Chlorophyll Fluorescence Method Research Articles

Molecular Mechanisms of Resistance against PSII-Inhibiting Herbicides in Amaranthus retroflexus from the Czech Republic.

Amaranthus retroflexus L. (redroot pigweed) is one of the most problematic weeds in maize, sugar beet, vegetables, and soybean crop fields in Europe. Two pigweed amaranth biotypes (R1 and R2) from the Czech Republic resistant to photosystem II (PSII)-inhibiting herbicides were analyzed in this study. This study aimed to identify the genetic mechanisms that underlie the resistance observed in the biotypes. Additionally, we also intended to establish the use of chlorophyll fluorescence measurement as a rapid and reliable method for confirming herbicide resistance in this weed species. Both biotypes analyzed showed high resistance factors in a dose-response study and were thus confirmed to be resistant to PSII-inhibiting herbicides. A sequence analysis of the D1 protein revealed a well-known Ser-Gly substitution at amino acid position 264 in both biotypes. Molecular docking studies, along with the wild-type and mutant D1 protein's secondary structure analyses, revealed that the S264G mutation did not reduce herbicide affinity but instead indirectly affected the interaction between the target protein and the herbicides. The current study identified the S264G mutation as being responsible for conferring herbicide resistance in the pigweed amaranth biotypes. These findings can provide a strong basis for future studies that might use protein structure and mutation-based approaches to gain further insights into the detailed mechanisms of resistance in this weed species. In many individuals from both biotypes, resistance at a very early stage (BBCH10) of plants was demonstrated several hours after the application of the active ingredients by the chlorophyll fluorescence method. The effective PS II quantum yield parameter can be used as a rapid diagnostic tool for distinguishing between sensitive and resistant plants on an individual level. This method can be useful for identifying herbicide-resistant weed biotypes in the field, which can help farmers and weed management practitioners develop more effective weed control tactics.

Toxic effect of ciprofloxacin on the photosynthesis reactions in microalga Scenedesmus quadricauda (Turp.) Bréb.

Ciprofloxacin (CIP) is widely used broad-spectrum antimicrobial drug of fluoroquinolone family. The widespread use of ciprofloxacin increases its release into the environment. Ciprofloxacin is detected in aquatic ecosystems potentially harming aquatic organisms. The CIP effect on photosynthetic organisms is not fully studied. In this study we examined the CIP effect on green freshwater microalgae Scenedesmus quadricauda (Turp.) Bréb. using chlorophyll fluorescence methods (JIP test parameters and rapid light curves). A significant decrease in the cell number was observed at ≥10 mg/L of сiprofloxacin in comparison with control. Analysis of chlorophyll fluorescence parameters obtained from OJIP transients revealed the changes in photosynthetic reactions in сiprofloxacin treatment. Ciprofloxacin was found to inhibit electron transport rate in photosystem II (PSII). The decrease in the quantum yield of electron transport in photosystem II (φEo) was accompanied by the decrease in performance index (PIABS) and an increase in energy dissipation (DI0/RC). Ciprofloxacin enhanced the photosensitivity of microalgae but did not inhibit the recovery of photosynthetic activity after the photooxidative stress. In this regard the effect of CIP differs from that of the well-known antibiotic chloramphenicol that inhibits the resynthesis of plastid proteins and, accordingly, the recovery of photosynthetic activity associated with the resynthesis of PSII protein D1. Among the fluorescence parameters, PIABS was found to be the most stress-specific; therefore it can be proposed to detect an early toxic CIP effect in microalgae.

Сryoresistance of Autotrophic Organisms From Polar Regions Sensed by Chlorophyll Fluorescence Method

Сryoresistance of Autotrophic Organisms From Polar Regions Sensed by Chlorophyll Fluorescence Method

Heat Stress Recovery of Chlorophyll Fluorescence in Tomato (Lycopersicon esculentum Mill.) Leaves through Nitrogen Levels

To study the impact of nitrogen application on the photosynthetic structure and photosystem activity of tomato (Lycopersicon esculentum Mill.) leaves during the recovery stage after heat stress, the OJIP curve and JIP parameters were determined through a control experiment in an artificial climate chamber. The tomato variety was “Jinfen No. 1”. Four day/night temperature levels (25 °C/15 °C as control CKT; 30 °C/20 °C, lightly high-temperature LHT; 35 °C/25 °C, moderate high-temperature MHT; 40 °C/30 °C, severe high-temperature SHT) were set for a duration of 7 days. Five nitrogen supply levels (N1–N5: 0, 1.3, 1.95, 2.6 and 3.75 g/plant, respectively; 2.6 g/plant is the recommended nitrogen application rate, CKTN4) were applied. The results showed that the O, K, J, I and P phases on the chlorophyll a fluorescence curve were significantly affected by different nitrogen treatments in heat stress recovery. Compared with CKT, with the increase in nitrogen supply, the fluorescence intensity of SHTN2-SHTN5 treatment increased significantly at P, I and J phases, while that of MHTN1-MHTN4 treatment decreased. The fluorescence intensity of SHTN5 and SHTN3 increased by 13.27% and 10.10% in the P phase, 13.52% and 12.1% in the I phase and 20.16% and 26.18% in the J phase, respectively. There were highly significant differences (p < 0.01) in the impact of high temperatures and nitrogen levels on the fluorescence parameters. On the 1st day after short-term heat stress, N had no significant effect on Fv/FM, Fv, Fo and FM; however, their interaction was significant (p < 0.05). On the 8th day, there were no significant interaction effects between HT and N for Fv/Fo, ABS/RC and DIo/RC. Fv/Fo proved to be sensitive to the application of both high temperatures and nitrogen. Under all five nitrogen applications, temperature played a significant role in increasing DIo/RC, especially for N2 and N3. The results indicated that decreasing the nitrogen application under SHT resulted in a higher number of active RCs and an increased value of specific energy flux (ABS/RC, TRo/RC and DIo/RC), indicating the enhanced ability of RC to reduce plastoquinone. The study provides a reference for the diagnosis of nitrogen nutrition under high-temperature stress using chlorophyll fluorescence methods.

Response of wheat cultivars to salt stress by leaf chlorophyll fluorescence method

Response of wheat cultivars to salt stress by leaf chlorophyll fluorescence method

Evaluation of the control effect of bighead carp and silver carp on cyanobacterial blooms based on the analysis of differences in algal digestion processes

The phytoplankton community in Qiandao Lake has typical seasonal succession characteristics, and Cyanophyta, especially the genus Microcystis, are dominant in summer. To evaluate the control effects of filter-feeding fish (silver carp and bighead carp) on cyanobacterial blooms, the changes in algal species composition along the fish intestine were analyzed by microscopic examination, chlorophyll fluorescence, high-throughput DNA sequencing and pigment ratios. The microscopic examination results showed that both silver carp and bighead carp have a certain control effect on bloom-forming cyanobacteria in spring. The digestion of silver carp in summer could still effectively remove cyanobacteria and reduce the dominance of Microcystis in the phytoplankton community, while the digestion of bighead carp seemed to have little effect on cyanobacteria. The results of the chlorophyll fluorescence method were similar to those of the microscopic analysis, which indicated that silver carp could reduce the cyanobacterial biomass in spring, while bighead carp could significantly promote the dominance of cyanobacteria (p < 0.001). High-throughput DNA sequencing showed that there were significant differences in filter-feeding plankton between silver carp and bighead carp. The midgut may be the main gathering site of intestinal microorganisms, and cyanobacterial digestion mainly occurs in the intestinal segments between the foregut and midgut. The analysis of pigment ratios indicated that selective digestion of phytoplankton by silver carp significantly reduced the dominance of Cyanophyta in its hindgut (p < 0.01), while bighead carp had the opposite effect (p < 0.05), especially in seasons other than spring. The results of the above four methods are basically the same, that is, the digestion effect of silver carp on cyanobacteria is better than that of bighead carp. Therefore, the stocking proportion of silver carp should be appropriately increased in some meso-eutrophic waterbodies.

An Operational Downscaling Method of Solar-Induced Chlorophyll Fluorescence (SIF) for Regional Drought Monitoring

Solar-induced chlorophyll fluorescence (SIF) has been shown to be a powerful proxy for photosynthesis and a promising indicator of drought monitoring, but the ability of high-resolution satellite-derived SIF for drought monitoring has not been widely investigated due to a lack of data. The lack of high spatiotemporal resolution satellite SIF hinders the resolution enhancement of SIF derived by downscaling or reconstruction algorithms. The TROPOspheric Monitoring Instrument (TROPOMI) SIF provides an alternative with finer spatiotemporal resolution. We present an operational downscaling method to generate 500 m 16-day SIF (TSIF) using Neural Networks over a local spatiotemporal window. The results showed that our method is very robust against overfitting, and TSIF has a strong spatiotemporal consistency with TROPOMI SIF (TROPOSIF) with R2=0.956 and RMSE=0.054 mWm−2sr−1nm−1. Comparison with another SIF product (CASIF) showed a spatiotemporal consistency with TSIF. Comparison with tower gross primary productivity (GPP) from AmeriFlux in California showed a strong correlation with R2 for multiple ecosystems ranging from 0.58 to 0.88. We explored the capacity of TSIF for monitoring a drought event in Henan, China, showing that TSIF is more sensitive to drought and precipitation compared to the Enhanced Vegetation Index. Our TSIF is a very promising indicator for regional drought monitoring.

Combined chlorophyll fluorescence techniques to study environmental impact on the mountain moss Polytrichum commune

Two chlorophyll fluorescence (ChlF) methods were used to study the effects of high light (photoinhibition) and dehydration, common stressors of the alpine environment, on primary photosynthetic processes in the moss Polytrichum commune from the Czech Republic, the Jeseníky Mountains. Photoinhibition (PI) was studied in fully hydrated thalli of P. commune and during the period of spontaneous desiccation. Time courses of Kautsky kinetics (KK) of ChlF and derived parameters: maximum quantum yield (FV/FM), effective quantum yeld (ΦPSII), and non-photochemical quenching parameters, were measured before and after the samples were treated with high light (1500 µmol m-2 s-1 PAR) for 60 min. Dehydration effects were tested in two sets of experiments with a Pulse-Amplitude-Modulation fluorometry (PAM) and Fast Chlorophyll Fluorescence induction curve (OJIP) techniques. In PAM tests, the desiccating samples were exposed to saturating light pulses every 10 min. in order to obtain ΦPSII and non-photochemical quenching (NPQ). In the second dehydration experiment, OJIP transients of ChlF were repeatedly recorded, OJIP-derived ChlF parameters were plotted against relative water content (RWC) monitored during desiccation. Combined ChF techniques provided insights into the mechanisms activated during P. commune desiccation, such as dissipation of excess absorbed energy through heat dissipation, and conformational changes or destructions of the light harvesting complexes. Combination of stressors resulted in amplified interference with the photosynthetic machinery, even when the added stressor (dehydration) was applied in low dose.

Evaluation of Responsivity to Drought Stress Using Infrared Thermography and Chlorophyll Fluorescence in Potted Clones of Cryptomeria japonica

As climate change progresses, the breeding of drought-tolerant forest trees is necessary. Breeding drought-tolerant trees requires screening for drought stress using a large number of individuals and a high-throughput phenotyping method. The aim of this study was therefore to establish high-throughput methods for evaluating the clonal stress responses to drought stress using infrared thermography and chlorophyll fluorescence methods in Cryptomeria japonica. The stomatal conductance index (Ig), maximum photochemical quantum yield of photosystem II (Fv/Fm), and axial growth of four plus-tree clones of C. japonica planted in pots were measured weekly for 85 days after irrigation was stopped. The phenotypic trait responsivity to drought stress was estimated by a nonlinear mixed model and by introducing the cumulative water index, which considers the past history of the soil water environment. These methods and procedures enabled us to evaluate the clonal stress responses in C. japonica and could be applied to large-scale clone materials to promote the breeding program for drought tolerance.

Chlorophyll Fluorescence of Summer Phytoplankton in Reservoirs of the Zvenigorod Biological Station of Moscow State University

The results of long-term observations and monitoring of three reservoirs of Zvenigorod Biological Station of Moscow State University using modern chlorophyll fluorescence methods are presented. A sharp increase in chlorophyll content (up to 431 μg/L) and photosynthesis activity (FV/FM up to 0.7) associated with the growth of a monoculture, Chlorella vulgaris, was found in 2017 Pozharnyi Pond pond constructed near University dormitory facilities. The high activity of light reactions of this phytoplankton was evident as changes in the following parameters: the maximum quantum yield of primary photochemistry in photosystem II (FV/FM), the maximum relative electron transport rate (ETRmax), maximal light utilization coefficient (α), the efficiency of electron transport (φEo) and the performance index of photosystem II (PIABS) increased. This was accompanied by a decrease in the density of QB-non-reducing centers (VJ) and dissipated energy flux per reaction center (DI0/RC). The most sensitive parameters of fluorescence induction curve (PIABS and φEo) and the coefficient of maximal light utilization coefficient (α) are proposed to monitor the state of phytoplankton in reservoirs.

Induction of chlorophyll fluorescence use for assessment of functioning of Gentiana lutea L. plants photosynthetic apparatus in different conditions of culturing in vitro

Aim. To study the peculiarities of functioning of photosynthetic apparatus of Gentiana lutea L. plants in vitro under different light qualities and source of carbon in the composition of nutrient medium by using the induction of chlorophyll fluorescence (ICF) method. Methods. Chlorophyll fluorescence was determined in light-adapted leaves of cultivated in vitro G. lutea plants by use of PAM fluorometry MultispeQ. The parameters change of photosynthetic apparatus functioning of cultivated in vitro plants was assessed with regard to light qualities (Variant 1: light intensity – 85 W/m2, when different spectra combinations of blue-wave band (Еb) and green-wave band (Еg) and red-wave band (Еr) was 33% : 42% : 25%; Variant 2: light intensity – 100 W/m2, with wave bands of spectra – Еb : Еg : Еr = 25% : 27% : 48%) and the source of carbon (10 g/l of sucrose or 3 g/l of mannite) in the composition of nutrient medium МS/2 (MS medium with half amount of macro- and microsalts), supplemented with 0.1mg/l of kinetin. Results. It was established that G. lutea plants cultivated in vitro for 90 days in light conditions of Variant 2 had a quantum yield photochemical of PS ІІ 8.3 % higher in comparison to G. lutea specimens cultured in light conditions of Variant 1. The vitality value of Variant 2 plants was 23 % higher. Change of carbon source in the composition of nutrient medium from sucrose (10 g/l) to mannite (3 g/l) was both increasing the efficiency of functioning of photosynthetic apparatus of Gentiana lutea L. plants in vitro and activating their resistance mechanisms to water deficit. Conclusions. The ICF method use shows that functioning of photosynthetic apparatus of G. lutea plants in vitro depends different qualities light and source of carbon in the composition of nutrient medium.&#x0D; Key words: induction of chlorophyll a fluorescence, plants in vitro, Gentiana lutea L.

Effects of viruses belonging to Potyviridae family on functional state and photosynthetic apparatus activity of beans

The effect of viral infection on functional state and activity of the plant photosynthetic apparatus, as well as on the metabolism of photosynthetic pigments in virus infection dynamics has been investigated. A reverse transcription-polymerase chain reaction (RT-PCR) was applied for the detection of bean yellow mosaic virus and bean common mosaic virus. Total RNA was isolated using AmpliSens Ribo-Sorb DNA/RNA extraction kit. The reverse transcription reactions were carried out using the PCR test kit AmpliSens Reverta-L-100 according to the manufacturer’s protocol. Plants were mechanically inoculated by rubbing freshly extracted sap from infected plants. Fluorescence induction measurements as a mark of plant photosynthetic system activity were taken with a «Floratest» fluorometer, which makes it possible to carry out measurements in the spectral range from 670 to 800 nm. Photosynthetic pigments content was measured spectrophotometrically using an SF-46 spectrophotometer. It was shown; BCMV causes a decrease in the photosynthetic activity of beans regardless of the arrangement of leaves on the stem. In bean plants infected by BCMV, chlorophylls amount that do not participate in the photosynthetic transfer of energy to the reaction centers was increased in 1.4–2.0 times while the quantum efficiency of FS II was decreased in the 2–3 times as much as in the control. It has been established, the pigment content in infected leaves reduced significantly compared to the control plants. The chlorophyll a, b and carotenoids content decreased to 64%, 53% and 36% of the control respectively. Such pathological changes are caused by declining of active chlorophyll content (the pigment of PS II protein complexes) and its destruction. The parameters of the CFI indicate a significant inhibition of photophysical and photochemical processes during photosynthesis, as well as a Calvin cycle interruption. The chlorophyll fluorescence method can be used for rapid screening of photosynthesis, which allows making conclusion about plant status under the virus infection in a short time period.

Comparing two measures of leaf photorespiration rate across a wide range of light intensities

Suppression of photorespiration by low O2 concentrations (Method 1) and simultaneous measurements of gas exchange and chlorophyll fluorescence (Method 2) are often used to estimate leaf photorespiration rate (Rp) of C3 plants. However, it is largely unknown whether Method 1 and Method 2 can be used equivalently in estimating Rp. Using a field experiment on two wheat cultivars (T. aestivum JM22 and T. aestivum Z39-118) whose leaf gas exchange and chlorophyll fluorescence at low and normal O2 concentrations (2% versus 21% O2) were simultaneously measured across a wide range of light intensities (I), this study assessed the impacts of the two measures on Rp and its response under changing irradiance conditions. All the above quantities increased with the increasing I until reaching the cultivar-specific maximum values and the corresponding saturation light intensities. However, there were significant differences between Rp estimated by Method 1 and Method 2 at the I range from 150 to 2000 μmol m−2 s−1 for T. aestivum JM22 and from 150 to 1000 μmol m−2 s−1 for T. aestivum Z39-118. These findings demonstrated that the two methods cannot be used equivalently under changing irradiance conditions.

Measuring and calculating methods of plant mesophyll conductance: A review.

Mesophyll conductance (gm) refers to the diffusion capacity of CO2 inside mesophyll cells, which is the reciprocal of resistance of mesophyll cells. In the early stage of photosynthesis research, mesophyll diffusion resistance to CO2 was usually assumed to be zero, namely the gm was infinite. In recent studies, however, the gm was found to be limited and changed with external environments. As gm directly determines CO2 diffusion and affects leaf photosynthetic efficiency, it is of great significance to mechanestic research of photosynthesis. Presently, simultaneous chlorophyll fluorescence and gas exchange, the curve-fitting and instantaneous carbon isotope (13CO2) discrimination are commonly used to estimate gm, but few literature have been introduced on those methods in China. Therefore, it is particularly necessary to elaborate the principles and processes of these methods and to compare their advantages and disadvantages. We synthesized the relevant literature, and introduced the three methods in detail from the aspects of principle, derivation process and advantages and disadvantages, aiming to provide a methodological basis to promote the research on gm in China. The curve-fitting method was easy to understand and operate. Its fitting model varied with the status of photosynthesis, which is needed to be divided strictly by researchers. Consequently, it was not conducive to be widely used. Although the instantaneous carbon isotope (13CO2) discrimination method improved the accuracy of results, it was complex in measurement and strict in operation. Furthermore, it was less sensitive to test errors with low reliability. Compared with the above two methods, simultaneous chlorophyll fluorescence and gas exchange was more operable and reliable, and was more conducive to the observation and analysis for large samples with multi-processing and multi-repetition. In addition, the use of chlorophyll fluorescence technology not only simplified the test procedures, but also reduced the accidental errors, making the results more scientific. Chlorophyll fluorescence technology also provided saturated pulse activation energy to maximize leaf photosynthetic potential. But this method also had many problems, for instance, to improve the accuracy of chlorophyll fluorescence parameters, a lower gas flow rate was needed, which would increase the risk of gas diffusion and leakage. Thus, this method had a high requirement for a reasonable gas flow rate. In general, simultaneous chlorophyll fluorescence and gas exchange method was most widely used in the actual determination of plant gm.

Calibration matters: On the procedure of using the chlorophyll fluorescence method to estimate mesophyll conductance

Estimates of mesophyll conductance (gm), when calculated from chlorophyll fluorescence, are uncertain, especially when the photosystem II (PSII) operating efficiency is measured from the traditional single saturation pulse methodology. The multiphase flash method has recently been recommended to replace the single saturation pulse method, allowing a more reliable estimation of gm. Also, many researchers still directly use the PSII operating efficiency to derive linear electron transport rate J (that is required to estimate gm), without appropriate calibration using measurements under non-photorespiratory conditions. Here we demonstrate for tomato and rice that (i) using the multiphase flash method did not yield realistic estimates of gm if no calibration was conducted; and (ii) using the single saturation pulse method still gave reasonable estimates of gm when calibration based on the non-photorespiratory measurements was properly conducted. Therefore, conducting calibration based on data under non-photorespiratory conditions was indispensable for a reliable estimation of gm, regardless whether the multiphase flash or the single saturation pulse method was used for measuring the PSII operating efficiency. Other issues related to the procedure of using the chlorophyll fluorescence method to estimate gm were discussed.

Concomitant effects of mercuric chloride on mesophyll conductance and carbonic anhydrase activity in Populus trichocarpa Torr. &amp; Gray

Mercuric chloride, an inhibitor of CO2 transport via aquaporins, reduces mesophyll conductance in black cottonwood, and more so in northern than in southern genotypes, and it also reduces carbonic anhydrase activity. To investigate the potential involvement of aquaporins (AQPs) in latitude-dependent variation in mesophyll conductance (g m) of Populus trichocarpa Torr. & Gray (black cottonwood), photosynthetic susceptibility to mercuric chloride (HgCl2; a chemical inhibitor for AQPs) was tested in three northern and three southern representative cottonwood genotypes. The chlorophyll fluorescence method combined with a gas exchange system, was used to estimate g m in leaves under distilled water (control) and 1.5 mM aqueous HgCl2 fed through the petiole. Compared to the control, in both northern and southern genotypes photosynthetic rate (A n), g m, stomatal conductance (g s) and chloroplast CO2 concentration (C c) decreased significantly under HgCl2 (P < 0.008). The effect of HgCl2 on A n was reversible at saturating CO2. In the northern genotypes, A n, g m and g s (which are intrinsically higher in northern genotypes than in southern genotypes), were more susceptible to HgCl2 in both absolute and percentage terms (P < 0.05). In contrast, northern and southern genotypes had similar C c under control conditions, and showed statistically similar reductions under HgCl2. These results are consistent with a greater proportional involvement of AQPs in determining g m in northern genotypes. However, treatment with HgCl2 resulted in a concurrent reduction (P < 0.05) in carbonic anhydrase (CA) activity, which has previously been linked to variation in g m in black cottonwood. Mercuric chloride may thus reduce g m by acting on either AQPs or CA, or the two in combination.

Biocrust ecology: unifying micro- and macro-scales to confront global change.

Biocrust ecology: unifying micro- and macro-scales to confront global change.

Water Deficiency Detection of Hevea brasiliensis Clones by Laser Induced Fluorescence

Water is the key nutritional element for the optimal development of plants. A water deficiency leads to lower crop productivity. As the health status of a plant influences the photosynthesis process, a photosynthetic diagnosis of a plant can be carried by laser induced chlorophyll fluorescence, a reliable and fast method that is non-destructive to the sample. In this study, we show that it is possible to detect the water deficiency of rubber tree hevea brasiliensis from the chlorophyll fluorescence ratio. The fluorescence ratio used in this study is called the effective ratio and it corresponds to the both fluorescence peaks ratio. We noticed that the water deficient plants fluorescence ratios were higher than those of normally watered plants. Moreover, the stressed plants' ratios are greater than a threshold value which depends on the duration of water deprivation application.

Resistance of grapevine varieties of Kvemo (lower) Kartli of Georgia to abiotic factors

The paper analyzes relative resistance to abiotic factors of Lower (Kvemo) Kartli, Georgia grape varieties such as Rkatsiteli, Saperavi, Asuretuli shavi and Tavkveri (Vitis vinifera L.) with chlorophyll fluorescence method. It is shown that Rkatsiteli and Asuretuli shavi are distinguished by the highest frost resistance, followed by Saperavi and Tavkveri. However, Asuretuli shavi is more resistant to spring frosts. Rkatsiteli reveals more resistance to high temperatures, followed by Saperavi, Asuretuli shavi and Tavkveri. As for droughts, the most resistant is Asuretuli shavi, followed by Rkatsiteli, Saperavi and Tavkveri.

Differences in the photosynthetic plasticity of ferns and Ginkgo grown in experimentally controlled low [O2]:[CO2] atmospheres may explain their contrasting ecological fate across the Triassic-Jurassic mass extinction boundary.

Background and Aims Fluctuations in [CO2] have been widely studied as a potential driver of plant evolution; however, the role of a fluctuating [O2]:[CO2] ratio is often overlooked. The present study aimed to investigate the inherent physiological plasticity of early diverging, extant species following acclimation to an atmosphere similar to that across the Triassic–Jurassic mass extinction interval (TJB, approx. 200 Mya), a time of major ecological change. Methods Mature plants from two angiosperm (Drimys winteri and Chloranthus oldhamii), two monilophyte (Osmunda claytoniana and Cyathea australis) and one gymnosperm (Ginkgo biloba) species were grown for 2 months in replicated walk-in Conviron BDW40 chambers running at TJB treatment conditions of 16 % [O2]–1900 ppm [CO2] and ambient conditions of 21 % [O2]–400 ppm [CO2], and their physiological plasticity was assessed using gas exchange and chlorophyll fluorescence methods. Key Results TJB acclimation caused significant reductions in the maximum rate of carboxylation (VCmax) and the maximum electron flow supporting ribulose-1,5-bisphosphate regeneration (Jmax) in all species, yet this downregulation had little effect on their light-saturated photosynthetic rate (Asat). Ginkgo was found to photorespire heavily under ambient conditions, while growth in low [O2]:[CO2] resulted in increased heat dissipation per reaction centre (DIo/RC), severe photodamage, as revealed by the species’ decreased maximum efficiency of primary photochemistry (Fv/Fm) and decreased in situ photosynthetic electron flow (Jsitu). Conclusions It is argued that the observed photodamage reflects the inability of Ginkgo to divert excess photosynthetic electron flow to sinks other than the downregulated C3 and the diminished C2 cycles under low [O2]:[CO2]. This finding, coupled with the remarkable physiological plasticity of the ferns, provides insights into the underlying mechanism of Ginkgoales’ near extinction and ferns’ proliferation as atmospheric [CO2] increased to maximum levels across the TJB.