Determination of photosynthetic parameters in two seawater-tolerant vegetables

It is difficult to determine the photosynthetic parameters of non-fiat leaves/green stems using photosynthetic instruments, due to the unusual morphology of both organs, especially for Suaeda salsa and Salicornia bigelovii as two seawater-tolerant vegetables. To solve the problem, we developed a simple, practical, and effective method to measure and calculate the photosynthetic parameters （such as PN, gs, E） based on unit fresh mass, instead of leaf area. The light/COftemperature response curves of the plants can also be measured by this method. This new method is more effective, stable, and reliable than conventional methods for plants with non-flat leaves. In addition, the relative notes on measurements and calculation of photosynthetic parameters were discussed in this paper. This method solves technical difficulties in photosynthetic parameter determination of the two seawater-tolerant vegetables and similar plants.

Measurement of algae PSII photosynthetic parameters using high-frequency excitation flashes

We establish a system to measure the functional absorption cross section of photosystem lI （PSII） （O-PSII） and maximum quantum yield of photochemistry in PSII （Fv/Fm）. The system utilizes a sequence of high-frequency excitation flashes at microsecond intervals to induce a microsecond-level fluorescence yield curve. Parameters o-Psii and Fv/Fm are calculated by fitting the curve using nonlinear regression. Experimental results show that the relative standard deviation （RSD） of the system is less than 3%, and the correlation coefficient of Fv/Fm values measured by this system and those measured by pulse amplitude modulation method is 0.950.

Photosynthetic Excitation Pressure Causes Violaxanthin De-epoxidation in Aging Cabbage （Brassica Oleracea L.） Leaves

The purpose of the present studies was analysis of the age induced changes in photochemical efficiency and xanthophyils cycle pigments of the primary cabbage （Brassica oleracea L. cv. Capitata f. alba） leaves. Photochemical efficiency of photosystem Ⅱ （PS Ⅱ） was studied by a pulse amplitude modulated chlorophyll fluorescence apparatus, chlorophyll concentration was analysis spectrophotometrically and xanthophyll cycle pigments were estimated by high-pressure liquid chromatography （HPLC）. Leaf senescence was accompanied with a decrease both in chlorophylls concentration, the photochemical efficiency and rate constant for PS Ⅱ photochemistry whereas non-photochemical parameters increased. Excitation pressure （1-qP） which is a measure of relative lumen acidification increased by 1.2x in aging leaves. The maximum quantum yield of PS Ⅱ showed no significant change. The level of de-epoxidised xanthophylls increased but the concentration of mono- and di-epoxy xanthophylls decreased in aging leaves. A linear relationship between the excitation pressure and the depoxidation state of the xanthophyll cycle pigments and lutein, during the onset of senescence suggests that excitation pressure can be used as a sensor for monitoring the onset of senescence as well for the de-epoxidation state of the xanthophylls responsible for non-photochemical quenching in stressed leaves.

Use of infrared thermal imaging to diagnose health of Ammopiptanthus mongolicus in northwestern China

Population of the rare and endangered species Ammopiptanthus mongolicus （Maxim.） Cheng f. declined rapidly in China＇s add region and Central Asia. There is an urgent need to protect this species, which is particularly important in maintaining biodiversity throughout the arid region of northwestern China. By analyzing the infrared thermal images based on plant-transpiration transfer coef- ficient （hat） and photosynthetic parameters, we made quantitative and accurate diagnoses of the plant growth and health status of A. mongolicus. Using an LI-COR6400 photosynthesis system, we measured the net photosynthetic rate （Pn）, stomatal conductance （Gs）, and transpiration rate （Tr）. Infrared thermal images obtained in the field were processed by ENVI4.8 software to calculate surface tem- peratures of the plant subjects. We found that the plant transpiration transfer coefficient of A. mongolicus was inthe order of old plants 〉young plants 〉intermediate-aged plants. Declining health levels of young, intermediate, and old plants were divided into three categories： 〈0.4, 0.4-0.7, and 〉0.7. The coefficient showed a significant negative correlation with Tr, Gs, and Pn, indicating that they can simultaneously reflect the state of plant growth. By estab- lishing hat and photosynthetic parameters in regression model Y = a-blnx, we can accurately diagnose plant growth and decline of plant health conditions.

Variations in leaf functional traits and physiological characteristics of Abies georgei var.smithii along the altitude gradient in the Southeastern Tibetan Plateau

Variations in leaf functional traits of Abies georgei var. smithii at 3700, 3900, 4100, 4300, and 4390 m altitude were investigated in 15 typical plots in the Southeastern Tibetan Plateau. In each plot, three seedlings were selected, of which functional leaves in current-year sunny branches were chosen for the measurement of morphological, photosynthetic, and physiological and biochemical characteristics, and their variations were analyzed. Results showed that significant variations existed among the leaf functional traits of A. georgei var. smithii along the altitudinal gradient, as well as their physiological adaption indicators. Leaf area decreased, while the mass per area and thickness of leaf increased at an altitude above 4,100 m. The maxima of pigment, total nitrogen concentration, net photosynthesis rate during light-saturated, and when water use efficiency appeared at 4100 m altitude. In addition, A. georgei var. smithii seedlings regulated the activities of superoxide dismutase and ascorbate peroxidase to resist abiotic stress under 4100 m altitude. Meanwhile, malondialdehyde concentration and the dark respiration rate rapidly increased, which indicates that A. georgei var. smithii seedlingssuffered from heavy abiotic stress from 4100 m to 4390 m altitude. Basing on variations in leaf functional traits along the altitude gradient, we inferred that 4100 m altitude was the suitable region for A. georgei var. smithii growth in the Sygera Mountain. Moreover, the harsh environment was the main limiting factor for A. georgei var. smithii population expansion to high altitude.

Effects of Different Potassium Stress on Leaf Photosynthesis and Chlorophyll Fluorescence in Maize (Zea Mays L.) at Seedling Stage

Leaf early senescence caused by nutrition deficiency is one of the major limitation reasons in the world crop production. Potassium (K) is one of important nutrient elements in crop growth, which modifies dozens of enzyme activations and controls stomatal movement of photosynthesis. The yield and quality of maize (Zea Mays L.) have been limited due to K deficiency in plough layer soil. However, the mechanism of K deficiency tolerance is not fully understood in maize. In this study, two inbred lines, 099 (tolerance to potassium deficiency) and 835 (sensitive to potassium deficiency) were carried out to investigate the variations of chlorophyll content, photosynthetic and chlorophyll fluorescence parameters related with senescence under different K+ concentrations in maize at seedling stage. The results showed that the Chlorophyll a, b and (a + b) of 835 were significantly decreased under different K deficiency treatments, whereas those of 099 were remained normal. In addition, 099 showed a lower stomatal restriction and higher electronic transition capacity under different K deficiency treatments. The variations of F0, Fv/Fm, ΦPSⅡ, qP and NPQ in 835 were largely higher than those in 099. These results indicated that the inbred line 099 tolerance to K deficiency could keep chlorophyll content to maintain photosynthesis and to alleviate the injury of PSII under K deficiency condition. This study should contribute to explaining the physiological mechanism tolerance nutrition deficiency and improving breeding program in maize.

Seasonal and interannual variations of ecosystem photosynthetic characteristics in a semi-arid grassland of Northern China

The ecosystem apparent quantum yield(α),maximum rate of gross CO_(2) assimilation(Pmax)and daytime ecosystem respiration rate(R.),reflecting the physiological functioning of ecosystem,are vital photosynthetic parameters for the estimation of ecosystem carbon budget.Climatic drivers may affect photosynthetic parameters both directly and indirectly by altering the response of vegetation.However,the relative contribution and regulation pathway of environmental and physiological controls remain unclear,especially in semi-arid grasslands.We analyzed seasonal and interannual variations of photosynthetic parameters derived from eddy-covariance observation in a typical semi-arid grassland in Inner Mongolia,Northern China,over 12 years from 2006 to 2017.Regression analyses and a structural equation model(SEM)were adopted to separate the contributions of environmental and physiological effects.The photosynthetic parameters showed unimodal seasonal patterns and significantly interannual variations.Variations of air temperature(T,)and soil water content(SWC)drove the seasonal patterns of photosynthetic parameters,while SWC predominated their interannual variations.Moreover,contrasting with the predominant roles of T,onαand Ra,SWC explained more variance of Pmax than T,Results of SEM revealed that environmental factors impacted photosynthetic parameters both directly and indirectly through regulating physiological responses reflected by stomatal conductance at the canopy level.Moreover,leaf area index(LAl)directly affectedα,Pmax and R,and dominated the variation of Pmax.On the other hand,SWC influenced photosynthetic parameters indirectly through LAl and canopy surface conductance(gc).Our findings highlight the importance of physiological regulation on the photosynthetic parameters and carbon assimilation capacity,especially in water-limitedgrassland ecosystems.

Wheat Growth and Photosynthesis as Affected by Oxytetracycline as a Soil Contaminant

Extensive worldwide use of oxytetracycline （OTC）, a member of the tetracyclines, has resulted in its accumulation in soils, posing a potential risk to food production and safety. A pair of OTC-sensitive （Heyou 1） and OTC-tolerant （Yannong 21） wheat （Tritieum aestivum L.） cultivars was compared hydroponically at 0.01, 0.02, 0.04, and 0.08 mmol L-10TC in terms of wheat growth and photosynthesis. Biomass and shoot length decreased significantly with the addition of OTC, with the decreases in dry biomass and shoot length being 5.61%-13.75% and 3.33%-8.57% larger, respectively, for Heyou 1 than Yannong 21. Photosynthesis of Heyou 1 was suppressed by OTC as indicated by the significant decreases in photosynthetic rate （PN）, transpiration rate （TR）, and stomatal conductance （GS） and the significant increase in intercellular CO2 concentrations （CI）, at all OTC levels. Stomatal limitation （LS） and water use eftlciencies （WUE） of Heyou i also increased significantly, but not at 0.08 mmol L-10TC. However, photosynthesis of Yannong 21 was suppressed by OTC only at high OTC levels from 0.02 to 0.08 mmol L-1 as indicated by the decreases in PN, GS, TR, and LS; at 0.01 mmol L-10TC, PN, CI, GS, and TR significantly increased. It was noted that WUE of Yannong 21 was not affected by OTC addition. The results from this hydroponic test suggested that OTC had a potential risk to crop growth through inhibition of photosynthesis, requiring further confirmation with soil tests.

Effects of drought stress on photosynthesis and chlorophyll fluorescence images of soybean(Glycine max)seedlings

The main purpose of this research is to provide a theoretical foundation for the screening of drought-resistant soybean varieties and to establish an efficient method to detect the PSII actual photochemical quantum yields efficiently.Three soybean varieties were compared in this experiment after 15 d when they were planted in a greenhouse.These varieties were then exposed to light drought stress(LD)and serious drought stress(SD)conditions.With five times’measurement,chlorophyll fluorescence and soil-plant analysis development considered as the main basis for this study.Several parameters in SD conditions significantly reduced,such as net photosynthetic rates(Pn),stomatal conductance(Gs),PSII primary light energy conversion efficiency(Fv/FM),PSII actual photochemical quantum yields[Y(II)],photochemical quenching coefficient(qP)and non-photochemical quenching coefficient(qN).The soybeans in the seedling stage adapted to the inhibitory effect of drought stress on photosynthesis through stomatal limitation.Under serious drought stress,non-stomatal limitation damaged the plant photosynthetic system.The amplitudes of Pn and Y(II)of drought-resistant Qihuang 35 were lower than those of the two other varieties.Based on the data of this study,a new method had been developed to detect Y(II)which reflected the photosynthetic capacity of plant,R=0.85989,u=0.048803 when using multiple linear regression,and R=0.84285,u=0.054739 when using partial least square regression.

A comparative study on different multiple cropping patterns of Bupleurum chinense

Bupleurum chinense is a genuine medicinal material in Shanxi Province,and planting B.chinense is one of the main sources for local farmers to increase their income.In B.chinense cultivation,wheat-B.chinense,maize-B.chinense and soybean-B.chinense are commonly used as multiple cropping patterns.In the present study,we studied the effects of three different multiple cropping patterns on N,P and K levels of soil,photosynthetic parameters,agronomic characteristics,saikosaponin A,C and D contents,yield and economic benefits of B.chinense.The results showed that the soybean-B.chinense multiple cropping pattern was beneficial to the enrichment of N in the soil,thus promoting photosynthetic parameters,growth,saikosaponin accumulation,yield and economic benefits of B.chinense.It is suggested that soybean-B.chinense multiple cropping was an appropriate multiple cropping pattern for local cultivation of B.chinense.

Influence of night-time light pollution on the photosynthesis and physiological characteristics of the urban plants Euonymus japonicus and Rosa hybrida

Background Night-time light pollution(NLP),which breaks the natural cycle of day and night,has become a new threat to urban ecosystems.Plants are the main component of urban ecosystems and play an irreplaceable role in maintaining urban ecological balance.The effects of NLP with various radiation sources,including green,white,blue and red light provided by light-emitting diodes,on urban plants,Euonymus japonicus and Rosa hybrida,were examined in a block field experiment.Results NLP caused photoinhibition and oxidative stress in plants,and the extent of the deleterious effects varied with the spectral distribution of artificial light sources and species.Both E.japonicus and R.hybrida were more sensitive to blue and red light,which reduced the pigment concentration,net photosynthetic rate,stomatal limit value,effective quantum yield,apparent electron transfer rate and photochemical quenching coefficient,and markedly increased the malondialdehyde content and total antioxidant capacity.However,those negative effects under white light were only present in E.japonicus and not in R.hybrida.Furthermore,blue and red light significantly decreased the stomatal conductance of E.japonicus.In contrast,green light had no significant effect on the above indices for both species.All spectra did not significantly change the sugars and starch contents for either species.Conclusions Considering that the spectral distribution of artificial light at night in cities has great heterogeneity and that its effect varies with plant species,it is important to arrange tree species with NLP tolerance and install appropriate light sources in urban areas based on the corresponding physiological responses and adaptation of urban trees.

Changes in photosynthesis and chlorophyll fluorescence in two soybean (Glycine max) varieties under NaCl stress

Traditional detection methods of crop information are often destructive and low efficiency.In this study,a new evaluation method was developed based on photosynthesis and chlorophyll fluorescence.Via analysis of the changes under NaCl stress during the seedling stage of two varieties,the salt resistance mechanism of soybeans was explored and a non-destructive stress-recognition method was developed.In this experiment,two soybean varieties were treated with one of four levels of NaCl stress:CK(0 mmol/L),LS(50 mmol/L),MS(100 mmol/L),and HS(150 mmol/L),for 15 d.The normal functions of the photosynthetic system of soybeans were enhanced under LS NaCl stress,but were inhibited under HS NaCl stress.Biomass,net leaf photosynthetic rate(Pn),stomatal conductance(gs),intercellular carbon dioxide concentration(Ci),transpiration rate(Tr),chlorophyll fluorescence parameters Y(II)and PSII decreased.However,in contrast to the findings of other studies on the influence of severe drought stress on soybean for long periods in which non-photochemical quenching coefficient(qN)decreased,this parameter increased under salt stress in soybean.The results demonstrate that the method developed is a promising tool for rapid and non-destructive detection of soybean photosynthetic responses under salt stress in the field.

Effects of nitrogen and salt on growth and physiological characteristics of processing tomato under drip irrigation

Xinjiang of China is one of the three largest planting bases of processing tomato in the world,but soil salinization has restricted the production of tomato processing.In order to study the effects of soil nitrogen,salt and their interaction on growth and physiological characteristics of processing tomato under drip irrigation,different amount of nitrogen fertilizer were added to reconcile different salt stress to explore the response mechanisms of growth and yield of processing tomato to soil nitrogen and salt contents with a two-year experiments.The results showed that the effects of soil salinity on the growth and physiological characteristics of processing tomato were significantly greater than that of input of nitrogen fertilizers.The higher soil salt content(≥5.0 g/kg)significantly inhibited the growth of processing tomato.The increase in addition of nitrogen fertilizer could alleviate the salt inhibition and promote the growth of processed tomato with the increase of soil salt content,and the maximum nitrogen application rate was 300 kg/hm2.The linear plus platform was selected to determine the nitrogen effect models of non-saline-alkali soil and weak saline-alkali soil,but the square root nitrogen effect model of moderate saline-alkali soil was selected to accurately predict the yield of processing tomato.It was suggested that the processing tomatoes should be planted in moderate saline-alkali soil to achieve higher yields due to lower input of nitrogen fertilizer,potentially reducing fertilizer costs and maximizing profits from high processing tomato yields.The results have a strong guiding significance for planting of processing tomato on saline-alkali land and appropriate fertilization to increase the yield of processing tomato.