Effect of light intensity on partitioning of photosynthetic electron transport to photorespiration in four subtropical forest plants

Photosynthetic rate (Pn) and the partitioning of noncyclic photosynthetic electron transport to photorespiration (Jo) in seedlings of four subtropical woody plants growing at three light intensities were studied in the summer time by measurements of chlorophyll fluorescence and CO2 exchange. Except Schima superba, an upper canopy tree species, the tree species Castanopsis fissa and two understory shrubs Psychotria rubra, Ardisia quinquegona had the highest Pn at 36% of sunlight intensity. The total photosynthetic electron transport rate (JF) and the ratio of Jo/JF were elevated in leaves under full sunlight. Jo/JF ratio reached 0.5-0.6 and coincided with the increasing of oxygenation rate of Rubisco (Vo), the activity of glycolate oxidase and photorespiration rate at full sunlight. It is suggested that an increasing partitioning proportion of photosynthetic electron transport to photorespiration might be one of the protective regulation mechanisms in forest plant under strong summer light and high tempe     

Effects of nitrogen addition on photosynthetic characteristics of Leymus chinensis in the temperate grassland of Nei Mongol,China北大核心CSCD

Aims The increased atmospheric nitrogen (N) deposition due to human activity and climate change greatly causes grassland ecosystems shifting from being naturally N-limited to N-eutrophic or N-saturated, and further affecting the growth of grass species. The aims of this study are: 1) to evaluate the effects of different N addition levels on morphology and photosynthetic characteristics of Leymus chinensis; 2) to determine the critical N level to facilitate L. chinensis growth. Methods We conducted a different N addition levels experiment in dominant species in the temperate steppe of Nei Mongol. The aboveground biomass, morphological and leaf physiological traits, pigment contents, chlorophyll a fluorescence parameters and biochemical parameters of L. chinensis were investigated. Important findings Our results showed that aboveground biomass first increased and then decreased with the increased N, having the highest values at the 10 g N·m-2·a?1 treatment, but the 25 g N·m-2·a?1 still significantly increased the aboveground biomass relative to 0 g N·m-2·a?1. Leymus chinensis accommodate low N situation through allocating less N to carboxylation system and decreasing leaf mass per area (LMA) in order to get more light energy. Moderate N addition captured more light energy through increasing total chlorophyll (Chl) contents and decreasing the ratio of Chl a/b. Moderate N addition increased LMA, carboxylation efficiency, maximum car boxylation rate (Vcmax), maximum electron transport rate (Jmax) and decreased Jmax/Vcmax, thus allocating more N to carboxylation system to enhance carboxylation capability. Moreover, the photochemical activity of PSII was increased through higher effective quantum yield of PSII photochemistry, electron transport rate and photochemical quenching coefficient. Excessive N addition had negative effects on physiological variables of L. chinensis due to lower carboxylation capability and photochemical activity of PSII, further leading to decreased net photosynthetic rate, whereas increased non-photochemical quenching coefficient and carotenoids played the role in the dissipation of excess excitation energy. Overall, moderate N addition facilitated the photosynthetic characteristics of dominant species, but excessive N addition inhibited photosynthetic characteristics. The most appropriate N addition for the growth of L. chinensis was 5-10 g N·m-2·a?1 in the temperate steppe of Nei Mongol, China.     

Maize grain concentrations and above-ground shoot acquisition of micronutrients as affected by intercropping with turnip, faba bean, chickpea, and soybean

Most research on micronutrients in maize has focused on maize grown as a monocrop. The aim of this study was to determine the effects of intercropping on the concentrations of micronutrients in maize grain and their acquisition via the shoot. We conducted field experiments to investigate the effects of intercropping with turnip (Brassica campestris L.), faba bean (Vicia faba L.), chickpea (Cicer arietinum L.), and soybean (Glycine max L.) on the iron (Fe), manganese (Mn), copper (Cu) and zinc (Zn) concentrations in the grain and their acquisition via the above-ground shoots of maize (Zea mays L.). Compared with monocropped maize grain, the grain of maize intercropped with legumes showed lower concentrations of Fe, Mn, Cu, and Zn and lower values of their corresponding harvest indexes. The micronutrient concentrations and harvest indexes in grain of maize intercropped with turnip were the same as those in monocropped maize grain. Intercropping stimulated the above-ground maize shoot acquisition of Fe, Mn, Cu and Zn, when averaged over different phosphorus (P) application rates. To our knowledge, this is the first report on the effects of intercropping on micronutrient concentrations in maize grain and on micronutrients acquisition via maize shoots (straw+grain). The maize grain Fe and Cu concentrations, but not Mn and Zn concentrations, were negatively correlated with maize grain yields. The concentrations of Fe, Mn, Cu, and Zn in maize grain were positively correlated with their corresponding harvest indexes. The decreased Fe, Mn, Cu, and Zn concentrations in grain of maize intercropped with legumes were attributed to reduced translocation of Fe, Mn, Cu, and Zn from vegetative tissues to grains. This may also be related to the delayed senescence of maize plants intercropped with legumes. We conclude that turnip/maize intercropping is beneficial to obtain high maize grain yield without decreased concentrations of Fe, Mn, Cu, and Zn in the grain. Further research is required to clarify the mechanisms underlying the changes in micronutrient concentrations in grain of intercropped maize.     

Variations and interrelationships of foliar hydraulic and photosynthetic traits for Larix gmelinii北大核心CSCD

Aims: Variations and potential trade-offs of leaf hydraulic and photosynthetic traits are essential for assessing and predicting the effect of climate change on tree survival, growth and distribution. Our aims were to examine variations and interrelationships of leaf hydraulic and photosynthetic traits in response to changes in site conditions for Dahurian larch (Larix gmelinii)-a dominant tree species in Chinese boreal forests. Methods: This study was conducted at the Maoershan Forest Ecosystem Research Station. A transect of 27 year-old Dahurian larch plantation was established that consisted of five plots extending from the valley to the ridge of a slope. The predawn leaf water potential (ψpre), area- and mass-based leaf hydraulic conductance (Karea and Kmass, respectively), resistance to embolism capacity (P50), leaf mass per area (LMA), net photosynthetic rate (A), and leaf nitrogen content (N) were measured in August 2016. Important findings: The ψpre, Karea, Kmass, P50, A, LMA, and N all varied significantly among the plots (p < 0.05), indicating significant intra-specific variations in these traits in response to the changes in site conditions. The P50 was significantly (p < 0.05) correlated with ψpre, Karea or Kmass, suggesting that a trade-off between hydraulic efficiency and safety exist within the species to some degree. There were significant (p < 0.05) pairwise correlations between A, LMA, and N. Nevertheless, there was no significant (p < 0.05) correlation between the measured photosynthetic traits and hydraulic traits. We concluded that the intra-specific variations and multiple interrelationships of the leaf hydraulic and photosynthetic traits for the larch reflect the plasticity of its leaf traits and strategies of its survival and growth as a result of its acclimation to diverse site conditions.     

Genetic analysis of biomass and photosynthetic parameters in wheat grown in different light intensities

Growth light intensities largely determine photosynthesis, biomass, and grain yield of cereal crops. To explore the genetic basis of light responses of biomass and Researchphotosynthetic parameters in wheat(Triticum aestivum L.),a quantitative trait locus(QTL) analysis was carried out in a doubled haploid(DH) population grown in low light(LL),medium light(ML), and high light(HL), respectively. The results showed that the wheat seedlings grown in HL produced more biomass with lower total chlorophyll content(Chl), carotenoid content, and maximum photochemical efficiency of photosystem II(Fv/Fm) while the wheat seedlings grown in LL produced less biomass with higher Chl compared with those grown in ML. In total, 48 QTLs were identified to be associated with the investigated parameters in relation to growth light intensities. These QTLs were mapped to 15 chromosomes which individually explained6.3%–36.0% of the phenotypic variance, of which chromo-somes 3A, 1D, and 6B were specifically involved in LL response, 5D and 7A specifically involved in ML response,and 4B specifically involved in HL response. Several light-responsive QTLs were co-located with QTLs for photosynthetic parameters, biomass, and grain weight under various conditions which may provide new hints to uncover the genetic control of photosynthesis, biomass, and grain weight.     

Impact of Elevated PCO2 on Mass Flow of Reduced Nitrogen in Trees

To analyze the effects of elevated carbon dioxide concentration （PCO2） on the mass flow of reduced nitro- gen （N） in the phloem and xylem of trees, juvenile beech （Fagus sylvatica L.） and spruce （Picea abies （L.） Karst.） were grown in phytotrons and exposed to ambient and elevated PCO2 （plus 687.5 mg/m^3 CO2） for three growing seasons. Elevated PCO2 significantly decreased the mass flow of N from the shoot to roots of beech by significantly reducing the concentration of soluble amino compounds in the phloem, even if the area of conductive phloem of cross-sectional bark tissue was significantly increased, because of less callus deposition in the sieve elements. In spruce, the downward mass flow of reduced N also tended to be decreased, similar to that in beech. Resembling findings in the phloem, N mass flow from roots to shoot in both tree species was significantly diminished owing to significantly reduced concentrations of amino compounds in the xylem and a lower transpiration rate. Therefore, the mass flow of reduced N between shoots and roots of trees was mainly governed by the concentrations of soluble amino compounds in the phloem and xylem in relation to the loading of reduced N in both long-distance transport pathways.     

Induction of the AOX1D Isoform of Alternative Oxidase in A. thaliana T-DNA Insertion Lines Lacking Isoform AOX1A Is Insufficient to Optimize Photosynthesis when Treated with Antimycin A

Plant respiration is characterized by two pathways for electron transfer to O2, namely the cytochrome pathway （CP） that is linked to ATP production, and the alternative pathway （AP）, where electrons from ubiquinol are directly transferred to O2 via an alternative oxidase （AOX） without concomitant ATP production. This latter pathway is well suited to dispose of excess electrons in the light, leading to optimized photosynthetic performance. We have characterized T- DNA-insertion mutant lines of Arabidopsis thaliana that do not express the major isoform, AOXIA. In standard growth conditions, these plants did not show any phenotype, but restriction of electron flow through CP by antimycin A, which induces AOXIA expression in the wild-type, led to an increased expression of AOXID in leaves of the aoxla-knockout mutant. Despite the increased presence of the AOX1D isoform in the mutant, antimycin A caused inhibition of photosyn- thesis, increased ROS, and ultimately resulted in amplified membrane leakage and necrosis when compared to the wild- type, which was only marginally affected by the inhibitor. It thus appears that AOX1 D was unable to fully compensate for the loss of AOXIA when electron flow via the CP is restricted. A combination of inhibition studies, coupled to metabolite profiling and targeted expression analysis of the P-protein of glycine decarboxylase complex （GDC）, suggests that the aoxla mutants attempt to increase their capacity for photorespiration. However, given their deficiency, it is intriguing that increase in expression neither of AOX1D nor of GDC could fully compensate for the lack of AOXIA to optimize pho- tosynthesis when treated with antimycin A. We suggest that the aoxla mutants can further be used to substantiate the current models concerning the influence of mitochondrial redox on photosynthetic performance and gene expression.     

Nitric Oxide Is Required for Homeostasis of Oxygen and Reactive Oxygen Species in Barley Roots under Aerobic Conditions

Oxygen, the terminal electron acceptor for mitochondrial electron transport, is vital for plants because of its role in the production of ATP by oxidative phosphorylation. While photosynthetic oxygen production contributes to the oxygen supply in leaves, reducing the risk of oxygen limitation of mitochondrial metabolism under most conditions, root tissues often suffer oxygen deprivation during normal development due to the lack of an endogenous supply and isolation from atmospheric oxygen.     

Modulating Effect of Far-Red Light on Activities of Alternative Electron Transport Pathways Related to Photosystem I

Barley (Hordeum vulgare L.) leaves were irradiated with far-red (FR) light of various intensities after different periods of dark adaptation in order to investigate activities of alternative electron transport pathways related to photosystem I (PSI). Photooxidation of P700, the primary electron donor of PSI, was saturated at FR light intensity of 0.15 μmol quanta/(m² s). As the photon flux density was raised in this range, the slow and middle components in the kinetics of P700⁺ dark reduction increased, whereas the fast component remained indiscernible. The amplitudes of the slow and middle components diminished upon further increase of FR photon flux density in the range 0.15–0.35 μmol quanta/(m² s) and remained constant at higher intensities. The fast component of P700⁺ reduction was only detected after FR irradiation with intensities above 0.15 μmol quanta/(m² s); the light-response curve for this component was clearly sigmoid. In dark-adapted barley leaves, three stages were distinguished in the kinetics of P700 photooxidation, with the steady state for P700⁺ achieved within about 3 min. In leaves predarkened for a short time, the onset of FR irradiation produced a very rapid photooxidation of P700. As the duration of dark exposure was prolonged, the amplitude of the first peak in the kinetic curve of photoinduced P700 photooxidation was diminished and the time for attaining the steady-state oxidation level was shortened. After a brief dark adaptation of leaves, ferredoxin-dependent electron flow did not appreciably contributed to the kinetics of P700⁺ dark reduction, whereas the components related to electron donation from stromal reductants were strongly retarded. It is concluded that FR light irradiation, selectively exciting PSI, suffices to modulate activities of alternative electron transport routes; this modulation reflects the depletion of stromal reductants due to continuous efflux of electrons from PSI to oxygen under the action of FR light. __________ Translated from Fiziologiya Rastenii, Vol. 52, No. 6, 2005, pp. 805–813. Original Russian Text Copyright ? 2005 by Egorova, Drozdova, Bukhov.     

The photosynthetic irradiance-response of Norway spruce exposed to a long-term elevation of CO2 concentration

During an open-top chamber experiment performed in a mountain stand of young (12-year-old) Norway spruce (Picea abies [L.] Karst.), the trees were exposed to one of two CO² concentrations (ambient CO², AC, or AC + 350 μmol mol-1 = elevated CO₂, EC) continuously over three growing seasons. To evaluate the EC influence, measurements of the relations between the rate of net CO₂ uptake (P _N ) and incidental photosynthetically active photon flux density (PPFD), as well as the content of photosynthetic pigments and chlorophyll (Chl) a fluorescence were taken in the third growing season. The short-term response to EC was evident mainly on ribulose-1,5-bisphosphate carboxylase/oxygenase kinetics without any significant change to the utilization of radiant energy. The long-term effect of EC was responsible for a decrease in P _N , content of Chl a + b, Fv/Fm ratio, quantum yield of fluorescence, and photochemical quenching. Changes of stoichiometry between the electron transport, Calvin cycle and the end-product synthesis were confirmed for responses to the long-term import of EC and led to a definition of the photosynthetic acclimation to EC in Norway spruce. This revised version was published online in August 2006 with corrections to the Cover Date.     

Physiological Responses of Zea mays Seedlings to Interactions Between Cadmium and Salinity

The effects of 0, 2.5, 5.0, and 10.0 pmol/L Cd^2＋（Cd（NO3）2.4H2O） and 0, 10, 25, 50, and 100 mmol/L NaCl on growth, photosynthesis and the content of some ions in maize （Zea mays L.） were investigated in the present study. With Increasing concentrations of Cd^2＋ or NaCI alone in Hoagland nutrient solution, the chlorophylls and starch content decreased. Combination treatment with salinity and cadmium increased the negative effects observed following the two stresses alone. Plants exhibiting growth retardation in response to one mild stress factor （25-50 mmol/L NaCl） became more tolerant to the other stress factor （Cd）. The exposure of plants to cadmium caused a partial reversal of the effects of salinity. Root and shoot growth, ion accumulation and levels of photosynthetic pigments were improved at moderate concentrations of the two stress factors Imposed jointly.     

The response of electron transport mediated by active NADPH dehydrogenase complexes to heat stress in the cyanobacterium Synechocystis 6803

The electron-transport machinery in photosynthetic membranes is known to be very sensitive to heat. In this study, the rate of electron transport (ETR) driven by photosystem I (PSI) and photosystem II (PSII) during heat stress in the wild-type Synechocystis sp. strain PCC 6803 (WT) and its ndh gene inactiva-tion mutants △ndhB (M55) and △ndhD1/ndhD2 (D1/D2) was simultaneously assessed by using the novel Dual-PAM-100 measuring system. The rate of electron transport driven by the photosystems (ETRPSs) in the WT, M55, and D1/D2 cells incubated at 30℃ and at 55℃ for 10 min was compared. Incubation at 55 ℃ for 10 min significantly inhibited PSII-driven ETR (ETRPSII) in the WT, M55 and D1/D2 cells, and the ex-tent of inhibition in both the M55 and D1/D2 cells was greater than that in the WT cells. Further, PSI-driven ETR (ETRPSI) was stimulated in both the WT and D1/D2 cells, and this rate was increased to a greater extent in the D1/D2 than in the WT cells. However, ETRPSI was considerably inhibited in the M55 cells. Analysis of the effect of heat stress on ETRPSs with regard to the alterations in the 2 active NDH-1 complexes in the WT, M55, and D1/D2 cells indicated that the active NDH-1 supercomplex and medi-umcomplex are essential for alleviating the heat-induced inhibition of ETRPSII and for accelerating the heat-induced stimulation of ETRPSI, respectively. Further, it is believed that these effects are most likely brought about by the electron transport mediated by each of these 2 active NDH-1 complexes.     

Impacts of Elevated CO2 Concentration on Biochemical Composition, Carbonic Anhydrase, and Nitrate Reductase Activity of Freshwater Green Algae

To investigate the biochemical response of freshwater green algae to elevated CO2 concentrations, Chlorella pyrenoidosa Chick and Chlamydomonas reinhardtii Dang cells were cultured at different CO2 concentrations within the range 3-186μmol/L and the biochemical composition, carbonic anhydrase (CA),and nitrate reductase activities of the cells were investigated. Chlorophylls (Chl), carotenoids, carbonhydrate,and protein contents were enhanced to varying extents with increasing CO2 concentration from 3-186μmol/L. The CO2 enrichment significantly increased the Chl a/Chl b ratio in ChloreUa pyrenoidosa, but not in Chlamydomonas reinhardtii. The CO2 concentration had significant effects on CA and nitrate reductase activity. Elevating CO2 concentration to 186μmol/L caused a decline in intracellular and extracellullar CA activity. Nitrate reductase activity, under either light or dark conditions, in C. reinhardtii and C. pyrenoidosa was also significantly decreased with CO2 enrichment. From this study, it can be concluded that CO2 enrichment can affect biochemical composition, CA, and nitrate reductase activity, and that the biochemical response was species dependent.     

Application and comparison of remote sensing GPP models with multi-site data in China北大核心CSCD

Aims Estimation of gross primary productivity (GPP) of vegetation at the global and regional scales is important for understanding the carbon cycle of terrestrial ecosystems. Due to the heterogeneous nature of land surface, measurements at the site level cannot be directly up-scaled to the regional scale. Remote sensing has been widely used as a tool for up-saling GPP by integrating the land surface observations with spatial vegetation patterns. Although there have been many models based on light use efficiency and remote sensing data for simulating terrestrial ecosystem GPP, those models depend much on meteorological data; use of different sources of meteorological datasets often results in divergent outputs, leading to uncertainties in the simulation results. In this study, we examines the feasibility of using two GPP models driven by remote sensing data for estimating regional GPP across different vegetation types. Methods Two GPP models were tested in this study, including the Temperature and Greenness Model (TG) and the Vegetation Index Model (VI), based on remote sensing data and flux data from the China flux network (ChinaFLUX) for different vegatation types for the period 2003-2005. The study sites consist of eight ecological stations located in Xilingol (grassland), Changbaishan (mixed broadleaf-conifer forest), Haibei (shrubland), Yucheng (cropland), Damxung (alpine meadow), Qianyanzhou (evergreen needle-leaved forest), Dinghushan (evergreen broad-leaved forest), and Xishuangbanna (evergreen broad-leaved forest), respectively. Important findings All the remote sensing parameters employed by the TG and VI models had good relationships with the observed GPP, with the values of coefficient of determination, R2, exceeding 0.67 for majority of the study sites. However, the root mean square errors (RMSEs) varied greatly among the study sites: the RMSE of TG ranged from 0.29 to 6.40 g·m-2·d-1, and that of VI ranged from 0.31 to 7.09 g·m-2·d-1, respectively. The photosynthetic conversion coefficients m and a can be up-scaled to a regional scale based on their relationships with the annual average nighttime land surface temperature (LST), with 79% variations in m and 58% of variations in a being explainable in the up-scaling. The correlations between the simulated outputs of both TG and VI and the measured values were mostly high, with the values of correlation coefficient, r, ranging from 0.06 in the TG model and 0.13 in the VI model at the Xishuangbanna site, to 0.94 in the TG model and 0.89 in the VI model at the Haibei site. In general, the TG model performed better than the VI model, especially at sites with high elevation and that are mainly limited by temperature. Both models had potential to be applied at a regional scale in China.     

Mapping of Defense Response Gene Homologs and Their Association with Resistance Loci in Maize

Defense response genes in higher plant species are involved in a variety of signal transduction pathways and biochemical reactions to counterattack invading pathogens. In this study, a total of 366 non-redundant defense response gene homologs （DRHs）, including 124 unigenes/expressed sequence tags, 226 tentative consensuses, and 16 DRH contigs have been identified by mining the Maize Genetics and Genomics and The Institute for Genomic Research maize databases using 35 essential defense response genes. Of 366 DRHs, 202 are mapped to 152 loci across ten maize chromosomes via both the genetic and in silico mapping approaches. The mapped DRHs seem to cluster together rather than be evenly distributed along the maize genome. Approximately half of these DHRs are located in regions harboring either major resistance genes or quantitative trait loci （QTL）. Therefore, this comprehensive DRH linkage map will provide reference sequences to identify either positional candidate genes for resistance genes and/or QTLs or to develop makers for fine-mapping and marker-assisted selection of resistance genes and/or QTLs.