Light Response Curves Research Articles

Unveiling the Biological Function of Phyllostachys edulis FBA6 (PeFBA6) through the Identification of the Fructose-1,6-Bisphosphate Aldolase Gene.

Fructose-1,6-bisphosphate aldolase (FBA) is a pivotal enzyme in various metabolic pathways, including glycolysis, gluconeogenesis, and the Calvin cycle. It plays a critical role in CO2 fixation. Building on previous studies on the FBA gene family in Moso bamboo, our study revealed the biological function of PeFBA6. To identify CSN5 candidate genes, this study conducted a yeast two-hybrid library screening experiment. Subsequently, the interaction between CSN5 and PeFBA6 was verified using yeast two-hybrid and LCI experiments. This investigation uncovered evidence that FBA may undergo deubiquitination to maintain glycolytic stability. To further assess the function of PeFBA6, it was overexpressed in rice. Various parameters were determined, including the light response curve, CO2 response curve, and the levels of glucose, fructose, sucrose, and starch in the leaves of overexpressing rice. The results demonstrated that overexpressed rice exhibited a higher saturation light intensity, net photosynthetic rate, maximum carboxylation rate, respiration rate, and increased levels of glucose, fructose, and starch than wild-type rice. These findings indicated that PeFBA6 not only enhanced the photoprotection ability of rice but also improved the photosynthetic carbon metabolism. Overall, this study enhanced our understanding of the function of FBA and revealed the biological function of PeFBA6, thereby providing a foundation for the development of excellent carbon fixation bamboo varieties through breeding.

Illuminating stomatal responses to red light: establishing the role of Ci-dependent vs -independent mechanisms in control of stomatal behaviour.

The stomatal response to red light appears to link stomatal conductance (gs) with photosynthetic rates. Initially, it was suggested that changes in intercellular CO2 (Ci) provide the main cue via a Ci-dependent response. However, evidence for Ci-independent mechanisms suggests an additional, more direct relationship with photosynthesis. While both Ci-dependent and -independent mechanisms clearly function in stomatal red-light responses, little is known regarding their relative contribution. The present study aimed to quantify the relative magnitude of Ci-dependent and -independent mechanisms on the stomatal red-light response, to characterise their interplay and to assess the putative link between plastoquinone (PQ) redox state and Ci-independent stomatal responses. Red light response curves measured at a range of Ci values for wild-type Arabidopsis thaliana (Col-0) and the CO2 hyposensitive mutant, ca1ca4, allowed deconvolution of Ci-dependent and -independent pathways. Surprisingly, we observed that both mechanisms contribute equally to stomatal red-light responses, but Ci-independent stomatal opening is suppressed at high Ci. The present data are also consistent with the involvement of PQ redox in coordinating the Ci-independent component. Overall, it seems that while Ci-independent mechanisms are distinct from responses to Ci, interplay between these two pathways is important to facilitate effective coordination between gs and photosynthesis.

Effects of Rainfall Exclusion Treatment on Photosynthetic Characteristics of Black Locust in the Sub-Humid Region of the Loess Plateau, China.

The mesic-origin species Robinia pseudoacacia L. (black locust) is widely planted in the semiarid and sub-humid areas of the Loess Plateau for the reforestation of vegetation-degraded land. Under the scenario of changing precipitation patterns, exploring the response of photosynthesis to drought allows us to assess the risk to sustainable development of these plantations. In this study, paired plots were established including the control and a treatment of 30% exclusion of throughfall (since 2018). The photosynthetic characteristics were investigated using a portable photosynthesis system for four periods in the full-leaf growing season of 2021-2022, the fourth and fifth years, on both treated and controlled sampling trees. Leaf gas exchange parameters derived from diurnal changing patterns, light response curves, and CO2 response curves showed significant differences except for period II (9-11 September 2021) between the two plots. The photosynthetic midday depression was observed in 2022 in the treated plot. Meanwhile, the decline of net photosynthetic rate in the treated plot was converted from stomatal limitation to non-stomatal limitation. Furthermore, we observed that black locust adapted to long-term water deficiency by reducing stomatal conductance, increasing water use efficiency and intrinsic water use efficiency. The results demonstrate that reduction in precipitation would cause photosynthesis decrease, weaken the response sensitivity to light and CO2, and potentially impair photosynthetic resilience of the plantations. They also provide insights into the changes in photosynthetic functions under global climate change and a reference for management of plantations.

Topography-mediated light environment regulates intra-specific seasonal and diurnal patterns of photosynthetic plasticity and plant ecophysiological adaptation strategies.

Due to substantial topographic variations in the Himalaya, incident solar radiation in the forest canopy is highly unequal. This results in significant environmental differences at finer scales and may lead to considerable differences in photosynthetic productivity in montane forests. Therefore, local-scale ecophysiological investigations, may be more effective and instructive than landscape-level inventories and models. We investigated leaf ecophysiological differences and related adaptations between two Quercus semecarpifolia forests in aspect-mediated, significantly varying light regimes in the same mountain catchment. Seasonal and diurnal rates of photosynthesis (A) were significantly higher in south aspect (S) than the north (N). Although temperature was a key contributor to seasonal fluctuations in photosynthetic physiology, photoperiod significantly determined intraspecific variations in seasonal and diurnal plasticity of leaf ecophysiological traits between the two topography-mediated light environments. The regression model for A as a function of stomatal conductivity (gsw) explained the critical role of gsw in triggering photosynthetic plasticity as an adaptive function against varying environmental stresses due to seasonal solar differences. We also examined, modifications in chlorophyll content between the two light regimes across seasons to determine the chlorophyll adaptation strategy. The N aspect had higher leaf chl a, b, and chl a + b and a lower chl-allocation ratio (a/b) than S, which helped to optimize the required light reception in the photoreaction centers for improved photosynthetic performance. The leaf light response curves for A and gsw were observed against varying incident photosynthetic photon flux densities (0-2000mol.m2s-1PPFD) for both aspects. We found that the same species developed significantly distinct light response strategies and photosynthetic capacities in S than in N for the given magnitudes of PPFD. Such acquired ecophysiological adaptations owing to varying light environments may provide significant clues for understanding the impact of future climate change on Himalayan tree species.

Effects of summer pruning on the growth and photosynthetic characteristics of pepper (Capsicum annuum L.)

The objective of the study is to investigate the mechanism by which summer pruning enhances the growth of pepper plants, as indicated by growth and fruit appearance indicators, photosynthetic rate and gas exchange parameters, rapid light response and induction kinetics curves and the related chlorophyll fluorescence parameters. The results indicated that the leaf growth rate, the individual pepper fruit weight, and the fruit longitudinal and cross diameters of the pruned group were significantly higher than those of the control. The stomatal conductance (Gs), intercellular CO2 concentration (Ci) and transpiration rate (Tr) of the pruned group were significantly higher than those of the control. The initial slope of the rapid light response curve, which represents light energy utilisation efficiency (α), the maximum electron transfer rate (Jmax) and saturated light intensity (PARsat) were all higher in the summer pruning group than in the control group. The F0 of the pruned group decreased by 16.83%, Fv/F0 increased by 23.69%, PIabs increased by 58.33%, and DIo/RC decreased by 22.09% compared to the control group. In summary, summer pruning significantly improves the leaf growth rate and fruit appearance quality of pepper, effectively promotes the photosynthesis of functional leaves, and reduces the degree of stress under adverse environmental conditions.

Ecophysiological traits of seedlings from different accessions of Stipa tenacissima along a climatic gradient

Predicting the future impact of climate change on Stipa tenacissima steppes is of paramount importance to prevent desertification. From this perspective, we selected seven populations, covering a rainfall range from 100 to 600 mm/year at the sites of seed collection, and we grew the seedlings at the same site. Gas exchange measurements of CO2, light response curves, chlorophyll content and isotopic analysis were investigated. Thala and Valencia populations displayed a contrasted gas exchange response. Both populations were subjected to A-Ci curve analysis. No significant difference was detected between these two different populations in the maximum rate of carboxylation (Vcmax) and the maximum rate of electron transport (Jmax). Stipa tenacissima exhibited a variable response in relation to different light intensities. Photosynthesis and chlorophyll fluorescence parameters proved to be significantly different among populations in response to light intensities. All populations exhibited similar chlorophyll content. The isotopic analysis highlighted a different carbon and nitrogen isotopic composition (δ13C and δ15N) and carbon content © among populations. Mesic populations presented a higher gas exchange activity and light response. The xeric populations performed a photosynthesis adjustment along with minimizing chlorophyll content. Under climate change, S. tenacissima limits productivity, which may lead to desertification.

The Difference between the Responses of Gross Primary Production and Sun-Induced Chlorophyll Fluorescence to the Environment Based on Tower-Based and TROPOMI SIF Data

The strong correlation between gross primary production (GPP) and sun-induced chlorophyll fluorescence (SIF) has been reported in many studies and is the basis of the SIF-based GPP estimation. However, GPP and SIF are not fully synchronous under various environmental conditions, which may destroy a stable GPP–SIF relationship. Therefore, exploring the difference between responses of GPP and SIF to the environment is essential to correctly understand the GPP–SIF relationship. As the common driver of GPP and SIF, the incident radiation could cause GPP and SIF to have similar responses to the environment, which may obscure the discrepancies in the responses of GPP and SIF to the other environmental variables, and further result in the ambiguity of the GPP–SIF relationship and uncertainties in the application of SIF. Therefore, we tried to exclude the dominant role of radiation in the responses of GPP and SIF to the environment based on the binning method, in which continuous tower-based SIF, satellite SIF, and eddy covariance GPP data from two growing seasons were used to investigate the differences in the responses of GPP and SIF to radiation, air temperature (Ta), and evaporation fraction (EF). We found that the following: (1) At both the site and satellite scales, there were divergences in the light response speeds between GPP and SIF which were affected by Ta and EF. (2) SIF and its light response curves were insensitive to EF and Ta compared to GPP, and the consistency in GPP and SIF light responses was gradually improved with the improvement of Ta and EF. (3) The dynamic slope values of the GPP–SIF relationship were mostly caused by the different sensitivities of GPP and SIF to EF and Ta. Our results highlighted that GPP and SIF were not highly consistent, having differences in environmental responses that further confused the GPP–SIF relationship, leading to complex SIF application.

Mulched Drip Fertigation with Growth Inhibitors Reduces Bundle-Sheath Cell Leakage and Improves Photosynthesis Capacity and Barley Production in Semi-Arid Regions.

A better understanding of the factors that reduce bundle-sheath cell leakage to CO2 (Փ), enhance 13C carbon isotope discrimination, and enhance the photosynthetic capacity of barley leaves will be useful to develop a nutrient- and water-saving strategy for dry-land farming systems. Therefore, barley plants were exposed to a novel nitrification inhibitor (NI) (3,4-dimethyl-1H-pyrazol-1-yl succinic acid) (DMPSA) and a urease inhibitor (UI) (N-butyl thiophosphorictriamide (NBPT)) with mulched drip fertigation treatments, which included HF (high-drip fertigation (370 mm) under a ridge furrow system), MF (75% of HF, moderate-drip fertigation under a ridge furrow system), LF (50% of HF, low-drip fertigation under a ridge furrow system), and TP (traditional planting with no inhibitors or drip fertigation strategies). The results indicated that the nitrification inhibitor combined with mulched drip fertigation significantly reduced bundle-sheath cell leakage to CO2 (Փ) as a result of increased soil water content; this was demonstrated by the light and CO2 response curves of the photosynthesis capacity (An), the apparent quantum efficiency (α), and the 13C-photosynthate distribution. In the inhibitor-based strategy, the use of the urease and nitrification inhibitors reduced Փ by 35% and 39% compared with TP. In the NI-HF strategy, it was found that barley could retain the maximum photosynthesis capacity by increasing the leaf area index (LAI), An, rubisco content, soluble protein, dry matter per plant, and productivity. The CO2 and light response curves were considerably improved in the NI-HF and NI-MF treatments due to a higher 13C carbon isotope (Δ‱), respiration rate (Rd), and Ci/Ca, therefore obtaining the minimum Փ value. With both inhibitors, there was a significant difference between HF and LF drip fertigation. The NI-MF treatment significantly increased the grain yield, total chlorophyll content, WUE, and NUE by 52%, 47%, 57%, and 45%, respectively. Collectively, the results suggest that the new nitrification inhibitor (DMPSA) with HF or MF mulched drip fertigation could be promoted in semi-arid regions in order to mitigate bundle-sheath cell leakage to CO2 (Փ), without negatively affecting barley production and leading to the nutrient and water use efficiency of barley.

Light Response Curves in Land Plants.

Light is the driving force for photosynthesis. Two techniques are commonly employed to help characterize the relationship between the light environment and photosynthesis in plants.Chlorophyll a fluorescence analysis is used to examine both the capacity for and the efficiency of the conversion of absorbed light into energy for photosynthesis. Additionally, gas exchange analysis is used to assess the utilization of that energy for carbon fixation. These techniques are used either in isolation or in combination to acquire light response curves that measure the response of the plant to sequential changes in irradiance. Light response curves can help users understand photosynthetic mechanisms, evaluate how plants respond to light conditions, or assess the extent of physiological plasticity within plants. In this chapter, we provide a generalized method for acquiring light response curves suitable for both chlorophyll a fluorescence and gas exchange techniques using commercially available apparatus. Depending on the equipment available, these methods can be applied individually or combined to acquire data simultaneously. The methods are broadly applicable to most land plants but are ideally suited to help those that are unfamiliar with these techniques.

Measurement of O2 Uptake and Evolution in Leaves In Vivo Using Stable Isotopes and Membrane Inlet Mass Spectrometry.

Oxygen is both product and substrate of photosynthesis and metabolism in plants, by oxygen evolution through water splitting and uptake by photorespiration and respiration. It is important to investigate these processes simultaneously in leaves, especially in response to environmental variables, such as light and temperature. To distinguish between processes that evolve or take up O2 in leaves in the light, in vivo gas exchange of stable isotopes of oxygen and membrane inlet mass spectrometry is used. A closed-cuvette system for gas exchange of leaf discs is described, using the stable isotopes 16O2 and 18O2, with a semi-permeable membrane gas inlet and isotope mass separation and detection by mass spectrometry. Measurement of evolution and uptake, as well as CO2 uptake, at a range of light levels allows composition of a light response curve, here described for French bean (Phaseolus vulgaris) and maize (Zea mays) leaf discs.

Physiological differences among cryptic species of the Mediterranean crustose coralline alga Lithophyllum stictiforme (Corallinales, Rhodophyta)

ABSTRACT The crustose coralline alga Lithophyllum stictiforme is an important reef builder, forming coralligenous concretions in the Mediterranean Sea. This algal species complex is composed of eight cryptic species (or clades). The objective of our study was to compare light-dependent physiological processes within and between the two most abundant cryptic species (C1 and C4) of L. stictiforme from the Bay of Marseille (France). Physiological rates of respiration, photosynthesis and calcification were measured using incubation chambers under various irradiance levels and in the dark during the summer period. We compared the physiology of the C1 and C4 cryptic species of L. stictiforme among three algal groups: C1 (the most common in the Marseille area) from 28 m depth, C4 from the same site and depth, and C1 from a deeper site at 45 m depth. We found both interspecific (between C1 and C4) and intraspecific (within C1) physiological differences. Photosynthetic parameters showed acclimation to light (or depth) with higher values of initial slope of photosynthetic light response curve (α) and lower values of saturating irradiance (Ek) and compensating irradiance (Ec) for C1 from 45 m than for C1 and C4 from 28 m depth. At the shallower depth, significant physiological differences were observed between C1 and C4 with a higher value of maximum rate of gross photosynthesis (Pg max) in C4, suggesting better ability to grow under high irradiance. Light and dark calcification rates differed only between C4 from 28 m and C1 from 45 m depth, being intermediate in C1 from 28 m depth. On a 24 h basis, diel net calcification rates were significantly higher in specimens from the shallower waters than from the deeper waters. Physiological differences suggest physiological plasticity within the regionally dominant cryptic species C1 and species-specific physiological traits between the cryptic species C1 and C4.

Effects of biofertilizers on the growth, leaf physiological indices and chlorophyll fluorescence response of spinach seedlings.

Chemcial fertilizer as the main strategy for improving the vegetable yields was excessively applied in recent years which led to progressively serious soil problems such as the soil acidification. According the situation, five different biofertilizer treatments [no fertilizer (CK), inoculations of Bacillus subtilis (Bs, T1), combination of Bs and Bacillus mucilaginosus (Bs+Bm, T2), Bs and Bacillus amyloliquefaciens (Bs+Ba, T3), and Bm+Ba (T4)] were conducted to investigate the effect of the growth, leaf physiological indices, and chlorophyll fluorescence of spinach seedlings in the growth chamber. The growth and physiological indices of the spinach seedlings attained a maximum under the T2 treatments. Under the T2 treatment, the ABS/RC (Absorption flux per RC), TR0/RC (Trapping flux per RC), and ET0/RC (Electron transport flux per RC) was significantly increased, while the DI0/RC [Dissipated energy flux per RC (at t = 0)] was decreased. The OJIP curve was improved under of the inoculations of fertilizers, and the increasing range was the largest under the T2 treatment. The leaf light response curve (LC) was also significantly increased under the T2 treatment. The plant growth characteristics [leaf length (LL), leaf weight (LW), plant height (PH)] were positively correlated with the J-I-P test chlorophyll fluorescence parameters [PIABS (Performance index for energy conservation from exciton to the reduction of intersystem electron acceptors), φP0 (Maximum quantum yield of primary photochemistry), φE0 (Quantum yield of electron transport), ψ0 (The probability that a trapped exciton moved an electron in electron transport chain further than QA-), TR0/RC, and ET0/RC] while negatively correlated with φD0 (Quantum yield of energy dissipation) and DI0/RC. The leaf physiological characteristics [SP (soluble protein concentrations), SC (soluble carbohydrate concentrations), Chl a (chlorophyll a), Chl b (chlorophyll b), Chl a+b, Chl a/b, and WP (water potential)] were positively correlated with the J-I-P test chlorophyll fluorescence parameters (PIABS, φP0, φE0, ψ0, ABS/RC, TR0/RC, and ET0/RC) while negatively correlated with φD0 and DI0/RC. These results indicated that the combination of Bs+Bm inoculations promoted the growth of the spinach and improved the adaptability of the vegetable to acid soil while Ba inoculation didn't have any effects to plants.

Atmospheric effects are stronger than soil moisture in restricting net CO2 uptake of managed grasslands in New Zealand

Climate change is exposing agricultural systems to more frequent weather extremes, threatening production and challenging the sustainability of current management practices. However, isolating the climatic drivers of CO2 exchange in managed systems can be complicated by the periodic removal of aboveground biomass through grazing or harvesting, abruptly shifting the potential for plant uptake and associated ecosystem biogeochemistry. We used eddy covariance datasets from managed grasslands across New Zealand to determine the relative effects of temperature, vapour pressure deficit, and soil moisture on net CO2 uptake. Using time since grazing or harvest as a proxy for above-ground biomass, we accounted for the shifting potential CO2 exchange associated with these management actions. We then fit light response curves to the outer envelope of data to estimate maximal potential NEE, and subsequently calculate NEE deficit for every measured half hour. Using this analytical framework, we combined data from seven locations making up sixteen individual flux datasets comprising >600 site months and found that high air temperature and vapour pressure deficit were stronger controls over NEE deficit than soil moisture. These results were also consistent with a controlled leaf-level experiment demonstrating increasing photosynthesis deficit as VPD increased under constant temperature. The dominance of atmospheric effects over soil moisture in determining grassland response to dry conditions has important implications because it may be more difficult to mitigate these responses with typical management approaches (e.g., irrigation). We found these patterns were consistent across a diverse range of managed grassland operations, but subtle differences suggest that expanding the approach to a wider array of climatic regions and soil types could provide additional insights into how we might avoid the worst effects of future drying on managed systems.

Effects of UV radiation on photosynthesis of Sargassum muticum

As an invasive species of macroalgae, Sargassum muticum (Yendo) Fensholt has invaded European shores and the Mediterranean, and even drifting individuals have been observed in sea area near the Canary Islands, becoming a potential species responsible for the “Sargassum golden tide”. When drifting on the sea surface, algae receive more ultraviolet radiation (UVR). However, photosynthetic responses and adaptation mechanism of S. muticum to UVR remain unclear. In this study, thalli of S. muticum were respectively exposed under two radiation treatments of 200 W m−2 PAR (photosynthetically active radiation, 400–700 nm), and 200 W m−2 PAR + 38 W m−2 UVR (280–700 nm) for 120 mins, and then recovered at a low light (PAR) of 10 μmol photons m−2 s−1 for 240 mins. During this treatment, the photosynthetic properties of algae were measured, to investigate the responses and protection mechanism of S. muticum to UVR. The results showed that photosynthesis of thalli was significantly inhibited by UVR, reflected by decreased maximum photochemical quantum yield (Fv/Fm) and chlorophyll content, and changes of parameters of rapid light response curve and chlorophyll fluorescence induction curve in PAR and PAR + UVR treatments. Meanwhile, algae actively adopted several strategies to alleviate the inhibition caused by UVR, including photoprotection characterized by increased contents of UV-absorbing compounds (UVACs) and carotenoids (Car), excess light energy dissipation by elevated non-photochemical quenching (NPQ) coupled to the xanthophyll cycle, and photorepair manifested as an accelerated synthesis of D1 protein and enhanced antioxidant for scavenging ROS. Benefiting from the effects of the above several pathways, after 240 mins of low light recovery, photosynthesis was greatly restored in these two radiation treatments, with the restoration of Fv/Fm and parameters of rapid light response curve and chlorophyll fluorescence induction curve. Based on these results, we conservatively speculate that the photosynthesis of drifting S. muticum individuals may be restored in the evening with low light levels after being damaged by UVR on the surface of sea at midday, resulting in maintaining rapid growth and forming a golden tide.

Potential of agrivoltaics systems into olive groves in the Mediterranean region

Agrivoltaics systems have emerged as an approach to alleviate competition for land use between food and energy production. Conducting a thorough analysis of the impact that shading from PV modules can have on crops is crucial for the correct design of the system, as excessive shading can lead to important crop yield reductions. This paper focuses on integrating agrivoltaics systems within super-intensive olive groves in the Mediterranean region. A dual model is used to calculate the suitable transparency of PV modules, representing the area not occupied by PV cells. This model customizes the results based on the site's meteorological parameters and the photosynthetic light-response curve of the olive cultivar. The results indicate that transparency levels vary between 0.57 and 0.71, with the lowest values observed in locations with higher solar radiation, such as Egypt and Tunisia. Using these transparency values and typical 20%-efficiency monocrystalline silicon modules, the annual average energy generation per m2 in the selected locations is 65.9 kWh. Another finding reveals that optimizing the model by considering only the months corresponding to the olive growth cycle can reduce the required transparency, thereby increasing the installed PV capacity by up to 3.5%. Furthermore, the potential deployment of these systems is evaluated in terms of installed PV capacity, energy generation, CO2 emissions and job creation. The calculations show that installing agrivoltaics systems into 1% of the total olive surface area in the Mediterranean region would: (i) result in a 2.5% increase in the global PV capacity, (ii) generate 1.8% of the current electricity demand in the selected Mediterranean countries, (iii) avoid the emissions of 4 Mt. (CO2) per year, and (iv) create around 560,000 jobs.

Photoinactivation vs repair of photosystem II as target of thermal stress in epipelic and epipsammic microphytobenthos communities.

Microphytobenthos (MPB) inhabiting intertidal flats are exposed to large and sudden changes in temperature, often simultaneously with exposure to direct sunlight. These conditions are expected to negatively impact photosynthesis by exacerbating the photoinhibition under high light. This study addressed the photoinhibitory effects of short-term exposure to cold (5°C) and moderate heat (35°C) on MPB dominated by motile epipelic (EPL) and immotile epipsammic (EPM) diatom species, by evaluating the seasonal variation of photoinactivation and repair of photosystem II (PSII). The susceptibility to PSII photoinactivation and the counteracting repair capacity were measured by the constant rates kPI and kREC, respectively. The photoacclimation state was characterized by hysteresis light-response curves (HLC) of the relative electron transport rate, rETR, and of the nonphotochemical quenching index Y(NPQ). Under non-stress conditions (20°C), kREC was on average almost 10x higher than the corresponding kPI (20.4 vs 2.70 × 10-4 s-1, respectively), indicating the operation of efficient repair mechanisms. Overall, the exposure to low and high temperatures affected both PSII photoinactivation and repair but causing smaller impacts in the former than in the latter. Also, cold stress caused larger effects on repair (decrease of kREC) than on photoinactivation (increase of kPI), but heat stress affected similarly the two processes. These effects varied seasonally, suggesting a role of thermal acclimation, as heat stress had stronger effects in cold-acclimated samples and cold stress resulted in stronger effects in heat-acclimated samples. The changes in kPI and kREC occurred despite the high light-acclimated phenotype found all year round, indicating that these processes vary independently from the photoacclimation state. The results also showed that photoprotection processes, as measured by energy-dependent non-photochemical index qE, appear to have an important role, both by preventing PSII photoinactivation and by alleviating the impacts on PSII repair under acute thermal stress.

Exploring carbon sequestration in broad-leaved Korean pine forests: Insights into photosynthetic and respiratory processes

A comprehensive understanding of carbon assimilation and sequestration in broad-leaved Korean pine forests is crucial for accurately estimating this significant aspect of temperate forests at a regional scale. In this study, we introduced a high-temporal resolution model designed for carbon assimilation insights at the plot scale, focusing on specific parameters such as leaf area dynamics, vertical leaf distribution, photosynthetically active radiation (PAR) fluctuations, and the photosynthetic traits of tree species. The findings reveal that most tree species in broad-leaved Korean pine forests exhibit an inverted U-shaped pattern in leaf area dynamics, with shorter leaf drop periods than leaf expansion events. Leaf distribution varies significantly among different canopy heights, with approximately 80 % of the leaves above 15 m. PAR decreases as canopy height decreases, with PAR at 25 m accounting for about 60 % of the PAR above the canopy. Our framework incorporates a leaf-scale light-response curve and empirical photosynthesis-temperature relationships to estimate forest carbon assimilation on daily and hourly scales accurately. Using the model, we assess the gross primary productivity (GPP), leaf net photosynthetic assimilation (LNPA), and carbon increment (ΔC) of broad-leaved Korean pine forests from 2017 to 2020. The results demonstrate GPP, LNPA, and ΔC values of 21.4 t·ha−1·a−1, 17.4 t·ha−1·a−1, and 4.0 t·ha−1·a−1, respectively. Regarding efficiency, GPP, LNPA, and ΔC per square meter of leaf per year are 179 g, 146 g, and 33 g, respectively. Notably, tree species in the canopy layer of the forest exhibit significantly higher efficiency than those in the understory layer. This research significantly contributes to our understanding of carbon cycling and the responses of forest ecosystems to climate change. Moreover, it provides a practical tool for forest management and the development of carbon sequestration strategies.

Continuous Cropping Inhibits Photosynthesis of Polygonatum odoratum.

Polygonatum odoratum (Mill.) Druce possesses widespread medicinal properties; however, the continuous cropping (CC) often leads to a severe consecutive monoculture problem (CMP), ultimately causing a decline in yield and quality. Photosynthesis is the fundamental process for plant growth development. Improving photosynthesis is one of the most promising approaches to increase plant yields. To better understand how P. odoratum leaves undergo photosynthesis in response to CC, this study analyzed the physiochemical indexes and RNA-seq. The physiochemical indexes, such as the content of chlorophyll (chlorophyll a, b, and total chlorophyll), light response curves (LRCs), and photosynthetic parameters (Fv/Fm, Fv/F0, Fm/F0, Piabs, ABS/RC, TRo/RC, ETo/RC, and DIo/RC) were all changed in P. odoratum under the CC system. Furthermore, 13,798 genes that exhibited differential expression genes (DEGs) were identified in the P. odoratum leaves of CC and first cropping (FC) plants. Among them, 7932 unigenes were upregulated, while 5860 unigenes were downregulated. Here, the DEGs encoding proteins associated with photosynthesis and carbon assimilation showed a significant decrease in expression under the CC system, such as the PSII protein complex, PSI protein complex, Cytochorome b6/f complex, the photosynthetic electron transport chain, light-harvesting chlorophyll protein complex, and Calvin cycle, etc., -related gene. This study demonstrates that CC can suppress photosynthesis and carbon mechanism in P. odoratum, pinpointing potential ways to enhance photosynthetic efficiency in the CC of plants.

Effects of measurement methods and growing conditions on phenotypic expression of photosynthesis in seven diverse rice genotypes.

Light response curves are widely used to quantify phenotypic expression of photosynthesis by measuring a single sample and sequentially altering light intensity within a chamber (sequential method) or by measuring different samples that are each acclimated to a different light level (non-sequential method). Both methods are often conducted in controlled environments to achieve steady-state results, and neither method involves equilibrating the entire plant to the specific light level. Here, we compare sequential and non-sequential methods in controlled (greenhouse), semi-controlled (plant grown in growth chamber and acclimated to field conditions 2-3 days before measurements), and field environments. We selected seven diverse rice genotypes (five genotypes from the USDA rice minicore collection: 310588, 310723, 311644, 311677, 311795; and 2 additional genotypes: Nagina 22 and Zhe 733) to understand (1) the limitations of different methods, and (2) phenotypic plasticity of photosynthesis in rice grown under different environments. Our results show that the non-sequential method was time-efficient and captured more variability of field conditions than the sequential method, but the model parameters were generally similar between two methods except the maximum photosynthesis rate (Amax). Amax was significantly lower across all genotypes under greenhouse conditions compared to the growth chamber and field conditions consistent with prior work, but surprisingly the apparent quantum yield (α) and the mitochondrial respiration (Rd) were generally not different among growing environments or measurement methods. Our results suggest that field conditions are best suited to quantify phenotypic differences across different genotypes and nonsequential method was better at capturing the variability in photosynthesis.

Shading contributes to Sphagnum decline in response to warming.

Experimental warming of an ombrotrophic bog in northern Minnesota has caused a rapid decline in the productivity and areal cover of Sphagnum mosses, affecting whole-ecosystem carbon balance and biogeochemistry. Direct effects of elevated temperature and the attendant drying are most likely the primary cause of the effects on Sphagnum, but there may also be responses to the increased shading from shrubs, which increased with increasing temperature. To evaluate the independent effects of reduction in light availability and deposition of shrub litter on Sphagnum productivity, small plots with shrubs removed were laid out adjacent to the warming experiment on hummocks and hollows in three blocks and with five levels of shading. Four plots were covered with neutral density shade cloth to simulate shading from shrubs of 30%-90% reduction in light; one plot was left open. Growth of Sphagnum angustifolium/fallax and S. divinum declined linearly with increasing shade in hollows, but there was no response to shade on hummocks, where higher irradiance in the open plots may have been inhibitory. Shading caused etiolation of Sphagnum-they were thin and spindly under the deepest shade. A dense mat of shrub litter, corresponding to the amount of shrub litter produced in response to warming, did not inhibit Sphagnum growth or cause increases in potentially toxic base cations. CO2 exchange and chlorophyll-a fluorescence of S. angustifolium/fallax from the 30% and 90% shade cloth plots were measured in the laboratory. Light response curves indicate that maximal light saturated photosynthesis was 42% greater for S. angustifolium/fallax grown under 30% shade cloth relative to plants grown under 90% shade cloth. The response of Sphagnum growth in response to increasing shade is consistent with the hypothesis that increased shade resulting from shrub expansion in response to experimental warming contributed to reduced Sphagnum growth.