Photosynthetic response dynamics in the invasive species Tithonia diversifolia and two co-occurring native shrub species under fluctuating light conditions

To determine the invasiveness of invasive plants,many studies have compared photosynthetic traits or strategies between invasive and native species.However,few studies have compared the photosynthetic dynamics between invasive and native species during light fluctuations.We compared photosynthetic induction,relaxation dynamics and leaf traits between the invasive species,Tithonia diversifolia and two native species,Clerodendrum bungei and Blumea balsamifera,in full-sun and shady habitats.The photosynthetic dynamics and leaf traits differed among species.T.diversifolia showed a slower induction speed and stomatal opening response but had higher average intrinsic water-use efficiency than the two native species in full-sun habitats.Thus,the slow induction response may be attributed to the longer stomatal length in T.diversifolia.Habitat had a significant effect on photosynthetic dynamics in T.diversifolia and B.balsamifera but not in C.bungei.In shady habitat,T.diversifolia had a faster photosynthetic induction response than in full-sun habitat,leading to a higher average stomatal conductance during photosynthetic induction in T.diversifolia than in the two native species.In contrast,B.balsamifera had a larger stomatal length and slower photosynthetic induction and relaxation response in shady habitat than in full-sun habitat,resulting in higher carbon gain during photosynthetic relaxation.Nevertheless,in both habitats,T.diversifolia had an overall higher carbon gain during light fluctuations than the two native species.Our results indicated that T.diversifolia can adopt more effective response strategies under fluctuating light environments to maximize carbon gain,which may contribute to its successful invasion.

Effects of thinning on the understory light environment of different stands and the photosynthetic performance and growth of the reforestation species Phoebe bournei

Light levels determine regeneration in stands and a key concern is how to regulate the light environment of different stand types to the requirements of the understory.In this study,we selected three stands typical in south China(a Cryptomeria japonica plantation,a Quercus acutissima plantation,and a mixed stand of both)and three thinning intensities to determine the best understory light environ-ment for 3-year-old Phoebe bournei seedlings.The canopy structure,understory light environment,and photosynthe-sis and growth indicators were assessed following thin-ning.Thinning improved canopy structure and understory light availability of each stand;species composition was the reason for differences in the understory light environ-ment.Under the same thinning intensity,the mixed stand had the greatest light radiation and most balanced spectral composition.P.bournei photosynthesis and growth were closely related to the light environment;all three stands required heavy thinning to create an effective and sustained understory light environment.In a suitable understory light environment,the efficiency of light interception,absorption,and use by seedlings was enhanced,resulting in a higher carbon assimilation the main limiting factor was stomatal conductance.As a shade-avoidance signal,red/far-red radia-tion is a critical factor driving changes in photosynthesis and growth of P.bournei seedlings,and a reduction increased light absorption and use capacity and height:diameter ratios.The growth advantage transformed from diameter to height,enabling seedlings to access more light.Our findings suggest that the regeneration of shade-tolerant species such as P.bournei could be enhanced if a targeted approach to thinning based on stand type was adopted.

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 thinning and understory removal on water use efficiency of Pinus massoniana:evidence from photosynthetic capacity and stable carbon isotope analyses

Understanding the relationship between forest management and water use efficiency(WUE)is important for evaluating forest adaptability to climate change.However,the effects of thinning and understory removal on WUE and its key controlling processes are not well understood,which limits our comprehension of the physiological mechanisms of various management practices.In this study,four forest management measures(no thinning:NT;understory removal:UR;light thinning:LT;and heavy thinning:HT)were carried out in Pinus massoniana plantations in a subtropical region of China.Photosynthetic capacity and needle stable carbon isotope composition(δ^(13)C)were measured to assess instantaneous water use efficiency(WUE_(inst))and long-term water use efficiency(WUE_(i)).Multiple regression models and structural equation modelling(SEM)identified the effects of soil properties and physiological performances on WUE_(inst)and WUE_(i).The results show that WUE_(inst)values among the four treatments were insignificant.However,compared with the NT stand(35.8μmol·mol^(-1)),WUE_(i)values significantly increased to 41.7μmol·mol^(-1)in the UR,50.1μmol·mol^(-1)in the LT and 46.6μmol·mol^(-1)in HT treatments,largely explained by photosynthetic capacity and soil water content.Understory removal did not change physiological performance(needle water potential and photosynthetic capacity).Thinning increased the net photosynthetic rate(A_n)but not stomatal conductance(g_s)or predawn needle water potential(ψ_(pd)),implying that the improvement in water use efficiency for thinned stands was largely driven by radiation interception than by soil water availability.In general,thinning may be an appropriate management measure to promote P.massoniana WUE to cope with seasonal droughts under future extreme climates.

The photosynthetic oxygen evolution does not exclude the important role and contribution of bicarbonate photolysis

Photosynthesis is the most important biochemical reaction on Earth. It has co-evolved and developed with the Earth, driving the biogeochemical cycle of all elements on the planet and serving as the only chemical process in nature that can convert light energy into chemical energy. Some heavy oxygen isotopic(^(18)O) labeling experiments have"conclusively" demonstrated that the oxygen released by photosynthesis comes only from water and are written into textbooks. However, it is not difficult to find that bicarbonate has never been excluded from the direct substrate of photosynthesis from beginning to end during the history of photosynthesis research. No convincing mechanism can be used to explain photosynthetic oxygen evolution solely from water photolysis. The bicarbonate effect, the Dole effect, the thermodynamic convenience of bicarbonate photolysis, the crystal structure characteristics of photosystem Ⅱ, and the reinterpretation of heavy oxygen isotopic labeling(^(18)O)experiments all indicate that the photosynthetic oxygen evolution does not exclude the important role and contribution of bicarbonate photolysis. The recently proposed view that bicarbonate photolysis is the premise of water photolysis, bicarbonate photolysis and water photolysis work together with a 1:1(mol/mol) stoichiometric relationship, and the stoichiometric relationship between oxygen and carbon dioxide released during photosynthetic oxygen evolution is also 1:1, has excellent applicability and objectivity, which can logically and reasonably explain the precise coordination between light and dark reactions during photosynthesis, the bicarbonate effect, the Dole effect, the Kok cycle and the neutrality of water and carbon in nature.This is of great significance for constructing the bionic artificial photosynthetic reactors and scientifically answering the question of the source of elemental stoichiometric relationships in nature.

Exogenous calcium enhances the physiological status and photosynthetic capacity of rose under drought stress

Drought(water shortage)can substantially limit the yield and economic value of rose plants(Rosa spp.).Here,we characterized the effect of exogenous calcium(Ca^(2+))on the antioxidant system and photosynthesis-related properties of rose under polyethylene glycol 6000(PEG6000)-induced drought stress.Chlorophyll levels,as well as leaf and root biomass,were significantly reduced by drought;drought also had a major effect on the enzymatic antioxidant system and increased concentrations of reactive oxygen species.Application of exogenous Ca^(2+)increased the net photosynthetic rate and stomatal conductance of leaves,enhanced water-use efficiency,and increased the length and width of stomata following exposure to drought.Organ-specific physiological responses were observed under different concentrations of Ca^(2+).Application of 5 mmol·L^(-1)Ca^(2+)promoted photosynthesis and antioxidant activity in the leaves,and application of 10 mmol·L^(-1)Ca^(2+)promoted antioxidant activity in the roots.Application of exogenous Ca^(2+)greatly enhanced the phenotype and photosynthetic capacity of potted rose plants following exposure to drought stress.Overall,our findings indicate that the application of exogenous Ca^(2+)enhances the drought resistance of roses by promoting physiological adaptation and that it could be used to aid the cultivation of rose plants.

Effects of dense planting patterns on photosynthetic traits of different vertical layers and yield of wheat under different nitrogen rates

A two-year field experiment was conducted to measure the effects of densification methods on photosynthesis and yield of densely planted wheat.Inter-plant and inter-row distances were used to define ratefixed pattern(RR)and row-fixed pattern(RS)density treatments.Meanwhile,four nitrogen(N)rates(0,144,192,and 240 kg N ha-1,termed N0,N144,N192,and N240)were applied with three densities(225,292.5,and 360×10^(4)plants ha^(-1),termed D225,D292.5,and D360).The wheat canopy was clipped into three equal vertical layers(top,middle,and bottom layers),and their chlorophyll density(Ch D)and photosynthetically active radiation interception(FIPAR)were measured.Results showed that the response of Ch D and FIPAR to N rate,density,and pattern varied with different layers.N rate,density,and pattern had significant interaction effects on Ch D.The maximum values of whole-canopy Ch D in the two seasons appeared in N240 combined with D292.5 and D360 under RR,respectively.Across two growing seasons,FIPAR values of RR were higher than those of RS by 29.37%for the top layer and 5.68%for the middle layer,while lower than those of RS by 20.62%for the bottom layer on average.With a low N supply(N0),grain yield was not significantly affected by density for both patterns.At N240,increasing density significantly increased yield under RR,but D360 of RS significantly decreased yield by 3.72%and 9.00%versus D225 in two seasons,respectively.With an appropriate and sufficient N application,RR increased the yield of densely planted wheat more than RS.Additionally,the maximum yield in two seasons appeared in the combination of D360 with N144 or N192 rather than of D225 with N240 under both patterns,suggesting that dense planting combined with an appropriate N-reduction application is feasible to increase photosynthesis capacity and yield.

Effect of Various Citrus Rootstock-scion Combinations on Tree Growth,Fruit Quality,and Photosynthetic Characteristics under Red Loam Soil Conditions

[Objectives]To investigate the effects of 15 distinct citrus rootstock-scion combinations on tree growth,fruit quality,and photosynthetic characteristics under red loam soil conditions and provide a theoretical foundation for the selection of appropriate citrus rootstock-scion combinations in the Zhaoqing region.[Methods]A total of 15 citrus rootstock-scion combinations were utilized as test materials for a comprehensive analysis of their phenological periods(budding,flowering,and fruiting),tree growth indicators(tree height,crown diameter,and growth),and fruit quality(appearance quality and intrinsic quality).The photosynthetic characteristics of the test materials,including the net photosynthetic rate(Pn),transpiration rate(Tr),water use efficiency(WUE),apparent quantum yield(AQY),and carboxylation efficiency(CE),were analyzed to determine their significance.Additionally,the leaf photosynthetic physiological indicators,such as soluble protein,specific leaf weight,chlorophyll,and carotenoids,were evaluated.[Results]There were notable differences observed in the phenological period,growth potential of trees,fruit quality,and photosynthetic characteristics among various citrus rootstock-scion combinations.The phenological periods exhibited variation contingent on the grafting varieties.In terms of tree growth potential,the Citrus tangerina Tanaka‘Hongju’and C.haniana Hort.‘Suanju’rootstocks demonstrated greater tree height,crown growth,and overall tree strength;however,they were also prone to excessive growth.Conversely,the C.limonia Osbeck‘Hongningmeng’and C.sinensis×P.trifoliata‘Zhicheng’rootstocks displayed medium growth potential,while the Poncirus trifoliate(L)Raf.‘Zhike’rootstock resulted in shorter trees.In terms of fruit quality,the single fruit weight of C.flamea Hort.‘Shatangju’ranged from 33 to 50 g,exhibiting a flat and round shape.The total soluble solids and titratable acid content of‘Shatangju’grafted onto the‘Zhike’rootstock were notably high.In contrast,the single fruit weight of C.haniana Hort.‘Chuntianju’varied between 65 and 81 g,characterized by a high flat round shape.The‘Suanju’rootstock demonstrated a higher sugar and acid content compared to other rootstocks.Additionally,the single fruit weight of C.nobilis Lour.‘Gonggan’ranged from 62 to 145 g,with the fruit shape being either round or oval.The soluble sugar and total soluble solids content associated with the‘Zhike’rootstock was also elevated.In relation to photosynthetic characteristics,the photosynthetic performance of the‘Shatangju’variety was superior when grafted onto the‘Zhike’and‘Hongju’rootstocks.Similarly,the‘Chuntianju’variety exhibited enhanced photosynthetic performance on the‘Zhike’,‘Zhicheng’,and‘Hongju’rootstocks.Furthermore,the‘Gonggan’variety demonstrated improved photosynthetic performance when grafted onto the‘Zhike’and‘Suanju’rootstocks.[Conclusions]Based on the characteristics of the red loam soil in the Zhaoqing region,the rootstocks‘Zhike’and‘Hongju’are conducive to the cultivation of the‘Shatangju’variety.Additionally,the rootstocks‘Zhike’,‘Zhicheng’,and‘Hongju’are optimal for the growth of the‘Chuntianju’variety,while the rootstocks‘Zhike’and‘Suanju’are appropriate for the growth of the‘Gonggan’variety.

Post Cryopreservation Growth Kinetic and Photosynthetic Assessment of an Acid Tolerant Strain of Stichococcus bacillaris

Preserving microbial diversity has become a strategic undertaking. Thus, ex situ microalgal culture conservation results in strategic and functional resource in both biodiversity protection and application domains. Cryopreservation of microalgae has been practiced since the 1960s and is now considered the optimal preservation strategy. Furthermore, the overall monitoring during growth of cultures after freezing/thawing protocols was hardly investigated and there is poor evaluation related to preserve especially the photosystem apparatus. The present study focuses on Stichococcus bacillaris as case study for short-term cryopreservation at −80 °C storage. Various freezing pretreatments using cryoprotective agents, and two thawing methods were compared introducing a novel variable to evaluate viability recovery and assessing growth kinetics of cultures immediately after thawing and after a series batch cultivation. Photosynthetic rate and pigments assessment were proposed to evaluate hidden metabolic cell damage. Results underline cryoprotective agents can increase the kinetic recovery of preserved cells in terms of reduction of lag phase during batch cultivation tests: the use of dimethyl sulfoxide and glycerol granted a growth comparable to unpreserved cells when sudden thawing occurs after 24 hours of storage, but recovery after preservation is less sensitive to cryoprotective agents when gradual thawing and 1 month of storage is considered. However, cells are always able to restore their physiological pathways even without agents, so their kinetic effect has been proved and quantified. Interestingly, both the photosynthetic efficiency and the ratio between total chlorophyll and carotenoids are comparable (0.75 Fv/Fm, 2.2 ± 0.25 g/g) to unpreserved cells and they are unsensitive to chosen agents, but the ratio between chlorophyll a and chlorophyll b was clearly altered (up to 10 times), suggesting that photoactive pigments relative proportions can result in similar growth kinetic performances. Long-term studies will be carried out to assess whether the differences found could cause chronic damage to photosystem efficiency of S. bacillaris cultures.

Comparative Analysis of the Photosynthetic Characteristics and Active Compounds of Semiliquidambar cathayensis Chang Heteromorphic Leaves

In the present study,the variation patterns of leaf shape in different populations of individual Semiliquidambar cathayensis plants were analyzed to investigate the relationship among leaf shape variation,photosynthetic properties,and active compounds to understand the genetic characteristics of S.cathayensis and screen elite germplasms.The leaf shape of 18 offspring from three natural S.cathayensis populations was analyzed to investigate the level of diversity and variation patterns of leaf shape.Furthermore,photosynthetic pigment content,physiological parameters of photosynthesis,and the active compounds in leaves of different shapes were determined.Statistical analysis showed that the leaf shape variation in S.cathayensis indicated a high level of genetic diversity among and within the populations.Cluster analysis showed that the three natural populations formed two clusters,one whose offspring was dominated by entire leaves and another characterized by palmately trifoliate leaves.The differences in photosynthetic characteristics and active compounds of leaves of three different shapes were comprehensively evaluated using principal component analysis.Two principal components with a cumulative contribution rate of 92.768%were extracted,of which the highest comprehensive score was for asymmetrically lobed leaves.The leaf shape in different S.cathayensis germplasms exhibited distinct patterns,and there were some correlations between the photosynthetic properties and active compounds in leaves of different shapes.Thus,the leaf shape can be used to predict active compound content,and in turn,select varieties based on that purpose;it also provides a simple and effective method to classify S.cathayensis germplasms.

Responses of photosynthetic characteristics and leaf senescence in summer maize to simultaneous stresses of waterlogging and shading

A field experiment was performed to investigate the physiological mechanism of the simultaneous stresses of waterlogging and shading on leaf photosynthetic and senescence during three growth stages of summer maize.The responses of leaf gas exchange parameters and antioxidant enzyme activities of the summer maize hybrids Denghai 605(DH605)to waterlogging(W),shading(S),and their combination(W+S)for 6 days at the third leaf stage(V3),the sixth leaf stage(V6),and the tasseling stage(VT)were recorded.Shading,waterlogging,and their combination disturbed the activities of protective enzymes and increased the contents of H2O2and O-2,accelerating leaf senescence and disordering photosynthetic characteristics.Under waterlogging,shading and their combination,leaf Pn,the photo-assimilates and grain yield was decreased.The greatest reduction for waterlogging and the combined stresses occurred at V3 and that for shading stress occurred at VT.The individual and combined stresses reduced the activities of protective enzymes and inhibited photosynthesis,reducing the accumulation of photosynthetic compounds and thereby yield.Waterlogging and the combined stresses at the V3 stage showed the greatest effect on leaf photosynthetic and senescence,followed by the V6 and VT stages.The greatest effect for shading stress occurred at VT,followed by the V6 and V3 stages,and the combined influence of shading and waterlogging was greater than that of either single stress.

Role of foliar spray of plant growth regulators in improving photosynthetic pigments and metabolites in Plantago ovata (Psyllium) under salt stress–A field appraisal

Salinity is one of the major abiotic factors that limit the growth and productivity of plants.Foliar application of plant growth regulators(PGRs)may help plants ameliorate the negative impacts of salinity.Thus,a field experiment was conducted at the Botanical Garden University of Balochistan,Quetta,to explore the potential role of PGRs,i.e.,moringa leaf extract(MLE;10%),proline(PRO;1μM),salicylic acid(SA;250μM),and thiourea(TU;10 mM)in ameliorating the impacts of salinity(120 mM)on Plantago ovata,an important medicinal plant.Salinity hampered plant photosynthetic pigments and metabolites but elevated oxidative parameters.However,foliar application of PGRs enhanced photosynthetic pigments,including Chl b(21.11%),carotenoids(57.87%)except Chl a,activated the defense mechanisms by restoring and enhancing the metabolites,i.e.,soluble sugars(49.68%),soluble phenolics(33.34%),and proline(31.47%),significantly under salinity stress.Furthermore,foliar supplementation of PGRs under salt stress led to a decrease of about 43.02%and 43.27%in hydrogen peroxide and malondialdehyde content,respectively.Thus,PGRs can be recommended for improved photosynthetic efficiency and metabolite content that can help to get better yield under salt stress,with the best and most effective treatments being those of PRO and MLE to predominately ameliorate the harsh impacts of salinity.

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.

Raised bed planting promotes grain number per spike in wheat grown after rice by improving spike differentiation and enhancing photosynthetic capacity

The yield of wheat in wheat–rice rotation cropping systems in the Yangtze River Plain, China, is adversely impacted by waterlogging. A raised bed planting(RBP) pattern may reduce waterlogging and increase the wheat yield after rice cultivation by improving the grain number per spike. However, the physiological basis for grain formation under RBP conditions remains poorly understood. The present study was performed over two growing seasons(2018/2019and 2019/2020) to examine the effects of the planting pattern(i.e., RBP and flat planting(FP)) on the floret and grain formation features and leaf photosynthetic source characteristics of wheat. The results indicated that implementation of the RBP pattern improved the soil–plant nitrogen(N) supply during floret development, which facilitated balanced floret development, resulting in a 9.5% increase in the number of fertile florets per spike. Moreover, the RBP pattern delayed wheat leaf senescence and increased the photosynthetic source capacity by 13.9%, which produced more assimilates for grain filling. Delayed leaf senescence was attributed to the resultant high leaf N content and enhanced antioxidant metabolism. Correspondingly, under RBP conditions, 7.6–8.6% more grains per spike were recorded, and the grain yield was ultimately enhanced by 10.4–12.7%. These results demonstrate that the improvement of the spike differentiation process and the enhancement of the leaf photosynthetic capacity were the main reasons for the increased grain number per spike of wheat under the RBP pattern, and additional improvements in this technique should be achievable through further investigation.

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.

Different Deficit Irrigation Lower Limits and Irrigation Quotas Affect the Yield and Water Use Efficiency of Winter Wheat by Regulating Photosynthetic Characteristics

To determine suitable thresholds for deficit irrigation of winter wheat in the well-irrigated area of the Huang-Huai-Hai Plain,we investigated the effects of different deficit irrigation lower limits and quotas on the photosynthetic characteristics and grain yield of winter wheat.Four irrigation lower limits were set for initiating irrigation(i.e.,light drought(LD,50%,55%,60%and 50%of field holding capacity(FC)at the seedling-regreening,jointing,heading and filling-ripening stages,respectively),medium drought(MD,40%,50%,55%and 45%of FC at the same stages,respectively),adequate moisture(CK1,60%,65%,70%and 60%of FC at the same stages,respectively),heavy drought(CK2,35%,40%,45%and 40%of FC at the same stages,respectively))and five irrigation quota per event(30,60,90,120 and 180 mm)were set for each lower limit.We found that the increase of drought stress is conducive to normal photosynthesis of winter wheat leaves which is supported by the following findings.First,photosynthetic rate(Pn)of LD60 treatment was higher than that of LD30,LD90,LD120,LD180,MD30,MD60,MD90,MD120 and MD180.Then,Under the 90 mm irrigation quota treatment,the yield of winter wheat basically increased with the increase of irrigation’s lower limit.Moreover,With the increase in irrigation quota,the yield of winter wheat increased,and the water use efficiency(WUE)of winter wheat increased at first and then decreased.In addition,compared with the LD30,MD30,MD60,MD90,MD120,and MD180,the yield of winter wheat in LD60 treatment increased by about 3.23%(3-year average),32.3%,19.9%,11.7%,10.1%,and 14.6%.At the same time,the WUE with LD60 treatment of winter wheat was significantly higher than LD90,LD120,LD180,MD30,MD60,MD90,MD120,MD180 treatments.There was a positive correlation between soil volumetric water content and Pn and between yield and Pn.The key period for yield formation in winter wheat is 180 days after sowing.In conclusion,to achieve the dual goals of stable winter wheat yield and efficient utilization of water resources in this region,the suitable threshold for initiating deficit irrigation of winter wheat is the LD60 treatment.This conclusion provides data support for water-saving and stable yield of winter wheat in this area.

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.

Study on Photosynthetic Characteristics of Hybrid Mulberry in Autumn under Herbaceous Cultivation

[Objectives]This study was conducted to clarify the physiological mechanism of growth of hybrid mulberry after autumn cutting in herbaceous cultivation.[Methods]The net photosynthetic rate(Pn),stomatal conductance(Gs),intercellular CO_(2) concentration(Ci)and transpiration rate(Tr)of leaves were measured under different treatment conditions using a Li-6400XT portable photosynthetic measurement system.[Results]After harvest of mulberry shoots in autumn,leaf Pn decreased with the extension of branch and leaf growth time,while Gs,Ci and Tr showed a trend of first increasing and then decreasing.The Pn was affected by factors such as leaf positions,mulberry varieties,cutting,and fertilization,which was manifested by the 6 th to 10 th mature leaves>the 2 nd to 4 th tender leaves,‘Nongsang 14’>hybrid mulberry,intermediate cut>uncut,and normal fertilization>no fertilization,all showing significant differences(P<0.05).Combined with the results of Gs,Ci and Tr measurements,it was found that the changes in leaf Pn were mainly related to non-stomatal factors.Timely cutting and harvesting during summer and autumn could significantly improve the photosynthetic rate of mulberry leaf,which was beneficial for extending the late autumn growth period of hybrid mulberry under herbaceous cultivation.[Conclusions]This study provides a theoretical reference for mulberry shoot harvesting techniques in summer and autumn.

Study on the Daily Change of Photosynthetic Rate for Prunus domestica × armeniacain Different Seasons

[Objective] The aim of this study was to explore the daily change of photosyntheticratefor Prunus domestica ×armeniacain different growing seasons. The study can provide theoretical basis for arid area high yield and quality cultivation.[Method] The photosynthetic physiological properties of leaves of different types of Prunus domestica × armeniaca were measured by the Li-6400 portable photosynthesis system indifferent seasons. By this method could analysis of photosyntheticcharacteristicsfor different types of Prunus domestica×armeniaca in different seasons.[Result] Daily change of photosyntheticrate（Pn） for Prunus domestica×armeniaca in differentseasons showed a ＂double-peak＂ curve. The peak values were at 10：00 and16：00. The Pn of ‘Fengweihuanghou＇, ‘Konglongdan＇, ‘Weihou＇, ‘Weiwang＇ and‘Weidi＇ reached the maximum in July, theywere 13.75, 14.76, 12.96, 13.3, and 11.9μmol/（m^2·s）, respectively. The Pn of Prunus domestica×armeniaca reached minimumin August, they were 9.78, 10.71, 12.02, 10.43 μmol/（m^2·s）. The Pn overall average of ‘Konglongdan＇ was highest,it reached 12.65 μmol/（m^2·s）.The Pn overall average of ‘Weiwang＇ was lowest, it reached 11.31μmol/（m^2·s）. There were extremely significant positive correlation between the Pn and Gs（P0.01）. [Conclusion] Daily change of photosyntheticrate for Prunus domestica ×armeniaca in differentseasons showed a ＂double-peak＂ curve, showing significant phenomenon of ＂midday depression＂.The photosynthesis intensity of Prunus domestica ×armeniaca was strongest in July, and the photosynthesis intensity was weakest in August. ‘Konglongdan＇showed the strongest photosynthesis capacity, ‘Weihou＇ and ‘Weiwang＇, followed.There were highest correlation between the Pn and stoma conductance（Gs）.

Functional Equilibrium Between Photosynthetic and Above-ground Nonphotosynthetic Structures of Plants: Evidence from a Pruning Experiment with Three Subtropical Tree Species

It is well known that plants have functional equilibrium between their above-ground parts (shoots) and below-ground parts (roots), but whether the above-ground parts of plants have functional equilibrium between their photosynthetic structures (leaves) and non-photosynthetic structures (branches and stem) is unknown. The purpose of this study is to test the hypotheses that: (1) the above-ground parts of plants have functional equilibriums between their photosynthetic structures and non-photosynthetic structures; (2) the maintenance of the equilibriums is guaranteed by the alteration of biomass partitioning to photosynthetic and non-photosynthetic structures. To test these hypotheses, a pruning experiment with four pruning intensities (0%, 20%, 50%, and 70%) were carried out with three subtropical Chinese tree species ( Ficus microcarpa, Ficus virens, Cinnamomum camphora). Pruning treatments were conducted in two successive years. The results were in conformity with the hypothesis, i.e. above-ground parts of trees had functional equilibriums between photosynthetic and non-photosynthetic structures. Pruning decreased instantaneously the mass ratios of photosynthetic structures to non-photosynthetic structures (P/NP) of all three tree species, the reduction in P/NP was strengthened with pruning intensity. However, one year after pruning, the P/NP of all pruned trees increased and were not smaller than those of unpruned trees. In agreement with the expectation, the biomass partitioning of pruned trees was altered, more newly produced above-ground biomass was partitioned to leaf growth and less to branch and stem growth, thus enabled the damaged trees to restore their functional equilibrium between photosynthetic and non-photosynthetic structures. It is clear that the maintenance of functional equilibrium between photosynthetic and non-photosynthetic structures guaranteed by the alteration of biomass partitioning provides plants a good strategy to resist external disturbance and damage.