Marine diatoms represent one of the most successful phytoplankton groups in the marine environment. Their ecological success has been attributed to their photosynthetic plasticity, and the protection afforded them by their rigid silica cell walls. In this study, we investigated the influence of light environments on the physiology and morphology of the centric diatom Thalassiosira oceanica. Specifically, we determined how irradiance influenced growth rates, cell stoichiometry, photobiology and silica production. We found that T. oceanica exhibited optimal growth at irradiance around 250 µmol photons m-2 s-1, and showed a 15%–23% increase in frustule thickness at growth irradiances at or above 480 µmol photons m-2 s-1. While we found no direct relationship between growth and silicification, we did find that heavier silicified cells showed reduced dependence on non-photochemical quenching and lower excitation pressure when exposed to high irradiances. The observed co-adjustment of cell properties and silicification in response to growth irradiance, suggests that T. oceanica uses both physiological and morphological plasticity in photo-acclimation. These findings shed light on the functionality of frustule morphology and plasticity on diatom photo-acclimation, whereby through coordinating cellular changes with frustule properties, T. oceanica may be able to modulate the intracellular light field of its cell to optimise growth. This light-induced frustule modulation may represent an important growth strategy for natural diatom assemblages found in environments where light exposure can be highly dynamic.
Diatoms inhabiting estuarine intertidal flats are regularly exposed to episodes of high irradiance and elevated temperature during daytime low tides, conditions prone to inducing strong photoinhibition of photosystem II (PSII). However, the extent to which different species cope with repeated exposure to these combined stressors, and how photoacclimation modulates these responses, remains poorly known. This study examined the interspecific diversity in PSII photoinactivation, photorepair and photoprotection of three estuarine pennate diatom species exposed to three consecutive daily periods of combined high light and heat: two benthic species, Navicula phyllepta and Entomoneis paludosa, and one tychoplanktonic species, Cylindrotheca closterium. Unialgal cultures of each species were also acclimated to contrasting low- (LL) and high-light (HL) regimes to further evaluate the influence of photoacclimation on the responses to light and heat stress. In the two benthic species, PSII photoinactivation was largely counterbalanced by efficient photorepair, leading to near-complete recovery after each stress event. In contrast, the tychoplanktonic C. closterium showed markedly higher photoinactivation rates and limited photorepair capacity, resulting in an overall poor recovery. The tested species also differed strongly in the operation of the xanthophyll cycle (XC). Although XC-mediated de-epoxidation of the pigment diadinoxanthin into diatoxanthin increased under stress in all LL-acclimated cultures, it was strongly reduced in the HL-acclimated benthic species. Despite pronounced short-term effects of each stress exposure, no significant accumulation of irreversible PSII damage occurred over the 3 days, likely due to extended recovery intervals that favored an effective PSII photorepair. Overall, the results show that species-specific physiological traits and photoacclimation state play a dominant role in determining the capacity of diatoms to cope with the extreme conditions found in the estuarine intertidal environments.
Essential plant nutrient elements are “eaten” along with light in the process of photosynthesis, primarily in the leaves. Two pigment-protein systems embedded in the thylakoid membrane, Photosystem I and Photosystem II, mediate light absorption, excitation energy transfer, primary photochemistry, electron transfer, oxidation of water, and reduction of NADP+ to NADPH. In addition to electron transfer, several membrane complexes release protons (H+) into the thylakoid lumen, generating an H+ gradient which is utilized by ATP synthase to produce ATP. Here, we describe how essential nutrient elements play vital roles in the metabolic pathways of photosynthesis and how their absences limit productivity because they are integral to the trafficking and turnover of metabolites. We provide an overview of key processes of photosynthesis, activation by metalloproteins, and the sites of their interactive roles in plants. An original open-source figure of the Z-Scheme of photosynthesis and the location of elements therein is provided for education and lectures. Signaling between nutrients, as well as crosstalk with plant growth regulators are important for directing metabolic pathways of photosynthates, such as sugars, highlighting the significance for management of minerals in the modulation of photosynthesis in the field.
Quantitative monitoring of motility in biological microswimmers is an essential instrument for understanding how microorganisms perceive, process, and translate external stimuli into dynamic behavioural responses. However, tactical responses emerge from complex biophysical mechanisms that operate simultaneously at the individual and collective levels, giving rise to intra-population heterogeneity that can be difficult to quantify with population-averaged approaches: when the trajectories of kinematically distinct subgroups are aggregated, coherent responses may appear weak or confused even in the presence of organised subpopulations. In this work, we present a single-cell tracking-based method for the rigorous kinematic characterisation of the phototactic response of Chlamydomonas reinhardtii, with the aim of resolving behavioural variability and its temporal evolution within heterogeneous populations. The workflow integrates automated large-scale tracking, detailed trajectory reconstruction, single-cell and population-level kinematic analysis, segmentation into coherent behavioural subpopulations (stationary, confined/circling, and directional) via clustering in circular feature space, and characterisation of dynamic motion regimes through time-windowed mean squared displacement (MSD) analysis. By explicitly decomposing the population into coherent kinematic components and quantifying their relative contributions, the method provides “behavioural resolution” of mixed phototactic responses. Based exclusively on open-source software and robust mathematical analysis, the method is highly reproducible and easily extendable to the study of other biological or synthetic microswimmers subjected to controlled external stimuli.
IntroductionUnderstanding how organisms adapt to complex and variable environments requires in situ analysis of ecological performance in different environments.MethodsIn this multi-year study, we investigate the photophysiological performance of dinoflagellate endosymbionts (Symbiodiniaceae) of the golden jellyfish Mastigias papua across a natural environmental gradient of marine lakes and semienclosed coves in the Palau Archipelago (Western Caroline Islands, Pacific Ocean).ResultsThese sites vary in terms of age, distance from the nearby ocean (lagoon) and underwater light conditions, all of which influence the ecology of the host and that of its symbionts. Jellyfish endosymbionts from isolated lakes ‐ remote from the ocean and characterized by more turbid conditions – were found to exhibit significantly lower photosynthetic performance (quantum yield and PSII performance index) than endosymbionts from sites more connected to the nearby ocean and with clearer waters. The pigment composition of endosymbionts varied little between those collected from inland lakes and ocean-connected coves, and showed little sign of adaptation to light spectra dominated by reddish wavelengths.DiscussionThis suggests a mismatch between the optical characteristics of waters in more turbid lake environments and those of pigments that appear to remain optimized for blue light use in marine dinoflagellates. While published studies show evidence of morphological and behavioral adaptations in Mastigias jellyfish living in Palau’s marine lakes, this study suggests that their symbionts are limited by reduced pigment plasticity and lower photosynthetic performance. These results highlight the importance of symbiont characteristics and physiological compatibility in driving host adaptation, and the potential for evolutionary mismatch in tightly integrated symbioses, under novel environmental conditions.
A less studied yet promising microalgal group within the field of Carbon Capture Usage and Storage (CCUS) is the calcifying marine microalgae known as coccolithophores. They could have significant potential for carbon capture since they can capture CO2, partitioning carbon into both their organic tissues and inorganic exoskeletons, composed of several micrometric plates of calcium carbonate (CaCO3), called coccoliths. Moreover, the complex coccolith architecture offers valuable potential for nanotechnological applications, promoting also their reuse within a circular economy. However, comprehensive knowledge of their biotechnological potential and preliminary strain screening for quality assessment remain limited. In this study, a screening aimed at identifying the most promising strains for potential industrial applications was carried out by testing their response and yield under increasing nutrient and carbon supplies: dry weight (DW) and nutrient consumption efficiency were measured for the species Gephyrocapsa huxleyi (formerly Emiliania huxleyi) and two strains of the species Chrysotila roscoffensis, to identify the most promising strain for industrial applications. We documented a positive effect of nutrient enrichment and an even stronger response to carbon supplementation in the form of sodium bicarbonate (NaHCO3) on the growth of C. roscoffensis and on CaCO3 production in G. huxleyi. One C. roscoffensis strain proved to be the most promising, exhibiting the highest DW (1,172.7 ± 42.2 mg/L) and CO2 absorption (1,210.7 ± 3.1 mg/L) compared to G. huxleyi (569.4 ± 20.5 mg/L; 329.9 ± 11.9 mg/L), as well as a stable ratio between Particulate Inorganic Carbon (PIC) and Particulate Organic Carbon (POC) during cultivation. Our experiments also highlighted the ability of G. huxleyi to produce significant amounts of carbonate (2.1 ± 1.1 PIC:POC) compared with the less calcified C. roscoffensis (0.34 ± 0.01 PIC:POC) under enhanced carbon supply. This study emphasizes the importance of preliminary screening to identify the most suitable strain for industrial exploitation, particularly among understudied microalgae such as coccolithophores.
Throughout their species seasonal succession, diatoms of the Arctic Ocean experience a radical habitat transformation, from surviving the dimly lit winter within sea-ice or in the water column, to rapid growth under increasing irradiances, forming massive spring blooms beneath melting ice and later in open waters. Therefore, their evolutionary path has been moulded by the opposing challenges of maximizing light capture part of the year while maintaining highly efficient photoprotection capacities to limit photodamage upon bursts of supra-optimal illumination. Two main photoprotection mechanisms exist in diatoms i) nonphotochemical quenching (NPQ) supported primarily by the xanthophyll cycle (XC) and stress-related Lhcx antenna proteins and, ii) a rapid repair cycle of photosystem (PS) II core protein, PsbA, upon photodamage. Previous studies suggest that freezing temperatures slow protein turnover and favour photoprotection strategies that rely primarily upon XC-NPQ in polar taxa. We aim to revisit this hypothesis by dissecting the high-light response of five Arctic diatom species that dominate contrasting ecological niches: sea-ice, marginal ice-zone and open waters. We exposed each species to a high-light stress and subsequent recovery period under low light, with and without, inhibitors of XC-NPQ (dithiothreitol) or of plastid protein translation (lincomycin), blocking de novo replacement of PsbA. We confirmed the crucial role of XC-NPQ in protecting PSII but also report unexpected observations that challenge our current understanding of psychrophile species response to light stress. First, the impact of lincomycin on PSII photoinhibition was stronger than that of DTT, despite PsbA turnover being undetectable by immunoblots in most cases. Second, while our data support planktonic species showing better tolerance to high light than sympagic species, we found unsuspected diversity in photoprotection strategies. We hypothesize that these differences support a gradient from conservative strategies, possibly optimized for survival in the extreme sea-ice habitat of sympagic species, to productivity-oriented strategies in open water planktonic species dominating during the bloom period. In the transforming, brighter, Arctic Ocean, the adaptedness of this community-wide strategy scheme could be undermined, shaking up the historical dominance of certain diatom taxa.
Plants have evolved with complex sensory systems to recognize signals from multiple environmental conditions. A light signal is one of the most important environmental factors that regulates not only photomorphogenesis but also the developmental strategy of plants throughout their life cycle. The molecular mechanisms of the light signaling modules and the interactions between light and other environmental signals have been studied extensively. However, to enhance plant growth, particularly in crop production, we need to gain a deeper understanding of how light regulates plant development within gene regulatory networks (GRNs). Understanding GRNs is important to identify not only the novel genes and transcription factors in light signaling pathways but also the factors that connect light signaling and other environmental signals. Weighted gene co-expression network analysis (WGCNA) has been used to study GRN. We applied WGCNA to 58 RNA-seq samples of wild-type Arabidopsis grown under different light treatments and built the gene co-expression networks. We identified 14 different modules that are significantly associated with different light treatments. Among them, the honeydew1 and ivory display significant association with the dark-grown seedlings. Many hub genes identified from these modules are significantly enriched in light responses, including responses to red, far-red, blue light, light stimulus, auxin responses, and photosynthesis. Although we found many known transcription factors in these modules, we also identified several unknown genes and transcription factors that are significantly associated with the honeydew1 module and highly differentially expressed between dark and light conditions. To examine whether the hub genes in the honeydew1 module play a role in light signaling, we isolated mutants in selected hub genes and measured hypocotyl lengths under dark, red, and far-red light conditions. These assays showed that four hub genes are involved in regulating light signaling pathways. This study provides a new approach to identifying novel genes in GRNs underlying light responses in Arabidopsis.
Earlier, we discovered that to reach the maximum chlorophyll-a (Chl-a) fluorescence level of photosystem II (PSII) in diuron-treated samples, and thus PSIIL, the light-adapted charge-separated state, multiple excitations with sufficiently long Δτ waiting times between excitations are required. Experiments of Chl-a fluorescence, elicited by single-turnover saturating flashes (STSFs), revealed that the Δτ1/2 half-waiting times between flashes depended on the lipid content of the reaction centre (RC) and on the temperature. We hypothesized that the gradual formation of PSIIL depends on protonatable residues (and bound water molecules) at the donor side of the RC. Here, we tested this hypothesis: we used diuron-treated isolated PSII core complexes of Thermostichus vulcanus and determined the pH dependence of Δτ1/2 and other Chl-a fluorescence parameters at different temperatures. Data recorded at 5°C revealed moderate and steep increases of Δτ1/2 between pH 5.0 and 6.5, and 6.5 and 8.0, respectively. Much weaker pH dependences were seen at cryogenic temperatures (−20 and −60°C), indicating the role of structural plasticity in the protonation-dependent reorganizations. Similar to the strong pH dependence of Δτ1/2 at 5°C, the magnitude of the F1 fluorescence level, induced by the first STSF, displayed moderate and steep increases between pH 5.0 and 6.5, and 6.5 and 8.0, respectively, at all temperatures. Corroborating data were received from fast Chl-a fluorescence transient measurements. Hence, our data provide experimental support to the hypothesized role of protonation processes in the formation of PSIIL. The protonophores, CCCP and FCCP significantly increased the Δτ1/2 at pH 6.0 and essentially eliminated the pH dependence of the F1 fluorescence level. These data provide experimental support to our hypotheses on the role of protonatable residues in determining the structural dynamics of PSII RCs.
The dinoflagellate algae Symbiodiniaceae live in endosymbiosis with Anthozoa, which is essential for the existence of coral reefs. The cells of Symbiodiniaceae exist in two distinct forms: the flagellated, motile form and the non-flagellated, coccoid form, which play specific roles in the life cycle of these algae. The regulation and distribution of the different cell forms have been intensively studied in the past, however, the behavior and changes of the cell cycle are less characterized under conditions that mimic the coral tissue versus the free living environment, e.g., by manipulating the viscosity of the medium and thereby altering cell motility. In this work, we applied precisely controlled microfluidic tools to manipulate the viscosity of the medium, using the polysucrose Ficoll. We found that by the application of Ficoll the diurnal cycle of the different cell forms undergoes remarkable changes, the motility of the cells decreases, and the motile phase of the cell cycle becomes significantly shorter compared to the absence of Ficoll. The slowed motile cells are also amenable for single-cell analysis of the activity of PSII (Fv/Fm). We therefore propose that the method developed here could serve as a sensitive monitoring system of the cell cycle changes and manipulation of cell motility mimicking the coral host environment, with concomitant single-cell photosynthetic activity analysis of Symbiodiniaceae.
Diatoms, heterokont microalgae found in all aquatic habitats, can be distinguished by their typical brown colour due to the presence of a characteristic light-harvesting carotenoid: fucoxanthin. The biosynthesis of fucoxanthin involves several intermediates, some of which also play a key role in photoprotection via the xanthophyll cycle, controlling the dissipation of excessively absorbed light energy in the form of Non-Photochemical Quenching (NPQ). The regulation of the fucoxanthin pathway is therefore crucial to direct xanthophyll biosynthesis towards light harvesting or photoprotective functions. Yet, until recent years most of the steps in this key metabolical route remained unknown. Interestingly, diatoms possess multiple homologs of the ancestral genes encoding the two xanthophyll cycle enzymes: Violaxanthin De-Epoxidase (VDE) and Zeaxanthin Epoxidase (ZEP). Here, we review the recent discoveries of the function of most VDE and ZEP isoforms in the fucoxanthin pathway of the model diatom Phaeodactylum tricornutum. Some of these enzymes have a central role in photoprotection, while other have been identified as ideal targets for engineering and industrial applications. We discuss the physiological role of these proteins and address missing links in the pathway and unknown properties of these enzymes. Finally, we argue that the expansion of the VDE and ZEP gene families represented a turning point in the evolution of xanthophyll cycling and fucoxanthin biosynthesis in diatoms.
Phytochromes are a small photoreceptor protein family regulating red/far-red light mediated plant growth and development. The five phytochromes in Arabidopsis, phyA-phyE, have distinct and overlapping functions partly due to their evolutionary divergence and heterodimerization. To define the regulatory roles of each phytochrome, quadruple mutants retaining only one phytochrome in the Landsberg erecta (Ler) accession of Arabidopsis thaliana were obtained and characterized. The most recently evolved phyB paralogs, phyD and phyE, individually poorly regulated red light-mediated seedling de-etiolation except for promoting cotyledon greening. The light-labile phyA positively regulated seedling photomorphogenic growth, dependent on its steady-state protein level in the light. PhyA specifically suppressed hypocotyl elongation under low red light but surprisingly antagonized phyB function under moderate red light to dampen photomorphogenesis. PhyB-only plants (a.k.a. phyACDE quadruple mutant) were significantly longer than Ler WT, which could not be complemented by any other phytochrome, thereby revealing that collective actions from more than two phytochromes are needed to achieve maximum photomorphogenic growth. In adult plants, phyB and phyE have undergone substantial subfunctionalization so that they equally and predominantly regulate photoperiodic flowering. Moreover, under short-day photoperiods, elevated light irradiance accelerated flowering of WT plants, delayed flowering of phyB-deficient plants, and had no statistically significant influence on flowering of phyB-only plants, unveiling the critical role of phyB to interpret the light intensity signal into flowering. The complete set of quadruple mutants and triple mutants retaining phyB and each other phytochrome represent foundational germplasms to assess genetic interactions between phytochromes and to explore phytochrome regulatory networks in response to varied environmental stimuli.
The light environment is a key factor regulating the growth and biomass production of microalgae. Photon flux density and spectral composition i.e., the relative contribution of different wavelengths, are among the most important light parameters influencing microalgal efficiency. The red, green and blue bands are used by microalgae as both energy source for photosynthesis and as external cue that triggers biological signaling and physiological adjustments. This study mechanistically explores the effects of light modulation on key metabolites in the emerging model Odontella aurita, the only diatom species currently approved as a food supplement in the EU. Four spectral compositions with red (590–656 nm) ranging from 0% to 60% and blue (422–496 nm) from 60% to 20% were set up under two light conditions: limiting and saturating intensities. Growth and photosynthetic performances were assessed, together with a wide set of metabolites involved in various biochemical pathways including vitamins (A, B1, B2, B6, B8, B9, B12, K1, D2, D3, C and E), auxin, amino acids and other compounds identified by NMR. In addition, the biomass was characterized for its macromolecular composition, carotenoids, phytosterols, total flavonoid and total phenolic content, iron and zinc content, and total antioxidant capacity of the biomass using different assays were evaluated. Results revealed the complementary roles of blue and red lights: blue light enhanced growth and photosynthesis, as well as the use or regulation of photoenergy, whereas red light promoted the regulation of key metabolites e.g., B vitamins or auxin, involved in the modulation of metabolic pathways. These findings provide insight for optimizing diatom cultivation under controlled light environments e.g., with the aim to boost growth and metabolism.
Photosynthetic activity of cyanobacteria is a prominent driver of cell-surface catalysed extracellular calcium carbonate (CaCO 3 ) precipitation. This natural process termed “biomineralization” occurs only under specific circumstances but has given rise to significant carbonate rock formation throughout geological time. Engineering cyanobacterial cell surfaces for enhanced and constitutive biomineralization of abundant ocean-water dissolved Ca 2+ and flue-gas CO 2 into CaCO 3 may allow for the biotechnological re-capture of CO 2 released by industrial processes such as thermal decarboxylation of CaCO 3 . This may both limit net greenhouse gas emissions and transform CaCO 3 into a sustainable resource. Drawing from geological precedent and basic biological research, this perspective outlines promising synthetic biology strategies to convert cyanobacterial biomineralization into a cornerstone technology for a sustainable carbonate economy.
Diatoms, one of the most ubiquitous phytoplankton in the oceans, have evolved a pyrenoid-based CO 2 -concentrating mechanism (CCM) to utilize limited CO 2 in seawater for photosynthesis. Recent proteomics analyses and molecular biological tools have deepened our understanding of the molecular mechanisms involved in diatom chloroplast architecture and the CCM. Here, we provide an update to our knowledge of the processes involved in high affinity photosynthesis for dissolved inorganic carbon (DIC) in diatoms. Based on the phenotype of genome-edited mutants, we propose a model of the diatom CCM composed of four phases of CO 2 -dependent photosynthesis at (I) less than 0.1 mM, (II) 0.1–2 mM, (III) 2–10 mM, and (IV) more than 10 mM of DIC concentrations, in which the rate-determining steps are the capture of unfixed CO 2 in the chloroplast stroma at Phases I and II, the evolution of CO 2 in the pyrenoid-penetrating thylakoid lumen at Phase III, and DIC transport to the stroma at Phase IV. Under natural seawater containing 2 mM DIC mainly in the form of HCO 3 − , the photosynthesis of marine diatoms is likely primarily in Phase III, shifting to Phase II when available CO 2 is limited.
Diatoms are crucial in global primary productivity and carbon sequestration, contributing significantly to marine food webs and biogeochemical cycles. With the projected increase in sea surface temperatures, climate change poses significant threats to these essential organisms. This study investigates the photobiological responses of nine diatom species to rapid changes in light and temperature, aiming to understand their adaptability and resilience to climate-induced environmental fluctuations. Using a high-throughput phenoplate assay, we evaluated the maximum quantum yield of photosystem 2 (Fv/Fm), non-photochemical quenching (NPQ) and additional photosynthetic parameters under varying temperature conditions. Our results revealed significant variability in the photophysiological responses among the species, with temperature emerging as a dominant abiotic factor relative to light, accounting for 13.2%–37.5% of the measured variability. Measurements of effect size of temperature and light on Fv/Fm showed that there is additional significant innate variability in the samples when a homogeneous culture is fractioned in 384 subpopulations. Furthermore, hierarchical clustering analysis of the effect size of temperature, light and innate variability on all measured photosynthetic parameters identified two distinct diatom groups. One group exhibited strong interaction between light intensity and temperature, suggesting active synergetic mechanisms to cope with fluctuating environments, while the other showed potential limitations in this regard. These findings highlight diatoms’ diverse strategies to optimize photosynthesis and manage light and thermal stress, providing insights into their potential responses to future climate scenarios. Furthermore, we demonstrate that using the method presented in this work we can functionally cluster different diatom species.
The study highlights the critical role of CDOM in coastal light attenuation and its impact on primary production (PP). We investigated the spectral attenuation of light due to water, phytoplankton pigments, detritus and coloured dissolved organic matter (CDOM) along a salinity gradient in the outer Oslofjord, Norway. By examining the effects of these components across different seasons, we aimed to elucidate their relative contributions to light absorption and PP. The findings suggest that increased terrestrial CDOM inputs, driven by climate, changed atmospheric deposition and land-use changes, could significantly affect coastal ecosystems by altering light attenuation and consequently PP and potentially leading to other ecological pressures. CDOM consistently dominated light absorption across all stations and seasons, contributing 50%–80% of the total absorption of photosynthetically active radiation. The absorption by CDOM and detritus decreased with increasing salinity, while phytoplankton absorption followed a seasonal succession. PP estimates show high seasonal variability from maximums in June to minimums in November, mainly attributed to, changes in seasonal light availability and phytoplankton biomass, followed by light attenuation by CDOM and differences in quantum yields of photosystem II (PSII). Nutrient analysis showed a seasonal pattern, with the highest nitrogen concentrations in November and depletion during more productive seasons, as well as conservative mixing throughout the salinity gradient. CDOM absorption played substantial, albeit not leading, role in influencing PP estimates, derived from a bio-optical model. CDOM was the main determinant of light attenuation across most wavelegnths.
Plants have developed specific mechanisms to tackle environmental challenges. During one annual period, a dioecious yerba mate with rhythmic growth can present two growth units (GU1 and GU2) intercalated with two rest periods (R1 and R2). We hypothesized that photosynthetic performance will be much higher under monoculture (MO, high light) than under an agroforestry system (AFS, low light) over annual growth and that secondary sexual dimorphism (SSD) will be more expressed during rest than during growth periods. We evaluated the maximum net photosynthesis ( A max ), apparent quantum efficiency of CO 2 assimilation (Ф), respiration rate in the dark ( R d ) and in the light ( R L ), R L / R d ratio, maximum apparent rate of electron transport ( J max ), maximum apparent RuBisCO carboxylation rate ( V cmax ), J max / V cmax ratio, and chlorophyll indexes in four (two male and two female) clones. Light was reduced by 92%–95% in AFS compared to MO. Photosynthetic traits generally varied over the annual rhythmic growth and revealed higher photosynthetic performance under MO than AFS. Lower A max and R d in all clones under AFS than MO occurred together with higher inhibition of respiration by light (low R L / R d ) under AFS than MO. Despite the strong effect of cultivation systems and growth rhythmicity on photosynthetic traits, our data did not suggest that the frequency of SSD in photosynthetic performance (with the exception of the J max / V cmax ratio) was related to the cultivation system or period of rhythmic growth. The SSD was expressed in a higher Chl b index and lower Chl a / b ratio in female than male plants during R2 and GU2, indicating lower sensitivity of females to extreme light conditions of two cultivation systems than males. Higher A max and similar respiration rates ( R d and R L ) in females compared to in males in early vegetative phases after pruning (herein R1 and GU1) could be considered as a fitness strategy of female plants in their additional effort to produce fruits and seeds in latter phases. Our results additionally revealed the importance of the evaluation period when assessing photosynthesis in plant species with rhythmic growth.
