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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.

Wild lowbush blueberries, an important fruit crop native to North America, contribute significantly to the economy of Maine, USA, Atlantic Canada, and Quebec. However, its photosynthetic capacity has not been well-quantified, with only a few studies showing its low photosynthetic rates. Its small leaves make accurate leaf-level photosynthetic measurements difficult and introduce potential uncertainties in using large leaf chambers. Here, we determined the photosynthetic rate for five different wild blueberry genotypes using a big leaf chamber enclosing multiple leaves and a small leaf chamber with a single leaf to test whether using big leaf chambers (branch-level measurements) underestimates the photosynthetic capacity. Photosynthetic rates of wild blueberries were significantly (35–47%) lower when using the big leaf chamber, and they are not a crop with low photosynthetic capacity, which can be as high as 16 μmol m−2 s−1. Additionally, wild blueberry leaves enclosed in the big chamber at different positions of a branch did not differ in chlorophyll content and photosynthetic rate, suggesting that the difference was not caused by variation among leaves but probably due to leaf orientations and self-shading in the big chamber. A significant linear relationship between the photosynthetic rate measured by the small and big leaf chambers suggests that the underestimation in leaf photosynthetic capacity could be corrected. Therefore, chamber-size effects need to be considered in quantifying photosynthetic capacity for small-leaf crops, and our study provided important guidelines for future photosynthesis research. We also established the relationship between the Electron Transport Rate (ETR) and photosynthetic CO2 assimilation for wild blueberries. ETR provides an alternative to quantify photosynthesis, but the correlation coefficient of the relationship (R2 = 0.65) suggests that caution is needed in this case.

Solar-induced fluorescence (SIF) is a promising tool to estimate photosynthesis across scales; however, there has been limited research done at the leaf level to investigate the relationship between SIF and photosynthesis. To help bridge this gap, a LI-COR LI-6800 gas exchange instrument was modified with a visible-near-infrared (VIS-NIR) spectrometer to measure active and passive fluorescence simultaneously. The system was adapted by drilling a hole into the bottom plate of the leaf chamber and inserting a fibre-optic to measure passive steady-state fluorescence (Ft,λ, analogous to SIF) from the abaxial surface of a leaf. This new modification can concurrently measure gas exchange, passive fluorescence and active fluorescence over the same leaf area and will allow researchers to measure leaf-level Ft,λ in the field to validate tower-based and satellite measurements. To test the modified instrument, measurements were performed on leaves of well-watered and water-stressed walnut plants at three light levels and a constant air temperature. Measurements on these same plants were also conducted using a similarly modified Walz GFS-3000 gas exchange instrument to compare results. We found a positive linear correlation between Ft,λ measurements from the modified LI-6800 and GFS-3000 instruments. We also report a positive linear relationship between Ft,λ and normalized steady-state chlorophyll fluorescence (Ft/Fo) from the pulse-amplitude modulation (PAM) fluorometer of the LI-6800 system. Accordingly, this modification will inform the link between spectrally resolved Ft,λ and gas exchange—leading to improved interpretation of how remotely sensed SIF tracks changes in the light reactions of photosynthesis.

Stomatal functioning is modulated by several factors and, in most circumstances, stomatal aperture declines with increasing leaf-to-air vapor pressure difference (VPDL) and temperature, but stomatal functioning under the humid conditions of the tropical rainforest understory has been scarcely investigated. The aim of this study was to determine how stomatal conductance of saplings responds to the changing understory temperatures of a tropical rainforest. We measured gas-exchange in four saplings of Guarea carinata (1–2 m tall). On each plant, stomatal conductance (g s), VPDL and leaf temperature were measured continuously at 3-min intervals during 24 h. We used a constant irradiance of 50 µmol m−2 s−1 and nearly constant relative humidity (75.8 ± 1.9%). Within the leaf chamber, leaf temperature over plants varied from 25.8 to 30.7 °C and VPDL from 0.62 to 0.93 kPa. Contrary to expectations, g s increased with the increase in leaf temperature and VPDL, and throughout the 24-h cycle, g s was maximum (0.123 mol m−2 s−1) at midday when temperatures were higher and minimum (0.016 mol m−2 s−1) after midnight, when the lower temperatures were recorded. There was a positive relationship between g s and both leaf temperature (p

Stomata control gaseous exchange between the leaf and bulk atmosphere limiting CO2 uptake for photosynthesis and water loss by transpiration, and therefore determine plant productivity and water use efficiency. In order to function efficiently, stomata must respond to internal and external signals to balance these two diffusional processes. However, stomatal responses are an order of magnitude slower than photosynthetic responses, which lead to a disconnection between gs and A. Here we discuss the influence of anatomical features on the rapidity of stomatal movement, and explore the temporal relationship between A and gs responses. We describe how these mechanisms have been included into recent modelling efforts, increasing the accuracy and predictive power under dynamic environmental conditions, such as those experienced in the field.

Photosynthesis is the most fundamental and intricate physiological process in all green plants. For the fruitful occurrence of photosynthesis, each plant has certain environmental requirements. They are impacted by the environmental factors and stress during all phases of growth and development. Examples include light availability, water (soil moisture), senescence, carbon strategy and nutrient deficiencies etc. that cause alteration of the net photosynthesis rate of plants. In this study, to determine the effect of different environmental factors on photosynthesis, a number of experiments were conducted where the net photosynthesis, transpirations, water use efficiency and photoinhibition were measured. To study the effect of light intensity, soil moisture, senescence, on net photosynthesis, respectively Ocimum basilicum, Vaccinium vitis-idaea, Cotinus coggygria, were used. To compare carbon strategy, Pisum sativum and Zea mays were grown under similar condition. How variable nutrient conditions can affect the photosynthesis was studied using a light adapted plant Epilobium augustifolium and shaded tolerant plant Glechoma hederacea. Observations resulted that light intensity at mid-range increases the rate of photosynthesis but exceeding a certain amount caused lowering the efficiency. Net photosynthesis was the maximum under moist condition for Vaccinium vitis- idaea. On the other hand, the senescent leaf had highly similar transpiration rates as the healthy green leaf. Net photosynthesis rate of C4 plants were higher than C3 plants. Overall, the impact of environmental factors on the photosynthesis rate of different plant species was quite apparent.

We measured the light dependence of gross photosynthesis and oxygen uptake rates by membrane inlet mass spectrometry in two open ocean regions: the Amundsen Sea (Antarctica), dominated by Phaeocystis antarctica, and the North Atlantic, dominated by Emiliania huxleyi. In the North Atlantic, respiration was independent of irradiance and was higher than the gross photosynthetic rate at all irradiances. In contrast, in the Amundsen Sea, oxygen uptake processes were light dependent; dark respiration was one order of magnitude lower than the maximal gross photosynthetic rate, but the oxygen uptake rate increased by 10 fold at surface irradiances. Our results suggest the light dependence of oxygen uptake in Amundsen Sea has two sources: one is independent of photosynthesis, and is possibly associated with the photo-reduction of O2 mediated by dissolved organic matter; the second reflects the activity of an oxidase fueled in the light with photosynthetic electron flow. Our results highlight the importance of improving our understanding of oxygen consuming reactions in the euphotic zone.

Freezing tolerant tea cultivars are urgently needed. The tea cultivars with highly freezing tolerance showed resistance to freezing stress induced photoinhibition. Freezing sensitivity index (H) of 47 tea clonal cultivars was investigated after severe freezing winter in 2016. To develop instrumental methods for freezing tolerance selection, the maximum photochemical efficiency of photosystem II (PSII) (Fv/Fm) and leaf color indicator a on the Hunter color scale were determined on control group (non-frozen) and frozen group (being frozen at &minus, 15 &deg, C for 2 h and then stood at 20 &deg, C for 5 h) of the cultivars. When the two indicators were expressed as the ratios (RFv/Fm and Ra) of frozen group to control group, linear regression of the freezing sensitivity index (H) upon the RFv/Fm and Ra produced significant relationship respectively, i.e., H = 60.31 &minus, 50.09 RFv/Fm (p &lt, 0.01) and H = 30.03 &minus, 10.82 Ra (p &lt, 0.01). Expression of gene psbA encoding D1 protein and gene psbD encoding D2 protein in PSII showed that the frezzing tolerant tea cultivars maintained a high expression level of psbA after freezing stress, which is considered to be beneficial to de novo synthesis of D1 protein and sustaining PSII activity. These findings can provide instrumental tools for assessing freezing tolerance of tea cultivars in tea breeding program.

Wounding is a key plant stress that results in a rapid, within seconds to a few minutes, release of ubiquitous stress volatiles and stored volatiles in species with storage structures. Understanding the timing and extent of wound-dependent volatile elicitation is needed to gain an insight into different emission controls, but real-time monitoring of plant emissions through wounding treatments has been hampered by the need to stop the measurements to perform the wounding, slow stabilization of gas flows upon chamber closure and smearing out the signal by large chambers and long sampling lines. We developed a novel leaf cutter that allows to rapidly perform highly precise leaf cuts within the leaf chamber. The cutter was fitted to the standard Walz GFS-3000 portable gas-exchange system leaf chamber and chamber exhaust air for analysis with a proton transfer reaction time-of-flight mass-spectrometer (PTR-TOF-MS) was taken right at the leaf chamber outlet. Wounding experiments in four species of contrasting leaf structure demonstrated significant species differences in timing, extent and blend of emitted volatiles, and showed unprecedently high emission rates of several stress volatiles and stored monoterpenes. In light of the rapid rise of release of de novo synthesized and stored volatiles, the results of this study suggest that past studies have underestimated the rate of elicitation and maximum emission rates of wound-dependent volatiles.

Papaya canopy architecture enables all the leaves to receive sufficient amounts of sunlight to optimize leaf gas exchange due to the spiral phyllotaxis. Thus, there may be a close relationship between photosynthesis and transpiration measurements at single-leaf and whole-canopy levels. We tested this hypothesis by simultaneously measuring single leaf and whole canopy gas exchange of ‘Gran Golden’ papaya during two seasons. Whole-canopy gas exchange was measured on five plants during four days in July (winter) from 08:00 to 1700 h and three days in December (summer) from 06:00 to 1700 h in 2006. Single-leaf gas exchange measurements were performed using the fully exposed 12th and 13th leaf from the apex on five plants adjacent to those with whole canopy chambers at the same time of the day. Net photosynthetic rate (A) values on a single-leaf or whole-canopy basis in field-grown papaya were similar and highly correlated under clear sky conditions since the open canopy architecture of papaya plants allowed saturating light intensities for photosynthesis to reach all leaves. Conversely, whole-canopy transpiration (Ec), was approximately 50% of single-leaf transpiration (El) likely due to high air temperature and VPDleaf-air and increased leaf fan speed in the LI-6200 leaf chamber (single leaf) compared to the whole canopy chamber. Therefore, water use efficiency measured on a single-leaf basis seems to have reduced applicability in papaya water relations studies.

Understanding the effects of elevated atmospheric CO2 on carbon (C) relations of mature forest trees is central to understanding ecosystem C fluxes and pools in a future high-CO2 world. Here, we investigated the CO2-induced photosynthetic enhancement and the diurnal variation in shoot carbon assimilation, stem CO2 efflux and soil respiration associated with ca. 110-year-old and 37 m tall Norway spruce trees (Picea abies (L.) H. Karst.) growing under free air CO2 enrichment (FACE) in a mixed, near-natural forest in Northern Switzerland. Diurnal measurements of these major C fluxes were conducted simultaneously on three occasions: one week before and after the start of CO2 enrichment, and one year later. Under controlled leaf chamber conditions, an increase in the atmospheric CO2 concentration of ca. 150 ppm above ambient stimulated light-saturated rates of photosynthesis in previous- and current-year upper-canopy shoots equally by 73 ± 2%. In the course of the day such large differences in C assimilation between trees growing under elevated CO2 (eCO2) and ambient conditions (aCO2) only occurred around midday under non-limiting light conditions. The CO2 efflux rates from spruce stems (CEstem) and surrounding soil (Rsoil) shared a similar range during night- and daytime (3–5 μmol m−2 s−1) but were not stimulated by eCO2. Both CEstem stem and Rsoil were still rising when photosynthesis approached evening light compensation potentially reflecting the time lag in assimilate allocation to stem tissue and fine roots. Our findings suggest a strong photosynthetic enhancement during the initial CO2 enrichment phase but provide no evidence for an overall or daytime-dependent stimulation of respiratory CO2 fluxes indicating that the extra C was not quickly returned to the atmosphere through respiratory processes in spruce stems or surrounding soil.

Free-Air CO2 Enrichment (FACE) was conceived as an experimental method to measure plant responses to elevated CO2 in natural environments rather than in chambered or controlled environments. However, due to the difficulty of controlling elevated CO2 concentrations in turbulent air, the range of fluctuations of CO2 in FACE experiments are more than 10-fold greater than plants experience in natural conditions. One early study reported that photosynthetic increases of leaves in 40- and 80-s periods of oscillating elevated CO2 were only about 68% of those in leaves exposed to constant elevated CO2 with the same mean CO2 concentration. Later whole-plant studies reported smaller increases of responses in 60-s periods of oscillating elevated CO2 compared to constant elevated CO2 with the same mean concentration. After eliminating problematic data from studies that predicted plant responses in FACE to be only 45% of responses in open top chambers, we calculated that yields increased 65% as much in fluctuating elevated CO2 of FACE as in constant elevated CO2. The smaller plant responses in fluctuating elevated CO2 can be attributed partially to the non-linear, convex-upward curved response of photosynthesis to CO2 concentration, but other unknown mechanisms must exist. Future leaf chamber studies and FACE studies should include fundamental photosynthetic physiologists who can focus on uncovering the mechanisms responsible for lower photosynthetic, biomass, and yield response in both regular waveform oscillating and irregular fluctuating elevated CO2. Because CO2 fluctuates in FACE and recent experiments indicate reduced photosynthesis and growth under fluctuating CO2, responses of plants in FACE are likely to underestimate the benefits of rising CO2. We found that a correction factor of about 1.5 needs to be applied to FACE results. While responses to elevated CO2 in FACE experiments are smaller than those in chamber experiments, FACE responses are obtained in natural conditions not available in chambers and thus are conservative regarding future projections of agricultural productivity.

Although CO2 and H2O exchange rates are often measured in experiments as indicators of physiological plant responses these gas exchange measurements are prone to large experimental error. Gas exchange equipment and technology have improved greatly over the past two decades which supports scrutinizing current issues of experimental error in measuring plant photosynthesis and stomatal conductance. This report shows results of a greenhouse experiment with the goal of identifying lessor understood sources of experimental error and variation in measurements with the LI-COR 6400XT gas exchange system. A variety of plant types were used to encompass differing species variation. We found significant sources of experimental error in 1) the time for initial adjustment when placing a leaf in the leaf chamber 2) the time-of-day when measuring 3) leaf age 4) having the chamber window full vs. partially full with leaf tissue 5) using a leaf chamber environment that greatly diverges from the whole plant environment 6) differing degree of experimental error depending upon plant species. A situation with multiple contributors to error would result in useless gas-exchange data. Recommendations for minimizing these experimental errors are given.

Photosynthesis, i.e. the assimilation of atmospheric carbon to organic molecules with the help of solar energy, is a fundamental and well understood process. Here, we connect theoretically the fundamental concepts affecting C3 photosynthesis with the main environmental drivers (ambient temperature and solar light intensity), using six axioms based on physiological and physical knowledge and yield straightforward and simple mathematical equations. The light and carbon reactions in photosynthesis are based on the coherent operation of the photosynthetic machinery, which is formed of a complicated chain of enzymes, membrane pumps and pigments. A powerful biochemical regulation system has emerged in evolution to match photosynthesis with the annual cycle in solar light and temperature. The action of the biochemical regulation system generates the annual cycle of photosynthesis and emergent properties, the state of photosynthetic machinery, and the efficiency of photosynthesis. The state and the efficiency of the photosynthetic machinery is dynamically changing due to biosynthesis and decomposition of the molecules. The mathematical analysis of the system, defined by the very fundamental concepts and axioms, resulted in exact predictions of the behaviour of daily and annual patterns in photosynthesis. We tested the predictions with extensive field measurements of Scots pine photosynthesis in Northern Finland. Our theory gained strong corroboration for the theory in the rigorous test.

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.

Mathematical models that incorporate knowledge of crop function and other greenhouse processes can inform the grower about the growing process. It can be assumed that models predict the behavior of a healthy, well-functioning plant. Hence, the difference between model-predicted values and accurate measurements can serve as a criterion of the status of the crop. A mechanistic transpiration model that predicts actual crop transpiration from the measured climate in the greenhouse was implemented in the process control computers of commercial tomato greenhouses to demonstrate the possibilities of this idea. In the same process, actual transpiration was available as measured with a ProDrain weighing gutter. Occasionally, measured transpiration was lower than predicted, which may indicate suboptimal crop function. When the difference exceeded a threshold value for a certain period, the process computer generated an alarm in order to warn the grower. Lower measured than predicted transpiration is probably caused by partial closing of stomata. To have an indication of the impact of stomatal behavior on crop production, a photosynthesis model was also implemented, and photosynthesis rate was calculated for theoretical as well as actual stomatal resistance. This study demonstrates that simulation models, when implemented in a greenhouse process computer and combined with the appropriate measurements, can automatically alert the grower of potentially damaging conditions, e.g., reduced crop performance or a system malfunction in the greenhouse, can provide the grower insight into factors affecting crop function and, finally, can help the grower reduce mistakes, optimize crop growth, maximize yield and save energy.

Since the emergence of modern science, photosynthesis has been the focus of interest of many researchers because of its importance for all forms of life on this planet. In particular, remarkable progress has been made during the last two decades. Of special importance is the determination of the three-dimensional structures of key proteins in photosynthesis, such as Photosystem I, Photosystem II, and cytochrome b6f complexes by X-ray crystallography. These crystallographic studies provide useful information about the static structures of these biomolecules. On the other hand, the dynamic aspects of these biomolecules are equally important, which have been revealed by various other techniques such as biochemical assays, fluorescence spectroscopy, magnetic resonance studies, and so on. These successful research activities have collected an impressive amount of scientific knowledge, although there is still much debate on various important aspects, which are under active research right now. From the viewpoint of chemistry, the situation looks somewhat different. Although we may be able to understand the molecular system of natural photosynthesis, we are far from being able to re-construct it in our hands. The latter challenge is still too complex for today’s chemists. Nevertheless, building up artificial photosynthetic systems on the basis of our knowledge about natural photosynthesis is a worthwhile goal.

Summary Using a stomatal optimization model, an abrupt change is foundnd in the relationship between carbon and water fluxes along the evolutionary gradient from C3 to C4 photosynthetic types., C4 photosynthesis evolved independently numerous times, probably in response to declining atmospheric CO2 concentrations, but also to high temperatures and aridity, which enhance water losses through transpiration. Here, the environmental factors controlling stomatal behaviour of leaf-level carbon and water exchange were examined across the evolutionary continuum from C3 to C4 photosynthesis at current (400 μmol mol–1) and low (280 μmol mol–1) atmospheric CO2 conditions. To this aim, a stomatal optimization model was further developed to describe the evolutionary continuum from C3 to C4 species within a unified framework. Data on C3, three categories of C3–C4 intermediates, and C4 Flaveria species were used to parameterize the stomatal model, including parameters for the marginal water use efficiency and the efficiency of the CO2-concentrating mechanism (or C4 pump); these two parameters are interpreted as traits reflecting the stomatal and photosynthetic adjustments during the C3 to C4 transformation. Neither the marginal water use efficiency nor the C4 pump strength changed significantly from C3 to early C3–C4 intermediate stages, but both traits significantly increased between early C3–C4 intermediates and the C4-like intermediates with an operational C4 cycle. At low CO2, net photosynthetic rates showed continuous increases from a C3 state, across the intermediates and towards C4 photosynthesis, but only C4-like intermediates and C4 species (with an operational C4 cycle) had higher water use efficiencies than C3 Flaveria. The results demonstrate that both the marginal water use efficiency and the C4 pump strength increase in C4 Flaveria to improve their photosynthesis and water use efficiency compared with C3 species. These findings emphasize that the advantage of the early intermediate stages is predominantly carbon based, not water related.

The LI-COR 6400 portable photosynthesis system is the most widely used and cited instrument for measuring leaf gas exchange in plant physiology. The focus of this paper is to evaluate three ways of computing/measuring leaf temperature: the LI-COR energy budget computation, the LI-COR leaf thermocouple (T/C), and an infra-red (IR) sensor chip (MLX90615) incorporated into the LI-6400 leaf chamber. The IR-sensor was calibrated against known targets, and then used to cross check the other two methods. The results showed that the IR-sensor was superior to the LI-COR thermocouple and agreed closer with the energy budget values of leaf temperature. The magnitudes of the errors were quantified in terms of °C difference in leaf temperature measured by T/C (as control) and IR sensor versus percentage difference in stomatal conductance (gs) and intercellular CO2 concentration (Ci) computed from leaf temperature. The temperature difference (IR versus other methods) in the range of -1.89 to 1.58 °C resulted in relative errors in gs from 14.7% to -18.0% and Ci from 16.5% to -7.8% of the values reported by the standard LI-6400 calculations depending on species and temperature. Reasons are given for trusting the IR-sensor over the other methods and it is suggested that the next generation LI-COR photosynthesis system include an IR-sensor.

To describe stomatal response to micro-environmental variations, optimization theories for canopy gas exchange are often used as alternatives to empirical or mechanistic but complex models of stomatal function. Solutions for optimal stomatal conductance have been proposed assuming leaf photosynthesis is limited by either Rubisco activity (and hence by CO2 at the photosynthetic site) or ribulose-1,5-biphosphate (RuBP) regeneration rate (and hence light availability). These contrasting assumptions result in different relations between the marginal water use efficiency λ (the key optimization parameter) and atmospheric CO2 concentration (ca). Contrasting predictions of stomatal responses to elevated ca ensue, begging the question as to which approach is most suitable. Here, it is proposed that stomatal aperture is optimized for shifting limitations, motivating the development of a framework where Rubisco activity and electron transport co-limit photosynthesis. This approach attempts to reconcile the two previously proposed optimality solutions. Based on a minimalist model of photosynthesis that accounts for both limitations, optimal stomatal conductance is derived as a function of photosynthetic parameters, λ, and leaf micro-environmental conditions. The optimal stomatal conductances resulting from the different formulations of photosynthesis and functional dependencies of λ on ca are compared for varying environmental conditions, with reference to often observed patterns and scaling relationships. The results suggest that short-term (e.g., sub-daily) fluctuations in ca trigger small adjustments in stomatal aperture at a constant λ, while long-term (e.g., growing season or longer) elevated ca may elicit acclimation mechanisms, potentially resulting in changes in λ.

The proportion of transpiration (T) in total evapotranspiration (ET) is an important parameter that provides insight into the degree of biological influence on the hydrological cycles. Studies addressing the effects of climatic warming on the ecosystem total water balance are scarce, and measured warming effects on the T/ET ratio in field experiments have not been seen in the literature. In this study, we quantified T/ET ratios under ambient and warming treatments in a grassland ecosystem using a stable isotope approach. The measurements were made at a long-term grassland warming site in Oklahoma during the May–June peak growing season of 2011. Chamber-based methods were used to estimate the δ2H isotopic composition of evaporation (δE), transpiration (δT) and the aggregated evapotranspiration (δET). A modified commercial conifer leaf chamber was used for δT, a modified commercial soil chamber was used for δE and a custom built chamber was used for δET. The δE, δET and δT were quantified using both the Keeling plot approach and a mass balance method, with the Craig–Gordon model approach also used to calculate δE. Multiple methods demonstrated no significant difference between control and warming plots for both δET and δT. Though the chamber-based estimates and the Craig–Gordon results diverged by about 12‰, all methods showed that δE was more depleted in the warming plots. This decrease in δE indicates that the evaporation flux as a percentage of total water flux necessarily decreased for δET to remain constant, which was confirmed by field observations. The T/ET ratio in the control treatment was 0.65 or 0.77 and the ratio found in the warming treatment was 0.83 or 0.86, based on the chamber method and the Craig–Gordon approach. Sensitivity analysis of the Craig–Gordon model demonstrates that the warming-induced decrease in soil liquid water isotopic composition is the major factor responsible for the observed δE depletion and the temperature dependent equilibrium effects are minor. Multiple lines of evidence indicate that the increased T/ET ratio under warming is caused mainly by reduced evaporation.

In the challenge to increase photosynthetic rate per leaf area mathematical models of photosynthesis can be used to help interpret gas exchange measurements made under different environmental conditions and predict underlying photosynthetic biochemistry. To do this successfully it is important to improve the modelling of temperature dependencies of CO₂ assimilation and gain better understanding of internal CO₂ diffusion limitations. Despite these shortcomings steady-state models of photosynthesis provide simple easy to use tools for thought experiments to explore photosynthetic pathway changes such as redirecting photorespiratory CO₂, inserting bicarbonate pumps into C₃ chloroplasts or inserting C₄ photosynthesis into rice. Here a number of models derived from the C₃ model by Farquhar, von Caemmerer and Berry are discussed and compared.

Photosynthetic characteristics of two Cymbidium hybrids, ‘Red Fire’ and ‘Yokihi’, were investigated at different developmental stages. The net CO2 assimilation rate (An) as a function of incident photosynthetic photon flux (PPF), intercellular CO2 concentration (Ci), and relative humidity (RH) in a leaf chamber head was determined in a greenhouse with 1- and 2-year-old plant leaves. The maximum net CO2 assimilation rate (Anmax) in response to PPF of 1-year-old ‘Red Fire’ was 6.11 μmol·CO2·m−2·s−1 at 700 μmol·m−2 ·s−1 PPF, whereas it was 4.9 μmol·CO2·m−2·s−1 at 500 μmol·m−2·s−1 PPF in ‘Yokihi’. Under low light intensity (below 250 μmol·m−2 ·s−1 PPF), An was more pronounced in ‘Yokihi’ than in ‘Red Fire’. In 2-year-old Cymbidium, however, the maximum An was less than 2 μmol·CO2·m−2·s−1 in both cultivars at the same CO2 condition of 600 μmol·CO2·mol−1 air. The An increased in the leaves of 2-year-old plant under an elevated CO2 condition up to 1,500 μmol·CO2·mol−1 air with increasing PPF up to about 800 μmol·m−2·s−1. The An increased with increasing Ci and showed the highest value when Ci was over 1,000 and 2,000 μmol·mol −1 air in ‘Red Fire’ and ‘Yokihi’, respectively. The carboxylation efficiency of ‘Red Fire’ and ‘Yokihi’ were 0.044 and 0.036 μmol·CO2·m−2·s−1, respectively, while An of ‘Yokihi’ was higher than that of ‘Red Fire’ at above 1,000 μmol·mol−1 air Ci. The An tended to increase with RH, increasing from 15 to 70% in both hybrids. The Anmax of ‘Yokihi’ was observed at over 70% of RH, whereas 45% of RH was sufficient enough to show Anmax in ‘Red Fire’. The results shows that the photosynthetic characteristics of Cymbidium ‘Red Fire’ and ‘Yokihi’ can be increased by controlling the PPF, CO2, and RH conditions and the optimal conditions for maximum photosynthetic efficiency vary by cultivar, developmental stage, and greenhouse conditions.

Photosynthesis in vegetation is arguably the most important and variable part of the terrestrial carbon cycle. In terrestrial biospheric models, the photosynthesis rate of plant leaves is generally simulated based on the maximum carboxylation rate at an optimum temperature (often 25°C), which is often denoted as Vcmax25. In regional and global photosynthesis modeling, Vcmax25 is usually prescribed as constants for different plant functional types (PDF) based on ground measurements in order to capture the first order spatial variability associated with PTF distribution. However, experimental data show that Vcmax25 can vary by 2–3 factors for the same PFT, and it is also not a constant in different growing seasons because of leaf physiological change with season. It is therefore highly desirable to be able to map this critical parameter to address the issues of its spatial and temporal variabilities. Both terrestrial carbon and water cycle simulations can be greatly improved if we can achieve the global mapping of this parameter.

Understanding the photosynthetic responses of terrestrial plants to environments with high levels of CO2 is essential to address the ecological effects of elevated atmospheric CO2. Most photosynthetic models used for global carbon issues are based on steady-state photosynthesis, whereby photosynthesis is measured under constant environmental conditions; however, terrestrial plant photosynthesis under natural conditions is highly dynamic, and photosynthetic rates change in response to rapid changes in environmental factors. To predict future contributions of photosynthesis to the global carbon cycle, it is necessary to understand the dynamic nature of photosynthesis in relation to high CO2 levels. In this review, we summarize the current body of knowledge on the photosynthetic response to changes in light intensity under experimentally elevated CO2 conditions. We found that short-term exposure to high CO2 enhances photosynthetic rate, reduces photosynthetic induction time, and reduces post-illumination CO2 burst, resulting in increased leaf carbon gain during dynamic photosynthesis. However, long-term exposure to high CO2 during plant growth has varying effects on dynamic photosynthesis. High levels of CO2 increase the carbon gain in photosynthetic induction in some species, but have no significant effects in other species. Some studies have shown that high CO2 levels reduce the biochemical limitation on RuBP regeneration and Rubisco activation during photosynthetic induction, whereas the effects of high levels of CO2 on stomatal conductance differ among species. Few studies have examined the influence of environmental factors on effects of high levels of CO2 on dynamic photosynthesis. We identified several knowledge gaps that should be addressed to aid future predictions of photosynthesis in high-CO2 environments.

Photosynthesis is the most fundamentally important energy-converting process on Earth. It converts solar energy to chemical energy and provides all the food we eat, the fossil fuels we consume and the oxygen we breathe. The basic concepts underlying photosynthesis have been well established and a brief introduction is given in this chapter. The principles, especially those obtained from primitive photosynthetic organisms, are considered to serve as a guide for the development of artificial photosynthesis today.

Crop yield is determined by plant growth and more than 90% of crop biomass is derived from photosynthetic products. Therefore, photosynthesis is the basic process underlying plant growth and food production. Respiration is also a metabolic pathway that produces chemical energy to meet cell energy demands for growth and maintenance. Thus, plant growth is closely related to both photosynthesis and respiration. There is no growth without photosynthesis and respiration. Therefore, an understanding of the physiological processes of photosynthesis and respiration is necessary for a basic understanding of maximizing crop yield. In addition, plant growth rates are not simply determined by rates of photosynthesis and respiration at the single-leaf level, but are determined by rates of photosynthesis and respiration at the canopy level. In this chapter, the basic reactions of photosynthesis and respiration at the single-leaf level as well as the canopy level are summarized.

Responses of photosynthetic, respiratory, and transpiration rates of plants to the levels of physical environmental factors are outlined. Water vapor movement from a leaf to the atmosphere in transpiration is quantitatively described using a gas diffusion model that incorporates the concentration gradient of water vapor and the conductance for water vapor. Changes in the levels of environmental factors affect transpiration rate directly through changes in the driving force of water vapor diffusion or indirectly through changes in stomatal aperture. In plants, there are two types of respiration, namely, dark respiration and photorespiration, although they are completely different metabolisms. Dark respiratory rate is sensitive to changes in temperature, gas concentrations, and light intensity, and the effects are summarized. Photosynthetic carbon dioxide (CO2) influx of a leaf is spatially divided into CO2 diffusion from the atmosphere to the chloroplasts and biochemical CO2 fixation within the chloroplasts. The former can be described with a model in a similar manner to that for water vapor diffusion. Net photosynthetic rate in C3 leaves shows a saturating-type increase in response to increases in CO2 concentration or photosynthetic photon flux density (PPFD), and the response curves are characterized by several parameters. Net photosynthetic rate is low at extremely low and high temperatures and shows an optimum level at intermediate temperatures.

Considering that adventitious root formation (ARF) relies on adequate supply of carbon, the objectives of this study were (I) to evaluate how CO 2 assimilation contributes to the carbon balance of petunia cuttings and (II) to study the extent to which CO 2 assimilation depends on the progress of ARF and environmental key factors. CO 2 gas exchange and dry matter production of Petunia hybrida ‘Mitchell’ cuttings were monitored in a specifically designed multiple open chamber system using plastic covered rooting trays as measuring cuvettes connected to an infrared CO 2 sensor. Excised cuttings were rooted for two weeks in a growth chamber at 22/20 °C (day/night) at a photosynthetic photon flux density (PPFD) of 100 μmol m −2 s −1 and a CO 2 concentration of approximately 400 ppm. An increase in dry matter of 186 mg per cutting, or 158% of the initial dry matter, reflected high carbon assimilation. Whilst the shoot dry matter of cuttings increased substantially in the very first week root dry matter growth was not observed until day seven after planting. The short-term response of CO 2 gas exchange to environmental conditions revealed that net photosynthesis ( P N ) enhanced with increasing PPFD, with a maximum P N of 7.8 μmol m −2 s −1 . Temperature response curves exhibited only minor changes of P N ; dark respiration ( R D ) increased considerably when the temperature was temporarily increased. Furthermore, cuttings responded to an increase in CO 2 concentration from 300 to 1200 ppm by almost doubling P N . When cuttings were rooted permanently under PPFDs of 150 μmol m −2 s −1 and 80 μmol m −2 s −1 (22/20 °C day/night; CO 2 concentration 400 ppm) P N and R D of cuttings at the higher PPFD were constantly higher than under the lower PPFD. The CO 2 gas exchange of both treatments was relatively constant during ARF. The light response curves of P N differed after one week of exposure to the two light intensities. Light adaptation was comparable to that of stock plants measured using a portable infrared gas analyser equipped with a leaf chamber. The data indicates that petunia cuttings rooted under conditions frequently applied in young plant production in Central Europe show significant carbon assimilation from the first day onwards. The data also reveals that CO 2 gas exchange under such conditions is not affected by ARF, but is subject to prevailing environmental factors such as light intensity, temperature and CO 2 concentration.

Background and Aims: Net carbon gain commonly estimated from leaf photosynthesis measurements often overestimates grapevine production. This is usually attributed to canopy complexity and a lack of plant respiration data. The present study evaluates the significance of plant respiration in correcting this overestimation. Methods and Results: Non-grafted and non-productive young plants of four grapevine varieties were grown either under irrigation or controlled water stress for 30 days. Daily time courses of leaf photosynthesis and transpiration were determined along with measurements of leaf, stem and root respiration, from which whole plant carbon balance was estimated. Up to 30‐60% of carbon obtained by photosynthesis is used in respiration, with root respiration being the largest user of fixed carbon (up to 75%). Conclusions: Whole plant respiration represents a significant part of total carbon balance and accounts for the largest part of the discrepancy between photosynthesis-based estimates of plant production and actual plant production. Significance of the Study: The present study presents a quantitative evaluation of the importance of plant respiration in grapevine carbon balance and biomass production, highlighting that gas exchange studies aiming predict plant production should include estimates of respiration, especially of roots. Abbreviations AN net photosynthesis; AN/E instantaneous water use efficiency; AN/gs intrinsic water use efficiency; ANmax maximum leaf photosynthesis rate; E leaf transpiration rate; gs stomatal conductance; IRGA infrared gas analyzers; PB plant biomass; PCB plant carbon balance; RDleaf leaf dark respiration; Rroot root respiration; Rstem stem respiration; SWC soil water content; TBI total biomass increment; TDR Time Domain Reflectometry; d 13 C carbon isotope ratio; YMD midday leaf water potential.

Improving photosynthesis throughout the full canopy rather than photosynthesis of only the top leaves of the canopy is central to improving crop yields. Many canopy photosynthesis models have been developed from physiological and ecological perspectives, however most do not consider heterogeneities of microclimatic factors inside a canopy, canopy dynamics and associated energetics, or competition among different plants, and most models lack a direct linkage to molecular processes. Here we described the rationale, elements, and approaches necessary to build a dynamic systems model of canopy photosynthesis. A systems model should integrate metabolic processes including photosynthesis, respiration, nitrogen metabolism, resource re-mobilization and photosynthate partitioning with canopy level light, CO(2), water vapor distributions and heat exchange processes. In so doing a systems-based canopy photosynthesis model will enable studies of molecular ecology and dramatically improve our insight into engineering crops for improved canopy photosynthetic CO(2) uptake, resource use efficiencies and yields.

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 PN/Ci 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.

The stable isotopic composition of plant transpired water (δT) is a powerful tracer used to characterize plant processes in the fields of ecology, plant physiology and hydrology. However, δT is rarely directly measured due to the general difficulty in traditional water vapor isotopic measurements. We report a new direct method with the potential to continuously monitor δT utilizing a commercially available laser-based isotope analyzer coupled to a transparent leaf chamber in a flow-through system arrangement. The method is based on the mass balance of both water vapor and water vapor isotopes inside the chamber. We present the theoretical bulk water vapor and isotope mixing equations, which we verify using simulated water vapor of known isotopic compositions, producing a precision of 1.6‰ and 1.0‰ for δ2H and δ18O respectively. We demonstrate the applicability of our method to field observations and capture rapid (minute time scale) δT responses to shifts in transpiration driven by variation in irradiance.