Photochemical Yield Research Articles

Salinity as an Abiotic Stressor for Eliciting Bioactive Compounds in Marine Microalgae.

This study investigated the impact of culture medium salinity (5-50 PSU) on the growth and maximum photochemical yield of photosystem II (Fv/Fm) and the composition of carotenoids, fatty acids, and bioactive substances in three marine microalgae (Chrysochromulina rotalis, Amphidinium carterae, and Heterosigma akashiwo). The microalgae were photoautotrophically cultured in discontinuous mode in a single stage (S1) and a two-stage culture with salt shock (S2). A growth model was developed to link biomass productivity with salinity for each species. C. rotalis achieved a maximum biomass productivity (Pmax) of 15.85 ± 0.32 mg·L-1·day-1 in S1 and 16.12 ± 0.13 mg·L-1·day-1 in S2. The salt shock in S2 notably enhanced carotenoid production, particularly in C. rotalis and H. akashiwo, where fucoxanthin was the main carotenoid, while peridinin dominated in A. carterae. H. akashiwo also exhibited increased fatty acid productivity in S2. Salinity changes affected the proportions of saturated, monounsaturated, and polyunsaturated fatty acids in all three species. Additionally, hyposaline conditions boosted the production of haemolytic substances in A. carterae and C. rotalis.

Vertical Variations of Photosystem Energy Partitioning in the Canopy of the Subtropical Cropland

AbstractLeaf‐level photosynthetic capacity exhibits vertical variations along the canopy profile. The dynamics of photosystem energy partitioning involved in dissipating absorbed light energy, namely photochemical yield (ΦP), fluorescence yield (ΦF), and the efficiency of non‐photochemical quenching yield (ΦN) in dissipating excess light energy as heat, along the vertical canopy profile remain unclear. Here, vertical variations in photosystem energy partitioning and photosynthetic nitrogen allocation were measured at different canopy positions of rice using active fluorescence detection and photosynthetic gas exchange measurement in subtropical southern China. We observed the decline in leaf nitrogen per leaf mass (Nmass) from the top to the bottom of the canopy. ΦP significantly decreased from vegetative growth stage to ripening stage, while ΦN showed an opposite trend. The top and bottom leaves had consistent relationships between photosynthetic nitrogen allocation and photosystem energy partitioning. Our findings reveal the vertical variations in physiological traits of subtropical rice.

Improved estimation of gross primary productivity (GPP) using solar-induced chlorophyll fluorescence (SIF) from photosystem II

Solar-induced chlorophyll fluorescence (SIF) contains contributions from both photosystem I (PSI) and photosystem II (PSII). In theory, SIF emitted from PSII (SIFPSII) should be extracted from at-sensor SIF to quantify photosynthetic CO2 assimilation, as PSI fluorescence yield is nearly insensitive to changes in photochemical yield. In many SIF-related studies, the fraction of chlorophyll-absorbed energy allocated to PSII (β2), a key factor controlling the flux of excitation energy for SIFPSII, is simply assigned a fixed value. However, β2 is regulated in response to variations in environmental conditions to avoid an energy imbalance between PSI and PSII. By quantifying the regulating effect of the cytochrome b6f complex (Cyt b6f) on the electron transport from PSII to PSI, and its interaction with energy dissipation in both photosystems, we develop a framework to estimate β2 and PSII fluorescence yield (ΦF2), two key determinants for SIFPSII, from SIF emission, PAR, air temperature, the maximum carboxylase activity of Rubisco (Vcmax), and the maximum activity of Cyt b6f (JCB6F_max). The framework is equipped with a two-leaf scheme, enabling us to estimate SIFPSII for sunlit and shaded leaves from top-of-canopy SIF observations (SIFTOC). Our simulation results showed that β2 and ΦF2 tend to change in opposite directions with varying PAR, making the contribution of PSII to SIFTOC relatively constant. We compare gross primary productivity (GPP) mechanistically estimated from SIFPSII obtained with fixed (GPPSIF_Fβ) and dynamic β2 (GPPSIF_Dβ) against the eddy-tower-derived GPP (GPPEC) at a winter-wheat experiment site. At a half-hourly time scale, GPPSIF_Dβ is better than GPPSIF_Fβ, showing higher correlations with GPPEC (R2 = 0.74 versus R2 = 0.64 and RMSE = 6.61 μmol m−2 s−1 versus RMSE = 7.67 μmol m−2 s−1). The study provides a practical way to estimate the contribution of SIFPSII to SIFTOC, giving a better theoretical basis to SIF-based GPP estimation models.

Assessing the levels of soil water availability that minimize the damage of heatwaves to potted grapevines

The adverse effects of heatwaves on viticulture could be, at least partly, mitigated by generous soil water availability. As climate change will also likely reduce irrigation water, knowing to which extent soil water availability could be decreased under the heatwaves without compromising plant performances would be important. In this pot experiment, we differentiated soil water availability by compensating 100% (T100), 70% (T70), 40% (T40) and 10% (T10) of vine transpiration. Grapevines (cv. Sauvignon) were then subjected to a 11-day heatwave (Tmax 40 °C) and to a post-heat stress recovery phase. Soil water potential between -0.05 to -0.2 MPa, respectively, in T100 and T70 enabled the plants to maintain high net CO2 assimilation (Pn), stomatal conductance (gs), and leaf transpiration (Eleaf) which kept the leaf temperature (Tleaf) below the ambient temperature and promoted the plant growth. During the heatwave, T100 and T70 vines decreased their photochemical yield and dissipated the excess energy via regulated non-photochemical heat dissipation, and resumed their photochemical activities upon removing the heat stress. Further reduction in soil water potential to -0.4 and and -1.2 MPa in T40 and T10, respectively, decreased Pn and gs and restrained Eleaf, causing a significant increase in Tleaf during the heatwave, and limited the plant recovery after the heat stress. Nonetheless, the maximum efficiency of PSII (Fv/Fm) showed quite high resistance to heat stress in all treatments. These findings suggest that decreasing soil water availability to reach soil water potential levels close to -0.2 MPa implies higher efficiency in using water resources during a heat wave without limiting plant growth.

Factors that Impact Photochemical Cage Escape Yields.

The utilization of visible light to mediate chemical reactions in fluid solutions has applications that range from solar fuel production to medicine and organic synthesis. These reactions are typically initiated by electron transfer between a photoexcited dye molecule (a photosensitizer) and a redox-active quencher to yield radical pairs that are intimately associated within a solvent cage. Many of these radicals undergo rapid thermodynamically favored "geminate" recombination and do not diffuse out of the solvent cage that surrounds them. Those that do escape the cage are useful reagents that may undergo subsequent reactions important to the above-mentioned applications. The cage escape process and the factors that determine the yields remain poorly understood despite decades of research motivated by their practical and fundamental importance. Herein, state-of-the-art research on light-induced electron transfer and cage escape that has appeared since the seminal 1972 review by J. P. Lorand entitled "The Cage Effect" is reviewed. This review also provides some background for those new to the field and discusses the cage escape process of both homolytic bond photodissociation and bimolecular light induced electron transfer reactions. The review concludes with some key goals and directions for future research that promise to elevate this very vibrant field to even greater heights.

Accounting for photosystem I photoinhibition sheds new light on seasonal acclimation strategies of boreal conifers.

The photosynthetic acclimation of boreal evergreen conifers is controlled by regulatory and photoprotective mechanisms that allow conifers to cope with extreme environmental changes. However, the underlying dynamics of photosystem II (PSII) and photosystem I (PSI) remain unresolved. Here, we investigated the dynamics of PSII and PSI during the spring recovery of photosynthesis in Pinus sylvestris and Picea abies using a combination of chlorophyll a fluorescence, P700 difference absorbance measurements, and quantification of key thylakoid protein abundances. In particular, we derived a new set of PSI quantum yield equations, correcting for the effects of PSI photoinhibition. Using the corrected equations, we found that the seasonal dynamics of PSII and PSI photochemical yields remained largely in balance, despite substantial seasonal changes in the stoichiometry of PSII and PSI core complexes driven by PSI photoinhibition. Similarly, the previously reported seasonal up-regulation of cyclic electron flow was no longer evident, after accounting for PSI photoinhibition. Overall, our results emphasize the importance of considering the dynamics of PSII and PSI to elucidate the seasonal acclimation of photosynthesis in overwintering evergreens. Beyond the scope of conifers, our corrected PSI quantum yields expand the toolkit for future studies aimed at elucidating the dynamic regulation of PSI.

Local habitat heterogeneity rivals regional differences in coral thermal tolerance

AbstractVariable temperature regimes that expose corals to sublethal heat stress have been recognized as a mechanism to increase coral thermal tolerance and lessen coral bleaching. However, there is a need to better understand which thermal regimes maximize coral stress hardening. Here, standardized thermal stress assays were used to determine the relative thermal tolerance of three divergent genera of corals (Acropora, Pocillopora, Porites) originating from six reef sites representing an increasing gradient of annual mean diel temperature fluctuations of 1–3 °C day−1. Bleaching severity and dark-acclimated photochemical yield (i.e., Fv/Fm) were quantified following exposure to five temperature treatments ranging from 23.0 to 36.3 °C. The greatest thermal tolerance (i.e., Fv/Fm effective dose 50) was found at the site with intermediate mean diel temperature variability (2.2 °C day−1), suggesting there is an optimal priming exposure that leads to maximal thermal tolerance. Interestingly, Acropora and Pocillopora originating from the least thermally variable regimes (< 1.3 °C day−1) had lower thermal tolerance than corals from the most variable sites (> 2.8 °C day−1), whereas the opposite was true for Porites, suggesting divergent responses across taxa. Remarkably, comparisons across global studies revealed that the range in coral thermal tolerance uncovered in this study across a single reef (< 5 km) were as large as differences observed across vast latitudinal gradients (300–900 km). This finding indicates that local gene flow could improve thermal tolerance between habitats. However, as climate change continues, exposure to intensifying marine heatwaves is already compromising thermal priming as a mechanism to enhance coral thermal tolerance and bleaching resistance.

Decoupling of nitrogen allocation and energy partitioning in rice after flowering.

Estimation of energy partitioning at leaf scale, such as fluorescence yield (ΦF) and photochemical yield (ΦP), is crucial to tracking vegetation gross primary productivity (GPP) at global scale. Nitrogen is an important participant in the process of light capture, electron transfer, and carboxylation in vegetation photosynthesis. However, the quantitative relationship between leaf nitrogen allocation and leaf energy partitioning remains unexplored. Here, a field experiment was established to explore growth stage variations in energy partitioning and nitrogen allocation at leaf scale using active fluorescence detection and photosynthetic gas exchange method in rice in the subtropical region of China. We observed a strongly positive correlation between the investment proportion of leaf nitrogen in photosynthetic system and ΦF during the vegetative growth stage. There were significant differences in leaf energy partitioning, leaf nitrogen allocation, and the relationship between ΦF and ΦP before and after flowering. Furthermore, flowering weakened the correlation between the investment proportion of leaf nitrogen in photosynthetic system and ΦF. These findings highlight the crucial role of phenological factors in exploring seasonal photosynthetic dynamics and carbon fixation of ecosystems.

Physiological and Biochemical Aspects of Silicon-Mediated Resistance in Maize against Maydis Leaf Blight.

Maydis leaf blight (MLB), caused by the necrotrophic fungus Bipolaris maydis, has caused considerable yield losses in maize production. The hypothesis that maize plants with higher foliar silicon (Si) concentration can be more resistant against MLB was investigated in this study. This goal was achieved through an in-depth analysis of the photosynthetic apparatus (parameters of leaf gas exchange chlorophyll (Chl) a fluorescence and photosynthetic pigments) changes in activities of defense and antioxidative enzymes in leaves of maize plants with (+Si; 2 mM) and without (-Si; 0 mM) Si supplied, as well as challenged and not with B. maydis. The +Si plants showed reduced MLB symptoms (smaller lesions and lower disease severity) due to higher foliar Si concentration and less production of malondialdehyde, hydrogen peroxide, and radical anion superoxide compared to -Si plants. Higher values for leaf gas exchange (rate of net CO2 assimilation, stomatal conductance to water vapor, and transpiration rate) and Chl a fluorescence (variable-to-maximum Chl a fluorescence ratio, photochemical yield, and yield for dissipation by downregulation) parameters along with preserved pool of chlorophyll a+b and carotenoids were noticed for infected +Si plants compared to infected -Si plants. Activities of defense (chitinase, β-1,3-glucanase, phenylalanine ammonia-lyase, polyphenoloxidase, peroxidase, and lipoxygenase) and antioxidative (ascorbate peroxidase, catalase, superoxide dismutase, and glutathione reductase) enzymes were higher for infected +Si plants compared to infected -Si plants. Collectively, this study highlights the importance of using Si to boost maize resistance against MLB considering the more operative defense reactions and the robustness of the antioxidative metabolism of plants along with the preservation of their photosynthetic apparatus.

Topologically engineering of π-conjugated macrocycles: Tunable emission and photochemical reaction toward multi-cyclic polymers

The topology of conjugated macrocycles had significant impacts on their photo-physical and photo-chemical properties. Herein, a series of π-conjugated macrocycles with diverse topology were synthesized via intramolecular McMurry coupling. Their chemical structure and macrocyclic topology were unambiguously confirmed via NMR, MALDI-TOF mass spectra, crystal analysis and scanning tunneling microscopy (STM). Depending on the structural topology and structural rigidity, these cyclic compounds display obviously distinctive emission behavior and photochemical reactions in the solution and in the solid state. Monocyclic phenylene vinylene macrocycle (denoted as MST) exhibiting aggregation-induced emission behavior, was more vulnerable to photo-cyclization in solution and triplet sensitizer promoted photo-dimerization due to lower strain and more flourishing intramolecular motions. After UV light irradiation, relatively more flexible MST could yield the anti-dimer via triplet excimer on the HOPG surface confirmed by STM investigation. By contrast, highly constrained bicyclic analogue (named as DMTPE) with central tetraphenylethene core, displayed high emission quantum yields of 68% both in solution and in the solid state, and was relatively inert to photochemical reactions and yield syn-dimer on the surface via singlet excimer involved [2 + 2] photo-dimerization. Based on the solution-mediated photo-polymerization of MST moiety, multicyclic porous carbon-rich ribbon connected with four-membered ring was successfully constructed and validated via STM imaging.

Hormetic Effect Caused by Sublethal Doses of Glyphosate on Toona ciliata M. Roem.

This study aimed to evaluate the response of Toona ciliata seedlings to sublethal doses of glyphosate. The increasing use of glyphosate in agriculture concerns the scientific community, as the drift of this pollutant into aquatic systems or atmospheric currents can affect non-target species. Therefore, we need to understand how non-target species respond to small doses of this herbicide. T. ciliata seedlings (clone BV-1110) were exposed to sublethal doses of glyphosate (0, 9.6, 19.2, 38.4, 76.8 g ae ha-1). Anatomical, physiological, and photochemical analyses were performed 60 days after herbicide application, and growth assessments were carried out after 160 days of cultivation. We found that sublethal doses of glyphosate above 19.2 g ae ha-1 induced toxicity symptoms in Toona ciliata leaves. These symptoms were mild in some cases, such as chlorosis, but severe in other cases, such as tissue necrosis. We observed a positive relationship between increased plant height and photochemical yield with plant exposure to sub-doses 9.6 and 19.2 g ae ha-1. A sublethal dose of 38.4 g ae ha-1 improved the photosynthetic rate and carboxylation efficiency. Thus, we confirmed the hypothesis of a hormetic effect when T. ciliata was exposed to sub-doses of glyphosate equal to or lower than 38.4 g ae ha-1. However, the sublethal dose of 76.8 g ae ha-1 must be considered toxic, impacting photosynthetic activity and, consequently, the height of T. ciliata. The stem diameter of T. ciliata responded positively to increasing glyphosate doses. This occurs to compensate for the negative effect of glyphosate on water absorption. Further research will provide valuable information for harnessing the potential benefits of hormesis to improve the productivity of T. ciliata.

Are tomato plants co-exposed to heat and salinity able to ensure a proper carbon metabolism? – An insight into the photosynthetic hub

Abiotic stress combinations, such as high temperatures and soil/water salinization, severely threaten crop productivity worldwide. In this work, an integrative insight into the photosynthetic metabolism of tomato plants subjected to salt (100 mM NaCl) and/or heat (42 °C; 4 h/day) was performed. After three weeks, the stress combination led to more severe consequences on growth and photosynthetic pigments than the individual stresses. Regarding the photochemical efficiency, transcript accumulation and protein content of major actors (CP47 and D1) were depleted in all stressed plants, although the overall photochemical yield was not negatively affected under the co-exposure. Gas-exchange studies revealed to be mostly affected by salt (single or combined), which harshly compromised carbon assimilation. Additionally, transcript levels of stress-responsive genes (e.g., HsfA1 and NHX2) were differentially modulated by the single and combined treatments, suggesting the activation of stress-signature responses. Overall, by gathering an insightful overview of the main regulatory hub of photosynthesis, we show that the impacts on the carbon metabolism coming from the combination of heat and salinity, two major conditioners of crop yields, were not harsher than those of single stresses, indicating that the growth impairment might be attributed to a proficient distribution of resources towards defense mechanisms.

Warming modulates the photosynthetic performance of Thalassiosira pseudonana in response to UV radiation.

Diatoms form a major component of phytoplankton. These eukaryotic organisms are responsible for approximately 40% of primary productivity in the oceans and contribute significantly to the food web. Here, the influences of ultraviolet radiation (UVR) and ocean warming on diatom photosynthesis were investigated in Thalassiosira pseudonana. The organism was grown at two temperatures, namely, 18°C, the present surface water temperature in summer, and 24°C, an estimate of surface temperature in the year 2,100, under conditions of high photosynthetically active radiation (P, 400-700 nm) alone or in combination with UVR (P + UVR, 295-700 nm). It was found that the maximum photochemical yield of PSII (Fv/Fm) in T. pseudonana was significantly decreased by the radiation exposure with UVR at low temperature, while the rise of temperature alleviated the inhibition induced by UVR. The analysis of PSII subunits turnover showed that high temperature alone or worked synergistically with UVR provoking fast removal of PsbA protein (KPsbA), and also could maintain high PsbD pool in T. pseudonana cells. With the facilitation of PSII repair process, less non-photochemical quenching (NPQ) occurred at high temperature when cells were exposed to P or P + UVR. In addition, irrespective of radiation treatments, high temperature stimulated the induction of SOD activity, which partly contributed to the higher PSII repair rate constant (Krec) as compared to KPsbA. Our findings suggest that the rise in temperature could benefit the photosynthetic performance of T. pseudonana via modulation of its PSII repair cycle and protective capacity, affecting its abundance in phytoplankton in the future warming ocean.

Analysis of Functional Single-Nucleotide Polymorphisms (SNPs) and Leaf Quality in Tea Collection under Nitrogen-Deficient Conditions.

This study discusses the genetic mutations that have a significant association with economically important traits that would benefit tea breeders. The purpose of this study was to analyze the leaf quality and SNPs in quality-related genes in the tea plant collection of 20 mutant genotypes growing without nitrogen fertilizers. Leaf N-content, catechins, L-theanine, and caffeine contents were analyzed in dry leaves via HPLC. Additionally, the photochemical yield, electron transport efficiency, and non-photochemical quenching were analyzed using PAM-fluorimetry. The next generation pooled amplicon-sequencing approach was used for SNPs-calling in 30 key genes related to N metabolism and leaf quality. The leaf N content varied significantly among genotypes (p ≤ 0.05) from 2.3 to 3.7% of dry mass. The caffeine content varied from 0.7 to 11.7 mg g-1, and the L-theanine content varied from 0.2 to 5.8 mg g-1 dry leaf mass. Significant positive correlations were detected between the nitrogen content and biochemical parameters such as theanine, caffeine, and most of the catechins. However, significant negative correlations were observed between the photosynthetic parameters (Y, ETR, Fv/Fm) and several biochemical compounds, including rutin, Quercetin-3-O-glucoside, Kaempferol-3-O-rutinoside, Kaempferol-3-O-glucoside, Theaflavin-3'-gallate, gallic acid. From our SNP-analysis, three SNPs in WRKY57 were detected in all genotypes with a low N content. Moreover, 29 SNPs with a high or moderate effect were specific for #316 (high N-content, high quality) or #507 (low N-content, low quality). The use of a linear regression model revealed 16 significant associations; theaflavin, L-theanine, and ECG were associated with several SNPs of the following genes: ANSa, DFRa, GDH2, 4CL, AlaAT1, MYB4, LHT1, F3'5'Hb, UFGTa. Among them, seven SNPs of moderate effect led to changes in the amino acid contents in the final proteins of the following genes: ANSa, GDH2, 4Cl, F3'5'Hb, UFGTa. These results will be useful for further evaluations of the important SNPs and will help to provide a better understanding of the mechanisms of nitrogen uptake efficiency in tree crops.

Effects of sowing date on photosynthetic characteristics, chlorophyll fluorescence and yield of different Echium plantagineum L. cultivars

The seed oil of Echium plantagineum L. is rich in unsaturated fatty acids. With the gradual development of the value of echium oil in food, medical care and cosmetics, the corresponding market demand has also increased. The selection of suitable cultivars and the increase of yield per unit area has also become one of the main objectives of current breeding and cultivation of E. plantagineum. To effectively use the local photothermal resources, to improve the use of light energy by E. plantagineum, and to enhance the growth and yield of E. plantagineum. E. plantagineum cultivars Blue Bedder and Mixed Bedding were used as research subjects to study the effects of different sowing dates (1 May, 8 May, 15 May, 22 May and 29 May) on the photosynthetic characteristics and yield of E. plantagineum. Under the same cultivar conditions, with the delay in sowing date, the leaf chlorophyll content (SPAD), photosynthetic rate (Pn), transpiration rate (Tr), stomatal limitation value (Ls), photochemical quenching (qP), electron transfer rate (ETR), actual photochemical efficiency (ΦpsII) and yield of Blue Bedder decreased and reached a maximum at T1, while the SPAD, Pn, Tr, water use efficiency (WUE), Ls, initial fluorescence (Fo), maximum fluorescence (Fm), qP, ETR, ΦpsII and yield of Mixed Bedding reached the maximum at T4. Blue Bedder should be sown early at T1 and Mixed Bedding late at T4 during planting, which will help to improve the photosynthetic characteristics and grain yield of E. plantagineum.

Potassium alleviates over-reduction of the photosynthetic electron transport chain and helps to maintain photosynthetic function under salt-stress.

Potassium ions enhance photosynthetic tolerance to salt stress. We hypothesized that potassium ions, by minimizing the trans-thylakoid proton diffusion potential difference, can alleviate over-reduction of the photosynthetic electron transport chain and maintain the functionality of the photosynthetic apparatus. This study investigated the effects of exogenous potassium on the transcription level and activity of proteins related to the photosynthetic electron-transport chain of tobacco seedlings under salt stress. Salt stress retarded the growth of seedlings and caused an outflow of potassium ions from the chloroplast. It also lowered qP (indicator of the oxidation state of QA , the primary quinone electron acceptor in Photosystem II (PSII) and YPSII (average photochemical yield of PSII in the light-adapted state) while increasing YNO+NF (nonregulatory energy dissipation in functional and nonfunctional PSII), accompanied by decreased expression of most light-harvesting, energy-transduction, and electron-transport genes. However, exogenous potassium prevented these effects due to NaCl. Interestingly, lincomycin (an inhibitor of the synthesis of chloroplast-encoded proteins in PSII) significantly diminished the alleviation effect of exogenous potassium on salt stress. We attribute the comprehensive NaCl-induced downregulation of transcription and photosynthetic activities to retrograde signaling induced by reactive oxygen species. There probably exist at least two types of retrograde signaling induced by reactive oxygen species, distinguished by their sensitivity to lincomycin. Exogenous potassium appears to exert its primary effect by ameliorating the trans-thylakoid proton diffusion potential difference via a potassium channel, thereby accelerating ATP synthesis and carbon assimilation, alleviating over-reduction of the photosynthetic electron transport chain, and maintaining the functionality of photosynthetic proteins.

Dual effect of picolinic acid in the photosynthetic performance of rice plants infected by Bipolaris oryzae

AbstractBrown spot, caused by Bipolaris oryzae, is one of the most important diseases of rice. The non‐host toxin α‐picolinic acid (PA) has great potential to be used to enhance plant resistance against pathogen infection. The present study investigated the effect of spraying PA [0 (control), 1, 3, and 5 mg/mL] on the photosynthetic performance of rice plants (cultivar Metica‐1) infected or not with B. oryzae. Moreover, whether the PA treatment, especially at the highest concentration, could affect brown spot development was also evaluated. The chlorophyll a fluorescence parameters such as variable‐to‐maximum chlorophyll a fluorescence ratio (Fv/Fm), photochemical yield [Y(II)], yield for dissipation by down‐regulation [Y(NPQ)], the yield for non‐regulated dissipation [Y(NO)], and electron transport rate (ETR) as well as the concentration of photosynthetic pigments were determined. Based on the in vitro assay, PA inhibited mycelial growth of B. oryzae in a dose‐dependent manner and conidial germ tube length only decreased at 5 mg PA/mL. Conidia germination was not affected by the PA treatment. Necrotic lesions caused by PA were observed on leaves of non‐inoculated plants at 3 and 5 mg PA/mL. Symptoms of the brown spot were reduced on plants sprayed with 1 and 3 mg PA/mL compared to the control treatment. Brown spot lesions and those originating from PA toxicity overlapped for inoculated plants sprayed with 3 and 5 mg PA/mL. The photochemical performance of non‐inoculated plants was hampered by treatments with 3 and 5 mg PA/mL. Greater concentration of photosynthetic pigments and less impairment on the photosynthetic performance of inoculated plants sprayed with 1 mg PA/mL were noticed based on the values of Fv/Fm, Y(II), Y(NPQ), Y(NO), and ETR compared to inoculated plants non‐sprayed with PA. In conclusion, spraying rice plants with a low concentration of PA could decrease brown spot severity while preserving the photosynthetic capacity of the infected plants. The cellular damage generated by spraying the plants with the highest PA concentration did not favour the infection process of B. oryzae.

Excess energy and photosynthesis: responses to seasonal water limitations in co-occurring woody encroachers of the semi-arid Southern Great Plains

Woody plant areal encroachment is pervasive throughout the Southern Great Plains, USA. The ability of woody plants to dissipate excess solar radiation - dynamically over the day and sustained periods without recovery overnight -is key for maintaining photosynthetic performance during dry stretches, but our understanding of these processes remains incomplete. Photosynthetic performance and energy dissipation were assessed for co-occurring encroachers on the karst Edwards Plateau (<i>Juniperus ashei</i>, <i>Prosopis glandulosa</i>, and <i>Quercus fusiformis</i>) under seasonal changes in water status. Only <i>J. ashei </i>experienced mild photoinhibition from sustained energy dissipation overnight while experiencing the lowest photochemical yields, minimal photosynthetic rates, and the highest dynamic energy dissipation rates at midday during the dry period - indicating susceptibility to photosynthetic downregulation and increased dissipation under future drought regimes. Neither other encroacher experienced sustained energy dissipation in the dry period, though <i>P. glandulosa</i> did experience marked reductions in photosynthesis, photochemical yields, and increased regulatory dynamic energy dissipation.

Reproductive compensatory photosynthesis in a semi-arid rangeland bunchgrass

While increased foliar photosynthesis is well documented across many plant species in response to diverse modes of herbivory, the compensatory ability of photosynthetically active reproductive structures is unknown. To address this, we partially defoliated basal florets in seed heads of crested wheatgrass (Agropyron cristatum (L.) Gaertn.), an exotic Eurasian perennial bunchgrass widely distributed across North American sagebrush steppe. We followed direct and indirect responses by tracking post-clipping photosynthesis in clipped basal and unclipped distal florets, respectively, and comparing these to similar florets on unclipped seed heads. Compensatory photosynthesis was apparent 24 h after clipping; over the pre-anthesis period, clipped basal floret photosynthesis was + 62%, stomatal conductance was + 82%, and PSII photochemical yield was − 39% of unclipped controls. After anthesis, intact florets distal to clipped florets had modestly higher photosynthetic rates compared to controls, while basal floret rates did not differ between treatments. Compensatory photosynthesis reduced intrinsic water use efficiency (iWUE; photosynthesis/stomatal conductance) 68–40% below controls over pre- and post-anthesis periods, respectively. Specific mass (dry mass/area) of clipped florets was − 15% of controls, while florets distal to these had specific mass 11% greater than distal or basal florets on unclipped seed heads. These results suggest damaged basal florets provided carbon to unaffected distal florets. This could explain crested wheatgrass’s ability to produce viable seeds under conditions limiting to native bunchgrasses, and presents a novel mechanism germane to the development of convergent drought- and grazing-tolerance traits important to arid and semi-arid rangeland plant community resilience to climate variability.

Comparing the efficiency of solar water treatment: Photovoltaic-LED vs compound parabolic collector photoreactors

This work analyses how to optimise efficiency in the use of solar light for different UV-based photochemical water treatment processes. The direct use of sunlight in state-of-the-art compound parabolic collector (CPC) photoreactors is compared with the use of solar energy for electricity generation in photovoltaic (PV) power systems to feed LED lighting sources. Seven different solar processes (CPC, PV-UVA LED, PV-UVC LED, CPC+TiO2, CPC+H2O2, PV-UVA LED+TiO2 and PV–UVC LED+H2O2) were investigated, both for the oxidation of chemicals and the inactivation of bacteria. The results showed that, for the oxidation of chemicals, the best photochemical yield (in terms of the use of photons) is achieved by the PV-UVC LED+H2O2 process. However, the low electrical efficiency of current UVC LED sources makes the CPC+TiO2 process the most efficient in the use of solar light. In contrast, for bacterial inactivation, the significantly higher effectiveness of the UVC spectral range in damaging DNA makes the PV-UVC LED+H2O2 the most efficient in the use of sunlight. When costs are considered, the PV-UVA LED+TiO2 may be the most efficient process for chemical oxidation, while the PV-UVC LED+H2O2 process could be the most efficient for bacterial inactivation. These findings highlight the need to evaluate the optimal approach in reactor engineering for applications in the water-energy nexus, since the most efficient process for the use of solar light strongly depends on the electrical efficiency of the available PV and LED technology, which can be expected to be largely improved in the near future.