Response Of Photosynthesis Research Articles

Independent Responses of Photosynthesis and Plant Morphology to Alterations of PIF Proteins and Light-Dependent MicroRNA Contents in Arabidopsis thaliana pif Mutants Grown under Lights of Different Spectral Compositions

The effects of the quality of light on the content of phytochrome interacting factors (PIFs) such as PIF3, PIF4 and PIF5, as well as the expression of various light-dependent microRNAs, in adult Arabidopsis thaliana pif mutant plants (pif4, pif5, pif3pif5, pif4pif5, pif3pif4pif5) were studied. We demonstrate that under blue light, the pif4 mutant had maximal expression of most of the studied microRNAs (miR163, miR319, miR398, miR408, miR833) when the PIF4 protein in plants was reduced. This finding indicates that the PIF4 protein is involved in the downregulation of this group of microRNAs. This assumption is additionally confirmed by the fact that under the RL spectrum in pif5 mutants, practically the same miRNAs decrease expression against the background of an increase in the amount of PIF4 protein. Unlike the WT and other mutants, the pif4 mutant responded to the BL spectrum not only by activating the expression of light-dependent miRNAs, but also by a significant increase in the expression of transcription factors and key light signalling genes. These molecular reactions do not affect the activity of photosynthesis but may be involved in the formation of a light quality-dependent phenotype.

Responses of Leaf Ion Content, Photosynthesis and Chlorophyll Fluorescence to Nacl Stress in Soybean

Responses of Leaf Ion Content, Photosynthesis and Chlorophyll Fluorescence to Nacl Stress in Soybean

Removal of tetracycline from water by catalytic photodegradation combined with the microalga Scenedesmus obliquus and the responses of algal photosynthesis and transcription

The antibiotic tetracycline (TC) and its degradation products (TDPs) in degradation solution present serious environmental problems, such as human health damage and ecological risk; thus further treatment is required before being released into the aquatic environment. Furthermore, their environmental impact on microalgae remains unclear. In this study, TC was degraded by photocatalysis using birnessite and UV irradiation, followed by biological purification using the microalga Scenedesmus obliquus. In addition, the photosynthetic activity and transcription of the microalgae were examined to evaluate the toxicity of TC and TDPs. The results show that photocatalytic degradation efficiency reached 92.7% after 30 min, and 11 intermediate products were detected. The microalgae achieved a high TC removal efficiency (99.7%) after 8 days. Exposure to the degraded TC solution (D) resulted in significantly lower (p < 0.05) biomass than the pure TC (T), and S. obliquus in the T treatment showed better resilience than the D treatment. Transcriptomic assays for different treatments revealed differential gene expression mainly involving the photosynthesis, ribosome, translation and peptide metabolic progresses. The up-regulation of photosynthesis-related genes and differential expression of chloroplast genes may be important for S. obliquus to acquire high photosynthetic efficiency and growth recovery when exposed to TC and TDPs. Our study provides a reference for TC removal using a combination of catalytic degradation and microalgal purification, and it is also helpful for understanding the environmental risk of TDPs in natural aquatic environments.

Effects of chilling at different growth stages on rice photosynthesis, plant growth, and yield

Chilling is the main limiting factor for rice production in high-altitude and high-latitude regions. Many studies have reported the impacts of chilling on leaf photosynthesis and biomass accumulation, but few of them explored the response of photosynthesis to chilling at different growth stages of rice and whether the decrease of photosynthesis at each stage is caused by stomatal or non-stomatal limiting factor. In order to achieve high grain yield for rice, it is critical to understand how chilling affects leaf photosynthesis and plant growth. In this study, we conducted a two-year field experiment (in 2018 and 2019) to investigate the effects of chilling at booting, flowering, and grain filling stages on leaf photosynthesis, plant growth, and grain yield for a japonica rice cultivar (Songjing6). At each target growth stage, the treatment included four chilling temperatures (12, 15, 18, and 21 ℃, respectively) and four chilling durations (2, 4, 6, and 8 days, respectively). The results showed that rice photosynthesis gradually decreased as the chilling temperature was decreasing and the chilling duration was increasing. The net photosynthetic rate decreased the most at the booting stage, followed by the flowering stage, and the grain filling stage. Compared with the chilling treatment at 2 days, the chilling treatment at 12, 15, and 18 ℃ for 4, 6, and 8 days reduced net photosynthetic rate by 15.1–36.1 %, 18.7–27.2 %, and 15.2–17.2 % at the booting, flowering, and grain filling stages, respectively. The chilling-induced decrease in net photosynthetic rate was mainly attributed to stomatal limiting factor at the booting and flowering stages but non-stomatal limiting factor at the grain filling stage. During the chilling treatment, the available light for rice plants was reduced and the rice plants were impaired in their ability to use weak light. The decrease in photosynthesis lead to reduced leaf source capacity and crop growth rate, hence the reduced aboveground biomass and increased source and sink increment ratio, and ultimately decreased the grain yield for rice. Our results indicate that maintaining efficient photosynthetic functioning at the booting and flowering stages is the key to combat chilling stress for rice. • Chilling decreased the net photosynthetic rate of rice most at the booting stage, followed by the flowering stage and the grain filling stage. • Chilling-induced decrease in the net photosynthetic rate was mainly attributed to stomatal limiting factor at the booting and flowering stages, but non-stomatal limiting factor at the grain filling stage. • The simulation of light response curve showed chilling at the booting and flowering stages decreased photosynthetic capacity and photosynthetic effective time，while chilling mainly affects the ability of using strong light at the grain filling stage.

High aerosol loading decreases the transpiration of poplars both in the day- and night-time

Aerosols alter plant photosynthesis and ecosystem carbon uptake through radiative effects. These effects inevitably change plant transpiration and ecosystem water use as CO2 and water exchange couple through leaf stomatal conductance. However, because of lacking field observations, we know poorly about how elevated aerosols could affect plant transpiration, which greatly hinders our confidence in projecting aerosol's climate impacts. In this study, taking the advantage of aerosol loading in northern China fluctuated periodically over a wide range, we conducted five year-site observations of the stem sap flow of poplar saplings (Populus euramericana Neva.), and simultaneously monitored environmental factors such as PM2.5 concentration, total and diffuse radiation, air temperature, humidity, and soil water content. These observations enabled us to comprehensively explore how aerosols affect the daily dynamics of plant canopy transpiration in the field. We found that high aerosol loading significantly decreased the sap flow density of poplars both in the day- and night-time, indicating that aerosols decreased canopy transpiration. Furthermore, during the day-time, a reduction in total solar radiation and moisture demand (vapor pressure deficit, VPD) dominated the decrease of sap flow density, but an increase in diffuse radiation had an insignificant impact. In the night-time, VPD significantly decreased under high aerosol loading conditions, thereby reducing nocturnal sap flow density. Our in-situ observations revealed that different from the positive response of canopy photosynthesis associated with the diffuse fertilization effect, aerosols inhibit canopy transpiration mainly because of the declined VPD. Our findings highlighted that plant carbon and water fluxes are governed by different meteorological factors under elevated aerosol.

The responses of photosynthetic light response parameters to temperature among different seasons in a coniferous plantation of subtropical China

A deep understanding of the responses of photosynthesis to air temperature (Ta) is essential for accurately assessing carbon budgets. Photosynthetic light response (PLR) parameters, including apparent quantum yield (α), maximum photosynthesis rate (Pmax) and daytime ecosystem respiration (Rd), are widely used to describe and quantify photosynthesis at the ecosystem scale. However, an understanding of the specific responses of PLR parameters to temperature in different seasons is still lacking. Therefore, this study aimed to address this issue based on 17-year continuous eddy covariance measurements (2003–2019) in a subtropical coniferous plantation. The responses of PLR parameters to air temperature (Ta) were obtained by classifying the observed net ecosystem exchange (NEE) and the corresponding photosynthetically active radiation (PAR) according to Ta with a class width of 2 °C. The general regulations showed that α, Rd and Pmax first increased with Ta until the optimal Ta and then decreased. The optimal Ta for α, Rd and Pmax were 28, 30 and 32 °C, and the inflection points were consistent with the soil water content (SWC) at depths of 5, 20, and 50 cm, respectively. For the specific seasonal responses, the optimal Ta for α and Rd was highest in summer, with a value as high as 30 °C, and the optimal Ta was highest in autumn, with a value of 32 °C. Interestingly, although the temperature environments were similar in spring and autumn, the optimal Ta for α was 2 °C higher in spring than in autumn, but the optimal Ta for Pmax was 6 °C higher in autumn than in spring. Some special response patterns were also found according to delicate studies on a seasonal scale, which were found to be related to SWCs at different depths. These findings reflected the inner function changes of the ecosystem and the potential effects of SWC, which should be given special attention when the PLR parameters are used in models to predict the carbon budgets in the future.

Long-term drought effects on the thermal sensitivity of Amazon forest trees.

The continued functioning of tropical forests under climate change depends on their resilience to drought and heat. However, there is little understanding of how tropical forests will respond to combinations of these stresses, and no field studies to date have explicitly evaluated whether sustained drought alters sensitivity to temperature. We measured the temperature response of net photosynthesis, foliar respiration and the maximum quantum efficiency of photosystem II (Fv /Fm ) of eight hyper-dominant Amazonian tree species at the world's longest-running tropical forest drought experiment, to investigate the effect of drought on forest thermal sensitivity. Despite a 0.6°C-2°Cincrease in canopy air temperatures following long-term drought, no change in overall thermal sensitivity of net photosynthesis or respiration was observed. However, photosystem II tolerance to extreme-heat damage (T50 ) was reduced from 50.0 ± 0.3°C to 48.5 ± 0.3°Cunder drought. Our results suggest that long-term reductions in precipitation, as projected across much of Amazonia by climate models, are unlikely to greatly alter the response of tropical forests to rising mean temperatures but may increase the risk of leaf thermal damage during heatwaves.

Tradeoff in the supply and demand for CO2dominates the divergence of net photosynthesis rates of functional plants in alpine ecosystems

AbstractThe responses of photosynthesis to change of temperature and CO2concentration are divergent among various alpine plant species at high altitude regions; however, very few direct in situ measurements have been conducted to compare photosynthetic capacity among different functional plants along altitude gradients in the Qinghai‐Tibet Plateau (QTP). This study measured the net photosynthetic assimilation rate (An), maximum carboxylation rate (Vcmax), maximum electron transport rate (Jmax), stomatal conductance (gs) and mesophyll conductance (gm) for CO2of three plant functional types (PFTs, sedge, grass and shrub) and functional traits at different altitudes in the Qinghai Lake watershed during growing season. Meanwhile we simulated An of the PFTs under potential future scenario. Results indicate that grass maintain a relatively stable An by decreasingVcmax,Jmax, ratio ofJmaxtoVcmax(J/V) andgs, while slightly increasinggmwith increasing altitudes. In contrast, the An of sedge and shrubs increased with risingVcmax,Jmax,gsandgmvalues, resulting in a large increment in the An at low altitudes. Grass was less sensitive to temperature by reducing the supply of CO2, while sedge and shrub increased.Cawas a more dominant factor thanTain affecting the An of grass. The order of rising An in PFTs was shrub &gt; sedge &gt; grass, and the An of alpine meadow was found to increase more under the Representative Concentration Pathways (RCP) 4.5 and 8.5 scenarios. Our results indicate that grass may be more resistant to future warming and suggested that considering PFTs is of great significance for improving the simulating of the response of vegetation physiological and ecological processes to future climate change in alpine regions.

An insight into algicidal characteristics of Bacillus altitudinis G3 from dysfunctional photosystem and overproduction of reactive oxygen species

Cyanobacterial blooms negatively affect aquatic ecosystems and human health. Algicidal bacteria can efficiently kill bloom-causing cyanobacteria. Bacillus altitudinis G3 isolated from Dianchi Lake shows high algicidal activity against Microcystis aeruginosa. In this study, we investigated its algicidal characteristics including attack mode, photosynthesis responses, and source and the contribution of reactive oxygen species (ROS). The results showed that G3 efficiently and specifically killed M. aeruginosa mainly by releasing both thermolabile and thermostable algicidal substances, which exhibited the highest algicidal activity (99.8%, 72 h) in bacterial mid-logarithmic growth phase. The algicidal ratio under full-light conditions (99.5%, 60 h) was significantly higher than under dark conditions (<20%, P < 0.001). G3 filtrate caused photosystem dysfunction by decreasing photosynthetic efficiency, as indicated by significantly decreased Fv/Fm and PIABS (P < 0.001) values. It also inhibited photosynthetic electron transfer as indicated by significantly decreased rETR (P < 0.001), especially QA− downstream, as revealed by significantly decreased φEo and ψo, and increased Mo (P < 0.001). These results indicated that the algicidal activity of G3 filtrate is light-dependent, and the cyanobacterial photosystem is an important target. Cyanobacterial ROS and malondialdehyde contents greatly increased by 37.1% and 208% at 36 h, respectively. ROS levels decreased by 49.2% (9 h) when diuron (3-(3-4-dichlorophenyl)-1,1-dimethylurea) partially blocked photosynthetic electron transport from QA to QB. Therefore, excessive ROS were produced from disrupted photosynthesis, especially the inhibited electron transport area in QA− downstream, and caused severe lipid peroxidation with significantly increased MDA content and oxidative stress in cyanobacteria. The ROS scavenger N-acetyl-l-cysteine significantly decreased both cyanobacterial ROS levels (34%) and algicidal ratio (52%, P < 0.05) at 39 h. Thus, excessive ROS production due to G3 filtrate administration significantly contributed to its algicidal effect. G3 could be an excellent algicide to control M. aeruginosa blooms in waters under suitable light conditions.

Long-Term Warming and Nitrogen Addition Regulate Responses of Dark Respiration and Net Photosynthesis in Boreal Bog Plants to Short-Term Increases in CO2 and Temperature

Boreal bog plants adapted to cold and low available nutrient conditions might be strongly affected by global changes, including elevated CO2 (eCO2), warming (W), and increasing nitrogen (N) availability. Here, we examined responses of dark respiration (Rd) and net photosynthesis (Anet) in four dominant bog plants to five levels of short-term increases in both CO2 and temperature (CTI); and the effects of long-term (6 years) W and N addition on these responses. Results indicated that CTI increased Rd; meanwhile, the increase of these environmental variables decreased Anet in all these boreal bog plants. Long-term nitrogen addition simulated the increases of Rd and decreases of Anet in Trichophorum cespitosum. Long-term warming mitigated the increases of Rd in Andromeda glaucophylla and Gaylussacia bigeloviana, and the decrease of Anet in Gaylussacia bigeloviana. These findings highlight the importance of long-term warming and nitrogen addition in regulating responses of boreal bog plants to short-term CTI, suggesting the necessity to investigate the long-term effects of these environmental changes when projecting responses of boreal bog vegetation to global changes.

Photosynthesis in Response to Different Salinities and Immersions of Two Native Rhizophoraceae Mangroves.

Mangrove ecosystems are vulnerable to rising sea levels as the plants are exposed to high salinity and tidal submergence. The ways in which these plants respond to varying salinities, immersion depths, and levels of light irradiation are poorly studied. To understand photosynthesis in response to salinity and submergence in mangroves acclimated to different tidal elevations, two-year-old seedlings of two native mangrove species, Kandelia obovata and Rhizophora stylosa, were treated at different salinity concentrations (0, 10, and 30 part per thousand, ppt) with and without immersion conditions under fifteen photosynthetic photon flux densities (PPFD μmol photon·m−2·s−1). The photosynthetic capacity and the chlorophyll fluorescence (ChlF) parameters of both species were measured. We found that under different PPFDs, electron transport rate (ETR) induction was much faster than photosynthetic rate (Pn) induction, and Pn was restricted by stomatal conductance (Gs). The Pn of the immersed K. obovata plants increased, indicating that this species is immersed-tolerant, whereas the Pn level of the R. stylosa plants is salt-tolerant with no immersion. All of the plants treated with 30 ppt salinity exhibited lower Pn but higher non-photochemical quenching (NPQ) and heat quenching (D) values, followed by increases in the excess energy and photoprotective effects. Since NPQ or D can be easily measured in the field, these values provide a useful ecological monitoring index that may provide a reference for mangrove restoration, habitat creation, and ecological monitoring.

Solar-induced chlorophyll fluorescence imperfectly tracks the temperature response of photosynthesis in winter wheat.

Solar-induced fluorescence (SIF) is a promising proxy for photosynthesis, but it is unclear whether it performs well in tracking the gross primary productivity (GPP) under different environmental conditions. In this study, we investigated the dynamics of the two parameters from October 2020 to June 2021 in field-grown winter wheat (Triticum aestivum) and found that the ability of SIF to track GPP was weakened at low temperatures. Accounting for the coupling of light and temperature at a seasonal scale, we found that SIF yield showed a lower temperature sensitivity and had a lower but broader optimal temperature range compared with light-use efficiency (LUE), although both SIF yield and LUE decreased in low-temperature conditions. The discrepancy between the temperature responses of SIF yield and GPP caused an increase in the ratio of SIF/GPP in winter, which indicated the variation in the relationship between them during this period. The results of our study highlight the impact of low temperature on the relationship between SIF and GPP and show the necessity of reconsidering the dynamics of energy distribution inside plants under changing environments.

Development of a carbon accumulation model for estimating the concentration of 14C in Japanese radish

ABSTRACT Atmospheric 14C released from nuclear fuel reprocessing plants can accumulate in crop plants. Japanese radish (daikon) is a major crop plant in the area surrounding the Japan’s first commercial nuclear fuel reprocessing plant in Rokkasho. We previously developed a dynamic two-compartment model for 14C accumulation in the leaves and roots of Japanese radish. This model was constructed using measured data obtained under controlled experimental conditions in a growth chamber; however, it was not capable of simulating plant carbon accumulation in actual fields resulting from photosynthesis and respiration under fluctuating environments. In order to apply our previous model to actual fields, the present study aims to modify the model by incorporating the environmental responses of photosynthesis and respiration. The modified model was validated with observed temporal changes in the carbon inventories of the leaves and roots of Japanese radish in the field. The model estimates were found to be in relatively good agreement with the observed data. In addition, our modified model provides reasonable simulation results for 14C accumulation in Japanese radish exposed to 14CO2 at different growth stages. The results of this study indicate that our modified model could contribute to the estimation of 14C accumulation in Japanese radish under field conditions.

Temperature-induced changes in Arabidopsis Rubisco activity and isoform expression.

In many plant species, expression of the nuclear encoded Rubisco small subunit (SSu) varies with environmental changes, but the functional role of any changes in expression remains unclear. In this study, we investigated the impact of differential expression of Rubisco SSu isoforms on carbon assimilation in Arabidopsis. Using plants grown at contrasting temperatures (10 °C and 30 °C), we confirm the previously reported temperature response of the four RbcS genes and extend this to protein expression, finding that warm-grown plants produce Rubisco containing ~65% SSu-B and cold-grown plants produce Rubisco with ~65% SSu-A as a proportion of the total pool of subunits. We find that these changes in isoform concentration are associated with kinetic changes to Rubisco in vitro: warm-grown plants produce a Rubisco having greater CO2 affinity (i.e. higher SC/O and lower KC) but lower kcatCO2 at warm measurement temperatures. Although warm-grown plants produce 38% less Rubisco than cold-grown plants on a leaf area basis, warm-grown plants can maintain similar rates of photosynthesis to cold-grown plants at ambient CO2 and 30 °C, indicating that the carboxylation capacity of warm-grown Rubisco is enhanced at warmer measurement temperatures, and is able to compensate for the lower Rubisco content in warm-grown plants. This association between SSu isoform expression and maintenance of Rubisco activity at high temperature suggests that SSu isoform expression could impact the temperature response of C3 photosynthesis.

Hysteresis light curves: a protocol for characterizing the time dependence of the light response of photosynthesis.

Photosynthesis vs. light curves (LCs) have played a central role in photosynthesis research for decades. They are the commonest form of describing how photosynthesis responds to changes in light, being frequently used for characterizing photoacclimation. However, LCs are often interpreted exclusively regarding the response to light intensity, the effects of time of exposure not being explicitly considered. This study proposes the use of 'hysteresis light curves' (HLC), an experimental protocol focused on the cumulative effects of light exposure to obtain information on the time dependence of photosynthetic light responses. HLC are generated by exposing samples to a symmetrical sequence of increasing and decreasing light levels. The comparison of the light-increasing and the light-decreasing phases allows the quantification of the hysteresis caused by high-light exposure, the magnitude and direction of which inform on the activation, and subsequent relaxation of high-light-induced photosynthetic processes. HLCs of the chlorophyll fluorescence indices rETR (relative electron transport rate of photosystem II) and Y(NPQ) (index of non-photochemical quenching) were measured on cyanobacteria, algae, and plants, with the aim of identifying main patterns of hysteresis and their diversity. A non-parametric index is proposed to quantify the magnitude and direction of hysteresis in HLCs of rETR and Y(NPQ). The results of this study show that HLCs can provide additional relevant information on the time dependence of the light response of photosynthetic samples, not obtainable from conventional LCs, useful for phenotyping photosynthetic traits, including photoacclimation state and kinetics of light activation and relaxation of electron flow and energy dissipation processes.

Mechanisms of cerium-induced stress in plants: A meta-analysis

A comprehensive evaluation of the effects of cerium on plants is lacking even though cerium is extensively applied to the environment. Here, the effects of cerium on plants were meta-analyzed using a newly developed database consisting of approximately 8500 entries of published data. Cerium affects plants by acting as oxidative stressor causing hormesis, with positive effects at low concentrations and adverse effects at high doses. Production of reactive oxygen species and its linked induction of antioxidant enzymes (e.g. catalase and superoxide dismutase) and non-enzymatic antioxidants (e.g. glutathione) are major mechanisms driving plant response mechanisms. Cerium also affects redox signaling, as indicated by altered GSH/GSSG redox pair, and electrolyte leakage, Ca2+, K+, and K+/Na+, indicating an important role of K+ and Na+ homeostasis in cerium-induced stress and altered mineral (ion) balance. The responses of the plants to cerium are further extended to photosynthesis rate (A), stomatal conductance (gs), photosynthetic efficiency of PSII, electron transport rate, and quantum yield of PSII. However, photosynthesis response is regulated not only by physiological controls (e.g. gs), but also by biochemical controls, such as via changed Hill reaction and RuBisCO carboxylation. Cerium concentrations <0.1–25 mg L−1 commonly enhance chlorophyll a and b, gs, A, and plant biomass, whereas concentrations >50 mg L−1 suppress such fitness-critical traits at trait-specific concentrations. There was no evidence that cerium enhances yields. Observations were lacking for yield response to low concentrations of cerium, whereas concentrations >50 mg Kg−1 suppress yields, in line with the response of chlorophyll a and b. Cerium affects the uptake and tissue concentrations of several micro- and macro-nutrients, including heavy metals. This study enlightens the understanding of some mechanisms underlying plant responses to cerium and provides critical information that can pave the way to reducing the cerium load in the environment and its associated ecological and human health risks.

Contrasting responses in growth, photosynthesis and hydraulics of two subtropical tree species to cadmium contamination as affected by elevated CO2 and nitrogen addition.

Plant growth, photosynthesis, and hydraulics are affected by heavy metals but also by elevated atmospheric CO2 concentration (e[CO2]) and nitrogen (N) deposition. However, few studies have investigated the response of woody species to the combined effects of these three factors. We conducted an open-top chamber experiment with two common subtropical trees (Acacia auriculiformis and Syzygium hainanense) to explore the effects of cadmium (Cd)-contamination, e[CO2], and N addition on plant eco-physiological traits. We found that the growth of A. auriculiformis was insensitive to the treatments, indicating that it is a Cd-tolerant and useful afforestation species. For S. hainanense, in contrast, e[CO2] and/or N addition offset the detrimental effects of Cd addition by greatly increasing plant biomass and reducing the leaf Cd concentration. We then found that e[CO2] and/or N addition offset the detrimental Cd effects on S. hainanense biomass by increasing its photosynthetic rate, its N concentration, and the efficiency of its stem water transport network. These offsetting effects of e[CO2] and/or N addition, however, came at the expense of reduced xylem hydraulic safety resulting from wider vessels, thinner vessel walls, and therefore weaker vessel reinforcement. Our study suggests that, given future increases in global CO2 concentration and N deposition, the growth of Cd-tolerant tree species (like A. auriculiformis) will be probably stable while the growth of Cd-sensitive tree species (like S. hainanense) might be enhanced despite reduced hydraulic safety. This also suggests that both species will be useful for afforestation of Cd-contaminated soils given future global change scenarios.

Comparison of C3 Photosynthetic Responses to Light and CO2 Predicted by the Leaf Photosynthesis Models of Farquhar et al. (1980) and Goudriaan et al. (1985)

AbstractThe leaf photosynthesis models developed by Farquhar et al. (1980, https://doi.org/10.1007/BF00386231) (FvCB) and Goudriaan et al. (1985, https://doi.org/10.1007/978‐1‐4899‐3665‐3_10) (G85) are both used in Earth system and weather models to quantify ecosystem carbon assimilation. Despite their common role, a systematic comparison between these two photosynthesis models is currently lacking in scientific literature. In this technical report we compared the two models in a systematic way. Hereto we performed a comparative analysis of the model structures as well as the modeled responses of photosynthesis to light and CO2 at leaf level. To facilitate future model comparison, we also constructed a lookup table that presents FvCB model parameters fitted to CO2‐response curves from G85 in a wide natural range in photosynthetic capacity at standardized temperature. The structure of the FvCB model differs fundamentally from the G85 model as the FvCB model considers rate‐limiting processes due to Rubisco capacity, electron transport and triose phosphate utilization in parallel, whereas the G85 model considers Rubisco activity and triose phosphate utilization limitation to act in series scaled with quantum use efficiency. The models also differ fundamentally in terms of the parametrization of dark respiration. Still, both models calculate near‐similar responses of photosynthesis to changes in light and CO2 across a wide range in photosynthetic capacity with only two free parameters each. Our work thereby highlights functional similarities between these model approaches despite fundamental differences in model structure. Hence, standardized parameter sets that yield similar photosynthesis responses to light and CO2 may facilitate intercomparison of Earth system and weather models.

Photosynthesis and growth of Amaranthus tricolor under strontium stress

Amaranthaceae are effective plants for cleaning soil contaminated by heavy metals and radionuclides. In this paper, Amaranthus tricolor was used to investigate the response of the plant photosynthesis to various concentration of strontium ions (0.2, 0.6, 3 and 6 mM), in order to determine the possibility of A. tricolor to remediate strontium contamination. The results showed that strontium ions (0.2–6 mM) had effect on light energy conversion and utilization in A. tricolor. Low level of strontium (0.2 mM) promoted the energy utilization in A. tricolor, while higher Sr concentration (3 mM or higher) increased the excess light energy in the plants. Under strontium stress of 6 mM, the acceptor side of PSII in A. tricolor leaves was more vulnerable to strontium stress than the donor side. Furthermore, strontium stress led to accumulation of QA− and block in QB downstream of the electron transfer chain in PSII of A. tricolor leaves. The tolerance ability of A. tricolor to strontium and remediation is also reflected in its biomass and strontium content in plants. Strontium at 3 mM or below promoted the growth of A. tricolor, while higher concentration inhibited the plant growth, but without obvious wilting or curling of leaves. The maximal dry weight increased by 36.29% in shoots, and 60.14% in roots when the spiked-strontium concentration reached 0.2 mM. The maximal strontium content achieved 8.75 mg/g dry wt in shoots, and 1.71 mg/g dry wt in roots respectively, when strontium concentration was 6 mM. Transfer factors (TFs: ratio of Sr content in shoots to that in roots) of strontium in A. tricolor ranged from 2.85 to 5.93, while bio-concentration factors (BCFs: ratio of Sr content in shoots to that in solutions) ranged from 22.57 to 49.66. In summary, A. tricolor showed the excellent potential to remediate strontium contamination.

The CO2 fertilization effect on leaf photosynthesis of maize (Zea mays L.) depends on growth temperatures with changes in leaf anatomy and soluble sugars

Understanding the potential mechanisms and processes of leaf photosynthesis in response to elevated CO2 concentration ([CO2]) and temperature is critical for estimating the impacts of climatic change on the growth and yield in crops such as maize (Zea mays L.), which is a widely cultivated C4 crop all over the world. We examined the combined effect of elevated [CO2] and temperature on plant growth, leaf photosynthesis, stomatal traits, and biochemical compositions of maize with six environmental growth chambers controlling two CO2 levels (400 and 800 μmol mol−1) and three temperature regimes (25/19°C, 31/25°C, and 37/31°C). We found that leaf photosynthesis was significantly enhanced by increasing growth temperature from 25/19°C to 31/25°C independent of [CO2]. However, leaf photosynthesis drastically declined when the growth temperature was continually increased to 37/31°C at both ambient CO2 concentration (400 μmol mol−1, a[CO2]) and elevated CO2 concentration (800 μmol mol−1, e[CO2]). Meanwhile, we also found strong CO2 fertilization effect on maize plants grown at the highest temperature (37/31°C), as evidenced by the higher leaf photosynthesis at e[CO2] than that at a[CO2], although leaf photosynthesis was similar between a[CO2] and e[CO2] under the other two temperature regimes of 25/19°C and 31/25°C. Furthermore, we also found that e[CO2] resulted in an increase in leaf soluble sugar, which was positively related with leaf photosynthesis under the high temperature regime of 37/31°C (R2 = 0.77). In addition, our results showed that e[CO2] substantially decreased leaf transpiration rates of maize plants, which might be partially attributed to the reduced stomatal openness as demonstrated by the declined stomatal width and stomatal area. These results suggest that the CO2 fertilization effect on plant growth and leaf photosynthesis of maize depends on growth temperatures through changing stomatal traits, leaf anatomy, and soluble sugar contents.