Internal CO2 in Leaves Closing Their Stomata.

Analyzing the assimilation rate (A) relative to the CO(2) concentration inside leaves (C(i)) has been a useful approach for investigating plant responses to various environments. Nevertheless, there are uncertainties in calculating C(i) when stomata close, restricting the application. Here, A-C(i) curves were traced in sunflower (Helianthus annuus L.) leaves using a method for directly measuring C(i). The method was incorporated into an LI-6400 open gas exchange system, and stomata were closed by feeding 10 µM ABA through petioles. The conductance to CO(2) was derived from the directly measured C(i) and compared with the conductance from the water vapor flux (i.e. the standard calculation). When stomata were open, measured and calculated C(i) gave similar A-C(i) curves. When stomata were closed, the curves differed because measured C(i) departed from the calculated value. This difference caused the calculation to trace an artifactual limitation of photosynthesis. The direct measurement avoided this problem and followed the curve for leaves with open stomata. Largely because of the cuticle, the calculation overestimated CO(2) entry into the leaf because the cuticle transmitted more water vapor than CO(2), and the calculation relied on water vapor. Consequently, the standard calculation gave conductances larger than those from directly measured C(i). Although the cuticle conductance to water vapor remained constant as stomata closed, it increasingly contributed to the overestimation of C(i). The system provided here is not affected by these cuticle properties and thus is expected to open up the opportunity for A-C(i) analysis in plant physiology.

Two distinct plant respiratory physiotypes might exist which correspond to fast-growing and slow-growing species

The origin of the carbon atoms in CO2 respired by leaves in the dark of several plant species has been studied using 13C/12C stable isotopes. This study was conducted using an open gas exchange system for isotope labeling that was coupled to an elemental analyzer and further linked to an isotope ratio mass spectrometer (EA–IRMS) or coupled to a gas chromatography–combustion-isotope ratio mass spectrometer (GC–C-IRMS). We demonstrate here that the carbon, which is recently assimilated during photosynthesis, accounts for nearly ca. 50% of the carbon in the CO2 lost through dark respiration (Rd) after illumination in fast-growing and cultivated plants and trees and, accounts for only ca. 10% in slow-growing plants. Moreover, our study shows that fast-growing plants, which had the largest percentages of newly fixed carbon of leaf-respired CO2, were also those with the largest shoot/root ratios, whereas slow-growing plants showed the lowest shoot/root values.

Individual- and stand-level stem CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; efflux in a subtropical &amp;lt;I&amp;gt;Schima superba&amp;lt;/I&amp;gt; plantation

Abstract. Stem respiration is an important, but poorly studied component of total forest ecosystem respiration. Stem CO2 efflux was investigated with an open gas exchange system while stand microclimate and stem temperature were continuously monitored in a Schima superba plantation in South China for several days in August and December 2010. The temperature response of respiration in the different seasons, the vertical variation in stem CO2 efflux along the stem, and the stand-level stem CO2 efflux were examined. Stem volume was identified as the better correlate for stem CO2 efflux and was used as the scalar for the stand-level estimates of stem CO2 efflux in this S. superba plantation. Volume-based stem CO2 efflux was higher at 2 m than at 1.3 m. Mean stem CO2 efflux was 268.9 and 104.6 μmol m−3 s−1 in August and December, respectively, indicating a dramatic seasonal variation of stem CO2 efflux. The temperature response of stem CO2 efflux remained constant during our study period with Q10 values of 1.9 and 1.8. In this subtropical S. superba plantation, stem CO2 efflux per unit ground area averaged 3.36 and 1.26 μmol m−2 s−1 based on the measurement data at 1.3-m height of the stem in August and December, respectively. Our results suggest that stem CO2 efflux has a constant temperature response, and the seasonal variation in stem CO2 efflux is mainly controlled by stem temperature, and the vertical variation in stem CO2 efflux needs to be considered in the stand-level estimation.

Quantifying the measurement errors in a portable open gas-exchange system and their effects on the parameterization of Farquhar et al. model for C&lt;sub&gt;3&lt;/sub&gt; leaves

A portable open gas-exchange system (Li-6400, Li-Cor, Inc., Lincoln, NE, USA) has been widely used for the measurement of net gas exchanges and calibration/parameterization of leaf models. Measurement errors due to diffusive leakage rates of water vapor (LW) and CO2 (LC) between inside and outside of the leaf chamber, and the inward dark transpiration rate (DW) and dark respiration rate (DC) released from the leaf under the gasket, can be significant. Rigorous model-based approaches were developed for estimating leakage coefficients of water vapor (KW) and CO2 (KC) and correcting for the combination of these errors. Models were based on mass balance equations and the Dusty Gas Model for a ternary gas mixture of water vapor, CO2, and dry air. Experiments were conducted using two Li-6400 systems with potato and soybean leaves. Results indicated that models were reliable for estimating KW and KC, and the values varied with instrument, chamber size, gasket condition, and leaf structure. A thermally killed leaf should be used for this determination. Measurement error effects on parameterization of the Farquhar et al. (1980) model as determined by P N/C i curves were substantial and each parameter had its own sensitivity to measurement errors. Results also indicated that all four error sources should be accounted for when correcting measurements.

Whole-Canopy Gas Exchange and Light Interception of Vertically TrainedVitis viniferaL. under Direct and Diffuse Light

A portable, open gas exchange system was developed that enabled the simultaneous measurement of net carbon dioxide exchange (NCE) and transpiration of eight mature Sauvignon blanc grapevines in the field. On clear and cloudy days NCE and transpiration were closely related to the modeled interception of photosynthetically active radiation (PAR). On clear days, the relationship between photosynthesis and incident PAR was poor and NCE peaked in the vertically trained, north-south orientated rows three hours before and after solar noon, resulting in a distinct bimodal pattern to vine gas exchange, which was not evident on cloudy days. Under diffuse light (cloudy) conditions, the vines appeared to be more efficient, photosynthesizing at a higher rate per calculated unit of light intercepted. This efficiency was probably due to the saturation of the exterior and shading of interior leaves under clear conditions, while under diffuse conditions the increased scattered light enhanced the irradiance received by the leaves in the interior of the canopy. Despite the improved light use efficiency under diffuse conditions, lower light intensities meant that CO₂ exchange was normally lower than that recorded during clear days. The effect of the chambers on the sap flux velocity up the vine stems was minor, which suggests that their effect on vine microclimate and resulting transpiration was minimal. There was a strong relationship between concurrent transpiration and sap flux velocity, which was not improved by the use of a time delay between transpiration and sap flux, and suggests that the vines do not rely greatly on water stored in the trunk and other vegetative organs above the ground (capacitance) for transpiration under these conditions.

Elevational change in woody tissue CO2 efflux in a tropical mountain rain forest in southern Ecuador

Much uncertainty exists about the magnitude of woody tissue respiration and its environmental control in highly diverse tropical moist forests. In a tropical mountain rain forest in southern Ecuador, we measured the apparent diurnal gas exchange of stems and coarse roots (diameter 1-4 cm) of trees from representative families along an elevational transect with plots at 1050, 1890 and 3050 m a.s.l. Mean air temperatures were 20.8, 17.2 and 10.6 degrees C, respectively. Stem and root CO(2) efflux of 13 to 21 trees per stand from dominant families were investigated with an open gas exchange system while stand microclimate was continuously monitored. Substantial variation in respiratory activity among and within species was found at all sites. Mean daily CO(2) release rates from stems declined 6.6-fold from 1.38 micromol m(-2) s(-1) at 1050 m to 0.21 micromol m(-2) s(-1) at 3050 m. Mean daily CO(2) release from coarse roots decreased from 0.35 to 0.20 micromol m(-2) s(-1) with altitude, but the differences were not significant. There was, thus, a remarkable shift from a high ratio of stem to coarse root respiration rates at the lowest elevation to an apparent equivalence of stem and coarse root CO(2) efflux rates at the highest elevation. We conclude that stem respiration, but not root respiration, greatly decreases with elevation in this transect, coinciding with a substantial decrease in relative stem diameter increment and a large increase in fine and coarse root biomass production with elevation.

A PHYSIOLOGICAL DISORDER OF SALINE STRESS RELEASED GREENHOUSE TOMATO PLANTS

A PHYSIOLOGICAL DISORDER OF SALINE STRESS RELEASED GREENHOUSE TOMATO PLANTS

Analysis of leakage in IRGA's leaf chambers of open gas exchange systems: quantification and its effects in photosynthesis parameterization

The measurement of the response of net photosynthesis to leaf internal CO2 (i.e. A-Ci curves) is widely used for ecophysiological studies. Most studies did not consider CO2 exchange between the chamber and the surrounding air, especially at the two extremes of A-Ci curves, where large CO2 gradients are created, leading to erroneous estimations of A and Ci. A quantitative analysis of CO2 leakage in the chamber of a portable open gas exchange system (Li-6400, LI-COR Inc., NE, USA) was performed. In an empty chamber, the measured CO2 leakage was similar to that calculated using the manufacturer's equations. However, in the presence of a photosynthetically inactive leaf, the magnitude of leakage was substantially decreased, although still significant. These results, together with the analysis of the effects of chamber size, tightness, flow rate, and gasket material, suggest that the leakage is larger at the interface between the gaskets than through the gaskets. This differential leakage rate affects the parameterization by photosynthesis models. The magnitude of these errors was assessed in tobacco plants. The results showed that leakage results in a 10% overestimation of the leaf maximum capacity for carboxylation (Vc,max) and a 40% overestimation of day respiration (Rl). Using the manufacturer's equations resulted in larger, non-realistic corrections of the true values. The photosynthetic response to CO2 concentrations at the chloroplast (i.e. A-Cc curves) was significantly less affected by leakage than A-Ci curves. Therefore, photosynthetic parameterization can be improved by: (i) correcting A and Ci values for chamber leakage estimated using a photosynthetically inactive leaf; and (ii) using A-Cc instead of A-Ci curves.

A new measurement technique reveals rapid post‐illumination changes in the carbon isotope composition of leaf‐respired CO2

We describe an open leaf gas exchange system coupled to a tunable diode laser (TDL) spectroscopy system enabling measurement of the leaf respiratory CO(2) flux and its associated carbon isotope composition (delta(13)C(Rl)) every 3 min. The precision of delta(13)C(Rl) measurement is comparable to that of traditional mass spectrometry techniques. delta(13)C(Rl) from castor bean (Ricinus communis L.) leaves tended to be positively related to the ratio of CO(2) produced to O(2) consumed [respiratory quotient (RQ)] after 24-48 h of prolonged darkness, in support of existing models. Further, the apparent fractionation between respiratory substrates and respired CO(2) within 1-8 h after the start of the dark period was similar to previous observations. In subsequent experiments, R. communis plants were grown under variable water availability to provide a range in delta(13)C of recently fixed carbohydrate. In leaves exposed to high light levels prior to the start of the dark period, CO(2) respired by leaves was up to 11 per thousand more enriched than phloem sap sugars within the first 10-15 min after plants had been moved from the light into the dark. The (13)C enrichment in respired CO(2) then decreased rapidly to within 3-7 per thousand of phloem sap after 30-60 min in the dark. This strong enrichment was not observed if light levels were low prior to the start of the dark period. Measurements of RQ confirmed that carbohydrates were the likely respiratory substrate for plants (RQ > 0.8) within the first 60 min after illumination. The strong (13)C enrichment that followed a high light-to-dark transition coincided with high respiration rates, suggesting that so-called light-enhanced dark respiration (LEDR) is fed by (13)C-enriched metabolites.

Respiratory carbon metabolism following illumination in intact French bean leaves using (13)C/(12)C isotope labeling.

The origin of the carbon atoms in the CO(2) respired by French bean (Phaseolus vulgaris) leaves in the dark has been studied using (13)C/(12)C isotopes as tracers. The stable isotope labeling was achieved through a technical device that uses an open gas-exchange system coupled online to an elemental analyzer and linked to an isotope ratio mass spectrometer. The isotopic analysis of the CO(2) respired in the dark after a light period revealed that the CO(2) was labeled, but the labeling level decreased progressively as the dark period increased. The pattern of disappearance depended on the amount of carbon fixed during the labeling and indicated that there were several pools of respiratory metabolites with distinct turnover rates. We demonstrate that the carbon recently assimilated during photosynthesis accounts for less than 50% of the carbon in the CO(2) lost by dark respiration and that the proportion is not influenced by leaf starvation in darkness before the labeling. Therefore, most of the carbon released by dark respiration after illumination does not come from new photosynthates.

PHOTOSYNTHETIC INHIBITION OF 'SEYVAL BLANC' GRAPEVINES WITH TERBACIL

PHOTOSYNTHETIC INHIBITION OF 'SEYVAL BLANC' GRAPEVINES WITH TERBACIL

Disentangling CO2 fluxes: direct measurements of mesocosm‐scale natural abundance 13CO2/12CO2 gas exchange, 13C discrimination, and labelling of CO2 exchange flux components in controlled environments

ABSTRACTA 13C/12C mass spectrometer was interfaced with a open gas exchange system including four growth chambers to investigate CO2 exchange components of perennial ryegrass (Lolium perenne L.) stands. Chambers were fed with air containing CO2 with known δ13C (δCΟ2−2.6 or −46.8‰). The system did not fractionate C isotopes and no extraneous CO2 leaked into chambers. The on‐line 13C discrimination (Δ) of ryegrass stands in light was independent of δCΟ2 when δCΟ2 was constant. The δ of CO2 exchanged by the stands in light (δNd) and darkness (δRn) differed by 0.7‰, suggesting some Δ in dark respiration at the stand‐level. However, Δ decreased by ∼ 10‰ when δCΟ2 was switched from −46.8 to −2.5‰, and increased by ∼ 10‰ following a shift from −2.6 to −46.7‰ due to isotopic disequilibria between photosynthetic and respiratory fluxes. Isotopic imbalances were used to assess (non‐photorespiratory) respiration in light and the replacement of the respiratory substrate pool(s) by new photosynthate. Respiration was partially inhibited by light, but increased during the light period and decreased in darkness, in association with temperature changes. The labelling kinetics of respiratory CO2 indicated the existence of two major respiratory substrate pools: a fast pool which was exchanged within hours, and a slow pool accounting for ∼ 60% of total respiration and having a mean residence time of 3.6 d.

Measurements of photosynthesis and respiration in plants.

Methods for measuring the rates of photosynthesis and respiration in plants are reviewed. Closed systems that involve manometric techniques, 14CO2 fixation, O2 electrodes and other methods for measuring dissolved and gas phase O2 are described. These methods typically provide time-integrated rate measurements, and limitations to their use are discussed. Open gas exchange systems that use infra-red CO2 gas analysers and differential O2 analysers for measuring instantaneous rates of CO2 and O2 exchange are described. Important features of the analysers, design features of gas exchange systems, and sources of potential error are considered. The analysis of chlorophyll fluorescence parameters for estimating the quantum yield for O2 evolution and CO2 fixation is described in relation to new fluorescence imaging systems for large scale screening of photosynthetic phenotypes, and the microimaging of individual chloroplasts.