Quantum Yield Of PSII Photochemistry Research Articles

Coordinated changes in photosynthetic machinery performance and water relations of the xerophytic shrub Ziziphus lotus (L.) Lam. (Rhamnaceae) following soil drying

Aim of this study was to investigate the effect of water shortage in wild jujube plants, Ziziphus lotus (L.) Lam, and how it is related to its ecological success. All leaf anatomical traits were significantly affected following soil drying. Stressed plants displayed more negative stem water potential (ψw) and osmotic potential values of ca. -3.5 and -4.5 MPa, respectively, after 30 d. The relative water content declined although it still maintained high values (≥ 75%). The net photosynthetic rate, stomatal conductance, and transpiration rate were significantly inhibited as ψw decreased. However, the intrinsic water-use efficiency increased as water deficit was intensified; the difference became significant only after 30 d. As a consequence, the effective quantum yield of PSII photochemistry and the photochemical quenching coefficient significantly decreased although the maximal quantum yield of PSII photochemistry ratio remained statisticaly unchanged. Plants could maintain their water status sufficiently by increasing proline 1.7-fold and sucrose 1.8-fold in their leaves, respectively. The largest accumulation of both solutes may avoid photodamages at cellular level and play a critical role in maintaining osmotic adjustment.

Photosynthetic and yield performance of wild barley (Hordeum vulgare ssp. spontaneum) under terminal heat stress

Terminal heat stress is one of the major constraints of cereal production. A two-year field investigation was performed to assess the response of Hordeum vulgare ssp. spontaneum genotypes to terminal heat stress using gas-exchange parameters, photosystem efficiency, proline accumulation, cell membrane leakage, and grain yield traits. Results of analysis of variance revealed the significant effects of heat stress (E), genotype (G), and G × E on the studied traits. The results of linear regression analysis showed that yield loss was inversely correlated with the maximum quantum yield of PSII photochemistry (Fv/Fm) and chlorophyll content. Path-coefficient analysis revealed that high Chl contents were either directly related to the grain yield or indirectly through the higher net photosynthetic rate and higher Fv/Fm values under high temperatures at the reproductive growth stage. Overall, the adapted wild genotypes exhibited physiological mechanisms capable of sustainable maintaining their yield capacity and plasticity flow, which could be exploited by crossing with cultivated barley to introgress heat tolerance.

Morphological, anatomical and physiological traits of Euryodendron excelsum as affected by conservation translocation (augmentation vs. conservation introduction) in South China

Euryodendron excelsum is a rare and endangered evergreen tree in South China. We conducted two experimental translocations (augmentation and conservation introduction) on this species and assessed morphological, anatomical and physiological traits of leaves after translocation. The introduction plants showed smaller specific leaf area, less developed palisade tissues, smaller palisade/spongy tissue ratio, stomata density and anthocyanin content, lower values of maximal quantum yield of PSII photochemistry, photochemical quenching coefficient, net photosynthetic rate, light-saturated net photosynthetic rate, light-saturation point, but higher light-compensation point. These differences in traits help explain why augmented plants grew faster than introduced plants. We found that E. excelsum can adapt to wide ranges of light intensity and water availability, including conditions encountered at the introduction site. Our findings suggest that some endemic and endangered plants with narrow distribution may adapt to different habitat conditions by rapidly altering their morphological, anatomical, and physiological traits.

Diurnal and seasonal variations in the photosynthetic performance and chlorophyll fluorescence of cassava 'Rayong 9' under irrigated and rainfed conditions

Diurnal photosynthesis responses of cassava cultivar Rayong 9 ('RY9') three months after planting, grown in a field conditions under irrigated and rainfed conditions, were evaluated during the rainy, cool, and hot seasons. Under the mild conditions of the rainy and cool seasons, net photosynthetic rates (PN) increased in parallel with light intensity and attained the maximum at 13.00 or 11.00 h. In the hot season, PN attained the prominent peak at 9.00 h, after which stomatal conductance decreased rapidly coordinated with declining PN and nonphotochemical quenching was enhanced. Photosynthetically active radiation was the major factor influencing PN in the rainy and cool seasons, whereas vapor pressure deficit was the major factor in the hot season. 'RY9' adapted extremely well in this climate because the maximal quantum yield of PSII photochemistry recovered fully in the evening even under the rainfed conditions in the hot season.

Brassinosteroids increase electron transport and photosynthesis in soybean plants under water deficit

Drought frequently results in significant losses in agricultural systems, including the soybean yield. Brassinosteroids exhibit multiple actions on essential processes, including chlorophyll fluorescence and gas exchange. Considering that the electron transport rate (ETR) into photosystems can exercise interference on net photosynthetic rate (PN), this research aims to determine whether 24-epibrassinolide (EBR) affects electron transport and find out if there is any repercussion on photosynthesis in soybean plants affected by the water deficit. The experiment was performed using a randomized factorial design, with two water conditions (control and water deficit) and three EBR concentrations (0, 50, and 100 nM EBR). The water deficit reduced effective quantum yield of PSII photochemistry, ETR, PN, and water-use efficiency. However, the exogenous application of 100 nM EBR mitigated these negative effects, increasing these variables. EBR reduced the oxidant compounds (superoxide and hydrogen peroxide) and membrane damages (malondialdehyde and electrolyte leakage) in stressed plants. Our study proved that EBR increased ETR and PN in control and stressed plants, revealing that ETR had a strong relationship with PN. These results suggest that soybean plants with higher values of ETR are more efficient in relation to PN.

Machine learning in determination of water saturation deficit in wheat leaves on basis of Chl a fluorescence parameters

Water saturation deficit (WSD) is a parameter commonly used for detection of plant tolerance to temporary water shortages. However, this parameter does not meet criteria set for screening. On the other hand, measurement of chlorophyll (Chl) a fluorescence is a fast and high-throughput method. This work presents the application of learning systems to set up a model between WSD and Chl a fluorescence parameters allowed for development of a new screening test. Multilayer perceptron (MLP) was trained to predict WSD values on the basis of Chl a fluorescence. The best MLP consisted of three inputs: maximal quantum yield of PSII photochemistry, approximated number of active PSII reaction centres per absorption, and measure of forward electron transport, three hidden nodes and one output (WSD). The MLP precision was 82% with a correlation coefficient of 0.98. Continuous improvement of MLP structure and model adaptation to new data takes place. (1)

Tolerance of the photosynthetic apparatus in recombinant lines of wheat adapting to water stress of varying intensity

The stress tolerance index (STI) of leaf photosynthetic parameters was analysed in recombinant introgression lines of spring wheat (Triticum aestivum L.) grown under water stress of varying intensity in the simulated conditions of soil and soil-atmospheric drought. STI for the chlorophyll content was >1 regardless of experimental conditions. Carotenoids content increased only when soil drought occurred. Maximum quantum yield of PSII photochemistry was the most stable and stress-resistant parameter. Minimal fluorescence yield of the dark-adapted state was only sensitive to soil-atmospheric drought. Nonphotochemical quenching decreased under water stress, while parameters of the fast light curve based on chlorophyll fluorescence increased proportionally to the level of the stress load. We believe that these parameters are the most sensitive to the changes in the water supply of wheat plants, and are convenient for the rapid and noninvasive assessment of the wheat photosynthetic apparatus state under drought conditions.

Assessment of the adaptive and phytoremediation potential of Miscanthus×giganteus grown in flotation tailings

Mining activities produce enormous amounts of metal-contaminated waste that is the source of ecosystem pollution by metals. Owing to complex adverse environmental conditions, the surface of abandoned flotation tailings is completely devoid of vegetation cover and is therefore very susceptible to fluvial erosion, wind dispersal to neighboring ecosystems and leaching of heavy metals into ground waters. The aim of this study was to estimate the adaptive potential of Miscanthus?giganteus (Poaceae) to grow on flotation tailings without any input. In this field experiment, plants were grown for four months in flotation tailings and in unpolluted control chernozem soil. Plants accumulated and retained the major part of metals within their roots, exhibiting their very low transfer to aerial parts, which all define M.?giganteus as a phytoexcluder plant species. Plants grown in flotation tailings showed significant reduction in the net CO2 assimilation rate and growth parameters, and there was no negative impact on pigment content, maximum quantum yield of PSII photochemistry, lipid peroxidation level and total antioxidative capacity in leaves. The obtained results indicate that despite reduced growth, M.?giganteus can be cultivated for phytoremediation of flotation tailings.

秦王川盐沼湿地芦苇叶片比叶面积与光合效率的关联分析

PDF HTML阅读 XML下载 导出引用 引用提醒 秦王川盐沼湿地芦苇叶片比叶面积与光合效率的关联分析 DOI: 10.5846/stxb201807271607 作者: 作者单位: 西北师范大学地理与环境科学学院,西北师范大学地理与环境科学学院,西北师范大学地理与环境科学学院,西北师范大学地理与环境科学学院,西北师范大学地理与环境科学学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（41461013，41861009） The correlation analysis between specific leaf area and photosynthetic efficiency of Phragmites australis in salt marshes of Qinwangchuan Author: Affiliation: Northwest Normal University,Research Center of Wetland Resources Protection and Industrial Development Engineering of Gansu Province, College of Geography and Environmental Science, Northwest Normal University, Lanzhou,,, Fund Project: The Knowledge Innovation Program of the Chinese Academy of Sciences,China Postdoctoral Science Foundation,Joint Research Fund for Overseas Chinese Young Scholars 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:植物比叶面积（SLA）与光合效率的关联性分析，有助于理解植物叶片的光合产物分配与能量分配之间的权衡机制。该研究以秦王川国家湿地公园芦苇（Phragmites australis）种群为研究对象，沿芦苇群落末端至水域边缘分别依次设置：（I：土壤电导率（EC）2.3-2.8 ms/cm）、（Ⅱ：1.8-2.2 ms/cm）、（Ⅲ：0.8-1.5 ms/cm）3个试验样地，研究了秦王川盐沼湿地不同土壤盐分条件下芦苇叶片SLA与光合效率的关系。结果表明：随着土壤盐分含量的降低，湿地群落的高度、地上生物量逐渐增大，密度、光合有效辐射（PAR）呈逐渐减小的趋势；叶面积、株高、净光合速率（P < sub>n）、水分利用效率（WUE）和蒸腾速率（Tr）均呈逐渐增大的趋势，叶厚度逐渐减小，比叶面积呈先增加后减少的变化趋势，叶干重的变化趋势与比叶面积完全相反；芦苇叶片实际光合效率（Y（Ⅱ））、光化学淬灭系数（QP）和电子传递速率（ETR）呈先减少后增大的变化趋势，非光化学猝灭系数（NPQ）、调节性能量耗散的量子产额（Y（NPQ））和最大光化学效率（Fv/Fm）呈先增加后减少的变化趋势，非调节性能量耗散的量子产量（Y（NO））呈逐渐增大的变化趋势。在3个样地中，芦苇SLA与Y（Ⅱ）和ETR之间均呈极显著负相关关系（P < 0.01），SMA斜率的绝对值均呈先增大后减少的变化趋势。随土壤含盐量的梯度性变化，芦苇种群适时调整叶片构件模式以改变叶片电子传递速率和实际光化学效率，实现植物光合效率的最大化，反映了盐沼湿地植物的特殊生存策略和叶片构件模式。 Abstract:The analysis of the response of plant specific leaf area (SLA) and photosynthetic efficiency to soil salinity is helpful to understand the balance mechanism between photosynthetic product distribution and energy distribution in plant leaves. This study aims to examine the relationship between specific leaf area and photosynthetic efficiency of Phragmites australis in response to the soil salt gradient. The study area is located in Qinwangchuan National Wetland Park (36.47° N, 103.65° E), Gansu Province, China. The range of the selected site with the area of 100 m×100 m is from the edge to the central of the wetland, where the reed is the single dominant species. There are three sample plots set on the basis of the soil salt content. The results showed that with the soil salt content decreased gradually, the height of the wetland community and the ground biomass presented increasing trend correspondingly, while density, photosynthetic active radiation (PAR), and leaf thickness had the opposite trend. Plant height, leaf area, net photosynthetic rate (P < sub>n), transpiration rate (Tr), and water use efficiency (WUE) increased gradually, and the specific leaf area increased at the beginning and decreased afterwards, and leaf dry weight presented opposite trends compared with SLA. From plot I to plot Ⅲ, with the decreasing of the soil salt content, the effective quantum yield of PSⅡ photochemistry (Y(Ⅱ)), the photochemical quenching (QP), and the electron transport rate (ETR) firstly reduced then increased. The non-photochemical quenching (NPQ), the quantum yield of regulatory energy dissipation (Y(NPQ)), and the maximum efficiency of photosystem (PS) Ⅱ photochemistry (Fv/Fm) performed the increased-decreased changing trends. The quantum yield of non-regulatory energy dissipation (Y(NO)) showed increase trend. There were highly significantly negative correlation (P < 0.01) between SLA and Y(Ⅱ), and between SLA and ETR among three plots, and the absolute value of SMA slope firstly increased and then decreased. With the soil salinity gradient changes, the reeds species adjusted blade component model timely by changing ETR and Y(Ⅱ) to maximize plant photosynthetic efficiency, which reflected that the special survival strategy and leaf component model of plants in salt marsh wetland. 参考文献 相似文献 引证文献

Is time important in response of morpho-physiological parameters in Withania coagulans L. landraces to water deficit stress?

Withania coagulans is one of the most important medicinal species of the Solanaceae which has pharmacological properties for future research in drug development. Photosynthesis and morphological parameters in response to drought of this species have not been investigated as yet, though the issue is of interest. The factorial combination of four water deficit stress (20% (un-stressed control), 30%, 40% and 50% of FC depletion) and four landraces of W. coagulans (Fanuj, Khash, Saravan and Sarbaz) were laid out in a randomized complete design in a phytotron over the course of 180 days. The first, second, third and fourth samplings were performed every 45 day after imposing the treatments (DAT). The results demonstrated that increase in the water deficit stress levels, decreased minimal fluorescence (F0), leaf greenness, photosynthesis rate, plant height, leaf area, dry weight and quantum yield of PSII photochemistry )ФPSII(in all landraces and maximum photochemical efficiency of PSII (Fv/Fm) in Fanuj, but increased non-photochemical quenching)NPQ(and Fv/Fm in Saravan and Sarbaz landraces. The W. coagulans landraces such as Fanuj with the highest vector loadings of ФPSII at 135 and 180 DAT and Fv/Fm at 45 DAT and Sarbaz with the highest vector loading of F0 at 45 DAT were found suitable for unstressed and severe stress conditions, respectively. Among the chlorophyll fluorescence and morphological parameters, total dry weight had the significant positive correlations with plant height, leaf area and F0 at 45 DAT. Thus, this study indicated chlorophyll florescence should be measured at different phases and future studies should focus on the sensitivity of these parameters to detect potential times among subjects of different stresses. These parameters are easy, cheap, efficient and reliable physiological characteristics which can be used to guide the breeding of new resistant genotypes. According to results, W. coagulans can be called "Xerophytes Camel".

Elevated CO2 reduces the adverse effects of drought stress on a high-yielding soybean (Glycine max (L.) Merr.) cultivar by increasing water use efficiency

Soybean (Glycine max (L.) Merr.) is the world's most important grain legume. The impacts of climate change such as elevated CO2 and drought on soybean physiological and morphological responses are not well understood. This study evaluated the effects of elevated CO2 (ambient concentration + 200 mmol mol−1) and drought stress (35–45% of relative water content) on soybean leaf photosynthesis, chlorophyll fluorescence, stress physiological indexes, morphological parameters, biomass and yield over 2 years at the open-top chamber (OTC) experimental facility in North China. We found that drought decreased intrinsic efficiency of PSII (Fv'/Fm'), effective quantum yield of PSII photochemistry (ΦPSII), photochemical quenching coefficient (qP), and yield of soybean, increased nonphotochemical quenching (NPQ), peroxidase (POD), and malondialdehyde (MDA), but had no effect on superoxide dismutase (SOD) or soluble sugar content. Elevated [CO2] increased net photosynthetic rate (PN), water-use efficiency (WUE), ΦPSII, qP, SOD, soluble sugar content and yield of soybean. Elevated [CO2] enhanced the positive effects of drought on WUE, but reduced the negative effects of drought on ΦPSII and qP. Elevated [CO2] enhanced the resistance to drought by improving the capacity of photosynthesis and WUE in soybean leaves.

A correlative approach, combining chlorophyll a fluorescence, reflectance, and Raman spectroscopy, for monitoring hydration induced changes in Antarctic lichen Dermatocarpon polyphyllizum

Lichens are successful colonizers in extreme environments worldwide, and they are considered to have played an important role during the evolution of life. Here, we have used a correlative approach, combining three optical signals (chlorophyll a fluorescence (ChlF), reflectance, and Raman spectra), to monitor hydration induced changes in photosynthetic properties of an Antarctic chlorolichen Dermatocarpon polyphyllizum. We measured these three signals from this lichen at different stages (after 4 h, 24 h, and 48 h) of hydration, and compared the data obtained from this lichen in "dry state" as well as in different "hydrated state". We found that dry state of this lichen has: (1) no variable ChlF, (2) high reflectance, with no red-edge and almost zero photochemical reflectance index (PRI), and (3) low-intensity Raman bands of their carotenoids. Furthermore, 4 h of hydration, increased its relative water content (RWC) by 93%, showed red-edge in reflectance spectra, and changed the maximum quantum yield of PSII photochemistry (Fv/Fm) from 0 to 0.57 ± 0.01. We found that reflectance indices, normalized difference index (NDVI) and PRI, significantly differed between brown and black/green surface areas, at all hydration stages; whereas, a shift in the Raman ν1(CC) band, between brown and black/green surface areas, occurred in 24 h or 48 h hydrated samples. These data indicate that hydration shortly (within 4 h) activated functions of photosynthetic apparatus, and the de novo synthesis of carotenoids occured in 24 h or 48 h. Furthermore, exposure to high irradiance (2000 μmol photons m-2 s-1), in 48 h hydrated lichen, significantly reduced Fv/Fm (signifies photoinhibition) and increased PRI (represents changes in xanthophyll pigments). We conclude that the implication of such a correlative approach is highly useful for understanding survival and protective mechanisms on extremophile photosynthetic organisms.

Effects of paclobutrazol on the physiological characteristics of Malus halliana Koehne Seedlings under drought stress via principal component analysis and membership function analysis

To study the effect of paclobutrazol (PBZ) on Malus halliana seedlings under water stress, principal component analysis (PCA) and membership function analysis (MFV) were employed to evaluate the effects of PBZ on gas exchange, fluorescence, and physiological characteristics. M. halliana seedlings, each with approximately ten leaves, were subjected to drought conditions and different concentrations of exogenous PBZ (CK, C0, C1, C2, C3, and C4) were then applied in pot experiments. The results showed that the effects of PBZ were concentration dependent. Compared to the CK treatment, the use of PBZ increased the intercellular CO2 concentration (Ci), nonphotochemical quenching coefficient (NPQ), peroxidase activity (POD), relative electrical conductivity (REC), and proline (Pro) and malondialdehyde (MDA) contents. The POD activity was higher by 124.24, 132.26, 93.75, 77.42, 85.29, and 90.63% in the CK, C0, C1, C2, C3, and C4 groups, respectively, at 15 days than at 0 day. The decrease in the net photosynthetic rate (PN), stomatal conductance (gs), transpiration rate (E), maximum quantum yield of PS2 (ΦPSII), maximal quantum yield of PSII photochemistry (Fv/Fm), photochemical quenching coefficient (qP), catalase (CAT), and superoxide dismutase (SOD) activity were effectively controlled. The gs of the CK and C2 groups at 15 days were reduced by 55.74% and 22.55%, respectively, compared to that of the treated seedlings at 0 day. In summary, the results of the evaluation by PCA and MFV showed that the effect of PBZ on M. halliana seedlings under water stress was most significant when the concentration was 100 mg L−1.

Effects of leaf-to-fruit ratio on chlorophyll fluorescence parameters of walnut (Juglans regia L.) leaves

In this study, we investigated maximal quantum yield of PSII photochemistry(Fv/Fm),effective quantum yield of PSII photochemistry (ΦPSII), and nonphotochemical quenching (NPQ) of walnut (Juglans regia 'Xinxin2') leaves with different leaf-to-fruit ratios (LFRs). The results indicated that the increasing LFR increased the values of Fv/Fm, ΦPSII, and NPQ in leaves on the girdled shoot with one and two leaves, and decreased the values of Fv/Fm and ΦPSII in leaves on the girdled shoot with five leaves, whereas had no effect on the chlorophyll (Chl) fluorescence in leaves on the girdled shoot with three and four leaves. These results indicate that the effects of LFR on Chl fluorescence depend on a LFR range and show a transitional trend transition, and that excessive fruit load accelerates leaf senescence resulting in the destruction of the reaction center in PSII.

Chlorophyll fluorescence, yield and yield components of bread wheat affected by phosphate bio-fertilizer, zinc and boron under late-season heat stress

We examined effects of late-season heat stress (L-SHS) on chlorophyll (Chl) fluorescence parameters and yield of bread wheat as well as roles of phosphate bio-fertilizer (PB-F) and Zn and B to compensate for the likely effects of heat stress. Factors were planting date (21 November and 5 January to coincide with grain filling to L-SHS) as the main factor, no inoculation (control) and inoculation of the seeds with PB-F as the sub-factor, and foliar application of water (control), Zn, B, and Zn + B as 3 L ha-1 as sub-sub factor. Results revealed that L-SHS reduced maximal quantum yield of PSII photochemistry, effective quantum yield of PSII photochemistry, efficiency of PSII in the light-adapted state, and the grain yield. Moreover, L-SHS increased the nonphotochemical quenching. The PB-F mitigated the effects of L-SHS on Chl fluorescence, yield, and yield components. Among nutrients, the combined Zn + B was more effective in reducing the effects of L-SHS than that of Zn and B alone. Nevertheless, there was an interaction between foliar nutrients application and PB-F, suggesting that Zn application alone had a profound influence on improving Chl fluorescence parameters and increased yield in combination with PB-F.

Zinc accumulation, photosynthetic gas exchange, and chlorophyll a fluorescence in Zn-stressed Miscanthus × giganteus plants

Accumulation and distribution of zinc within Miscanthus × giganteus plants grown on elevated Zn concentrations and their photosynthetic performance were investigated. High concentrations of Zn in soils caused an increase of its concentrations in all plant organs. The bioconcentration factor, bioaccumulation factor, and translocation factor were lower than one indicating that M. × giganteus is an excluder plant species. Excessive Zn induced visible leaf damage, i.e. chlorosis and necrosis, only in the oldest leaves, pointing to Zn accumulation. Elevated amounts of Zn in leaves significantly lowered the photosynthetic rate, transpiration rate, stomatal conductance, intercellular CO2 concentrations, parameters of chlorophyll a fluorescence, and chlorophyll b content. Despite Zn excess in leaves, there was no severe reduction in the maximal quantum yield of PSII photochemistry, indicating a high photosynthetic capacity, high tolerance to elevated Zn concetrations, and ability of M. × giganteus to grow on Zn-contaminated soils.

Photochemistry and Antioxidative Capacity of Female and Male Taxus baccata L. Acclimated to Different Nutritional Environments.

In dioecious woody plants, females often make a greater reproductive effort than male individuals at the cost of lower growth rate. We hypothesized that a greater reproductive effort of female compared with male Taxus baccata individuals would be associated with lower female photochemical capacity and higher activity of antioxidant enzymes. Differences between the genders would change seasonally and would be more remarkable under nutrient deficiency. Electron transport rate (ETRmax), saturation photosynthetic photon flux corresponding to maximum electron transport rate (PPFsat), quantum yield of PSII photochemistry at PPFsat (ΦPPFsat), and chlorophyll a fluorescence and activity of antioxidant enzymes were determined in needles of T. baccata female and male individuals growing in the experiment with or without fertilization. The effects of seasonal changes and fertilization treatment on photochemical parameters, photosynthetic pigments concentration, and antioxidant enzymes were more pronounced than the effects of between-sexes differences in reproductive efforts. Results showed that photosynthetic capacity expressed as ETRmax and ΦPPFsat and photosynthetic pigments concentrations decreased and non-photochemical quenching of fluorescence (NPQ) increased under nutrient deficiency. Fertilized individuals were less sensitive to photoinhibition than non-fertilized ones. T. baccata female and male individuals did not differ in photochemical capacity, but females showed higher maximum quantum yield of PSII photochemistry (Fv/Fm) than males. The activity of guaiacol peroxidase (POX) was also higher in female than in male needles. We concluded that larger T. baccata female reproductive effort compared with males was not at the cost of photochemical capacity, but to some extent it could be due to between-sexes differences in ability to protect the photosynthetic apparatus against photoinhibition with antioxidants.

Effect of ammonium/nitrate ratio on pak choi (Brassica chinensis L.) photosynthetic capacity and biomass accumulation under low light intensity and water deficit

We conducted a hydroponic experiment in order to study effects of the ammonium/nitrate ratio (0:15, 5:10, 7.5:7.5, and 10:5) on photosynthetic characteristics and biomass accumulation in Brassica chinensis under low light intensity and water stress. Results showed that net photosynthetic rate, transpiration rate, intrinsic water-use efficiency, stomatal conductance, intercellular CO2 concentration, effective quantum yield of PSII photochemistry, electron transport rate, and nonphotochemical quenching were lower in the treatment (low light intensity and water deficit) than those in the control, whereas stomatal limitation increased. Minimum fluorescence, maximal quantum yield of PSII photochemistry, and photochemical quenching were largely unchanged. Pigment contents first increased and then decreased as the ammonium/nitrate ratios were altered, with significant differences between treatment and control observed at all ratios except for 10:5. Biomass first increased slightly and then decreased both in treated and control plants. Results suggest that economic losses caused by extreme conditions can be minimized by a proper adjustment of the ammonium/nitrate ratio.

The effect of galling aphids feeding on photosynthesis photochemistry of elm trees (Ulmus sp.)

Changes of chlorophyll (Chl) a fluorescence and photosynthetic pigment contents were analysed in galled leaves (visibly damaged and undamaged parts) and intact leaves. The values of minimal fluorescence of the dark-adapted state, maximal quantum yield of PSII photochemistry, effective quantum yield of PSII photochemical conversion, and photochemical quenching coefficient decreased in Ulmus pumila L. leaves galled by Tetraneura ulmi (L.) and in U. glabra Huds. galled by Eriosoma ulmi (L.). Colopha compressa (Koch.) feeding affected these parameters only in damaged parts of U. laevis Pall. galled leaves. The increasing number of T. ulmi galls progressively decreased photosynthetic performance. In gall tissues of all analysed aphid species, the lowest photosynthetic pigment content was found, indicating that the photosynthetic capacity must have been low in galls. Significant reduction of Chl and carotenoid contents were observed in damaged and undamaged portions of galled leaves only in the case of T. ulmi feeding.

Combined stresses of light and chilling on photosynthesis of Fraxinus mandschurica seedlings in northeastern China

The chilling and light stresses were experimentally created to explore photosynthesis of Fraxinus mandshurica seedlings in northeast China. Net photosynthetic rate, stomatal conductance, and transpiration rate decreased significantly with the decline of temperature and light. Significant interaction effects of light and chilling were observed on gas exchange of photosynthesis. The minimal fluorescence yield of the dark-adapted state (F0) increased with increasing light and decreasing temperature. Both high and low light stresses induced the decreases of the maximal quantum yield of PSII photochemistry (Fv/Fm), photochemical quenching coefficient (qP), nonphotochemical quenching (NPQ), and electron transport rate. Decline of Fv/Fm and increased F0 were observed under decreasing temperatures. Decreased NPQ and qP at frost temperature suggest that F. mandschurica failed to dissipate excess light energy. No interactive effects of chilling and light on chlorophyll fluorescence parameters suggests that F. mandschurica seedlings might be adapted to combined stresses of light and chilling.