Photosynthetic Fluorescence Characteristics Research Articles

Additional far-red light promotes the healing and quality of double-root-cutting grafted watermelon seedlings

Graft healing is an important factor that determines the survival of the double-root-cutting (DRC) grafted plants. Recent studies have shown that adding far-red light (FR) to change the red/far-red (R/FR) ratio plays a crucial role in plant growth and development. However, there have been few studies on how R/FR ratio affects the grafting union healing process of DRC grafted seedling. In this study, we applied four light quality treatments: dark (D), white (R/FR=6.0, W), R/FR ratios of 3 (H) and 0.3 (L). The effects of different ratios of R/FR on the survival rate, photosynthetic fluorescence characteristics, graft union healing and growth of DRC grafted watermelon seedlings during the healing period were analyzed using darkness (D) as a control. The results showed that compared with the control L treatment could significantly improve the survival rate, growth indicators and photosynthetic capacity of grafted seedlings, significantly increased the activities of SOD and POD, and contents of soluble sugar and protein in the graft union, and significantly reduced the accumulation of O2−, H2O2 and MDA, which was conducive to the production of callus cell and the healing of grafted union. Meanwhile, qRT-PCR results showed that the expression levels of graft healing-related genes, ClaIAA, ClaSOD, ClaPOD, ClaWOX4, ClaGH9B14 and ClaGH9B1 were significantly induced L treatment. The current study can contribute to speeding up the development of industrialized production with high-quality watermelon grafted seedlings.

Effects of Long-Term High Temperatures in the Root Zone on the Physiological Characteristics of Grapevine Leaves and Roots: Implications for Viticulture Practices

Ridging cultivation and root restriction cultivation are beneficial due to their improvement of the soil permeability in the root zone of grapevine, and they are widely used in southern China, Japan, and other countries. However, with the intensification of global warming, when using ridging or root restriction cultivation, the soil temperature in the root zone can often reach 30 °C or even more than 35 °C during the summer, which is not conducive to the growth of grapevines. The aim of this study was to explore the effects of high root zone temperatures on the photosynthetic fluorescence characteristics of grapevine leaves, root respiration, and degree of lignification of roots and shoots, as well as to provide a theoretical foundation for the management of grapevine production and cultivation. One-year-old potted ‘Kyoho’ was used as the study material. Three root temperature treatments were implemented for 15 days (9:00–16:00): 25 °C (CK), 30 °C (T1), and 35 °C (T2). The results showed that the malondialdehyde and H2O2 levels in leaves increased, while the chlorophyll content decreased. The oxygen-evolving complex was inactivated, and PSII donor and acceptor sides were blocked, thus reducing the photosynthetic gas exchange capacity at high root zone temperatures. The grapevine root activity and root/shoot ratio decreased. Simultaneously, the lignin content in the roots and shoots increased. In addition, there was a significant increase in the expression of key genes (PAL, C4H, 4CL, F5H, COMT, CCR, and CAD) in the root lignin synthesis pathway. Heightened root zone temperatures increased cyanide-resistant respiration in roots and heat release in the PPP pathway to alleviate stress damage. Therefore, it is recommended to use grass, mulching, and other cultivation management methods to maintain root zone temperatures below 30 °C in order to ensure the normal growth of grapevines and promote a high and stable yield.

Quantifying Chilling Injury on the Photosynthesis System of Strawberries: Insights from Photosynthetic Fluorescence Characteristics and Hyperspectral Inversion.

Chilling injury can adversely affect strawberry bud differentiation, pollen vitality, fruit yield, and quality. Photosynthesis is a fundamental process that sustains plant life. However, different strawberry varieties exhibit varying levels of cold adaptability. Quantitatively evaluating the physiological activity of the photosynthetic system under low-temperature chilling injury remains a challenge. In this study, we investigated the effects of different levels of chilling stress on twenty photosynthetic fluorescence parameters in strawberry plants, using short-day strawberry variety "Toyonoka" and day-neutral variety "Selva" as representatives. Three dynamic chilling treatment levels (20/10 °C, 15/5 °C, and 10/0 °C) and three durations (3 days, 6 days, and 9 days) were applied to each variety. WUE, LCP, Y(II), qN, SIFO2-B and rSIFO2-B were selected as crucial indicators of strawberry photosynthetic physiological activity. Subsequently, we constructed a comprehensive score to assess the strawberry photosynthetic system under chilling injury and established a hyperspectral inversion model for stress quantification. The results indicate that the short-day strawberry "Toyonoka" exhibited a recovery effect under continuous 20/10 °C treatment, while the day-neutral variety "Selva" experienced progressively worsening stress levels across all temperature groups, with stress severity higher than that in "Toyonoka". The BPNN model for the comprehensive assessment of the strawberry photosynthetic system under chilling injury showed optimal performance. It achieved a stress level prediction accuracy of 71.25% in 80 validation samples, with an R2 of 0.682 when fitted to actual results. This study provides scientific insights for the application of canopy remote sensing diagnostics of strawberry photosynthetic physiological chilling injury in practical agricultural production.

Effects of Elevated Surface Ozone Concentration on Photosynthetic Fluorescence Characteristics and Yield of Soybean Parents and Offspring

Global climate change presents a significant threat to food security. Analyzing the effects of elevated ozone (O3) concentration on photosynthetic fluorescence characteristics and yield addresses the damage of climate change on crops, which would serve food security. With open-top chambers (OTCs) and Tiefeng-29 soybeans, we investigated the responses of chlorophyll concentration, fluorescence characteristics, net photosynthetic rate (Pn) and yield components to different O3 concentrations, which included CK (ambient concentration approximately 45 nL·L−1, T1 (80 ± 10) nL·L−1 and T2 (120 ± 10) nL·L−1 O3. The parent soybeans (S1) were planted in the current year, and O3 fumigation commenced 20 days after seedling emergence. Aeration was stopped at maturity, and the offspring soybeans (S2) were retained after harvest for further experiments. In the following year, S1 and S2 soybeans were planted, and O3 fumigation began 20 days after seedling emergence. The results show that leaf chlorophyll a (chla) and chlorophyll b (chlb) significantly decreased with longer O3 fumigation time both in parents and offspring, causing damage to the light-trapping ability while the offspring suffered an earlier decrease. The elevated O3 damaged the electron transfer process by significantly reducing the original and actual photochemical efficiencies of PSII both in parents and offspring. The electron transfer rate (ETR) of the parents and offspring decreased, while the difference between them was not significant after O3 treatment. The non-photochemical quenching coefficient (NPQ) showed an increasing trend along time but showed no significant difference between parents and offspring. An elevated concentration of O3 significantly reduced Pn, while the differences in Pn between the parents and the offspring were not significant. Elevated O3 resulted in reduced yields in both parent and offspring soybeans. Although it was found that the offspring soybeans exhibited higher yields than the parents, their reduction in yield was more significant. Therefore, elevated O3 concentration reduced soybean yield through damaging photosynthetic process and electron transfer capacity by impairing energy conversion and material accumulation capacity. The offspring had relatively higher light energy conversion efficiency than the parents, resulting in a higher yield than the parents under all treatments.

Effects of Shading on the Growth and Photosynthetic Fluorescence Characteristics of Castanopsis hystrix Seedlings of Top Community-Building Species in Southern Subtropical China

Castanopsis hystrix is a major community-building species in the top communities of southern subtropical China, with a high natural regeneration capacity. However, excessive logging and the introduction of exotic tree species have substantially reduced the area of natural forest patches of Castanopsis hystrix, and seedling regeneration is essential for the long-term continuation of Castanopsis hystrix populations. To explore the effects of light intensity on the seedling emergence and early growth of Castanopsis hystrix, shading experiments were conducted under four shading treatments (0%, 40%, 60%, and 80%). The growth, biomass accumulation, and distribution, the quality index of seedlings, the morphology and structure of the root systems of seedlings, and the leaf chlorophyll content and chlorophyll fluorescence properties of seedlings under different shading treatments were analyzed. The results displayed the following: (1) Shade intensity impacts growth of Castanopsis hystrix seedlings and biomass allocation, with optimal results observed at 60% shade, leading to the promotion of organic matter production in leaves and the limitation of stem growth. (2) Using a multi-indicator composite index, it was determined that seedling quality for Castanopsis hystrix peaks at 60% shade intensity. (3) Shade significantly impacts the morphology and structure of Castanopsis hystrix’s root system, with most root characteristics peaking at 60% shade, indicating a substantial increase in root development compared to no-shade conditions. (4) The D-values indicated the most suitable shade intensity for seedling growth to be 60%, suggesting that Castanopsis hystrix seedlings are sensitive to light and excessive light can be detrimental to their growth. (5) The 60% shade treatment showed the maximum values of chlorophyll fluorescence characteristics and photochemical activity, with variations in energy conversion efficiency and dissipation reflected in parameters like photochemical burst coefficient (qP), photochemical burst coefficient (qN), the actual photometric yield of PSII under light acclimation (YII), and the maximum photosynthetic electron transport rate in photoinhibition (ETR), thereby supporting seedling growth and maintaining the normal function of photosynthetic organs. In conclusion, 60% shade treatment can effectively improve the growth and photosynthetic characteristics of Castanopsis hystrix seedlings and promote the accumulation of nutrient elements, ultimately promoting their growth.

Effects of exogenous NO on the growth and photosynthetic fluorescence characteristics of ryegrass seedlings under B[a]P stress

Benzoapyrene (B[a]P) pollution poses a threat to the environment and the food chain and consequently to human health. However, the alleviation of the harmful effects of B[a]P pollution in perennial ryegrass (Lolium perenne L.) by the application of exogenous nitric oxide (NO) has been ignored. Thus, in this paper the effects of exogenous sodium nitroprusside (SNP, a NO donor) on the growth, photosynthetic fluorescence characteristics, and antioxidant enzyme activity of ryegrass exposed to B[a]P stress are investigated. B[a]P stress induced the reduction of the aboveground and belowground dry weights, chlorophyll (a, b), the total chlorophyll contents, the carotenoid content, the net photosynthetic rate (Pn), the intercellular carbon dioxide concentration (Ci), the water use efficiency (WUE), the photosystem II (PSII) potential activity (Fv/F0), the maximum quantum yield of PSII photochemistry (Fv/Fm), the steady-state fluorescence yield (Fs), and the non-photochemical quenching (qN), while enhancement was recorded in response to the foliar spray of SNP at 200 and 300 μmol·L-1 under B[a]P stress. Gray correlation and principal component analyses show that 200 μmol·L 1 of SNP more drastically alleviated the damage caused by B[a]P stress than 300 μmol·L 1 of SNP. The exogenous NO-mediated alleviation of B[a]P toxicity in ryegrass was associated with preserved photosynthetic characteristics and activation of antioxidant enzymes.

A mixed acid treatment for the prevention of Ulva prolifera attachment to Neopyropia aquaculture rafts: Laboratory experimentation.

The sessile green macroalgae in the Neopyropia aquaculture areas of the Subei Shoal are a confirmed source of green tides in the Southern Yellow Sea (SYS) of China. The green tides have a significant impact on local economic development (tourism, aquaculture, etc.) and ecological stability. In order to develop an effective method for eliminating the green macroalgae attached to Neopyropia aquaculture rafts, this study investigated the effects of mixed acid solutions (0.0475% hydrochloric acid [HCl] and pH2.0 citric acid) on cell damage, chlorophyll composition, phycobiliprotein content, and the photosynthetic fluorescence characteristics of Ulva prolifera and Neopyropia yezoensis. The chlorophyll contents of U. prolifera and N. yezoensis were significantly affected by the mixed acid solutions. After treatment with a mixed acid solution (4:3 volume ratio of HCl to citric acid) for 5s, the photosynthetic pigment content of U. prolifera was significantly different from that of normal U. prolifera. However, photosynthetic pigment content in the treated N. yezoensis increased significantly. In addition, mixed acid solution treatment had a significant effect on the Fv/Fm of U. prolifera and N. yezoensis. After mixed acid treatment (4:3 HCl to citric acid), U. prolifera completely died, but the Fv/Fm of N. yezoensis was restored after 3 d. Therefore, a mixed acid solution comprising 0.0475% HCl and pH2.0 citric acid (at a volume ratio of 4:3) can be used as an agent for the removal of green macroalgae from Neopyropia aquaculture areas.

The Effects of Water Depth on the Growth of Two Emergent Plants in an In-Situ Experiment

With the degradation of the global lake ecosystem, aquatic plants are more and more widely used in lake ecological restoration. The effects of water depths on the growth and photosynthetic fluorescence characteristics of two emergent plants (Typha orientalis and Zizania caduciflora) were studied in eutrophic Lake Gehu by in-situ experiments. The results showed that water depth had no significant effect on germination of emergent plants. The water depth changed the morphological characteristics of emergent plants. Plant height, tiller number, leaf length, leaf width, the number of leaf, and the root-shoot ratio decreased with increasing water depth, whereas the number of dead leaves increased with increasing water depth. The biomass of emergent plants was highest when water depth was 40 cm. Water depth had a significant effect on the photosynthetic fluorescence of the emergent plant. Fv/Fm tended to decrease first and then increase with increasing water depth. When the water depth was 20 cm, the ETRmax of emergent plants was significantly higher than that of plants at the other water depths. These results show the suitable water depth range for T. orientalis and Z. caduciflora is 20–60 cm. A deeper water depth for a long time is not conducive to the growth of emergent plants.

Effects of canopy spectral composition on growth and photosynthetic fluorescence characteristics of Pinus koraiensis and Quercus mongolica seedlings

We investigated the responses of leaf and individual traits, growth, and fluorescence characteristics of seedlings of two dominant species of broad-leaved Korean pine forest in Changbai Mountain, i.e., Pinus koraiensis and Quercus mongolica, to five spectrum-attenuation treatments. Results showed that the architecture and growth of P. koraiensis and Q. mongolica seedlings were mainly regulated by ultraviolet B (UV-B) radiation and blue light. The attenuation of blue light significantly decreased leaf area ratio and relative growth rate of two species. The attenuation of UV-B radiation significantly increased leaf area ratio and relative growth rate of P. koraiensis seedlings by 41.8% and 47.7%, respectively, and significantly decreased plant height, total leaf area, and biomass accumulation of Q. mongolica seedlings. Furthermore, the attenuation of UV-B radiation significantly decreased the fluorescence regulation ability of two tree seedlings, with lower magnitude of P. koraiensis than Q. mongolica. The non-regulatory quantum yield (ΦNO) of P. koraiensis increased by 31.6%, and the ΦNPQ/ΦNO ratio, an indicator for photosynthetic fluorescence regulation ability, decreased by 37.5%. These results suggested that those two species might have evolved adaptation strategies to changes in canopy spectral compositions of their respective habitats. Q. mongolica seedlings tended to improve light capture ability through rapid morphological responses, while P. koraiensis seedlings preferred to increase carbon assimilation efficiency by adjusting fluorescence characteristics.

Performance and mechanism of the in situ restoration effect on VHCs in the polluted river water based on the orthogonal experiment: photosynthetic fluorescence characteristics and microbial community analysis

Volatile halogenated hydrocarbons (VHCs) attracted many attentions due to its toxicity and persistence in the environment. In this research, a novel in situ ecological restoration reactor was applied to the degradation of VHCs in polluted river water. The optimized working condition adaptation of the in situ restoration technique was evaluated through orthogonal tests. The experiments showed that when the water depth was 0.4 m, the HRT was 5 days, and the current velocity was 1 m/s, the optimal removal efficiency of VHCs in the reactor was achieved. And the removal rates of CHCl3, CCl4, C2HCl3, and C2Cl4 reached 70.27%, 70.59%, 67.74%, and 81.82%, respectively. The results showed that both HRT and water depth were significantly related to the removal efficiency of reactor. The physiological state of the plants was analyzed by fitting rapid light curve (RLC) model, which showed that the accumulation of VHCs inhibited the photosynthetic performance of plants. Moreover, the microbial community structures of fillers were tested by high-throughput sequencing, and the findings supported that the microbial community made a great response to adapt to the changes in environment of the reactor. The relative abundance of Rhodocyclaceae increased slightly, which hinted that it had good adaptability to VHCs in polluted river water. The research results confirmed that in situ ecological restoration reactor was a potential approach for removal VHCs in polluted river water.

Relationships between leaf color changes, pigment levels, enzyme activity, photosynthetic fluorescence characteristics and chloroplast ultrastructure of Liquidambar formosana Hance

Relationships between leaf color changes, pigment levels, enzyme activity, photosynthetic fluorescence characteristics and chloroplast ultrastructure of Liquidambar formosana Hance

Comparison of photosynthetic fluorescence characteristics of several submerged plants in Honghu Lake, China

Submerged plants are the pioneer species of eutrophic water remediation, and they are important for maintaining the health of aquatic ecosystem, while light is the main limiting factor for the growth of submerged plants. In this study, we measured the maximal quantum yields of photosystemⅡ(Fv/Fm) and rapid light curves (RLCs) of five dominant submerged macrophytes in situ by using pulse-amplitude modulated fluorometer (Diving-PAM). Results revealed that P. crispus L. and M. verticillatum L. had the highest Fv/Fm value, all species’ Fv/Fm are less than 0.8. In addition, the variation trends of Fv'/Fm' and Fv/Fm were same. All species showed statistically significant differences in α, while P. crispus L. and M. verticillatum L. showed the highest α value in the five species. And the variation trends of rETRm and Ek were basically the same. It indicated that P. crispus L. and M. verticillatum L., both of which had high photosynthetic efficiency, had excellent ability to withstand hard light. Compared five species, P. crispus L. and M. verticillatum L. had resistance capacity to hard light as well as faster photosynthetic rate, and V. natans (Lour.) Hara had higher resistance capacity to low light. Thus, when submerged plants are used for water restoration, V. natans (Lour.) Hara could be regarded as a pioneer species in eutrophication water restoration. P. crispus L. and M. verticillatum L. will have better effects when used in shallow water areas.

Effects of flooding stress on leaf color and photosynthetic fluorescence characteristics of Liquidambar styraciflua cutting seedlings in summer

Effects of flooding stress on leaf color and photosynthetic fluorescence characteristics of Liquidambar styraciflua cutting seedlings in summer

The effects of water depth on the growth of two submerged macrophytes in an in situ experiment

An in situ experiment was designed in which Potamogeton crispus and Hydrilla verticillata were planted in plastic pots 25, 50, 75, 100, 125, 150, 175 and 200 cm underwater to study the effect of water depth on the growth and photosynthetic fluorescence characteristics of the two submerged macrophytes in Lake Gehu, China. The results showed that: 1) Water depth had no significant effect on the germination of both submerged macrophytes. The final germination rate of P. crispus turions was higher than 80%, and the final germination rate of the H. verticillata winter buds was 100%; 2) Water depth affected the survival rate of both submerged macrophytes, and the seedlings at depths of 150, 175 and 200 cm all eventually died; 3) Water depth altered the morphological characteristics of P. crispus and H. verticillata seedlings. (4) Increasing water depth significantly affected biomass (p < .05), with the biomass initially tending to increase, but then decreasing. The root to shoot ratio of both submerged macrophytes decreased with increasing water depth; 5) Chlorophyll contents of P. crispus and H. verticillata increased with water depth from 25 to 150 cm; 6) Water depth had an obvious effect on the photosynthetic fluorescence of submerged macrophytes. The Fv/Fm increased slightly from water depths from 25 to 75 cm, and then decreased significantly when water depth exceeded 100 cm. The ETRmax was significantly different among all treatment groups, and ETRmax was obviously higher at water depths of 25 and 50 cm than at all other depths. These results showed that submerged macrophytes have a limited water depth tolerance range. In Lake Gehu, the recovery of submerged macrophytes will be better in areas with water depths less than 125 cm.

Photosynthesis product allocation and yield in sweet potato with spraying exogenous hormones under drought stress

This study investigated the alleviation effects of spraying phytohormones on the physiological characteristics and yield of sweet potato under drought stress during the early vine development and storage root bulking stage, respectively. The endogenous hormone contents, photosynthetic fluorescence indexes, photosynthetic products transfer allocation (based on 13C labeling method), and yield of sweet potato were studied by spraying water, 6-benzylaminopurine (6-BA), abscisic acid (ABA), and combined with the two exogenous hormones under artificial dry shed and dry pond. Results indicated that the yield was increased by spraying 6-BA or ABA separately in comparison with the control treatment under drought stress, and the alleviation effects of spraying 6-BA at the early stage were better than at the storage root bulking stage, while spraying ABA at the storage root bulking stage was better than at the early stage. The sweet potato yield increased when sprayed with 6-BA, especially at the early vine development stage, and sweet potato yield was further enhanced by the addition of ABA. When sprayed together, exogenous 6-BA and ABA increased plant shoot and storage root biomass, as well as leaf area and yield, at both stages. The combination of exogenous 6-BA and ABA also increased shoot 13C accumulation at the early vine development stage and storage root 13C accumulation at the storage root bulking stage, in comparison with 6-BA or ABA alone under drought stress. Spraying exogenous hormones under drought stress increased the endogenous hormone contents, enhanced carbon metabolism enzyme activities, improved the photosynthetic fluorescence characteristics of leaves, and regulated the source-sink balance, all of which alleviated the yield reduction caused by drought stress. Application of the combination of 6-AB and ABA yielded better results than that of the 6-BA or ABA alone.

The effect of plant extracts on growth and photosynthetic fluorescence characteristics of Microcystis flos-aquae.

The cyanobacteria Microcystis flos-aquae can cause harmful algal blooms in waterbodies, which threaten the normal functioning of aquatic ecosystems and human health. Some plant extracts are considered as promising algaecides. In this study, the effects of ten plant extracts (Cinnamomum camphora, Ginkgo biloba, Firmiana platanifolia, Salix babylonica, Euphorbia humifusa, Erigeron annuus, Solidago canadensis, Alternanthera philoxeroides, Thalia dealbata and Eichhornia crassipes) against M. flos-aquae were investigated. The results showed that all ten plant extracts had a significant inhibitory effect on M. flos-aquae growth after 96 h (P < 0.01). The inhibition rates of S. babylonica, E. humifusa, S. canadensis and A. philoxeroides were over 70.00%. Furthermore, the E. humifusa extract had the best inhibitory effect on the photosynthesis of M. flos-aquae, with the effective quantum yield of photosystem II and maximal relative electron transport rate decreasing by 97.50% and 97.00%, respectively, after 96 h. Additionally, the E. humifusa extract was found to be non-toxic to non-target organisms such as Brachydanio rerio and Vallisneria spiralis within 96 h. This study contributes to the existing knowledge and data of freshwater cyanobacteria blooms, and provides insights for their control and the restoration of freshwater systems affected by cyanobacteria blooms.

Effects of exogenous plant hormones on physiological characteristics and yield of sweet potato under drought stress

To explore the alleviation effect of spraying phytohormone on physiological characteristics and yield of sweet potato under drought stress in different periods, and to determine the best period of spraying external plant hormones, the effects on endogenous hormone content, photosynthetic fluorescence characteristics and yield of sweet potato were examined by spraying 6-benzylaminopurine (6-BA), α-naphthylacetic acid (NAA) and abscisic acid (ABA) respectively under drought stress after transplanting for 20 days (early stage), 60 days (middle stage) and 100 days (later stage) under artificial water control. The results showed that compared with spraying water, exogenous phytohormones significantly increased the yield of sweet potato under drought stress, among which 6-BA had the highest effect, followed by NAA and ABA. The effect of spraying in early stage was better than that in middle and late stages. Exogenous phytohormones significantly increased photosynthetic and chlorophyll fluorescence parameters of sweet potato leaves under drought stress at different stages, alleviated the decrease in eatin ribonucleoside (ZR) and auxin (IAA) caused by drought. Stepwise regression analysis showed that endogenous hormones and photosynthetic characteristics were key factors affecting yield of sweet potato. Results of path analysis showed that spraying exogenous plant hormone affected sweet potato yield by changing net photosynthetic rate (Pn), IAA, ZR, maximal photochemical efficiency and photochemical performance index under drought stress at early stage. Therefore, spraying 6-BA could regulate the content of endogenous hormones and improve photosynthetic characteristics of sweet potato at the early growth stage, and thus effectively alleviate the loss of yield caused by drought stress.

The effects of sesame/peanut intercropping on photosynthetic fluorescence characteristics in functional leaf of sesame.

To unravel functional leaf photosynthetic mechanisms underlying enhanced yield of sesame in sesame/peanut intercropping, a field experiment was carried out in 2017 and 2018 with four treatments including (1) three-row sesame intercropped with six-row peanut (IC 3:6), (2) two-row sesame intercropped with four-row peanut (IC 2:4), (3) sole cropped sesame (SS), and (4) sole cropped peanut (SP). We measured the parameters of gas exchange, characteristics of photosynthetic response curve to light and CO2, and characteristics of chlorophyll rapid fluorescence induction kinetic curves of the functional leaves of sesame. The results showed that the partial land equivalent ratio of intercropped sesame was greater than 1/3. The light saturation point (Isat), maxi-mum net photosynthetic rate (Pn max), maximum electron transport rate (Jmax), triose phosphate utilization rate (TPU), maximum carboxylation rate of Rubisco (Vc max) were increased significantly under intercropping. Further, absorption energy flux per CS (ABS/CSo), trapping energy flux per CS (TRo/CSo), number of active reaction centers per CS (RC/CSm), and electron transport flux per CS (ETo/CSo) in intercropped treatments were enhanced compared to that under sesame monoculture. However, the ratio between variable fluorescence Fk to amplitude Fj-Fo (Wk) and ratio between variable fluorescence Fj to amplitude Fp-Fo (Vj) in functional leaves of intercropped sesame were significantly decreased. The efficiency of converting light energy into electricity of PS2 reaction center (Ψo), electron transfer efficiency from PS2 to end acceptor of PS1 (ΨRo), electron transfer efficiency of the electron transport chain (δR), PS1 photochemical activity, and the coordination between PS2 and PS1 in functional leaves of intercropped sesame were increased. The net photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (Tr), Pn max, Jmax, Vc max, TPU, Ψo, ΨRo and δR were significantly higher in IC 3:6 than those in IC 2:4. We conclude that intercropping improves net photosynthetic rate and yield of sesame by increasing light absorption, electronic transmission, activity of PS2 donator/receptor sides, and CO2 fixation, with stronger effects in IC 3:6 than IC 2:4.

Regulation and stimulation of photosynthesis of mixotrophically cultured Haematococcus pluvialis by ribose

The low cell growth rate of Haematococcus pluvialis is a major barrier to achieve low-cost production of the biomass. Our previous study demonstrated that ribose could significantly enhance the growth rate and cell activity of H. pluvialis under mixotrophic conditions. This study showed the photosynthetic rate of the algal cells cultured with ribose was two-fold higher than that of phototrophic after 2-day cultivation. The increased photosynthetic activity of the cells with mixotrophic culture using ribose occurred earlier than that with sodium acetate. Similar photosynthetic fluorescence characteristics was observed for cells grown in phototrophic and ribose-fed culture. Photosystem (PS) I of ribose-fed cells was enlarged relative to PS II after two days. The difference in rubisco activity and subunit gene (rbcL and rbcS) expression however, was not significant between phototrophic and mixotrophic cultivation. The photosynthetic rate of H. pluvialis doubled with ribose mainly due to the high reaction of the Calvin cycle. The results suggested that metabolites derived from ribose could provide additional substrates for the Calvin cycle. This study provides the evidence about unique ribose utilization patterns by H. pluvialis during photosynthesis processes in mixotrophic culture mode. By understanding the mechanism of ribose metabolism in H. pluvialis under mixotrophic cultivation, it offers a promising route for improvement of biomass accumulation.

Photosynthetic fluorescence characteristics of six macroalgae species in seaweed beds of Gouqi Island, Zhejiang, China.

The study of photosynthetic fluorescence characteristics of algae is important for the analy-sis of photosynthesis and carbon sequestration of algae. In July 2017, six common species of macroalgae found in Gouqi seaweed beds were collected, including Ulva pertusa, Cladophora stimpsonii, Grateloupia livida, Sargassum thunbergii, Polysiphonia urceolata, and Hizikia fusifarme. In the field, the maximal quantum yieids of photosystem2(Fv/Fm) and rapid curves (RLCs) were mea-sured by using pulse-amplitude modulated fluorometer (Diving-PAM). The results showed that the measured maximal quantum yields of U. pertusa, C. stimpsonii, G. livida, S. thunbergii, P. urceolata, and H. fusiforme were 0.702, 0.704, 0.457, 0.618, 0.421 and 0.567, respectively. The Fv'/Fm' of six species were in order of C. stimpsonii>U. pertusa>S. thunbergii＞H. fusiforme＞G. livida＞P. urceolata. The difference between each species and significant difference was found in U. pertusa, C. stimpsonii, and H. fusiforme. H. fusiforme, S. thunbergii and U. pertusa had higher Pm and α than other species, indicating their higher photosynthetic capacity and better adaptation in higher light condition. However, G. livida had higher α but lower Ik, indicating G. livida had higher photosynthetic capacity in low light condition. In a word, differences of photosynthetic capacity and light intense tolerance between the three phyla of macroalgae were found and we suggested H. fusiforme, S. thunbergii and U. pertusa had stronger photosynthetic capacity and light intense tolerance. Our results could provide theoretical basis for the seaweed bed conservation and carbon sequestration of macroalgae.