Grain Yield,Biomass Accumulation,and Leaf Photosynthetic Characteristics of Rice under Combined Salinity-Drought Stress

Simultaneous stresses of salinity and drought often coincide during rice-growing seasons in saline lands,primarily due to insufficient water resources and inadequate irrigation facilities.Consequently,combined salinity-drought stress poses a major threat to rice production.In this study,two salinity levels(NS,non-salinity;HS,high salinity)along with three drought treatments(CC,control condition;DJ,drought stress imposed at jointing;DH,drought stress imposed at heading)were performed to investigate their combined influences on leaf photosynthetic characteristics,biomass accumulation,and rice yield formation.Salinity,drought,and their combination led to a shortened growth period from heading to maturity,resulting in a reduced overall growth duration.Grain yield was reduced under both salinity and drought stress,with a more substantial reduction under the combined salinity-drought stress.The combined stress imposed at heading caused greater yield losses in rice compared with the stress imposed at jointing.Additionally,the combined salinity-drought stress induced greater decreases in shoot biomass accumulation from heading to maturity,as well as in shoot biomass and nonstructural carbohydrate(NSC)content in the stem at heading and maturity.However,it increased the harvest index and NSC remobilization reserve.Salinity and drought reduced the leaf area index and SPAD value of flag leaves and weakened the leaf photosynthetic characteristics as indicated by lower photosynthetic rates,transpiration rates,and stomatal conductance.These reductions were more pronounced under the combined stress.Salinity,drought,and especially their combination,decreased the activities of ascorbate peroxidase,catalase,and superoxide dismutase,while increasing the contents of malondialdehyde,hydrogen peroxide,and superoxide radical.Our results indicated a more significant yield loss in rice when subjected to combined salinity-drought stress.The individual and combined stresses of salinity and drought diminished antioxidant enzyme activities,inhibited leaf photosynthetic functions,accelerated leaf senescence,and subsequently lowered assimilate accumulation and grain yield.

Effects of paclobutrazol application on plant architecture,lodging resistance,photosynthetic characteristics,and peanut yield at different single-seed precise sowing densities

The key to high-yielding peanut cultivation is the optimization of agricultural production practices.Regulating single-seed precise sowing(SSPS)density and paclobutrazol(Pbz)application concentration are effective practices that increase peanut yield by improving plant architecture,lodging resistance,and photosynthetic characteristics.Therefore,we conducted a two-factor field optimization experiment for the sowing density(D1:1.95×10^(5)plants ha^(-1),D52:2.40×10plants ha^(-1),D3:2.85×10^(5)plants ha^(-1),and D4:3.30×10^(5)plants ha^(-1))and Pbzapplication concentration(P0:0 mg L^(-1)and P1:100 mg L^(-1)).The objective was to optimize agricultural production practices and provide a theoretical basis for highyielding peanut cultivation by evaluating the effects of sowing density and Pbzapplication on plant architecture,lodging resistance,photosynthetic characteristics,and yield.The results showed that at the same Pbzapplication concentration,increasing sowing density increased lodging percentage and reduced leaf photosynthetic capacity.At the same sowing density,Pbzapplication reduced lodging percentage by decreasing plant height(PH),improving lignin biosynthesis-related enzyme activities,and enhancing stem puncture strength(SPS)and breaking strength(SBS).The paclobutrazol-induced alterations in plant architecture and lodging resistance improved light transmission at the middle and bottom leaf strata,resulting in the increase in relative chlorophyll content and net photosynthetic rate(Pn)of leaves.Furthermore,D3P1treatment had the highest peanut yield among all treatments.In summary,the production strategy combining the sowing density of 2.85×10^(5)plants ha^(-1)with the application of100 mg L^(-1)Pbzwas found to be the optimal agricultural production practice for giving full play to production potential and achieving higher peanut yield.

Osmotic Regulation,Antioxidant Enzyme Activities and Photosynthetic Characteristics of Tree Peony(Paeonia suffruticosa Andr.)in Response to High-Temperature Stress

Tree peony(Paeonia suffruticosa Andr.)is a traditional Chinese flower,which prefers cool weather.However,high temperature in summer in the middle and lower reaches of the Yangtze River restricts its growth and development.In this study,osmotic regulation,antioxidant enzyme activities,and photosynthetic characteristics of tree peony in response to high-temperature stress were investigated.The results showed that high-temperature stress had destroyed the cell membrane,manifested as the increased relative electrical conductivity and malondialdehyde content.Moreover,high-temperature stress led to excessive accumulation of reactive oxygen species,thereby,activating antioxidant enzyme activities.Also,photosynthetic parameters and chlorophyll fluorescence parameters directly reflected the damage to the photosystem II reflection center under high-temperature stress.In addition,high-temperature stress led to stomatal closure and chloroplast damage.This study revealed the physiological responses of tree peony to high-temperature stress,laying a foundation for the promotion of tree peony in high-temperature areas and the improvement of high-temperature resistance.

Effects of drought and heat on the productivity and photosynthetic characteristics of alpine meadow plants on the Qinghai-Tibetan Plateau

Alpine meadow plants,adapted to humid and cold environments,are highly sensitive to environmental factors such as drought and heat.However,the physiological responses of individual alpine meadow species to drought and heat stress remain unclear.In this study,four representative species of typical functional groups in an alpine meadow of the Qinghai-Tibet Plateau were selected as experimental materials.Heat(H1,H2),drought(D1,D2),and combined stress(D1H1,D2H2)treatments were implemented to reveal the biomass and physiological characteristics’response to a constant drought and heat environment.Our results showed that the leaf water content(LWC)of Kobresia humilis and Poa annua increased significantly under heat stress and the compound stress(P<0.05).The effect of a single factor on LWC was greater than that of multiple factors.The aboveground biomass(AGB)of Oxytropis ochrocephala and Saussurea pulchra decreased significantly under compound stress(P<0.05).The response patterns of the net photosynthetic rate(Pn)and transpiration rate(Tr)of K.humilis and P.annua under various stress treatments were similar;as were those of O.ochrocephala and S.pulchra.The stomatal conductance(Gs)variation in K.humilis,P.annua,O.ochrocephala,and S.pulchra were the same under three kinds of stress treatments.The photosynthetic characteristics were more sensitive to the effects of composite than those of single factors.The drought×heat×species treatment had a significant influence on various indexes except on height(Ht)and the belowground biomass(BGB)(P<0.01).Within a certain range,daytime temperature(DT)promoted the Ht and increased the LWC of the plants,while it inhibited their AGB and intercellular CO2 concentration(Ci).The Pn,Tr,and Gs were more sensitive to soil moisture than to DT.The results help improve understanding of the physiological response regularity of representative alpine meadow plant species to continuous drought and high temperature conditions at the species level,and provided experimental data and theoretical basis to identify the decisive factors of stress response.

Effect of Light Intensity on Leaf Photosynthetic Characteristics and Accumulation of Flavonoids in Lithocarpus litseifolius (Hance) Chun. (Fagaceae)

The active compounds in herb drugs are mainly secondary metabolites, which are greatly influenced by external conditions. Particularly, light intensity has a great influence on the photosynthesis and accumulation of secondary metabolites. In this study, the light intensity was changed, and the influence of the light intensity on leaf photosynthetic characteristics, antioxidant enzyme activity and flavone contents of Lithocarpus litseifoliusp (Hance) Chun. was discussed. The results showed that (1) L. litseifolius is a typical heliophyte. As the light intensity decreased, the contents of chlorophyll a (Chl a), chlorophyll b (Chl b) and total chlorophyll (Chl a + b) all increased. However, the Chl a/b ratio gradually decreased. The daily variation of net photosynthetic rate changed from a double-peak curve under natural light to single-peak curve under 20% full light two shading nets. (2) As the light intensity decreased, the SOD and POD activities and the soluble proteins content decreased in the leaves. In contrast, the malondialdehyde content increased. (3) The flavone content was the highest in leaves at one shading nets 60% of full light, and the lowest occurred in leaves at two shading nets 20% of full light. A comprehensive analysis indicated that an appropriate shading could induce shade tolerance in the leaves of L. litseifolius, which promoted the accumulation of flavonoids. L. litseifolius should be planted in the lower position of sunny slope or the upper position of shady slope to increase the content of flavone in the leaves.

Effects of Nitrogen Application on Photosynthetic Characteristics and Nitrogen Use Efficiency in Wheat after Rice

In the present study, appropriate nitrogen(N) application mode in Jianghan Plain was explored by investigating the effects of different N applications on the photosynthetic characteristics of flag leaves and nitrogen use efficiency(NUE) in a wheat cultivar Zhengmai 9023. Nitrogen was top-dressed before sowing, before winter, and during the jointing stage, at different ratios:1:1:0(N1), 1:0:1(N2), 2:1:1(N3), 1:1:1(N4), and 0:0:1(N5), under the same amount of total N(180 kg/hm^2) during the growing season. No nitrogen fertilizer was used in the control(N0). Results showed that the SPAD values and photosynthetic rate(Pn) of different treatments in flag leaves increased initially and then decreased around the anthesis stage. The two indices in N1 and N5 treatments decreased rapidly after flowering, whereas those in N2, N3, and N4 treatments maintained at high levels for a long period after anthesis. Thus, reasonable nitrogen application could retard the decline of SPAD and Pn after anthesis.N4 and N1 treatments showed large dry matter accumulation. In decreasing order of crop yield, the treatments were: N4 >N1 >N3 >N5 >N2 >N0. The effective panicle number and grain number per spike of N2 were significantly lower than those of other treatments, and there was no significant difference among other treatments. No significant correlation was found between nitrogen application and 1 000-grain weight in this experiment. The nitrogen accumulation, agronomic efficiency of nitrogen fertilizer,nitrogen uptake and use efficiency of above-ground parts, nitrogen uptake and use efficiency of grain of N4 treatment were higher than those of other treatments, but the nitrogen harvest index of N4 was at a low level. In summary, N4 treatment is the most suitable nitrogen application mode in wheat after rice.

Effects of Intelligent Irrigation on Photosynthetic Characteristics of Citrus Leaves and Fruit Quality

[Objectives]This study was conducted to improve the water use efficiency and fruit quality of citrus,and realize the automatic irrigation and standardized production in citrus orchards.[Methods]With Orah as the research object,the effects of intelligent irrigation management in citrus orchards on citrus leaf chlorophyll content,photosynthetic characteristics and fruit quality were investigated by comparing with conventional farmer management.[Results]The smart irrigation measure in citrus orchards significantly increased the SPAD value of leaves at the maturation stage of citrus,and simultaneously significantly improved the photosynthetic rate,transpiration rate and stomatal conductance at the flower bud differentiation stage,as well as the photosynthetic rate,transpiration rate,stomatal conductance and intercellular CO_(2) concentration at the maturation stage.However,the effects on the photosynthetic characteristic indexes in the rainy season were not significant.Compared with conventional experience management,the smart irrigation management measure of citrus orchards increased the edible rate and juice rate of citrus by 4.53 and 3.69 percentage points,respectively,and increased soluble solids,total sugar,vitamin C and sugar-acid ratio by 16.75%,20.86%,24.10%and 13.17%,respectively.[Conclusions]The smart irrigation management fully met the water demand for citrus growth due to timely irrigation,significantly improved the photosynthesis indicators of citrus leaves during drought,and significantly improved the quality of citrus.

Effects of Bioorganic Fertilizers on the Leaf Antioxidant Enzyme Activity and the Photosynthetic Characteristics of Replanted Szechuan Pepper, Zanthoxylum simulans

Continuous cropping obstacles hamper the efficient growth and yield of Szechuan pepper,Zanthoxylum simulans.The current study investigated the impact of different levels of bioorganic fertilizer on the leaf physiological and photosynthetic characteristics of Z.simulans to provide a theoretical reference for continuous Z.simulans crop cultivation.A bioorganic fertilizer was used to treat seedlings growing in 25-year-old continuous cropping soil.Five fertilizer treatments were applied.The impacts of the treatments on the activity of defense enzyme and photosynthetic parameters of Z.simulans leaves were determined.The different concentrations of bioorganic fertilizer reduced to varying degrees the malondialdehyde(MDA)content and intercellular CO2 concentration(Ci),and increased the activity of peroxidase(POD),superoxide dismutase(SOD),and ascorbate peroxidase(APX),as well as the chlorophyll content,net photosynthetic rate(Pn),stomatal conductance(Gs)and transpiration rate(Tr)of Z.simulans leaves.The results showed that most significant increases or decreases were achieved with 100 g/L bioorganic fertilizer(Y2).Thus,the application of bioorganic fertilizer at a rate of 100 g/L can significantly improve the activity of relevant defense enzymes and photosynthetic parameters of Z.simulans,and reduce the MDA content,enhancing the stress resistance of the plants,promoting their growth and addressing,to some extent,obstacles associated with continuous cultivation.

Effects of Light-Emitting Diode (LED) Red and Blue Light on the Growth and Photosynthetic Characteristics of <i>Momordica charantia</i>L.

With andromonoecious Momordica charantia L. (bitter gourd) as material, three light qualities (50 μmol·m-2·s-1) including white LED light (WL), blue monochromatic light (B, 465 nm), and red monochromatic light (R, 650 nm) were carried out to investigate their effects on seed germination, physiological and biochemical parameters, sex differentiation and photosynthetic characteristics of bitter gourd. The results showed that compared to the WL treatment, the R treatment significantly promoted seed germination, seedling height elongation and soluble sugar content, the B treatment significantly increased seedling stem diameter, reducing sugar content and soluble protein content, the R and B treatments both significantly reduced sucrose content, but their POD activity showed no significant difference. Compared with the R treatment, the B treatment significantly increased the total female flower number and female flower nod ratio in 30 nods of main stems. The study of photosynthetic characteristics found that the R and B treatments could effectively increase the stomatal conductance (GS) of leaves, significantly improved the net photosynthetic rate (Pn) compared to the WL treatment, and the effect of the B treatment was better. Compared to the R and WL treatments, the B treatment increased the maximum photosynthetic rate (Pmax), apparent quantum efficiency (AQE) and light saturation point (LSP), and reduced the dark respiration rate (Rd) and light compensation point (LCP) of the leaves. Fit light response curves showed that the adaptability and utilization of weak light in bitter gourd were middle or below, but it showed higher adaptability and utilization of strong light. Thus, it suggests that Momordica charantia is a typical sun plan with lower Rd. In summary, it is concluded that blue light has a positive effect on the seed germination, seedling growth, sex differentiation and improving the photosynthetic performance, and this will lay the foundation for artificially regulating optimum photosynthesis using specific LEDs wavelength, and help to elucidate the relationship how light quality influences the sex differentiation of plant.

Photosynthetic Characteristics of Clerodendrum trichotomum Thumb. Responses to Drought, Salt and Water-logging Stresses

In order to reveal the photosynthetic characteristics of C.trichotomum responses to drought,salt and water-logging stresses,one-year-old potted seedlings were taken as materials,and the several stresses including natural drought,submergence stress,water-logging and different salt treatments(0.2%,0.4%,0.6%and 0.8%Na Cl)were carried out on August 15,2012.The morphological and photosynthetic characteristics were observed and determined.The results showed that adverse enviromental stress had a significant effect on the morphological changes and photosynthetic characteristics of C.trichotomum.On the 14th day after natural drought,the leaves wilted and could not recovery at night,and 60%of the seedlings could recover after re-watering.From the7th day to the 10th day after submergence stress treatment,the 2nd and the 3rd leaves at the base of 60%seedling turned yellow and the lenticels were observed.At the early stage of water-logging stress,white lenticels appeared at the base of seedlings,and the leaves wilted,chlorina and fallen off on the 8th day.A large number of leaves fallen off under 0.6%Na Cl or more salt stress,and even the whole plant died.The chlorophyll content,net photosynthetic rate(Pn)and transpiration rate(Tr)decreased gradually with the stress process,such as 8 days after natural drought,less than 0.4%salt stress and water-logging stress,but the changes were not significant compared with those of the control.With the increase of the stress intensity and the prolonged time,the changes of photosynthetic index were significant.All the results indicated that C.trichotomum had a certain degree of tolerance to drought,water and salt,but it was not suitable for living in water-logging condition for a long time.

Effects of Uniconazole on Photosynthetic Characteristics of Dahlia pinnata Cav.under Drought Stress

[Objectives]This study was conducted to explore the physiological mechanism of uniconazole in response to drought stress in Dahlia pinnata.[Methods]With potted seedlings of D.pinnata variety‘Danbanhuang’as an experimental material,the effects of different concentrations(10,20,30 and 50 mg/L)of uniconazole on the photosynthetic characteristics of D.pinnata under drought stress and rewatering conditions were discussed.[Results]With the extension of drought time,the chlorophyll SPAD value,net photosynthetic rate,transpiration rate,and stomatal conductance of each treatment group decreased significantly,while the intercellular CO_(2)concentration showed a trend of first decreasing and then increasing;and after pretreatment of uniconazole spraying on leaves,it could alleviate the inhibition of drought stress on the photosynthesis of D.pinnata,and was beneficial to the recovery of photosynthetic capacity of D.pinnata after rewatering,and the effect of leaf application concentration of 30 mg/L was the best.It showed that exogenous uniconazole helps to improve the drought resistance of D.pinnata.[Conclusions]This study provides a new experimental basis for the chemical regulation of stress resistance in D.pinnata and its production and application.

Stimulatory effect of lanthanum nitrate on the root tuber yield of Pseudostellaria heterophylla via improved photosynthetic characteristics

The stimulatory effects and associated mechanism of lanthanum nitrate on the root tuber yield of the traditional Chinese medicinal plant Pseudostellaria heterophylla, by means of improved photosynthetic characteristics, were investigated. Field experiments were conducted and the foliage was sprayed with varying concentrations of lanthanum nitrate. The results indicated that growth indexes, chlorophyll and carotenoid contents initially increased, and then decreased in a dose-dependent manner with increasing concentrations of lanthanum nitrate. The fresh and dry weights of root tuber yield per unit area significantly increased by 58.34% and 56.87% with a lanthanum nitrate concentration of 100 mg/L, respectively, compared with the control. Appropriate concentrations of lanthanum nitrate were found to alleviate photosynthetic depression at midday, as well as improve the mean values of photosynthetic rate(P_n), stomatal conductance(G_s) and transpiration rate(T_r) associated with the diurnal variation in photosynthetic parameters, while reducing intercellular CO_2 concentration(C_i). During the experiment, the chlorophyll fluorescence parameters Fv/Fm, Fv'/Fm', ΦPSII and qP increased initially and then decreased along with the increasing concentration of lanthanum nitrate, while NPQ followed the opposite trend. Correlation analysis revealed that Pn had a significantly positive relationship with seedling height, ground diameter, chlorophyll and carotenoid contents, G_s and ΦPSII, while a negative relationship was observed with C_i and NPQ. Grey relational analysis(GRA) indicated that photosynthetic pigments, ΦPSII and qP were the primary factors impacting photosynthesis. These results suggested that the application of an appropriate concentration of lanthanum nitrate(100 mg/L) was effective in improving growth, root tuber yield and photosynthetic characteristics of Psendoste llaria(P) heterophylla. The regulatory effect of lanthanum nitrate on photosynthesis was related to the promotion of light energy absorption and conversion, improvement in photochemical efficiency and the alleviation of photoinhibition. The improvement of the non-stomatal limitation factor was the primary basis for the mitigation of midday photosynthetic depression.

Changes in growth and photosynthetic characteristics of Ocimum sanctum under growth regulator treatments

A field experiment was conducted to investigate the effect of growth regulators on growth characteristics such as root length,shoot length,total leaf area,number of inflorescence per plant,number of flower per inflorescence,whole plant fresh weight and whole plant dry weight.Photosynthetic characteristics were also analyzed based on the same experiment.For this,various photosynthetic pigment contents such as chlorophyll,carotenoid,anthocyanin and xanthophyll content were calculated.The conventional growth regulator abscisic acid(ABA)and non-conventional growth regulator triazole compound paclobutrazol(PBZ)were used.Root length increased due to growth regulator treatment,but shoot length decreased.Leaf area was decreased due to growth regulator treatment.The number of inflorescence increased in ABA treated plants,but it was decreased in PBZ treated plants.In ABA treated plants,the number of flowers per inflorescence was increased.In PBZ treated plants the number of inflorescence was reduced.The whole plant fresh weight(FW)and dry weight(DW)were increased in ABA and PBZ treated plants.There was an increase in chlorophyll content in growth regulator treated plants compared to control,and it was more in PBZ treated plants.The carotenoid content was also increased in ABA and PBZ treated plants.

Effects of Potassium-Solubilizing Bacteria on Growth, Antioxidant Activity and Expression of Related Genes in Fritillaria taipaiensis P. Y. Li

This study aimed to examine the effects of inoculating Fritillaria taipaiensis P.Y.Li leaves with different strains ofpotassium-solubilizing bacteria (KSB), or combinations thereof, focusing on aspects of photosynthesis and physiologicaland biochemical characteristics. At present, some studies have only studied the rhizosphere microbialcommunity characteristics of F. taipaiensis and have not discussed the effects of different microbial species on thegrowth promotion of F. taipaiensis. This paper will start from the perspective of potassium-solubilizing bacteria toconduct an in-depth study. Seed cultivation commenced at the base with three different KSBs in early October2022. The growth of F. taipaiensis leaves was observed after different treatments. Both single-plant and compoundinoculations were executed. A total of eight treatment groups were established, with aseptic fertilizer and sterilizedsoil functioning as the control group. The results reveal that intercellular CO_(2) concentration (Ci), stomatal conductance(Gs), and transpiration rate (Tr) were at their apex in the S7 group. Most treatment groups exhibited anincrease in leaf area, photosynthetic pigment content, soluble sugar, soluble protein, Superoxide Dismutase(SOD), Peroxidase (POD), Catalase (CAT) activities, and proline content. The expression levels of POD, SOD,and CAT genes were evaluated, following inoculation with different KSB. The highest was the S7 group. Theinoculation with various KSB, or combinations thereof, appears to bolster the growth and development of F. taipaiensis.The composite inoculation group S7, comprising Bacillus cereus, Burkholderia cepacia, and Bacillus subtilis,manifested the most favorable impact on the diverse indices of F. taipaiensis, thereby furnishing valuableinsights for the selection of bacterial fertilizer in the artificial cultivation of F. taipaiensis.

Effects of drip irrigation modes on growth and physiological characteristics of Arabica coffee under different N levels

The objective of this study was to obtain the water-saving and efficient production mode of Arabica coffee. The effects of three drip irrigation modes,conventional drip irrigation( CDI),alternate drip irrigation( ADI) and fixed drip irrigation( FDI) on growth,photosynthetic characteristics,biomass accumulation and irrigation water use efficiency of Arabica coffee were investigated under three nitrogen levels,high nitrogen( NH),middle nitrogen( NM) and low nitrogen( NL). The results show that there was a significant Logistic curve between the plant height,the stem diameter of Arabica coffee and growth days. Compared with CDI,ADI had no significant effects on leaf net photosynthetic rate,stomatal conductance,instantaneous water use efficiency and biomass accumulation above ground of Arabica coffee,while FDI decreased significantly,ADI and FDI increased irrigation water use efficiency by 50. 59% and 32. 85%,respectively. Compared with NH,with the reduction of N application rate,net photosynthetic rate,stomatal conductance,biomass accumulation above ground and irrigation water use efficiency decreased by 6. 81%-12. 30%,13. 70%-22. 69%,9. 61%-16. 67% and 9. 78%-15. 64%,respectively. Compared with CDINH,ADINHdecreased net photosynthesis rate and the stomatal conductance not significantly,other treatments decreased by 9. 16%-19. 22%,14. 49%-32. 91%,and decreased biomass accumulation above ground by 8. 26%-27. 34% except ADINH,and increased irrigation water use efficiency by 16. 46%-60. 95% except CDINMand CDINL. Therefore,alternate drip irrigation under high N level( ADINH) is the best water and nitrogen coupling mode of young Arabica coffee tree for water efficiency.

Wheat growth, photosynthesis and physiological characteristics under different soil Zn levels

In recent years,heavy metal hazards in the soil have seriously affected agricultural production.This study aims to examine the effects of different levels of heavy metal Zn on the growth,photosynthesis and physiological characteristics of wheat,and provide a theoretical basis for the diagnosis and control of heavy metal pollution in agricultural production.The field test method was used to explore the changes of wheat agronomic traits,photosynthetic capacity,chlorophyll fluorescence parameters,spectral characteristic curve,active oxygen metabolism system,cell ultrastructure,and yield,under different Zn levels(0,250,500,750,and 1000 mg kg^(-1)).The results show that,low-level Zn treatments can effectively promote the synthesis of wheat chlorophyll,improve photosynthetic capacity,and increase yield.The yield of ZnL1(250 mg kg^(-1))was the highest in the two-year test,which increased by 20.4%in 2018 and 13.9%in 2019 compared with CK(0 mg kg^(-1)).However,a high Zn level had a significant stress effect on the photosystem of wheat.PIabs(reaction center performance index)and Fv/Fm(maximum photochemical efficiency)were significantly reduced,the active oxygen metabolism system was damaged,and the photosynthetic capacity was reduced,which in turn led to reduced yield.Among them,the yield of ZnL4(1000 mg kg^(-1))was the lowest in the two-year test,which was 28.1 and 16.4%lower than CK in 2018 and 2019,respectively.The green peak position of ZnL3 and ZnL4 had"red shift"to the long wave direction,while the red valley position of ZnL4 had"blue shift"to the short wave direction.Under ZnL4,some wheat leaf organelles began to decompose,vacuoles increased,cytoplasm decreased,cell walls thickened,chloroplast basal lamellae were disordered,and mitochondrial membranes disintegrated.Stepwise regression and Path analysis showed that Pn(net photosynthetic rate)played a leading role in the formation of yield.Redundancy(RDA)analysis showed that the optimal Zn level for wheat growth was about 250 mg kg^(-1),and wheat would be stressed when the soil Zn level exceeded 500 mg kg^(-1) in the test condition of this study.Findings of this study provide a theoretical basis for the diagnosis and prevention of heavy metal(Zn)pollution in the soil.

Effects of NaCl and NaHCO3 Stress on Photosynthesis and Chlorophyll Fluorescence Characteristics of Hemerocallis fulva ‘Golden Doll’

With Hemerocallis fulva‘Golden Doll'as an experimental material,the effects of different concentrations of neutral salt( NaCl) and alkaline salt( NaHCO3) stresses on photosynthesis and chlorophyll fluorescence characteristics in H. fulva seedlings were studied. The results showed that salt stress treatment significantly reduced the photosynthetic capacity of H. fulva. Under the NaCl and NaHCO3 stresses,the photosynthetic characteristics and chlorophyll fluorescence parameters of H. fulva seedlings were basically the same,but the photosynthetic characteristics and chlorophyll fluorescence parameter values of H. fulva seedlings were significantly different under different salt types and salt concentrations. With the extension of days of salt stress and the increase of salt concentration,the initial fluorescence yield( Fo) and non-photochemical quenching coefficient( NPQ) increased;the maximum fluorescence yield( Fm),maximum photochemical efficiency( Fv/Fm),PSII actual photosynthetic quantum yield( Y) and apparent quantum efficiency( AQY) all showed a downward trend;and moreover,with the extension of days of salt stress and the increase of salt concentration,the net photosynthetic rate( Pn) decreased and the intercellular CO2 concentration( Ci) increased. It was speculated that under salt stress,the photosynthetic characteristics of H. fulva leaves were inhibited. On the one hand,the non-stomatal limiting factor,i. e.,the chlorophyll content decreased,which led to the inhibition of photosynthetic characteristics. On the other hand,the decrease in the photosynthetic performance of mesophyll cells led to a decrease in the net photosynthetic rate of H. fulva. The changes of photosynthetic characteristics and chlorophyll fluorescence parameters in H. fulva caused by salt stress were closely related to the types of salts and salt concentration. High salt stress significantly inhibited the photosynthetic capacity of H. fulva‘Golden Doll',and the effect of NaHCO3 on H. fulva seedlings was significantly greater than that of NaCl.

Study on Growth Rules and Photosynthetic Physiology of Biennial Container Seedlings and Bare Root Seedlings of Phoebe

Transplantation experiment was carried out using biennial container seedlings and bare root seedlings of Phoebe zhennan S. Lee as materials. In the experiment,it measured the growth indicators such as the seedling height,basal diameter,and number of branches and leaves. Besides,it also measured net photosynthetic rate( Pn),transpiration rate( Tr),stomatal conductance( Gs),intercellular CO_2 concentration( Ci) and soluble sugar,soluble protein,malondialdehyde( MDA) content,superoxide dismutase activity and root activity. The results indicated that the growth indicators of the Phoebe container seedlings performed the best in the plant height,basal diameter,and number of branches and leaves; photosynthetic capacity was the strongest,and the fertilization could enhance the photosynthetic capacity of seedlings; soluble sugar,soluble protein content,superoxide dismutase activity and root activity of Phoebe container seedlings were higher than that of bare root seedlings.

Photosynthetic Physiological Response to Drought Stress of Populus euphratica at Different Ages in Minqin

[Objectives]This study was conducted to investigate the photosynthetic physiological characteristics of Populus euphratica trees at different forest ages in the desert area of Minqin in response to drought stress.[Methods]With P.euphratica trees of different ages in Minqin as the research object,the water characteristics and photosynthetic physiological indexes(chlorophyll,soluble sugar,POD,SOD and MDA)were compared under different conditions.[Results]On the time gradient,the soil water contents of P.euphratica of different ages decreased continuously with the extension of irrigation stop time,but the decreases were small.Under the same stress treatment,the soil water contents of P.euphratica of different ages increased with the deepening of soil layer,but the differences were not significant(P>0.05).Under normal condition,the chlorophyll contents of P.euphratica at three ages gradually increased with the increase of age.The chlorophyll contents in leaves of P.euphratica at different ages were all lower under normal condition and higher under water stress.The changes of POD and SOD activity in leaves of P.euphratica at different ages under different conditions were basically the same,showing that the enzyme activity was higher under water stress than under normal under.The MDA contents in leaves of the young and middle P.euphratica forests were higher under water stress at 7 and 21 d than under normal condition,and the differences were not significant(P>0.05);and the MDA content in leaves of the mature P.euphratica forest was higher under water stress at 21 and 35 d than under normal condition.Drought stress has a certain effect on the photosynthetic physiological characteristics of P.euphratica.In summary,under drought stress,the chlorophyll content,SOD and POD activity,and MDA molar concentration in the leaves of P.euphratica were basically higher than under normal condition,indicating that P.euphratica could resist drought environment through osmotic adjustment and showed strong drought resistance.[Conclusions]This study provides a theoretical reference for the restoration,protection and reconstruction of natural P.euphratica forests in the desert area of Minqin.

Imbalance between nitrogen and potassium fertilization influences potassium deficiency symptoms in winter oilseed rape (Brassica napus L.) leaves

Chlorosis at leaf margins is a typical symptom of potassium(K) deficiency, but inappropriate application of K with other nutrients often masks symptoms of K deficiency. A two-year field experiment was conducted to measure the interactive effects of N and K on leaf photosynthesis and dry matter accumulation and the resulting growth dilution effect on K concentration and leaf K deficiency symptoms. N application aggravated the imbalance of N and K nutrients and further exacerbated K deficiency symptoms under K limitation. Synergistic effects of N and K promoted plant growth, amplified the growth dilution effect, and reduced the critical K concentration in leaves. Using 90% of the maximum shoot biomass as a threshold,the critical K concentration was 0.72% at the recommended N(N180) fertilization level. The critical K concentration increased by 62.5% owing to the reduced biomass under insufficient N(N;) supply. In contrast, high N(N;) reduced the critical K concentration(0.64%), accelerating chlorophyll decomposition and exacerbating K deficiency symptoms. The basis of changing the critical K concentration by magnifying growth dilution effect was the functional synergistic effect of N and K on photosynthetic characteristics. Under insufficient N, the low maximum carboxylation rate(V;) limited the net photosynthetic rate(An) and necessitated more K to maintain high CO;transmission capacity, to improve the total conductance g;/V;ratio. High N supply increased gtotand V;possibly mitigating the effect of K reduction on photosynthesis. In conclusion, it is unwise to judge K status of plants only by K concentration without accounting for crop mass(or dilution effect), critical K concentration and deficiency symptoms are affected by N fertilization, and the synergistic effect of N and K on leaf photosynthesis is the foundation of maximal growth of plants under diverse critical K concentrations.