Comparison of Net Photosynthetic Rate in Leaves of Soybean with Different Yield Levels

A total of nine soybean(Glycine max(L.) Merr.) cultivars were divided into three yield levels which were planted under the same environmental condition.The net photosynthetic rate was measured by LI-6400 portable photosynthesis system.The chlorophyll content and specific leaf weight were measured with regular methods.The results showed that the specific leaf weight,chlorophyll content and net photosynthetic rate of high yield varieties were higher than those of low yield varieties.The yield had a significantly positive correlation with the net photosynthetic rate.With the improvement of modern technology,the net photosynthetic rate could be measured quickly and exactly.Hence,net photosynthetic rate could be used as an effective index in the selection of high yield soybean.

Effect of Water Deficit Stress on Photosynthetic Characteristics of Jatropha curcas

The need to mitigate climate change cannot be more emphasized, which arises, as a result of increases in CO2 emissions due to anthropogenic activities. Given the current world energy problems of high fossil fuel consumption which plays a pivotal role in the greenhouse effect, Jatropha curcas biodiesel has been considered a potential alternative source of clean energy (biodiesel is carbon neutral). However, the ability of Jatropha curcas, as a candidate source of alternative of clean energy, to grow in marginal and dry soils, has been poorly elucidated. This study, therefore aimed at investigating whether Jatropha curcas leaves could switch from carrying out C3 photosynthetic pathway to Crassulacean Acid Metabolism (CAM) as a strategy to improve its water deficit tolerance. Thirty-five-day-old Jatropha curcas accessions, from three different climatic zones of Botswana, viz., Mmadinare (Central zone), Thamaga (Southern zone) and Maun (Northern zone), were subjected to water stress, by with-holding irrigation with half-strength Hoagland culture solution. Net photosynthetic rate, transpiration and stomatal conductance were measured at weekly intervals. The leaf pH was measured to determine whether there was a decrease in pH (leaf acidification) of the leaves during the night, when the plants experienced water deficit stress. All the accessions exhibited marked reduction in all the measured photosynthetic characteristics when experience water deficit stress. However, a measurable CO2 uptake was carried out by leaves of all the accessions, in the wake of marked decreases in stomatal conductance. There is evidence to suggest that when exposed to water stress J. curcas accessions switch from C3 mode of photosynthesis to CAM photosynthetic pathway. This is attested to by the slightly low leaf pH at night. Thamaga accession exhibited an earlier stomatal closure than the other two accessions. This resulted in Thamaga accession displaying a slightly lower dry weight than both Mmadinare and Maun accessions. It could be concluded that Jatropha curcas appeared to tolerate water deficit stress due to its ability of switching from C3 photosynthetic pathway to the CAM photosynthetic pathway, but with a cost to biomass accumulation, as demonstrated by slightly more reduced CO2 assimilation by Thamaga accession, than the other two accessions.

Effects of nitrogen application rates and irrigation regimes on grain yield and water use efficiency of maize under alternate partial rootzone irrigation

Faced with the scarcity of water resources and irrational fertilizer use,it is critical to supply plants with water and fertilizer in a coordinated pattern to improve yield with high water use efficiency(WUE).One such method,alternate partial root-zone irrigation(APRI),has been practiced worldwide,but there is limited information on the performance of different irrigation regimes and nitrogen(N)rates under APRI.The objectives of this study were to investigate the effects of varying irrigation regimes and N rates on shoot growth,grain yield and WUE of maize(Zea mays L.)grown under APRI in the Hexi Corridor area of Northwest China in 2014 and 2015.The three N rates were 100,200 and 300 kg N ha–1,designated N1,N2 and N3,respectively.The three irrigation regimes of 45–50%,60–65%and 75–80%field capacity(FC)throughout the maize growing season,designated W1,W2 and W3,respectively,were applied in combination with each N rate.The results showed that W2 and W3 significantly increased the plant height,stem diameter,crop growth rate,chlorophyll SPAD value,net photosynthetic rate(Pn),biomass,grain yield,ears per ha,kernels per cob,1000-kernel weight,harvest index,evapotranspiration and leaf area index(LAI)compared to W1 at each N rate.The N2 and N3 treatments increased those parameters compared to N1 in each irrigation treatment.Increasing the N rate from the N2 to N3 resulted in increased biomass and grain yield under W3 while it had no impact on those under the W1 and W2 treatments.The W3 N3 and W2 N2 and W2 N3 treatments achieved the greatest and the second-greatest biomass and grain yield,respectively.Increasing the N rate significantly enhanced the maximum LAI(LAI at the silking stage)and Pn under W3,suggesting that the interaction of irrigation and fertilizer N management can effectively improve leaf growth and development,and consequently provide high biomass and grain yield of maize.The W2 N2,W2 N3 and W3 N3 treatments attained the greatest WUE among all the treatments.Thus,either 60–65%FC coupled with 200–300 kg N ha–1 or 75–80%FC coupled with 300 kg N ha–1 is proposed as a better pattern of irrigation and nitrogen application with positive regulative effects on grain yield and WUE of maize under APRI in the Hexi Corridor area of Northwest China and other regions with similar environments.These results can provide a basis for indepth understanding of the mechanisms of grain yield and WUE to supply levels of water and nitrogen.

Effects of Multi-Stage Continuous Drought on Photosynthetic Characteristics, Yield and Water Use Efficiency of Winter Wheat

A drought event can cause entire crops to fail or yield loss.In order to study the effects of continuous drought on photosynthetic characteristics,yield,and water use efficiency(WUE)of winter wheat(Triticum aestivum L.),the winter wheat variety“Aikang 58”was selected as test material with controlling the water of the pot-planted winter wheat under a mobile rainout shelter.Based on foot planting and safe wintering,winter wheat was evaluated under different drought conditions,including light,moderate and severe drought at the jointing(B),heading(C),and filling(G)stages.The soil water content was controlled in a range of 60%to 70%,50%to 60%,and 40%to 50%of the field capacity,respectively.In the experiment,there were 9 single-stage droughts,3 three-stage droughts,and 1 test control(totaling 13 trials).The results are as follows:Under a single-stage drought,the change of net photosynthetic rate(Pn)and stomatal conductance(Gs)have similar trends,and they both decrease significantly with the severity of the drought.Under three-stage continuous droughts,the change curve of Gs shows a constant downward trend;the change curve of Pn showed a“valley shape,”and the minimum value of Pn appeared at the heading stage.All droughts will reduce the yield of winter wheat.Under the three-stage continuous drought conditions,except for light drought,moderate drought and severe drought will cause significant yield reduction,mainly due to lack of water at the jointing and heading stages.Continuous drought will reduce the WUE,and the difference will reach a significant level under moderate and severe drought.The present results suggested that when water resources are scarce,it is a better irrigation model to save water and achieve high grain yield by applying appropriate water stress(60%–70%FC)during the critical growth period of winter wheat.

Effects of Different Potassium (K) Fertilizer Rates on Yield Formation and Lodging of Rice

As one of the most important nutrients for plants,potassium(K)has substantial effects on growth and development of crops.Present study was conducted in three different sites in South China in late season in 2019 with the objective to study the effects of different applied amounts of K fertilizer on yield formation and lodging of rice.Four K fertilizer treatments,K_(0):0 kg potassium oxide(K_(2)O)ha^(−1)(control);K_(1):64.20 kg K_(2)O ha^(−1);K_(2):128.55 kg K_(2)O ha^(−1) and K_(3)153.90 kg K_(2)O ha^(−1) were applied in the field experiment.The results showed that K_(2) and K_(3) treatments significantly increased panicle number per unit area,grain number per panicle,seed-setting rate and the grain yield of rice compared with K_(0) treatment.Higher net photosynthetic rates were recorded in K_(2) and K_(3) treatments than K_(0) treatment at tillering stage,heading stage and maturity stage.K fertilizer treatments also increased the chlorophyll content and dry matter accumulation by 6.16–23.52%and 21.32–64.59%compared with K_(0) treatment,respectively.Moreover,the total N and K accumulation in the aboveground tissues of rice significantly increased under K_(2) and K_(3) treatments compared with K_(0) treatment.Furthermore,compared with K_(0) treatment,K fertilizer treatments significantly enhanced the breaking-resistant strength by 40.94–144.24%and reduced the lodging index of rice by 13.14–36.72%.

Analysis on Pigment and Photosynthetic Characteristics of Leaves of New Strain of Rehmannia glutinosa

Through the analysis on the leaf color and photosynthetic characteristics of new strains and main cultivars of Rehmannia glutinosa,it is expected to provide theoretical basis for breeding of new varieties. Chlorophyll,anthocyanin,and net photosynthetic rate（Pn）,stomatal conductance（Cond）,transpiration rate（Tr）,and intercellular CO2concentration（Ci） in 8 varieties of Rehmannia glutinosa were measured by spectrophotometer and LI-6400 XT Portable Photosynthesis System. The results showed that the chlorophyll content of Huaidijin 8（2. 84 mg/g）,Huaidi 81（2. 71 mg/g）,Huaidi 85-5（2. 69 mg/g）,Jinjiu（2. 66 mg/g） and Huaidi 83（2. 63 mg/g） was higher; the anthocyanin content of Jinjiu（0. 169） and Huaidijin 8（0. 165） was higher,while the anthocyanin content Huaidi 83（0. 060） was the lowest; Pn of Huaidi81[2. 41 μmol/（m2·s） ],Huaidi 83[2. 37 μmol/（m2·s） ]and Huaidijin 8[2. 25 μmol/（m2·s） ]was higher,and the anthocyanin content was positively correlated with Pn,while the anthocyanin content was negatively correlated with Pn; Huaidijin 8 and Huaidi 83 showed dominant advantages in single plant fresh weight,indicator component,and resistance over the main cultivars. This indicates that the new variety Huaidijin 8 and Huaidi 83 have excellent comprehensive traits and can be properly popularized.

Diurnal Variation of Photosynthetic Physiological Characteristics of Kadsura coccinea(Lem.)A.C.Smith

[Objectives]This study was conducted to investigate the diurnal variations of photosynthetic and physiological characteristics in 3-year-old Kadsura coccinea(Lem.)A.C.Smith plants.[Methods]A Li-6400 portable photosynthetic system was used to study the diurnal variations of the photosynthetic physiological characteristics of K.coccinea.[Results]The diurnal variation of the net photosynthetic rate(Pn)of K.coccinea leaves showed a"double peak"curve,and there was a lunch break at noon.The maximum value of Pn[4.51 mmol/(m^(2)·s)]appeared at 10:00,and the daily average Pn was 3.98 mol/(m^(2)·s);and the stepwise regression analysis showed that photosynthetically active radiation(PAR)and stomatal conductance(Gs)were the main factors affecting Pn.The partial correlation analysis and path analysis showed that the order of effects on Pn was Gs>PAR.[Conclusions]This study provides a reference for further research on the development and utilization of K.coccinea.

Enhanced Efficiency Phosphorus Fertilizer Impact on Physiological Characteristics of Coffee Seedlings

The effects of phosphorus (P) nutrition on various aspects of photosynthetic metabolism have been examined for coffee plants (Coffea arabica) grown under greenhouse conditions. The experimental design was completely randomized, and the treatments were carried out in a 2 × 5 factorial scheme: two P sources [Triple Superphosphate - TSP (46% P2O5) and Policote coated TSP - TSP + Policote (43.7% P2O5)] and five P rates (0;5;10;15 and 20 g P2O5 plot-1), with three replications. The net photosynthetic rate (A), the leaf temperature (LT), the atmospheric CO2 concentration (Ca), the stomatal conductance (gs), the transpiration rate (E), the substomatal CO2 concentration (Ci) and carboxylation efficiency (Ce) were measured in the youngest fully expanded leaf, with the use of an infrared gas analyzer. All photosynthesis measurements were affected by P fertilization. P fertilization increased net photosynthetic rate, leaf temperature, substomatal CO2 concentration, stomatal conductance, transpiration rate, and carboxylation efficiency. Policote coated P fertilizer resulted in a higher net photosynthetic rate, leaf temperature, stomatal conductance, and transpiration rate than conventional P fertilizer. The data indicated that Policote coated P fertilizer, a kind of enhanced efficiency P fertilizer (EEPF), alters the plant’s photosynthetic carbon metabolism, explaining higher crop development and yield resulted from this EEPF.

Peach yield and fruit quality is maintained under mild deficit irrigation in semi-arid China

We conducted a two-year study of deficit irrigation impact on peach yield and quality in semi-arid northwest China. Over two years, four-year-old peach trees were irrigated at 100, 75, 50 and 25% of peach evapotranspiration(ET_c), here, ET_c= Coefficient(Kc)×Local reference evapotranspiration(ET_o). During the April-July fruit production season we measured root zone soil water depletion, sap flow velocity, net photosynthetic rate(P_n), transpiration rate(T_r), stomatal conductance(G_s), water use efficiency(WUE=P_n/T_r), fruit quality, and yield under a mobile rain-out shelter. Increased soil water depletion reasonably mirrored decreasing irrigation rates both years, causing progressively greater water stress. Progressive water stress lowered G_s, which in turn translated into lower T_r as measured by sap flow. However, mild deficit irrigation(75% ET_c) constricted T_r more than P_n. P_n was not different between 100 and 75% ET_c treatments in both years, and it decreased only 5–8% in June with higher temperature than that in May with cooler temperature. Concurrently under 75% ET_c treatment, T_r was reduced, and WUE was up to 13% higher than that under 100% ET_c treatment. While total fruit yield was not different under the two treatments, because 75% ET_c treatment had fewer but larger fruit than 100% ET_c trees, suggesting mild water stress thinned fruit load. By contrast, sharply decreased T_r and P_n of the driest treatments(50 and 25% ET_c) increased WUE, but less carbon uptake impacted total fruit yield, resulting 13 and 33% lower yield compared to that of 100% ET_c treatment. Irrigation rates affected fruit quality, particularly between the 100 and 75% ET_c trees. Fewer but larger fruit in the mildly water stressed trees(75% ET_c) resulted in more soluble solids and vitamin C, firmer fruit, and improved sugar:acid ratio and fruit color compared to the 100% ET_c treatment. Overall, trees deficit irrigated at 75% ET_c maintained yield while improving fruit quality and using less water.

Effects of salt and nitrogen on physiological indices and carbon isotope discrimination of wheat cultivars in the northeast of Iran

In order to study the effects of different levels of salt stress and nitrogen(N) on physiological mechanisms,carbon isotope discrimination(△13C),and yield of two wheat cultivars(cv.),a two-year field experiment was carried out during 2013-2015.The treatments included three levels of salt stress(1.3,5.2,and 10.5 dS m^-1),three levels of N(50,100,and 150 kg N ha-1),and two wheat cultivars,Bam and Toos.Under salt stress,N application(100 and 150 kg N ha^-1) produced a significant effect on both cultivars with respect to physiological traits,i.e.,net photosynthetic rate(Pn),stomatal conductance(gs),chlorophyll index(Cl),Na^+/K^+ ratio as well as the grain yield(GY).The salt-tolerant and-sensitive cultivars exhibited the maximum values of physio-biochemical and yield attributes at 100 and 150 kg N ha-1,respectively.The results of △13C showed a significant difference(P<0.001) between wheat cultivars under the control and salt stress.According to our result,salt-tolerant cultivar Bam seems to be more efficient in terms of higher GY,Pn,gs,Cl,and lower Na^+/K^+ ratio as well as higher △13C as compared with salt-sensitive cultivar Toos,under salt stress.Therefore,a significant positive correlation that observed between △13C and GY,indicated that △13C may be an effective index for indirect selection of yield potential in wheat under irrigation regimes with saline water.

Photosynthesis adaption in Korean pine to gap size and position within Populus davidiana forests in Xiaoxing’anling, China

Forest gaps restrict the restoration of temperate secondary forest to broad-leaved Korean pine forest in zonal climax vegetation by affecting the growth of Korean pine(Pinus koraiensis).However,the photo synthetic adaptability of Korean pine to gap size and position within the gap is unclear.In order to explore the adaptability of young Korean pine(35 years) to different gap sizes in Xiaoxing’anling,photo synthetic capacity and microenvironmental factors(leaf temperature,light transmittance) of Korean pine needles in three positions in the gap(central,transition,and edge areas) were investigated.Three gaps were identified in the secondary Populus davidiana forest:a large 201 m^(2) gap,a middle 112 m^(2) gap,and a small 50 m^(2) gap;12 m^(2) of the understory was sampled as a control.The results show that:(1) maximum net photosynthetic rate(P_(max)) in needles of Korean pine growing in the large gap was higher than in the small gap,and P_(max) in the centre in the same gap was higher than in the transition and edge areas;(2) light saturation point(LSP) and photosynthetic quantum yield(AQY)of needles in the large gap were higher than in the small gap,while the light compensation point(LCP) and chlorophyll contents of needles were lower in the small gap;and,(3)P_(max) had a significant positive correlation with temperature and light transmittance.It is suggested that the larger the gap in secondary Populus davidiana forests,the greater the change in light intensity and temperatures,the stronger the light adaption of Korean pine needles and the higher the photosynthetic capacity.Therefore,in the recovery of broadleaved/Korean pine forests,suitable gaps should be created and gap microhabitats fully utilized to accelerate the restoration process.

Variation of nitric oxide emission potential in plants: a possible link to leaf N content and net photosynthetic activity

Aims Ecological systems,especially soils,have been recently recognized as an important source of atmospheric nitric oxide(No).However,the study on the contribution of plants to atmospheric No budget is significantly lagged.The specific objectives of this study are to reveal the phylogenetic variation in No emission potential existing in various plant species and find out the possible leaf traits affecting No emission potential.Methods We measured No emission potential,leaf N and C content,C:N ratio,specific leaf area,net photosynthetic rate(Pn)and estimated photosynthetic N use efficiency(PNuE)of 88 plant species.Further investigation of the relationships between No emission potential and leaf traits were performed by simple linear regression analysis and pair-wise correlation coefficients analysis.Important Findingsmajor results are as follows:(1)No emission from plant species exhibited large variations,ranging from 0 to 41.7 nmol m^(−2) h^(−1),and the species frequency distributions of No emission potential could be fitted to a log-normal curve.(2)among 88 species,No emission potential was the highest in Podocarpus macrophyllus,but lowest in Zanthoxylum nitidum and Vernicia montana.(3)No emission potential has strong correlation to leaf N content,Pn and PNuE.The variations in No emission potential among diverse plant species may be closely related to leaf N level and net photosynthetic ability.

Study of Spectral Response Characteristics of Oilseed Rape (Brassica napus) to Particulate Matters Based on Hyper-Spectral Technique

Haze is mainly caused by the suspended particulate matters in the air,of which the particulate matters pollution harms leaf vegetables.In this paper,oilseed rapes at four different growing periods were investigated in a simulated particulate pollution environment.In combination of hyper-spectral technology and micro examination,the response of hyper-spectral characteristics of the leaf to particulate matters was investigated in-depth.The hyperspectral,chlorophyll content,net photosynthetic rate and stomatal conductance of leaf were obtained.The deposition and adsorption of particulate matters on the leaf were observed by Environmental Scanning Electron Microscope(ESEM).Normalized difference vegetation index(NDVI),modified red edge normalized(mNDVI705)and modified red edge simple ratio index(mSR705)were selected as characteristic parameters and the range of 510 nm~620 nm as the sensitive band.16 methods were used to establish the physiological information inversion model.The main results were as follows:Under the influence of particulate matters,the spectral reflectance decreased as a whole.With the increase of leaf age,the phenomenon of blue shift aggravated.The amplitude of yellow and blue edge decreased with overall decreasing vegetation indices.The furrows and irregular band protrusions in leaves were favorable for keeping particulate matters.With longer affecting time and more deposition of particle matters on the leaf,the stomatal opening became smaller.After comparing,principal component regression(PCR)+multiple scatter correction(MSC)+second derivative(SD)+Savitzky-Golay smooth(SG),and partial least square(PLS)+multiple scatter correction(MSC)+first derivative(FD)+Savitzky-Golay smooth(SG)were determined the best method to establish the inversion model of chlorophyll content and net photosynthetic rate respectively.This study may bring novel ideas for the diagnosis and analysis of the physiological response of leaf vegetables under particulate matters pollution using hyper-spectral technology.

Adjusting Nitrogen Application in Accordance with Soil Water Availability Enhances Yield and Water Use by Regulating Physiological Traits of Maize under Drip Fertigation

Knowledge of the interactive effects of water and nitrogen(N)on physio-chemical traits of maize(Zea mays L.)helps to optimize water and N management and improve productivity.A split-plot experiment was conducted with three soil water conditions(severe drought,moderate drought,and fully water supply referring to 45%-55%,65%-75%,and 85%-95%field capacity,respectively)and four N application rates(N0,N150,N240,and N330 referring to 0,150,240,330 kg N ha^(-1)respectively)under drip fertigation in 2014 and 2015 in the Huang-Huai-Hai Plain of China.The results indicated that drought stress inhibited physiological activity of plants(leaf relative water content,root bleeding sap,and net photosynthetic rate),resulting in low dry matter accumulation after silking,yield,and N uptake,whereas increased WUE and NUE.N application rates over than 150 kg ha^(-1)aggravated the inhibition of physiological activity under severe drought condition,while it was offset under moderate drought condition.High N application rates(N330)still revealed negative effects under moderate drought condition,as it did not consistently enhance plant physiological activity and significantly reduced N uptake as compared to the N240 treatment.With fully water supply,increasing N application rates synergistically enhanced physiological activity,promoted dry matter accumulation after silking,and increased yield,WUE,and N uptake.Although the N240 treatment reduced yield by 5.4%in average,it saved 27.3%N under full water supply condition as compared with N330 treatment.The results indicated that N regulated growth of maize in aspects of physiological traits,dry matter accumulation,and yield as well as water and N use was depended on soil water status.The appropriate N application rates for maize production was 150 kg ha^(-1)under moderate drought or 240 kg ha^(-1)under fully water supply under drip fertigation,and high N supply(>150 kg ha^(-1))should be avoided under severe drought condition.

Development of a Compound Photorespiration Inhibitor and Its Application on Sweet Cherry

[Objectives]This study was conducted to investigate the effects of compound photorespiration inhibitors on related indexes of sweet cherry.[Methods]With the main sweet cherry variety‘Meizao’as a test material,relevant research work was carried out.[Results]Several compound photorespiration inhibitors had a better promotion effect on the photosynthetic capacity,yield and quality of sweet cherry variety‘Meizao’,and especially,the combination of 300 mg/L sodium bicarbonate,300 mg/L sodium bisulfite,300 mg/L 2,3-epoxypropionic acid and 1.5%tween-80 had the best effect.[Conclusions]The combined use of the three photorespiration inhibitors is better than the single use,and produces a good synergistic effect.

Effects of Low Temperature and Poor Light Environments under LED Lighting on Quality Change of Pepper Seedlings during Storage

Storage and transportation of vegetable commercial seedlings becomes an important link along with the continuous expansion of planting areas of facility vegetables and vegetable seedling culture industry. In this study,pepper variety‘Nongda 24' was as the experimental material,and changes in the morphological and physiological indicators of plug seedlings in different low temperature( 6 and 11℃) and poor light environments were studied to find suitable storage environmental conditions. The results showed that pepper seedlings could be stored and transported for 14 days when storage temperature was 11℃ and light conditions such as light intensity and photoperiod were 30 μmol/( m^2·s)and 12 h/d by using a fluorescent lamp with R∶ B ratio of 1. 9,and 15 μmol/( m^2·s) and 24 h/d by using LED with R∶ B ratio of 1. 3,respectively. Moreover,the quality of pepper seedlings could be protected effectively. Compared to the fluorescent lamp,LED with high luminous efficiency and low energy consumption was suitable for the storage or long-distance transportation of pepper seedlings in low temperature and poor light environments.

Short-term Response of Photosynthesis and Chlorophyll Content to Salinity Stress in Two Mangrove Species:Aegiceras corniculatum and Kandelia candel

There were fewer comparative studies on the adaptability of mangrove plants with two different salt secretion mechanisms to salinity stress. In this study,the seedlings of mangrove plants Aegiceras corniculatum and Kandelia candel were selected as the research objects,and the methods of hydroponics with different salinity gradients were used. The salinity of 0‰,10‰,and 30‰ was applied respectively to simulate the adaptability of seedlings at low,moderate,and severe salinity stresses. Based on the results,the short-term responses of photosynthesis and chlorophyll content to salinity stress in two mangrove species with different salt secretion mechanisms were analyzed and discussed. The results show that A. corniculatum was more tolerant to10‰ salinity than K. candel,and the net photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance( Gs) and water use efficiency(WUE)were also relatively higher;both A. corniculatum and K. candel could acclimate the low salinity(0‰),but showed severe osmotic stress at 30‰ salinity;A. corniculatum was more sensitive to severe salinity(30‰) than K. candel. These results can be of help to provide a theoretical support for the selection of species for mangrove wetlands restoration and seedlings acclimatization in tidal flats.

Effects of environment lighting on the growth,photosynthesis,and quality of hydroponic lettuce in a plant factory

Leafy vegetable production under controlled environment using artificial lighting has many advantages over conventional greenhouses and open-field production.However,high initial investment and operation costs are restricting the wide application of this technology.In order to design an optimal artificial lighting environment for lettuce production,effects of different combinations of light intensity,photoperiod,and light quality on growth,quality,photosynthesis,and energy use efficiency of lettuce(Lactuca sativa L.cv Ziwei)were investigated under a closed plant factory.Lettuce transplants were grown under photosynthetic photon flux density(PPFD)at 150μmol/m^(2)·s,200μmol/m^(2)·s,250μmol/m^(2)·s,and 300μmol/m^(2)·s provided by fluorescent lamps(FL)with a red to blue ratio(R:B ratio)of 1.8 and light-emitting diode(LED)lamps with R:B ratio of 1.2 and 2.2,in combination with photoperiod of 12 and 16 h/d.In order to examine the“long term”photosynthetic characteristics,net photosynthetic rates of hydroponic lettuce leaves were continuously measured for 2 d(15^(th) and 16^(th) day after transplanting)before harvest.There was no difference in leaf fresh weight(FW)between PPFD of 250μmol/m^(2)·s and 300μmol/m^(2)·s with photoperiod of 16 h/d,regardless of light quality,and same results showed in contents of nitrate,soluble sugar,and vitamin C,respectively.The results of continuous measurements of net photosynthetic rate of lettuce leaves before harvest indicated that plants grown at PPFD of 250μmol/m^(2)·s had consistently higher compared to those grown at PPFD of 300μmol/m^(2)·s.Combining the results from growth,photosynthesis,quality,and energy consumption,it can be concluded that PPFD at 250μmol/m^(2)·s with photoperiod of 16 h/d under LED with R:B ratio of 2.2 is a suitable light environment for maximum growth and high quality of commercial lettuce(cv.Ziwei)production under indoor controlled environment.

A photosynthesis continuous monitoring system for CAM plants

Diurnal CO_(2) exchanges in crassulacean acid metabolism(CAM)plants are significantly different from those in C3 and C4 plants.The instantaneous short-time CO_(2) exchange of a single leaf measured by commercial portable photosynthesis measuring systems with a small leaf chamber cannot reflect the plant photosynthetic capacity for CAM plants because of the CO_(2) fixation property.Therefore,a photosynthesis continuous monitoring system with two canopy cuvettes was developed for measuring diurnal net CO_(2) exchange rates for CAM plants.To evaluate stability and applicability of the photosynthesis continuous monitoring system,continuous measurement of net CO_(2) exchange rates of plants with different photosynthetic pathways were conducted.An obligate CAM plant(Kalanchoe daigremontiana),four facultative CAM plants(Dendrobium officinale,D.chrysotoxum,D.nobile,and D.primulinum),a C3 plant(Strawberry,Fragaria ananassa),and a C4 plant(Corn,Zea mays)were selected as model plants.K.daigremontiana had a significant CO_(2) absorption during the dark period and its net CO_(2) exchange rates fluctuated around 0μmol/(m^(2)·s)during the photoperiod in a growth chamber.Net CO_(2) exchange rates of F.ananassa and Z.mays in a greenhouse gradually increased after sunrise,reaching a maximum at about 12:00,and then gradually decreased to negative values during the night time.It is interesting to observe that D.officinale in the greenhouse and growth chamber absorbed CO_(2) during both day and night times.The photosynthetic pathways of D.chrysotoxum,D.nobile,and D.primulinum were also well distinguished by this photosynthesis continuous monitoring system.The results showed that the photosynthesis continuous monitoring system is capable for quantitative evaluation of diurnal net CO_(2) exchange characteristics not only in the CAM plants but also in small size C3 and C4 plants with low net photosynthetic rates for long-time and high-accuracy measurements.