Rapid and straightforward estimates of photosynthetic characteristics using a portable gas exchange system

Procedures are described for estimating photosynthetic characteristics using a portable infra-red gas analysis (IRGA) system. Once the effects of stomatal limitation on CO2 assimilation have been established, up to ten parameters of photosynthesis can be estimated for a single leaf within 2 h, including: photosynthetic efficiency and capacity on both photon and CO2 bases; compensation irradiances and CO2 compensation concentrations; and light and dark respiration rates. These measurements can be made in the laboratory, glasshouse or field with relative ease. Methods for obtaining near instantaneous ("snapshot") measurements of leaf photosynthesis are also described, using carefully pre-set conditions within the leaf cuvette. Representative results are shown for Phaseolus vulgaris L. Important aspects of the procedure's experimental design, assumptions made in the analysis, and limitations of this approach are analysed.     

Calculator-assisted measurements of photosynthetic,respiration and photorespiration rates in a closed gas exchange system

A closed gas exchange system has been designed for connection to the Hewlett-Packard programmable calculator controlled data acquisition system to provide a complete process of measuring and control. The system enables routine measurements of photosynthetic and dark respiration rates at different irradiances and different carbon dioxide and oxygen concentrations and leaf temperatures, and also a simple and rapid automatic control of irradiance according to the actual photosynthetic rate.     

Evaluation of estimates of alveolar gas exchange by using a tidally ventilated nonhomogenous lung model

Busso, Thierry, and Peter A. Robbins. Evaluation ofestimates of alveolar gas exchange by using a tidally ventilated nonhomogenous lung model. J. Appl.Physiol. 82(6): 1963-1971, 1997.The purposeof this study was to evaluate algorithms for estimatingO₂ andCO₂ transfer at thepulmonary capillaries by use of a nine-compartment tidallyventilated lung model that incorporated inhomogeneities inventilation-to-volume and ventilation-to-perfusion ratios.Breath-to-breath O₂ andCO₂ exchange at the capillary level and at the mouth were simulated by using realistic cyclical breathing patterns to drive the model, derived from 40-min recordings in six resting subjects. The SD of the breath-by-breath gas exchange atthe mouth around the value at the pulmonary capillaries was 59.7 ± 25.5% for O₂ and 22.3 ± 10.4% for CO₂. Algorithmsincluding corrections for changes in alveolar volume and for changes in alveolar gas composition improved the estimates of pulmonary exchange, reducing the SD to 20.8 ± 10.4% forO₂ and 15.2 ± 5.8% forCO₂. The remaining imprecision ofthe estimates arose almost entirely from using end-tidal measurementsto estimate the breath-to-breath changes in end-expiratory alveolar gasconcentration. The results led us to suggest an alternative method thatdoes not use changes in end-tidal partial pressures as explicitestimates of the changes in alveolar gas concentration. The proposedmethod yielded significant improvements in estimation for the modeldata of this study.

     

Rapid lake mapping using a portable Laser Rangefinder

A lightweight LRF 104 laser rangefinder was used in lake mapping. As an example, the Malha crater (Darfur, West-Sudan), containing a lake, springs, wells, and vegetation, was mapped.     

Boll-leaf system gas exchange and its application in the analysis of cotton photosynthetic function

Photosynthesis Research - Estimating the boll development and boll yield from single-leaf photosynthesis is difficult as the source-sink relationship of cotton (Gossypium hirsutum L.) is...     

Climate-ameliorating measures influence photosynthetic gas exchange of apple leaves

Sunburn has become one of the major threats to apple fruit production in South Africa and other countries with Mediterranean climate. Some climate‐ameliorating measures have been developed to control sunburn in apples. Effects of the climate‐ameliorating measures, viz. evaporative cooling, Surround^® WP and shade net, on leaf gas exchange of a 5‐year‐old orchard of ‘Cripps’ Pink’ apple were investigated during hot summer days in Stellenbosch, South Africa. Evaporative cooling increased net photosynthetic rate (A) and stomatal conductance (g_s) because of its lowering of leaf temperature and leaf‐to‐air vapour pressure difference (VPD). Shade net also reduced leaf temperature because of reduction in photosynthetic photon flux density (PPFD). Quantum efficiency of photosynthesis was increased under shade net to compensate for reduced PPFD. Shade net also reduced transpiration rate more than A, resulting in increased midday water‐use efficiency. The diurnal trends of A and g_s in the Surround WP and control treatments were similar, indicating limited ameliorative impact of Surround WP. Furthermore, Surround WP typically reduced maximum rate of carboxylation and the light‐saturated rate of electron transport. In all treatments, A decreased by 70% when leaf temperature increased from 35°C to 40°C. In conclusion, all treatments affected leaf photosynthetic gas exchange. Evaporative cooling enhanced leaf A and g_s because of distinct ameliorative effects on leaf temperature and VPD. Shade net reduced leaf temperature with no consistent effects on leaf gas exchange attributes. Surround WP had limited or no impact on leaf temperature and negatively affected leaf gas exchange attributes.     

The influence of stomatal morphology and distribution on photosynthetic gas exchange

The intricate and interconnecting reactions of C₃ photosynthesis are often limited by one of two fundamental processes: the conversion of solar energy into chemical energy, or the diffusion of CO₂ from the atmosphere through the stomata, and ultimately into the chloroplast. In this review, we explore how the contributions of stomatal morphology and distribution can affect photosynthesis, through changes in gaseous exchange. The factors driving this relationship are considered, and recent results from studies investigating the effects of stomatal shape, size, density and patterning on photosynthesis are discussed. We suggest that the interplay between stomatal gaseous exchange and photosynthesis is complex, and that a disconnect often exists between the rates of CO₂ diffusion and photosynthetic carbon fixation. The mechanisms that allow for substantial reductions in maximum stomatal conductance without affecting photosynthesis are highly dependent on environmental factors, such as light intensity, and could be exploited to improve crop performance.     

Evaluation of photosynthetic electron flow using simultaneous measurements of gas exchange and chlorophyll fluorescence under photorespiratory conditions

Simultaneous measurements of leaf gas exchange and chlorophyll fluorescence for Koelreuteria paniculata Laxm. at 380 ± 5.6 and 600 ± 8.5 ??mol mol^?1 were conducted, and the photosynthetic electron flow via photosystem II (PSII) to photosynthesis, photorespiration, and other electron-consuming processes were calculated. The results showed that the photosynthetic electron flow associated with carboxylation (J _c), oxygenation (J _o), and other electron-consuming processes (J _r) were 72.7, 45.7, and 29.4 ??mol(e^?) m^?2 s^?1 at 380 ??mol mol^?1, respectively; and 86.1, 35.3, and 48.2 ??mol(e^?) m^?2 s^?1 at 600 ??mol mol^?1, respectively. Our results revealed that other aspects associated with electronconsuming processes, except for photosynthesis and respiration, were neither negligible nor constant under photorespiratory conditions. Using maximum net photosynthetic rate (P _max), day respiration (R), photorespiration rate (R _l), and maximum electron flow via PSII (J _max), the use efficiency of electrons via PSII at saturation irradiance to fix CO₂ was calculated. The calculated results showed that the use efficiency of electrons via PSII to fix CO₂ at 600 ??mo^l mol^?1 was almost as effective as that at 380 ??mol mol^?1, even though more electrons passed through PSII at 600 ??mol mol^?1 than at 380 ??mol mol^?1.     

A model evaluation of estimates of breath-to-breath alveolar gas exchange

A mathematical model has been implemented for evaluation of methods for estimating breath-to-breath alveolar gas exchange during exercise in humans. This model includes a homogeneous alveolar gas exchange compartment, a dead space compartment, and tissue spaces for CO2 (alveolar and dead space). The dead space compartment includes a mixing portion surrounded by tissue and an unmixed (slug flow) portion which is partitioned between anatomical and apparatus contributions. A random sinusoidal flow pattern generates a breath-to-breath variation in pulmonary stores. The Auchincloss algorithm for estimating alveolar gas exchange (Auchincloss et al., J. Appl. Physiol. 21: 810-818, 1966) was applied to the model, and the results were compared with the simulated gas exchange. This comparison indicates that a compensation for changes in pulmonary stores must include factors for alveolar gas concentration change as well as alveolar volume change and thus implies the use of end-tidal measurements. Although this algorithm yields reasonable estimates of breath-to-breath alveolar gas exchange, it does not yield a "true" indirect measurement because of inherent error in the estimation of a homogeneous alveolar gas concentration at the end of expiration.     

Effects of mannose on photosynthetic gas exchange in spinach leaf discs

When mannose is provided in the transpiration stream to spinach (Spinacia oleracea) leaf discs, a series of specific and nonspecific changes occur in CO₂ and H₂O vapor exchange as a function of feeding time. The initial increases in apparent photosynthesis and transpiration are nonspecific effects due to osmotic changes leading to passive stomatal opening. The mannose-specific effects are: (a) time-dependent changes in the CO₂ concentration required for saturation; (b) complex kinetics of the inhibition of CO₂ assimilation dependent on CO₂ and O₂ concentrations and the duration of feeding (high CO₂ and low O₂ lead to rapid inhibitions of photosynthesis); (c) elimination of the capacity of 2% O₂ to stimulate photosynthesis; and (d) oscillations in the CO₂ exchange rate following transitions from 20% to 2% O₂. The mannose-specific effects are reversible by orthophosphate. The mannose-dependent changes in gas exchange are attributed to altered [ATP]/[ADP] ratios.     

Effect of vacuum infiltration on photosynthetic gas exchange in leaf tissue

Using a manometric method, photosynthetic oxygen evolution and ¹⁴CO₂ fixation have been determined for leaf tissue of Triticum aestivum L., Hordeum vulgare L., Phaseolus vulgaris L., and Lemna minor L. Approximately similar values in the range 0.2 to 0.4 millimoles grams fresh weight⁻¹ hour⁻¹ were obtained for both gases. In tissue subjected to vacuum infiltration, O₂ evolution and ¹⁴CO₂ fixation were barely measurable. It is considered that the elimination of photosynthetic gas exchange results from a decreased supply of CO₂ to the chloroplasts. Chopping wheat laminae also leads to a reduction in photosynthetic gas exchange, slices 1 millimeter or less giving only 10 to 20% of the value for whole tissue. Respiration is unaffected by either treatment. Carbonic anhydrase did not improve photosynthetic gas exchange in infiltrated tissue. The use of sliced or vacuum-infiltrated leaf tissue in photosynthetic studies is discussed.     

Measuring and modelling environmental influences on photosynthetic gas exchange in Sphagnum and Pleurozium

A mechanistic model has been used to examine the environmental regulation of photosynthetic gas exchange in moss. The effects of water content on conductance to CO₂ and on photosynthetic capacity during desiccation were calculated from the carbon isotope discrimination data of Williams & Flanagan (1996 , Oecologia 108, pp. 38–46) and combined with the biochemical model of Farquhar et al. (1980 , Planta 149, pp. 78–90). The model includes a simple light attenuation function that imparts curvature to the light response curve for net assimilation, enabling the use of physiologically realistic values for the biochemical parameters. Measurements of gas exchange for Sphagnum and Pleurozium were made in an old black spruce ecosystem over a growing season in order to assign values to parameters in the model. The calculated maximum rates of carboxylation by Rubisco ( V _max) were 5, 14 and 6 μ mol m^–2 s^–1 for Sphagnum during the spring, summer and autumn seasons of 1996, respectively. The increase in V _max during the summer was consistent with an increased allocation of resources to the photosynthetic apparatus. In contrast, no seasonal variation in V _max was observed in Pleurozium with average values of 7, 5 and 7 μ mol m^–2 s^–1 during the spring, summer and autumn, respectively.     

A portable system for simultaneous measurement of transpiration and CO2 exchange

A portable field system for simultaneous measurement of transpiration and CO₂ exchange from leaves of fruit trees is described. CO₂ concentration is measured by means of infra-red gas analysis, using small gas samples collected in syringes. Methods for analysing small gas samples are compared. The leaf chamber described can also be used in a conventional laboratory open gas-exchange system, its small volume permitting measurement of very rapid changes in gas exchange in response to experimental stimuli.

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Resumen Este artículo describe un sistema portátil para medir simultaneamente transpiración e intercambio de CO₂ en hojas de árboles frutales en el campo. Para medir la velocidad de fotosíntesis se colectan pequeñas muestras de gas en jeringas y se inyectan al analizador de gases de luz infra-roja. Se comparan varios métodos para analizar las muestras. Se describe la cámara de absorción de CO₂ utilizada, la cual puede tambien incorporarse a un sistema abierto convencional, su pequeño volumen permite detectar cambios rápidos en el intercambio de gases cuando se producen alteraciones en el ambiente.

     

5-Aminolevulinic acid enhances photosynthetic gas exchange, chlorophyll fluorescence and antioxidant system in oilseed rape under drought stress

This study evaluates the role of exogenous foliar application of 5-aminolevulinic acid (ALA) on water relations, gas exchange, chlorophyll fluorescence, and the activities and gene expression patterns of antioxidant enzymes in leaves of oilseed rape under drought stress and recovery conditions. Seedlings at four-leaf stage were imposed to well-watered condition (80 % of water-holding capacity) or drought stress (40 % of water-holding capacity) and subsequently foliar sprayed with water or ALA (30 mg l^?1). Drought suppressed the accumulation of plant biomass and decreased chlorophyll content and leaf water status (relative water content and water potential). The actual quantum yield of photosystem II and electron transport rates were hampered in parallel to net photosynthetic rate. However, drought stress induced the accumulation of malondialdehyde (MDA) and hydrogen peroxide, enhanced the activities of catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), glutathione reductase (GR) and superoxide dismutase and up-regulated the expression of APX and GR. After rehydration for 4 days, the growth of drought-treated seedlings was restored to normal level for most of the physiological parameters. Foliar application of ALA maintained relatively higher leaf water status and enhanced chlorophyll content, net photosynthetic rate, actual quantum yield of photosystem II, photochemical quenching, non-photochemical quenching and electron transport rates in stressed leaves. Exogenous ALA also alleviated the accumulation of MDA and hydrogen peroxide, increased the activities of antioxidant enzymes and enhanced the expression of CAT and POD in drought-treated plants. These results indicate that ALA may effectively protect rapeseed seedlings from damage induced by drought stress.     

Rapid and accurate analyses of silicon and phosphorus in plants using a portable X-ray fluorescence spectrometer

The elemental analysis of plant material is a frequently employed tool across biological disciplines, yet accurate, convenient and economical methods for the determination of some important elements are currently lacking. For instance, digestion-based techniques are often hazardous and time-consuming and, particularly in the case of silicon (Si), can suffer from low accuracy due to incomplete solubilization and potential volatilization, whilst other methods may require large, expensive and specialised equipment. Here, we present a rapid, safe and accurate procedure for the simultaneous, nonconsumptive analysis of Si and phosphorus (P) in as little as 0.1 g dried and ground plant material using a portable X-ray fluorescence spectrometer (P-XRF). We used certified reference materials from different plant species to test the analytical performance of P-XRF and show that the analysis suffers from very little bias and that the repeatability precision of the measurements is as good as or better than that of other methods. Using this technique we were able to process and analyse 200 ground samples a day, so P-XRF could provide a particularly valuable tool for plant biologists requiring the simultaneous nonconsumptive analysis of multiple elements, including those known to be difficult to measure such as Si, in large numbers of samples.     

Deriving C4 photosynthetic parameters from combined gas exchange and chlorophyll fluorescence using an Excel tool: theory and practice

The higher photosynthetic potential of C₄ plants has led to extensive research over the past 50 years, including C₄‐dominated natural biomes, crops such as maize, or for evaluating the transfer of C₄ traits into C₃ lineages. Photosynthetic gas exchange can be measured in air or in a 2% Oxygen mixture using readily available commercial gas exchange and modulated PSII fluorescence systems. Interpretation of these data, however, requires an understanding (or the development) of various modelling approaches, which limit the use by non‐specialists. In this paper we present an accessible summary of the theory behind the analysis and derivation of C₄ photosynthetic parameters, and provide a freely available Excel Fitting Tool (EFT), making rigorous C₄ data analysis accessible to a broader audience. Outputs include those defining C₄ photochemical and biochemical efficiency, the rate of photorespiration, bundle sheath conductance to CO₂ diffusion and the in vivo biochemical constants for PEP carboxylase. The EFT compares several methodological variants proposed by different investigators, allowing users to choose the level of complexity required to interpret data. We provide a complete analysis of gas exchange data on maize (as a model C₄ organism and key global crop) to illustrate the approaches, their analysis and interpretation. © 2015 John Wiley & Sons Ltd