Modelling seedling development using thermal effectiveness and photosynthetically active radiation

Seedling quality is a prerequisite for successful field performance and therefore influences crop yields. Temperature and illumination are two major factors affecting seedling quality during nursery propagation. Suboptimal temperature or light of nurseries generally result in leggy or weak seedlings and great economic loss. However, production of healthy seedlings is challenging due to the lack of knowledge in systemic management of nursery environments. In this study, we have established simulation models to predict how temperature and illumination coordinately influence the growth of tomato and cabbage seedlings. Specifically, correlation between seedling quality characteristics(root-shoot ratio, G value(growth function: defined as ratio of whole plant dry weight to days of seedling), healthy indexes) and TEP(thermal effectiveness and photosynthetically active radiation) were explored to establish the models, which were validated with independent test data. Our results suggested that the curve of healthy index 1(HI1) and TEP fitted well with high coefficient of determination(R2) in both species, indicating that the model is highly reliable. The HI1 simulation models for tomato and cabbage are HI1=0.0009e0.0308TEP-0.0015 and HI1= 0.0003e0.0671TEP-0.0003, respectively, which can be used for predicting vigors of tomato and cabbage seedlings grown under different temperature and light conditions.

Effects of Photosynthetically Active Radiation and Air Temperature on CO_2 Uptake of Pterocarpus macrocarpus in the Open Field

Since trees and plants can absorb CO2, forests are widely regarded as a carbon sink that may control the amount of CO2 in the atmosphere. The CO2 uptake rate of plants is affected by the plant species and environmental conditions such as photosynthetically active radiation (PAR), temperature, water and nutrient contents. PAR is the most immediate environmental control on photosynthesis while air temperature affects both photorespiration and dark respiration. In the natural condition, PAR and temperature play an important role in net CO2 uptake. The effects of PAR and air temperature on the CO2 uptake of Pterocarpus macrocarpus grown in a natural habitat were studied in the present work. Due to many uncontrollable factors, a simple rectangular hyperbola could not represent the measured data. The data were divided into groups of 2oC intervals; CO2 uptake in each group may then be related to PAR by a rectangular hyperbola function. Using the obtained functions, the effect of PAR was removed from the original data. The PAR-independent CO2 uptake was then related to air temperature. Finally, the effects of PAR (I) and air temperature (Ta) on the CO2 uptake rate (A) were combined as: (-0.0575Ta2+2.6691Ta-23.264)I A= ——————————————— (-0.00766Ta2+0.40666Ta-3.99924) (-4.8794Ta2+227.13Ta-2456.9)+I

Simulation on Distribution of Photosynthetically Active Radiation in Canopy and Optimum Leaf Rolling Index in Rice with Rolling Leaves

By replacing leaf area index （LAI） with effective leaf area index （ELAI） through introduction of leaf rolling index （LRI）, the distributions of photosynthetically active radiation （PAR） in the canopies of three hybrid rice combinations, Liangyou E32 with high LRI, Liangyoupeijiu with moderate LRI and Shanyou 63 with non-rolling leaves （normal）, were simulated. The model based on ELAI could predict more accurately than that based on LAI. The PAR interception, conversion and utilization efficiency in the three combinations were studied to evaluate their optimal LRI and LAI. The PAR utilization efficiency of Liangyou E32 was lower due to excessive rolling leaves and less ELAI, and that of Shanyou 63 was also lower because of the faulty PAR interception and lower photosynthetic rate and saturation point at lower layer in canopy. Compared with the above two combinations, Liangyoupeijiu showed more appropriate distribution of PAR interception and conversion efficiency in canopy, and higher PAR utilization efficiency. The optimal LRI and LAI for Liangyoupeijiu were 0.11 and 7.6, respectively, which were close to the observed value, 0.11 and 7.9, respectively. However, the optimum LAI was 9.8 for Liangyou E32 and 6.2 for Shanyou 63, larger or smaller than those under the current plant density, which led to lower efficiency of PAR utilization. Besides, the optimum LRI for Liangyou E32 and Shanyou 63 were 0.12 and 0.08, respectively, which were close to the actual LRI for Liangyoupeijiu （0.11）.

Long-Term Trends in Photosynthetically Active Radiation in Beijing

A long-term dataset of photosynthetically active radiation （Qp） is reconstructed from a broadband global solar radiation （Rs） dataset through an all-weather reconstruction model. This method is based on four years＇ worth of data collected in Beijing. Observation data of Rs and Qp from 2005-2008 are used to investigate the temporal variability of Qp and its dependence on the clearness index and solar zenith angle. A simple and effcient all-weather empirically derived reconstruction model is proposed to reconstruct Qp from Rs. This reconstruction method is found to estimate instantaneous Qp with high accuracy. The annual mean of the daily values of Qp during the period 1958-2005 period is 25.06 mol m-2 d-1. The magnitude of the long-term trend for the annual averaged Qp is presented （-0.19 mol m-2 yr-1 from 1958-1997 and -0.12 mol m-2 yr-1 from 1958-2005）. The trend in Qp exhibits sharp decreases in the spring and summer and more gentle decreases in the autumn and winter.

Effects of cloud,atmospheric water vapor,and dust on photosynthetically active radiation and total solar radiation in a Mongolian grassland

Photosynthetically active radiation （PAR） is an important input parameter for estimating plant produc- tivity due to its key role in the growth and development of plants. However, a worldwide routine network for sys- tematic PAR measurements is not yet established, and PAR is often calculated as a constant fraction of total solar radiation （SR）. Although the ratio of PAR to SR （PAR/SR） has been reported from many places, few studies have been performed for dry regions. The present study was therefore carried out in an arid region of Mongolia to obtain PAP-JSR and examine its dependency on sky clearness （the clearness index）, water vapor in the atmosphere and aeolian dust. Continuous measurements of PAR and SR were taken every one second using quantum and pyranometer sensors, respectively, and the readings were averaged and recorded at intervals of 30 minutes for a period of 12 months. The lowest monthly mean daily PAR/SR occurred in April （0.420）, while the highest ratio was observed in July （0.459）. Mean daily PAR/SR during plant growing season （May-August） was estimated to be 0.442, which could be useful for modeling plant productivity in the study area. The annual mean daily PAR/SR （0.435） was lower than the values reported in many previous studies. This difference could be explained with the regional variation in climate： i.e. drier climatic condition in the study area. PAR/SR was negatively correlated with the clearness index （r= -0.36, P〈0.001）, but positively with atmospheric water vapor pressure （r=0.47, P〈0.001）. The average PAR/SR was significantly lower （P=0.02） on the dusty days compared to the non-dust days. Water vapor in the atmosphere was shown to be the strongest factor in the variation of PAR/SR. This is the first study examining PAR/SR under a semi-arid condition in Mongolia.

Light Meter for Measuring Photosynthetically Active Radiation

Measurement of photosynthetically active radiation (PAR) incident on photosynthetic organisms is a crucial measurement for understanding how organisms respond to various light conditions, and for calculating electron flow through the photosynthetic machinery. Measurements of PAR are typically performed in the region of the electromagnetic spectrum between 400 - 700 nm, which is the region of radiation that is responsible for promoting photosynthesis. Typically, to ensure that the sensor measures in this range, the implementation of long- and short-pass filters is required. Although this allows the exclusion of radiation outside of the PAR region, such filters can be expensive. Additionally, the implementation of autonomous PAR measurements requires costly commercial instruments. Here, a straight-forward, inexpensive apparatus has been designed and constructed using a sensor that can distinguish between red, green, blue and white light. The constructed apparatus was able to perform comparably to a commercial PAR sensor. Furthermore, the implementation of the device to measure PAR intensity over a three-day period shows how the apparatus can be implemented for use as a constant light monitor.

Spatio-temporal variation of photosynthetically active radiation in China in recent 50 years

Based on long-term measurement data of weather/ecological stations over China, this paper calculated and produced annually- and seasonally-averaged Photosynthetically Active Radiation （PAR） spatial data from 1961 to 2007, using climatological calculations and spatialization techniques. The spatio-temporal variation characteristics of annually- and seasonally-averaged PAR spatial data over China in recent 50 years were analyzed with Mann-Kendall trend analysis method and GIS spatial analysis techniques. The results show that： （1） As a whole, the spatial distribution of PAR is complex and inhomogeneous across China, with lower PAR in the eastern and southern parts of China and higher PAR in the western part. Mean annual PAR over China ranges from 17.7 mol m^-2 d^-1 to 39.5 mol m^-2 d^-1. （2） Annually- and seasonally-averaged PAR of each pixel over China are averaged as a whole and the mean values decline visibly with fluctuant processes, and the changing rate of annually-averaged PAR is -0.138 mol m^-2 d^-1/10a. The changing amplitudes among four seasons are different, with maximum dropping in summer, and the descending speed of PAR is faster before the 1990s, after which the speed slows down. （3） The analysis by each pixel shows that PAR declines significantly （α=0.05） in most parts of China. Summer and winter play more important roles in the interannual variability of PAR. North China is always a decreasing zone in four seasons, while the northwest of Qinghai-Tibet Plateau turns to be an increasing zone in four seasons. （4） The spatial distributions of the interannual variability of PAR vary among different periods. The interannual variabilities of PAR in a certain region are different not only among four seasons, but also among different periods.

Estimation of diffuse photosynthetically active radiation and the spatiotemporal variation analysis in China from 1981 to 2010

Photosynthetically active radiation （PAR） is the energy source of plant photosyn thesis, and the diffuse component can enhance canopy light use efficiency, thereby increasing the carbon uptake. Therefore, diffuse PAR is an important driving factor of ecosystem productivity models. In this study, we estimated the diffuse PAR of over 700 meteorological sites in China from 1981 to 2010 using an empirical model based on observational data from Chinese Ecosystem Research Network （CERN） and China Meteorology Administration. Then we derived the spatial data set of 10 km monthly diffuse PAR using ANUSPLIN software, and analyzed the spatiotemporal variation characteristics of diffuse PAR through GIS and trend analysis techniques. The results showed that： （1） The spatial patterns of annual average diffuse PAR during 1981-2010 are heterogeneous across China, lower in the northeast and higher in the west and south. The nationwide average value for 30 years ranges from 6.66 mol m-2 d-1 to 15.27 mol m-2 d-1, and the value in summer is the biggest while the value in winter is the smallest. （2） There is an evident increasing trend of annual diffuse PAR during recent 30 years, with the increasing amplitude at 0.03 mol m-2 d-l/10a. But a significant declining trend is shown in the first 10 years, and obvious anomalies can be seen in 1982, 1983, 1991 and 1992. And there is a downtrend in spring and an uptrend in all the other seasons. （3） The spatial distribution of temporal variation rates of diffuse PAR is inhomogeneous across the country, generally decreasing in the north and increasing in the south.

Photosynthetically active radiation retrieval based on HJ-1A/B satellite data

Photosynthetically active radiation(PAR) is essential for plant photosynthesis and carbon cycle,and is also important for meteorological and environmental monitoring.To advance China's disaster and environmental monitoring capabilities,the HJ-1A/B satellites have been placed in Earth orbit.One of their environmental monitoring objectives is the study of PAR.We simulated direct solar,scattered and environment radiation between 400 and 700 nm under different atmospheric parameters(solar zenith angle,atmospheric water vapor,atmospheric ozone,aerosol optical thickness,surface elevation and surface albedo),and then established a look-up table between these input parameters and PAR.Based on the look-up table,we used HJ-1A/B aerosol and surface albedo outputs to derive the corresponding PAR.Validation of inversed instantaneous and observed PAR values using HJ-1 Heihe experimental data had a root mean square error of 25.2 W m-2,with a relative error of 5.9%.The root mean square error for accumulated daily PAR and observed values was 0.49 MJ m-2,with a relative error of 3.5%.Our approach improved significantly the computational efficiency,compared with using directly radiation transfer equations.We also studied the sensitivity of various input parameters to photosynthetically active radiation,and found that solar zenith angle and atmospheric aerosols were sensitive PAR parameters.Surface albedo had some effect on PAR,but water vapor and ozone had minimal impact on PAR.

Circadian clock component, LHY, tells a plant when to respond photosynthetically to light in nature

The circadian clock is known to increase plant growth and fitness, and is thought to prepare plants for photosynthesis at dawn and dusk; whether this happens in nature was unknown. We transformed the native tobacco, Nicotiana attenuata to silence two core clock components, NaLHY （irLHY） and NaTOC1 （irTOC1）. We characterized growth and light- and dark-adapted photosynthetic rates （Ac） throughout a 24 h clay in empty vector-transformed （EV）, irLHY, and irTOC1 plants in the field, and in NaPhyA-and NaPhyB1-silenced plants in the glasshouse. The growth rates of irLHY plants were lower than those of EV plants in the field. While irLHY plants reduced Ac earlier at dusk, no differences between irLHY and EV plants were observed at dawn in the field, irLHY, but not EV plants, responded to light in the night by rapidly increasing Ac. Under controlled conditions, EV plants rapidly increased Ac in the day compared to dark-adapted plants at night; irLHY plants lost these time-dependent responses. The role of NaLHY in gating photosynthesis is independent of the light-depen- dent reactions and red light perceived by NaPhyA, but not NaPhyB1. In summary, the circadian clock allows plants not to respond photosynthetically to light at night by anticipating and gating red light-mediated in native tobacco.

Remote estimation of the fraction of absorbed photosynthetically active radiation for a maize canopy in Northeast China

Aims accurate remote estimation of the fraction of absorbed photosynthetically active radiation(fAPAR)is essential for the light use efficiency(LUE)models.Currently,one challenge for the LUE models is lack of knowledge about the relationship between fAPAR and the normalized difference vegetation index(NDVI).Few studies have tested this relationship against field measurements and evaluated the accuracy of the remote estimation method.this study aimed to reveal the empirical relationship between NDVI and fAPAR and to improve algorithms for remote estimation of fAPAR.Methods to investigate the method of remote estimation of fAPAR seasonal dynamics,the CASA(Carnegie-ames-stanford approach)model and spectral vegetation indices(VIs)were used for in situ measure-ments of spectral reflectance and fAPAR during the growing season of a maize canopy in Northeast China.Important Findingsthe results showed that the fAPAR increased rapidly with the day of year during the vegetative stage,it remained relatively stable at the stage of reproduction,and finally decreased slowly during the senescence stage.In addition,fAPAR green[fAPAR_(green)=fAPAR_(green) -fAPAR_(green) LAI_(max))]showed clearer seasonal trends than fAPAR.the NDVI,red-edge NDVI,wide dynamic range vegetation index,red-edge position(REP)and REP with sentinel-2 bands derived from hyperspectral remote sensing data were all significantly positively related to fAPAR green during the entire growing season.In a comparison of the predictive performance of VIs for the whole growing season,REP was the most appropriate spectral index,and can be recommended for monitoring seasonal dynamics of fAPAR in a maize canopy.

Comparison of Extrapolation and Interpolation Methods for Estimating Daily Photosynthetically Active Radiation(PAR)——A Case Study of the Poyang Lake National Nature Reserve,China

Measurements of photosynthetically active radiation （PAR）, which are indispensable for simulating plant growth and productivity, are generally very scarce. This study aimed to compare two extrapolation and one interpolation methods for estimating daily PAR reaching the earth surface within the Poyang Lake national nature reserve, China. The daily global solar radiation records at Nanchang meteorological station and daily sunshine duration measurements at nine meteorological stations around Poyang Lake were obtained to achieve the objective. Two extrapolation methods of PARs using recorded and estimated global solar radiation at Nanchang station and three stations （Yongxiu, Xingzi and Duchang） near the nature reserve were carried out, respectively, and a spatial interpolation method combining triangulated irregular network （TIN） and inverse distance weighting （IDW） was imple- mented to estimate daily PAR. The performance evaluation of the three methods using the PARs measured at Dahuchi Conservation Station （day number of measurement = 105 days） revealed that： （1） the spatial interpolation method achieved the best PAR estima- tion （R2 - 0.89, s.c. = 0.99, F= 830.02, P 〈 0.001 ）; （2） the extrapolation method from Nanchang station obtained an unbiased result （R2 = 0.88, s.c. = 0.99, F = 745.29, P 〈 0.001）; however, （3） the extrapolation methods from Yongxiu, Xingzi and Duchang stations were not suitable for this specific site for their biased estimations. Considering the assumptions and principles supporting the extrapolation and interpolation methods, the authors conclude that the spatial interpolation method produces more reliable results than the extrapolation methods and holds the greatest potential in all tested methods, and more PAR measurements should be recorded to evaluate the seasonal, yearly and spatial stabilities of these models for their application to the whole nature reserve of Poyang Lake.

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.

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.

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 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.

A Golden2-like transcription factor, BnGLK1a, improves chloroplast development, photosynthesis, and seed weight in rapeseed

Enhancing photosynthetic efficiency is a major goal for improving crop yields under agricultural field conditions and is associated with chloroplast biosynthesis and development.In this study,we demonstrate that Golden2-like 1a(BnGLK1a)plays an important role in regulating chloroplast development and photosynthetic efficiency.Overexpressing BnGLK1a resulted in significant increases in chlorophyll content,the number of thylakoid membrane layers and photosynthetic efficiency in Brassica napus,while knocking down BnGLK1a transcript levels through RNA interference(RNAi)had the opposite effects.A yeast two-hybrid screen revealed that BnGLK1a interacts with the abscisic acid receptor PYRABACTIN RESISTANCE 1-LIKE 1-2(BnPYL1-2)and CONSTITUTIVE PHOTOMORPHOGENIC 9 SIGNALOSOME 5A subunit(BnCSN5A),which play essential roles in regulating chloroplast development and photosynthesis.Consistent with this,BnGLK1a-RNAi lines of B.napus display hypersensitivity to the abscisic acid(ABA)response.Importantly,overexpression of BnGLK1a resulted in a 10%increase in thousand-seed weight,whereas seeds from BnGLK1a-RNAi lines were 16%lighter than wild type.We propose that BnGLK1a could be a potential target in breeding for improving rapeseed productivity.Our results not only provide insights into the mechanisms of BnGLK1a function,but also offer a potential approach for improving the productivity of Brassica species.

Tradeoffs of nitrogen investment between leaf resorption and photosynthesis across soil fertility in Quercus mongolica seedlings during the hardening period

The most important process before leaf senescence is nutrient resorption,which reduces nutrient loss and maximizes plant fitness during the subsequent growth period.However,plants must retain certain levels of nitrogen(N)in their leaves to maintain carbon assimilation during hardening.The objective of this study was to investigate the tradeoffs in N investment between leaf N resorption and N for photosynthesis in seedlings with increased soil fertility during the hardening period.A field experiment was conducted to determine if and how soil fertility treatments(17,34,or 68 mg N seedling−1)affected N resorption and allocation to the photosynthetic apparatus in Quercus mongolica leaves during the hardening period.Seedlings were sampled at T1(after terminal bud formation),T2(between terminal bud formation and end of the growing period),and T3(at the end of the growing period).Results showed that photosynthetic N content continued to rise in T2,while N resorption started from non-photosynthetic N.Leaf N allocation to the photosynthetic apparatus increased as soil fertility increased,delaying N resorption.Additionally,soil fertility significantly affected N partitioning among different photosynthetic components,maintaining or increasing photosynthetic traits during senescence.This study demonstrates a tradeoff in N investment between resorption and photosynthesis to maintain photosynthetic assimilation capacity during the hardening period,and that soil fertility impacts this balance.Q.mongolica leaves primarily resorbed N from the non-photosynthetic apparatus and invested it in the photosynthetic apparatus,whereas different photosynthetic N component allocations effectively improved this pattern.

Differences between two wheat genotypes in the development of floret primordia and contents of pigments and hormones

Promoting more floret primordia within a spike to acquire fertile potential during the differentiation and pre-dimorphism phases is critical for increasing the number of fertile florets per spike(NFFs).However,it is yet unknown the physiological mechanism regulating the complex and dynamic process.This study aimed to clarify how intra-spike hormones,pigments,and assimilates coordinate with each other to regulate spike morphology and then floret primordia development.A two-year field experiment was conducted with two winter wheat genotypes:N50(big-spike with greater NFFs)and SM22(mediumspike with fewer NFFs).We monitored high temporal and spatial-resolution changes in the number and morphology of floret primordia within a spike,as well as in intra-spike hormones,pigments,and assimilates.Our results revealed that the big-spike genotype had more NFFs than the medium-spike genotype,not only because they had more spikelets,but also because they had greater NFFs mainly at central spikelets.More floret primordia at central spikelets had sufficient time to develop and acquire fertile potential during the differentiation phase(167-176 d after sowing,DAS)and the pre-dimorphism phase(179 DAS)for the big-spike genotype than the medium-spike genotype.Floret primordia with fertile morphology during the pre-dimorphism phase always developed into fertile florets during the dimorphism phase.Those early-developed floret primordia most proximal and intermediate to the rachis in the big-spike genotype developed faster than the medium-spike genotype.Correspondingly,the spike dry matter and pigments(chlorophyll a,chlorophyll b,carotene,and carotenoids)content during 170-182 DAS,auxin(IAA)and cytokinin(CTK)content on 167 DAS were significantly higher in the big-spike genotype than in the medium-spike genotype,while jasmonic acid(JA)content was significantly lower in the big-spike genotype compared to the medium-spike genotype during 167-182 DAS.Since the significant differences in intra-spike hormone content of the two genotypes appear earlier than those in dry matter and pigments,we propose a possible model that helped the N50 genotype(big-spike)to form more fertile florets,taking the intra-spike hormone content as a signaling molecule induced assimilates and pigments synthesis,which accelerated the development of more floret primordia during the differentiation phase and then acquired fertile potential during the pre-dimorphism phase,finally improved the NFFs.Our high temporal and spatial-resolution analysis provides an accurate time window for precision cultivation and effective physiological breeding to improve the number of fertile florets in wheat.