Growth,leaf anatomy,and photosynthesis of cotton(Gossypium hirsutum L.)seedlings in response to four light-emitting diodes and high pressure sodium lamp

Background Light is a critical factor in plant growth and development,particularly in controlled environments.Light-emitting diodes(LEDs)have become a reliable alternative to conventional high pressure sodium(HSP)lamps because they are more efficient and versatile in light sources.In contrast to well-known specialized LED light spectra for vegetables,the appropriate LED lights for crops such as cotton remain unknown.Results In this growth chamber study,we selected and compared four LED lights with varying percentages(26.44%–68.68%)of red light(R,600–700 nm),combined with other lights,for their effects on growth,leaf anatomy,and photosynthesis of cotton seedlings,using HSP lamp as a control.The total photosynthetic photon flux density(PPFD)was(215±2)μmol·m-2·s-1 for all LEDs and HSP lamp.The results showed significant differences in all tested parameters among lights,and the percentage of far red(FR,701–780 nm)within the range of 3.03%–11.86%was positively correlated with plant growth(characterized by leaf number and area,plant height,stem diameter,and total biomass),palisade layer thickness,photosynthesis rate(Pn),and stomatal conductance(Gs).The ratio of R/FR(4.445–11.497)negatively influenced the growth of cotton seedlings,and blue light(B)suppressed stem elongation but increased palisade cell length,chlorophyll content,and Pn.Conclusion The LED 2 was superior to other LED lights and HSP lamp.It had the highest ratio of FR within the total PPFD(11.86%)and the lowest ratio of R/FR(4.445).LED 2 may therefore be used to replace HPS lamp under controlled environments for the study of cotton at the seedling stage.

Effects of Elevated CO 2 and High Temperature on Single Leaf and Canopy Photosynthesis of Rice

The increase of atmospheric CO 2 concentration is indisputable. In such condition, photosynthetic response of leaf is relatively well studied, while the comparison of that between single leaf and whole canopy is less emphasized. The stimulation of elevated CO 2 on canopy photosynthesis may be different from that on single leaf level. In this study, leaf and canopy photosynthesis of rice (Oryza sativa L.) were studied throughout the growing season. High CO 2 and temperature had a synergetic stimulation on single leaf photosynthetic rate until grain filling. Photosynthesis of leaf was stimulated by high CO 2, although the stimulation was decreased by higher temperature at grain filling stage. On the other hand, the simulation of elevated CO 2 on canopy photosynthesis leveled off with time. Stimulation at canopy level disappeared by grain filling stage in both temperature treatments. Green leaf area index was not significantly affected by CO 2 at maturity, but greater in plants grown at higher temperature. Leaf nitrogen content decreased with the increase of CO 2 concentration although it was not statistically significant at maturity. Canopy respiration rate increased at flowering stage indicating higher carbon loss. Shading effect caused by leaf development reached maximum at flowering stage. The CO 2 stimulation on photosynthesis was greater in single leaf than in canopy. Since enhanced CO 2 significantly increased biomass of rice stems and panicles, increase in canopy respiration caused diminishment of CO 2 stimulation in canopy net photosynthesis. Leaf nitrogen in the canopy level decreased with CO 2 concentration and may eventually hasten CO 2 stimulation on canopy photosynthesis. Early senescence of canopy leaves in high CO 2 is also a possible cause.

Effects of Different Levels of Phosphorus Nutrient on the Photosynthesis Characteristic of Rice Flag Leaf

[Objective] To provide scientific basis for high phosphorus efficiency cultivation and regulation of rice. [Method] Changbai9 （CB9） and Jijing81 （JJ81） were used as experimental materials for pot experiment, and five levels of phosphorus nutrient （ Po - P4 ） were set for each variety, the net photosynthesis rate, Chlorophyll Meter Readings （SPAD Readings）, stomatal conductance, transpiration rate, intercellular CO2 concentration, and stomatal limitation were observed and compared between five different phosphorus levels at filling stage. [ Result] The net photosynthesis rate of CB9 reached the highest at P3, and was significantly different from other treatments （P 〈0.05）;the net photosynthesis rate of groups with phosphorus of J J81 were higher than that of the control group,and reached the highest at P,. The SPAD Readings of CB9 and JJ81 all achieved the highest at P3, and stomatal conductance and transpiration rate were all at first increased then decreased with the phosphor- us increased in CB9 and JJ81. With the phosphorus increased, intercellular CO2 concentration of CB9 decreased at first and then increased, while in JJ81 the trend was inversed,but the tendency of intercellular CO2 concentration were opposite to that of stomatal limitation in both culti- vars. [ Conclusion] Appropriate adding phosphorus could improve photosynthetic characteristic of rice flag-leaf,but displayed significant genotypic difference.

Effect of Seedling Raising Methods on Leaf Photosynthesis and Grain Yield of Mechanically-transplanted Japonica Rice

This study was conducted to investigate the effects of seedling raising modes on photosynthetic charactedsticsand grain yield under wheat straw returning. Four representative cultivars in Huaibei area were selected as test materials. By setting potted seedlings and carpet seedlings, the effects of different nursery meth- ods on the photosynthesis of rice at different growth stages in Huaibei area were investigated. Compared with carpet seedlings, the leaf area index of potted seedlings decreased at the maturation stage, but the dry weight of leaf shewed no significant difference.The SPAD of potted seedlings had an increasing trend after transplanting, but the SPAD increased differently according to cultivars. The net photosynthetic rate, stomatal conductance and transpiration rate of the leaves of pot seeding rice were significantly higher than those of carpet seedling rice on the 85^th d after transplanting. However, theintracellular CO2 concentration and water use efficiency of leaves had no significant differences between different ＇treatments. The results indicate that the photosynthetic capacity of flag leaves of pot seedling rice is stronger in early and middle stages, but the decay rate of photosynthetic function is slightly faster than carpet seedling rice, which might be the main reason for the rice yield of potted seedlings having no remarkable difference from carpet seedlings.

Effects of Salicylic Acid on Photosynthesis and Chlorophyll Fluorescence Characteristics of Fluecured Tobacco Leaf in Subdued Light

[Objective] This study aimed to test whether salicylic acid （SA） can im-prove the physiological functions of flue-cured tobacco under subdued light condition, and to determine the mechanism of its action. [Method] The tobacco plants under subdued light were foliar-sprayed with 100 mg/L of SA. Then, the physiological in-dices such as plant fresh weight and dry weight, chlorophyl content, photosynthetic parameters and chlorophyl fluorescence parameters were measured. SPSS17.0 and Excellwere adopted for variance analysis and significance test. [Result] The leaf photosynthetic rate （Pn）, stomatal conductance （Gs） and transpiration rate （Tr） of tobacco plants in subdued light were al decreased while the intercellular CO2 con-centration （Ci） was increased, suggesting that non-stomatal limitation led to the de-crease of Pn under weak light intensity stress. SA released the inhibition of tobacco plant growth in weak light, as it elevated the leaf photosynthetic rate, the maximum photochemical efficiency of PSⅡ, potential activity of PSⅡ, effective photochemical efficiency of PSⅡ and photochemical quenching coefficient in weak light significant-ly, and reduced the non-photochemical quenching coefficient. [Conclusion] SA has significant effects on the photosynthetic characteristics of flue-cured tobacco in weak light, and it can improve the synthesis or distribution of photosynthesis product, and the efficiency of light energy, conducive to plant growth and development.

Leaf Turgor Potential, Plant Growth and Photosynthesis in Organically Fertilized Sweet Corn

A greenhouse pot experiment was conducted using a complete random design with six replications. A pressure-volume curve analysis was employed to study the effects of organic fertilizers on plant water relations in sweet corn (Zea mays L. cv. Honey-bantam) in terms of leaf osmotic concentration (Cs), osmotic potentials at full turgid status (πFT) and at incipient plasmolysis (πIP), and of symplastic (ζsym) and apoplastic (ζapo) fractions in the tissue water compartment in relation to photosynthetic capacity (Pc) and dry mass accumulation. At the seedling stage (day 15), plants with chemical fertilizer treatments showed lower πFT, πIP and ζapo and higher Cs, ζsym and PC than those with organic fertilizer treatments. Compared to PC and relative growth, where values from day 15 to day 75 were first lower for organic treatments and then higher, ζsym and Cs values were similar, while πFT and πIP were opposite being higher then lower. Dry mass production with organic fertilizer was higher than or close to the chemical fertilizer treatments in the later growth stage (day 75), though dry mass production with chemical fertilizers was much higher in the early and middle growing stages (days 15 and 45). Increased photosynthesis and dry mass production in later growth stages due to organic fertilizers were associated with increased osmotic concentration in the tissue and the symplastic fraction of the tissue water compartment. These might favor stomatal opening and biochemical activities.

Varietal difference in the correlation between leaf nitrogen content and photosynthesis in rice(Oryza sativa L.) plants is related to specific leaf weight

Increasing leaf photosynthesis per area（A） is of great importance to achieve yield further improvement. The aim of this study was to exploit varietal difference in A and its correlation with specific leaf weight（SLW）. Twelve rice cultivars, including 6 indica and 6 japonica varieties, were pot-grown under two N treatments, low N（LN） and sufficient N（SN）. Leaf photosynthesis and related parameters were measured at tillering stage. Compared with LN treatment, A, stomatal conductance（g_s）, mesophyll conductance（g_m）, leaf N content（N_（area））, and chlorophyll content were significantly improved under SN treatment, while SLW and photosynthetic N use efficiency（PNUE） were generally decreased. Varietal difference in A was positively related to both g_s and g_m, but not related to N_（area）. This resulted in a low PNUE in high N_（area） leaves. Varietal difference in PNUE was generally negatively related to SLW. Response of PNUE to N supply varied among different rice cultivars, and interestingly, the decrease in PNUE under SN was negatively related to the decrease in SLW. With a higher N_（area）, japonica rice cultivars did not show a higher A than indica rice cultivars because of possession of high-SLW leaves. Therefore, varietal difference in A was not related to N_（area）, and SLW can substantially interfere with the correlation between A and N_（area）. These findings may provide useful information for rice breeders to maximize A and PNUE, rather than over reliance on N_（area） as an indicator of photosynthetic performance.

Effect of Low Light on the Characteristics of Photosynthesis and Chlorophyll a Fluorescence During Leaf Development of Sweet Pepper

Low light stress is one of the main limiting factors which influence the production of sweet pepper under protected cultivation in China. In this experiment, two genotypes of sweet pepper, ShY （low light-tolerant genotype） and 20078 （low light-sensitive genotype）, were used to study the effects of low light （photosynthetic photon flux density, PPFD was 75- 100 umol m-2 s-1, control 450-500 umol m-2 s-1） on photosynthesis during leaf development. The result indicated that under low light chlorophyll content, net photosynthetic rate （PN）, photosynthetic apparent quantum efficiency （Фi） and carboxylation efficiency （CE） of sweet pepper leaves increased gradually and decreased after reaching the maximum levels. The time to reach the peak values for all the above parameters was delayed, whereas the light compensation point （LCP） decreased gradually along with leaf expansion. The decrease in maximum quantum yield of PS II （Fv/Fm） was not observed at any stages of the leaf development under low light condition, but the actual PS II efficiency under irradiance （ФPS II） was lower accompanied by an increased non-photochemical quenching （NPQ） in young and/or old leaves compared with mature leaves. The antenna thermal dissipation （D） was a main way of heat dissipation when young leaves received excessive light energy, while the decline in photosynthetic function in senescence leaf was mostly owing to the decrease in carbon assimilation capacity, followed by a significantly increased allocation of excessive energy （Ex）. Compared with 20078, ShY could maintain higher PN, ФPS II and lower QA reduction state for a longer time during leaf development. Thus, in ShY photosynthetic efficiency and the activity of electron transport of PS II were not significantly affected due to low light stress.

Yield photosynthesis and leaf anatomy of maize in inter-and mono-cropping systems at varying plant densities

Increasing plant density can increase cereal crop yields. However, the physiological and anatomical mechanisms of grain yield increase at high plant densities in maize-based intercropping systems are not well understood. A two-year field experiment was conducted in 2018 and 2019 to investigate grain yield, photosynthetic characteristics, stomatal traits, and leaf anatomy of maize plants in an intercropping system with high plant densities. Two cropping patterns(monocropping and intercropping) and three plant densities(D1, 78,000 plants ha^(-1);D2, 103,500 plants ha^(-1);D3, 129,000 plants ha;were arranged in a randomized block design. Increasing maize plant density significantly increased maize yield, and intercropping gave a significant yield advantage over monocropping under the same plant density. Intercropping combined with high plant density increased the leaf area and SPAD value of maize,increasing the photosynthesis rates after the harvest of pea. At the twelfth leaf stage, the stomatal density and stomatal area of intercrops combined with medium plant density increased by respectively 10.5%and 18.4% relative to their values for the corresponding density of monocrops. Although leaf thickness of maize was reduced by increasing plant density, the chloroplast number and grana lamella number were higher in intercropping than in monocropping under different plant densities. These positive changes in leaf anatomy resulted in increased photosynthesis, suggesting a physiological basis for the increase in grain yield.

Effect of Phosphorus Deficiency on Leaf Photosynthesis and Carbohydrates Partitioning in Two Rice Genotypes with Contrasting Low Phosphorus Susceptibility

To study the effect of phosphorus （P） deficiency on leaf photosynthesis and carbohydrates partitioning and to determine whether the characteristics of leaf photosynthesis and carbohydrates partitioning are related to low P tolerance in rice plants, a hydroponic culture experiment supplied with either sufficient P （10 mg/L） or deficient P （0.5 mg/L） was conducted by using two rice genotypes different in their responses to low P stress. Results showed that the plant growth of Zhenongda 454 （low P tolerant genotype） was less affected by P deficiency compared with Sanyang＇ai （low P sensitive genotype）. Under P-deficient conditions, photosynthetic rates of Zhenongda 454 and Sanyang＇ai were decreased by 16% and 35%, respectively, and Zhenongda 454 showed higher photosynthetic rate than Sanyang＇ai. Phosphorus deficiency decreased the stomatal conductance for both genotypes, but had no significant influence on leaf internal CO2 concentration （Ci）, suggesting that the decrease in leaf photosynthetic rate of rice plants induced by P deficiency was not due to stomatal limitation. Phosphorus deficiency increased the concentration of soluble carbohydrates and sucrose in shoots and roots for both genotypes, and also markedly increased the allocation of soluble carbohydrates and sucrose to roots. Under deficient P supply, Zhenongda 454 had higher root/shoot soluble carbohydrates content ratio and root/shoot sucrose content ratio than Sanyang＇ai. In addition, phosphorus deficiency increased the concentration of starch in roots for both genotypes, whereas had no effect on the content of starch in shoots or roots. Compared to genotype Sanyang＇ai, the better tolerance to low-P stress of Zhenongda 454 can be explained by the fact that Zhenongda 454 maintains a higher photosynthetic rate and a greater ability to allocate carbohydrates to the roots under P deficiency.

Leaf Photosynthesis in Response to Removing Fruit During Different Phenological Stages of Fruit Development in Peach Trees

Removing fruit (RF) and retaining fruit (CK) were carried out during different phenological stages of fruit development onone-year-old shoot of Okubo peach trees [Prunus persica (L.) Batsch.] under preventing exportation of the assimilates tothe non experimental parts of the tree by girdling one-year-old shoot and keeping the same leaves between RF and CK.The results showed that fruit removal significantly decreased net photosynthetic rate (Pn), stomatal conductance (Gs)and transpiration rate (E), but significantly increased leaf surface temperature (TLeaf ) at about midday as compared with CK.Internal CO2 concentration, soluble sugar content, reductive sugar content, starch content except that during the finalrapid fruit growth stage, ADP-glucose pyrophosphorylase and amylase activities in source leaves were not significantlyaffected by fruit removal. There was a significantly positive parabolic correlation between Pn and Gs, and a strongpositive linear correlation between Pn and E. Moreover, Pn increased with increased TLeaf if TLeaf was below 38°C, thendecreased sharply when TLeaf exceeded the above critical temperature for both RF and CK. Pn of RF was lower, however,than that of CK in the same TLeaf , especially if TLeaf exceeded 38°C. It is suggested that the decreased stomatal aperture andincreased TLeaf may be the important mechanism in regulating photosynthesis under a decreased strength of sink demandby RF in fruit trees.

QTL analysis of leaf photosynthesis rate and related physiological traits in Brassica napus

Rapeseed （Brassica napus L.） oil is the crucial source of edible oil in China. In addition, it can become a major renewable and sustainable feedstock for biodiesel production in the future. It is known that photosynthesis products are the primary sources for dry matter accumulation in rapeseed. Therefore, increasing the photosynthetic efficiency is desirable for the raise of rapeseed yield. The objective of the present study was to identify the genetic mechanism of photosynthesis based on the description of relationships between different photosynthetic traits and their quantitative trait loci （QTL） by using a recombinant inbred line （RIL） population with 172 lines. Specifically, correlation analysis in this study showed that internal CO2 concentration has negative correlations with other three physiological traits under two different stages. Totally, 11 and 12 QTLs of the four physiological traits measured at the stages 1 and 2 were detected by using a high-density single nu- cleotidepolymorphism （SNP） markers linkage map with composite interval mapping （CIM）, respectively. Three co-localized QTLs on A03 were detected at stage 1 with 5, 5, and 10% of the phenotypic variation, respectively. Other two co-localized QTLs were located on A05 at stage 2, which explained up to 12 and 5% of the phenotypic variation, respectively. The results are beneficial for our understanding of genetic control of photosynthetic physiological characterizations and improvement of rapeseed yield in the future.

Leaf photosynthesis and yield components of mung bean under fully open-air elevated[CO_2]

Mung bean（Vigna radiata L.） has the potential to establish symbiosis with rhizobia,and symbiotic association of soil micro flora may facilitate the photosynthesis and plant growth response to elevated[CO2].Mung bean was grown at either ambient CO2 400 μmol mol^（-1） or[CO2]（（550＋17） μmol mol^（-1）） under free air carbon dioxide enrichment（FACE） experimental facility in North China.Elevated[CO2]increased net photosynthetic rate（Pn）,water use efficiency（WUE） and the non-photochemical quenching（NPQ） of upper most fully-expanded leaves,but decreased stomatal conductance（Gs）,intrinsic efficiency of PSII（Fv ＇/Fm＇）,quantum yield of PSII（φ（PSll）） and proportion of open PSII reaction centers（qp）.At elevated[CO2],the decrease of Fv＇/Fm＇,φ（PSII）,qp at the bloom stage were smaller than that at the pod stage.On the other hand,Pn was increased at elevated[CO2]by 18.7 and 7.4%at full bloom（R2） and pod maturity stages（R4）,respectively.From these findings,we concluded that as a legume despite greater nutrient supply to the carbon assimilation at elevated[CO2],photosynthetic capacity of mung bean was still suppressed under elevated[CO2]particularly at pod maturity stage but plant biomass and yield was increased by 11.6 and 14.2%,respectively.Further,these findings suggest that even under higher nutrient acquisition systems such as legumes,nutrient assimilation does not match carbon assimilation under elevated[CO2]and leads photosynthesis down-regulation to elevated[CO2].

Effects of post-silking water deficit on the leaf photosynthesis and senescence of waxy maize

Waxy maize is widely cultivated under rainfed conditions and frequently suffers water shortage during the late growth stage.In this study,a pot trial was conducted to examine the effects of post-silking drought on leaf photosynthesis and senescence and its influence on grain yield.Two waxy maize hybrids,Suyunuo 5(SYN5)and Yunuo 7(YN7),were grown under the control and drought(soil moisture content was 70–80%and 50–60%,respectively)conditions after silking in 2016 and 2017.The decrease in yield was 11.1 and 15.4%for YN7 and SYN5,respectively,owing to the decreased grain weight and number.Post-silking dry matter accumulation was reduced by 27.2%in YN7 and 26.3%in SYN5.The contribution rate of pre-silking photoassimilates transferred to grain yield was increased by 15.6%in YN7 and 10.2%in SYN5,respectively.Post-silking drought increased the malondialdehyde content,but decreased the contents of water,soluble protein,chlorophyll,and carotenoid in the leaves.The weakened activities of enzymes involved in photosynthesis(ribulose-1,5-bisphosphate carboxylase and phosphoenolpyruvate carboxylase)and antioxidant system(catalase,superoxide dismutase and peroxidase)reduced the photosynthetic rate(Pn)and accelerated leaf senescence.The correlation results indicated that reduced Pn and catalase activity and increased malondialdehyde content under drought conditions induced the decrease of post-silking photoassimilates deposition,ultimately resulted in the grain yield loss.

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.

Effect of overnight temperature on leaf photosynthesis in seedlings of Swietenia macrophylla King

After exposure of one-year old seedlings of Swietenia macrophylla to an overnight temperature (13 C, 19 C, 25 C, 31 C or 35 C), the leaf net photosynthetic rate (Pn) was researched through measuring photosynthetic light-response curves at 360 mmolmol-1 CO2, and photosynthetic CO2-response curves at light-saturated intensity (1500 mmolm-2 s-1). The optimal temperature for photosynthesis measured at 360 mmol穖ol-1 CO2 was from 25 C to 31 C, but which was from 31C to 35 C at saturating CO2 concentration. At temperature of below 25 C, the decline in Pn was mainly due to the drop in carboxylation efficiency (Ce), while as temperature was over 31 C, the reduction in Pn resulted from both decrease in Ce and increase in leaf respiration. The CO2-induced stimulation of photosynthesis was strongly inhibited at temperatures below 13 C. The results showed that, the leaf photosynthesis of tropical evergreen plants should not be accelerated at low temperature in winter season with elevated CO2 concentration in the future.

Effects of mepiquat chloride and plant population density on leaf photosynthesis and carbohydrate metabolism in upland cotton

Background Mepiquat chloride(MC)application and plant population density(PPD)increasing are required for modern cotton production.However,their interactive effects on leaf physiology and carbohydrate metabolism remain obscure.This study aimed to examine whether and how MC and PPD affect the leaf morpho-physiological characteristics,and thus final cotton yield.PPD of three levels(D1:2.25 plants·m^(-2),D2:4.5 plants·m^(-2),and D3:6.75 plants·m^(-2))and MC dosage of two levels(MC0:0 g·ha^(-2),MC1:82.5 g·ha^(-2))were combined to create six treatments.The dynamics of nonstructual carbohydrate concentration,carbon metabolism-related enzyme activity,and photosynthetic attributes in cotton leaves were examined during reproductive growth in 2019 and 2020.Results Among six treatments,the high PPD of 6.75 plants·m^(-2)combined with MC application(MC1D3)exhibited the greatest seed cotton yield and biological yield.The sucrose,hexose,starch,and total nonstructural carbohydrate(TNC)concentrations peaked at the first flowering(FF)stage and then declined to a minimum at the first boll opening(FBO)stage.Compared with other treatments,MC1D3 improved starch and TNC concentration by 5.4%~88.4%,7.8%~52.0% in 2019,and by 14.6%~55.9%,13.5%~39.7% in 2020 at the FF stage,respectively.Additionally,MC1D3 produced higher transformation rates of starch and TNC from the FF to FBO stages,indicating greater carbon production and utilization efficiency.MC1D3 displayed the maximal specific leaf weight(SLW)at the FBO stage,and the highest chlorophyll a(Chl a),Chl b,and Chl a+b concentration at the mid-late growth phase in both years.The Rubisco activity with MC1D3 was 2.6%~53.2% higher at the flowering and boll setting stages in both years,and 2.4%~52.7% higher at the FBO stage in 2020 than those in other treatments.These results provided a explanation of higher leaf senescence-resistant ability in MC1D3.Conclusion Increasing PPD coupled with MC application improves cotton yield by enhancing leaf carbohydrate production and utilization efficiency and delaying leaf senescence.

Effects of Different Water and Fertilizer Combinations on Tree Structure,Leaf Parameters and Photosynthesis of Apple Saplings

[ Objective] This study aimed to investigate the effects of different water and fertilizer combinations on apple saplings. [ Method] ＇ Tianhong 2＇ Fuji /SH40/Malus robusta Rehd. was used as the experimental material to analyze the effects of different irrigation modes and combinations of basal fertilizer and dressing fertilizer on tree structure, leaf parameters and photosynthesis of apple saplings. [ Result] The results showed that different water and fertilizer combinations ex- hibited varying effects on tree structure, leaf parameters and photosynthesis of apple saplings. To be specific, applying 432 000 kg/hm2 basal fertilizer, 480 kg/hm2 urea and 915 kg/hmz organic fertilizer ＋ 0 ＋ 915 kg/hm2 organic fertilizer as dressing fertilizer, and 1% urea as leaf fertilizer was conducive to promoting growth of branches and leaves, increasing leaf thickness, individual leaf area and SPAD, and improving photosynthesis of apple saplings under half root irrigation and whole root irrigation conditions. In addition, the effects were more significant under whole root irrigation conditions. [ Conclusion] Selecting the appropriate water and fertilizer combination is conducive to the growth of apple saplings.

Synergistic effects of carbon cycle metabolism and photosynthesis in Chinese cabbage under salt stress

Chinese cabbage(Brassica rapa ssp. pekinensis) has a long cultivation history and is one of the vegetable crops with the largest cultivation area in China. However, salt stress severely damages photosynthesis and hormone metabolism, nutritional balances, and results in ion toxicity in plants. To better understand the mechanisms of salt-induced growth inhibition in Chinese cabbage, RNA-seq and physiological index determination were conducted to explore the impacts of salt stress on carbon cycle metabolism and photosynthesis in Chinese cabbage. Here, we found that the number of thylakoids and grana lamellae and the content of starch granules and chlorophyll in the leaves of Chinese cabbage under salt stress showed a time-dependent response, first increasing and then decreasing. Chinese cabbage increased the transcript levels of genes related to the photosynthetic apparatus and carbon metabolism under salt stress, probably in an attempt to alleviate damage to the photosynthetic system and enhance CO_(2) fixation and energy metabolism. The transcription of genes related to starch and sucrose synthesis and degradation were also enhanced;this might have been an attempt to maintain intracellular osmotic pressure by increasing soluble sugar concentrations. Soluble sugars could also be used as potential reactive oxygen species(ROS) scavengers, in concert with peroxidase(POD)enzymes, to eliminate ROS that accumulate during metabolic processes. Our study characterizes the synergistic response network of carbon metabolism and photosynthesis under salt stress.

ZmbZIP27 regulates nitrogen-mediated leaf angle by modulating lignin deposition in maize

In grain crops such as maize(Zea mays),leaf angle(LA)is a key agronomic trait affecting light interception and thus planting density and yield.Nitrogen(N)affects LA in plants,but we lack a good understanding of how N regulates LA.Here,we report that N deficiency enhanced lignin deposition in the ligular region of maize seedlings.In situ hybridization showed that the bZIP transcription factor gene ZmbZIP27 is mainly expressed in the phloem of maize vascular bundles.Under N-sufficient conditions,transgenic maize overexpressing ZmbZIP27 showed significantly smaller LA compared with wild type(WT).By contrast,zmbzip27_(ems)mutant showed larger LA under both N-deficient and N-sufficient conditions compared with WT.Overexpression of ZmbZIP27 enhanced lignin deposition in the ligular region of maize in the field.We further demonstrated that ZmbZIP27 could directly bind the promoters of the microRNA genes ZmMIR528a and ZmMIR528b and negatively regulate the expression levels of ZmmiR528.ZmmiR528 knockdown transgenic maize displayed erect architecture in the field by increasing lignin content in the ligular region of maize.Taken together,these results indicate that ZmbZIP27 regulates N-mediated LA size by regulating the expression of ZmmiR528 and modulating lignin deposition in maize.