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.

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.

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.

Low Light Stress Down-Regulated Rubisco Gene Expression and Photosynthetic Capacity During Cucumber (Cucumis sativus L.) Leaf Development

Low light stress is one of the most important factors affecting photosynthesis and growth in winter production of cucumber （Cucumis sativus L.） in solar greenhouses in northern China. Here, two genotypes of cucumber （Deltastar and Jinyan 2） are used to determine the effect of low light stress on Rubisco expression and photosynthesis of leaves from emergence to senescence. During leaf development, the net photosynthetic rate （PN）, stomatal conductance （gs）, Rubisco initial activity and activation state, transcript levels of rbcL and rbcS, and the abundance of rbcL and rbcS DNA in these two genotypes increase rapidly to reach maximum in 10-20 d, and then decrease gradually. Meanwhile, the actual photosystem II efficiency （OpSll） of cucumber leaves slowly increased in the early leaf developing stages, but it declined quickly in leaf senescent stages, accompanied by an increased non-photochemical quenching （NPQ）. Moreover, PN, gs, initial Rubisco activity, and abundance of protein, mRNA and DNA of Rubisco subunits of leaves grown under 100 μmol m^-2 s^-1 are lower, and require more time to reach their maxima than those grown under 600 μmol m^-2 s^-1 during leaf development. All these results suggest that lower photosynthetic capacity of cucumber leaves from emergence to senescence under low light stress is probably due to down-regulated Rubisco gene expression in transcript and protein levels, and decreased initial and total activity as well as activation state of Rubisco. Deltastar performs better than Jinyan 2 under low light stress.

Far-red light: A regulator of plant morphology and photosynthetic capacity

Plant photosynthetic capacity directly determines crop yield. Light quality regulates photosynthetic capacity. This review discusses plant responses to far-red light from the phenotypic to the molecular level, focusing specifically on the improvement of photosynthetic capacity by adjustment of photosynthetic electron transport and the path of light energy. Far-red light can also regulate leaf angle and increase plant height and leaf area, via expression of associated genes, to capture more light energy.Thus, far-red light regulates plant morphology and photosynthetic capacity. Identifying the mechanism of this regulation may lead to increased crop yields.

Grafting Onto Artemisia annua Improves Drought Tolerance in Chrysanthemum by Enhancing Photosynthetic Capacity

Drought stress drastically influences the yield and quality of chrysanthemums,and thus grafting has been widely used to improve tolerance to biotic and abiotic stresses.To explore the mechanisms underlying improvements in drought resistance afforded by grafting,we investigated the changes in growth,gas exchange,ribulose-1,5-bisphosphate carboxylase/oxygenase(Rubisco)expression and activity,sugar components,and the relative expression of photosynthesis-related genes of chrysanthemum(Chrysanthemum morifolium Ramat.‘Hangbaiju')plants grafted onto Artemisia annua rootstocks under drought stress by withholding water for 6 d.The results revealed that the growth declines in the grafted chrysanthemums were relatively lower than those of the non-grafted plants under drought stress,and net photosynthetic rate,stomatal conductance,water use efficiency,and transpiration rate in the non-grafted chrysanthemums were significantly decreased.Moreover,the intercellular CO_2 concentrations were significantly increased compared with the grafted plants at 5 and 6 d following drought stress.The grafted plants exhibited higher relative expression of the Cmrbc L,Cmrbc S,Cmpsa B,and Cmcab genes,as well as higher Rubisco activity and chlorophyll content under the drought treatment.Sugar accumulation also increased under drought stress,particularly in the non-grafted plants.This result suggested that non-grafted chrysanthemums were less able to resist dehydration,and repressed the genes encoding the expression of photosynthetic components.In conclusion,using A.annua rootstock could alleviate drought stress in chrysanthemums by improving gas exchange capacity and maintaining Cmrbc L,Cmrbc S,Cmcab,and Cmpsa B gene expression,thereby increasing Rubisco activity and improving photosynthetic performance.

An epiallele of rice AK1 affects photosynthetic capacity

Summary Epigenetic gene variants, termed epialleles, can broaden genetic and phenotypic diversity in eukaryotes. Here, we identify a natural epiallele of OsAK1, which encodes a rice adenylate kinase. The Epiak1 plants show albino in young leaf and panicle with abnormal chloroplast structures.

Response of leaf photosynthetic characteristics of Syringa oblata and Syringa reticulata var.mandshurica to chilling stress

Syringa species not only have good ornamental properties but also play an important role in the landscaping and environmental purification of cities.To investigate the chilling stress resistance of Syringa oblata Lindl.and Syringa reticulata var.mandshurica and provide theoretical grounds for the practical cultivation of Syringa species,in vitro leaves were used to study photosynthetic gas exchange parameters and chlorophyll fluorescence parameters.After nine hours of chilling,decreasing rates of net photosynthesis,stomatal conductance,and transpiration in S.reticulata var.mandshurica leaves were significantly greater than that of the S.oblata,while intercellular CO2 concentrations in S.oblata leaves were higher than those in S.reticulata var.mandshurica.The quantum yield of PSII reaction center(APSII)declined in S.reticulata and light capture efficiency(Fv 0/Fm 0)was stable.However,reduction percentages of Fv 0/Fm 0,APSII,and Fv/Fm in S.oblata were significant higher than those of S.reticulata var.mandshurica.After nine hours of chilling,the relative variable fluorescence of VJ and VI of S.oblata increased and the increasing rate of VJ was greater than VI.In contrast,the change of VJ and VI in S.reticulata var.mandshurica leaves was relatively small.This suggests that chilling primarily damaged the electron transport process of QA to QB at the receptor site of the PSII reaction center.Photosynthetic capacity of S.oblata was more sensitive to chilling stress compared to S.reticulate var.mandshurica,which the limitations were mainly due to non-stomatal factors such as the decrease in electron transport efficiency,activity in the PSII reaction center,and the destruction of the photodamage defense system.

Increasing the appropriate seedling density for higher yield in dry direct-seeded rice sown by a multifunctional seeder after wheatstraw return

Dry direct-seeded rice(DDR) sown using a multifunctional seeder that performs synchronous rotary tillage and sowing has received increased attention because it is highly efficient,relatively cheap,and environmentally friendly.However,this method of rice production may produce lower yields in a rice–wheat rotation system because of its poor seedling establishment.To address this problem,we performed field experiments to determine the rice yield at five seedling density levels(B1,B2,B3,B4,and B5=100,190,280,370,and 460 seedlings m-2,respectively) and clarify the physiological basis of yield formation.We selected a representative high-quality rice variety and a multifunctional seeder that used in a typical rice–wheat rotation area in 2016 and 2018.The proportion of main stem panicle increased with increasing seedling density.There was a parabolic relationship between yield and seedling density,and the maximum yield(9.34-9.47 t ha-1) was obtained under B3.The maximum yield was associated with a higher total spikelet number m-2 and greater biomass accumulation from heading to maturity.The higher total spikelet number m-2 under B3 was attributed to an increase in panicle number m-2 compared with B1 and B2.Although the panicle numbers also increased under B4 and B5,these increases were insufficient to compensate for the reduced spikelet numbers per panicle.Lower biomass,smaller leaf area,and lower N uptake per plant from the stem elongation stage to the heading stage were partially responsible for the smaller panicle size at higher seedling density levels such as B5.The higher biomass accumulation under B3 was ascribed to the increases in the photosynthetic rate of the top three leaves m-2 of land,crop growth rate,net assimilation rate,and leaf area index.Furthermore,the B3 rice population was marked by a higher grain–leaf ratio,as well as a lower export ratio and transport ratio of biomass per stem-sheath.A quadratic function predicted that 260-290 seedlings m-2 is the optimum seedling density for achieving maximum yield.Together,these results suggested that appropriately increasing the seedling density,and thereby increasing the proportion of panicles formed by the main stem,is an effective approach for obtaining a higher yield in DDR sown using a multifunctional seeder in a rice–wheat rotation system.

Variations in chlorophyll content, stomatal conductance, and photosynthesis in Setaria EMS mutants

Chlorophyll (Chl) content,especially Chl b content,and stomatal conductance (G_s) are the key factors affecting the net photosynthetic rate (P_n).Setaria italica,a diploid C_4 panicoid species with a simple genome and high transformation efficiency,has been widely accepted as a model in photosynthesis and drought-tolerance research.The current study characterized Chl content,G_s,and P_n of 48 Setaria mutants induced by ethyl methanesulfonate.A total of 24,34,and 35 mutants had significant variations in Chl content,G_s,and P_n,respectively.Correlation analysis showed a positive correlation between increased G_s and increased P_n,and a weak correlation between decreased Chl b content and decreased P_n was also found.Remarkably,two mutants behaved with significantly decreased Chl b content but increased P_n compared to Yugu 1.Seven mutants behaved with significantly decreased G_s but did not decrease P_(n )compared to Yugu 1.The current study thus identified various genetic lines,further exploration of which would be beneficial to elucidate the relationship between Chl content,G_s,and P_n and the mechanism underlying why C_4 species are efficient at photosynthesis and water saving.

Leaf Gas Exchange,Chlorophyll Fluorescence,and Fruit Yield in Hot Pepper (Capsicum anmuum L.) Grown Under Different Shade and Soil Moisture During the Fruit Growth Stage

Relative leaf chlorophyll （Chl.） content, leaf gas exchange, Chl. fluorescence, plant biological biomass, and fruit yield were evaluated in growing hot pepper （Capsicum annuum L.） during the fruit-growing stages in hot summer under three shade levels （un-shade, 30% shade, and 70% shade） and four soil water contents （SWC） of 40-55%, 55-70%, 70-85%, and 85- 100% of field moisture capacity （FMC）. Hot pepper crops were more affected by light irradiance than by soil moisture and by their interaction during the whole observed periods. Hot pepper attained greatest relative leaf Chl. content （expressed as SPAD value） and photosynthetic activity when cultivated with 30% shade, resulting in the highest plant biological biomass and fruit yield. Although 70% shade improved leaf photosynthetic efficiency （expressed as Fv/Fm or Fv＇/Fm＇）, crops obtained the lowest photosynthetic rate, photochemical quenching coefficient （qP）, and non-photochemical quenching coefficient （NPQ）. This showed that light irradiance was insufficiency in S70% （70% shade） treatment. The leaf net photosynthetic rates （PN）, Fc/Fm, and fruit yield increased gradually as SWC levels increased from 40-55% to 70- 85% FMC, but decreased as SWC was higher than 70-85% FMC. The water consumption increased progressively with SWC levels, but water-use efficiency （WUE） was the highest when soil moisture was 55-70% FMC. Interaction of shade and soil moisture had significant effects on PN and FJFm, but not on other parameters. Under drought stress （40-55% and 55-70% FMC）, 30% shade could relieve the droughty damage of crops and improve photosynthetic capacity and WUE, but 70% shade could not, oppositely, aggravate the damage. The positive correlation （r2 =0.72） between leaf PN and fruit yield was existent. This indicated that improvement of leaf photosynthesis would increase potentially marketable yield in hot pepper crops during the full fruit-growing stages. For agricultural purposes, approximately S30% （30% shade） with 70- 85% FMC is suggested to cultivate hot pepper during the fruit growth stage in hot summer months.

Morphology,growth,and physiological traits of greenhouse cucumber seedlings as affected by supplementary white and blue LEDs

Supplemental lighting can be applied in the greenhouse to obtain high-quality seedlings when the solar daily light integral(DLI)is insufficient.However,there is no optimal strategy for the supplementary light provided by white and blue light-emitting diodes(LEDs)with the same DLI in cucumber(Cucumis sativus L.)seedling production grown in the greenhouse in early spring.The objective of the study was to determine changes in morphology,photosynthesis,growth,and physiological characteristics in greenhouse-grown cucumber seedlings(cv.Tianjiao No.5)depending on different supplementary fractions(28.5%,33.5%,38.5%,43.5%,and 48.5%)of blue light(B)under constant DLI provided by combinations of white(B28.5%included)and blue LEDs,and cucumber seedlings were grown with sunlight only were set as the control.The results documented that supplementary light resulted in compact and robust greenhouse-grown cucumber seedlings with higher chlorophyll content and net photosynthetic rate compared to those grown without supplementary light.The plant height and hypocotyl length of cucumber seedlings decreased quadratically with an increase of blue light fractions provided by combinations of white and blue LEDs.Additionally,the leaf area and stem diameter of cucumber seedlings increased first and a decreased trend was observed subsequently with the increasing fraction of blue light in a quadratic function.Similar trends were found in root architecture(e.g.,root length,root surface area,and root volume)and root activity of cucumber seedlings;however,no significant differences were exhibited as blue light fraction increased from 38.5%to 43.5%provided by supplementary light.Stem firmness and cellulose content increased by 26.2%and 23.4%,respectively,as 15%blue light was added to white LEDs.In conclusion,the 43.5%blue light created by supplementary broad-spectrum white and blue LEDs resulted in compact and stoutest cucumber seedlings along with well-developed root system and higher stem firmness,thus improving the mechanical strength of the greenhouse-grown cucumber seedlings for transplanting.