Photosynthetic Diurnal Variation of Soybean Cultivars with High Photosynthetic Efficiency

The photosynthetic characters were investigated among soybean cultivars with high photosynthetic efficiency and high yield. The results indicated that: 1) There were significant differences in photosynthetic rate (Pn) and dark respiration rate (DR) under saturation light intensity and appropriate temperature. 2) There were a little difference in light compensation point among them. Photo flux density (PFD) were about 360μmol/m2·s when Pn tended to zero. 3) When PFD>1 900 μmol/m2·s, photoinhibition occuried a-mong the cultivars. Diurnal variation of Pn was shown a curve with two peaks. 4) The cultivars with high photosynthetic efficiency were subjected less to photoinhibition than that with high yield. Critical temperatures of photoinhibition in high photosynthetic efficiency cultivars were higher than that of high yield.

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.

Comparative analysis of the photosynthetic physiology and transcriptome of a high-yielding wheat variety and its parents

Photosynthesis is the fundamental basis of plant growth and development,and the improvement of photosynthetic efficiency can therefore promote increased crop yields.In this study,a comparative analysis of photosynthetic physiology and transcriptome was conducted between the high photosynthetic efficient variety BN207 and its parents BN64 and ZM16.The higher chlorophyll fluorescence,chlorophyll and carotenoid contents,and Lhcb1 protein accumulation in BN207 improved photosynthetic efficiency by promoting light energy absorption and conversion.Chloroplasts being distributed more closely to the cell membrane and the higher Rubisco enzyme activity of BN207 enhanced carbon assimilation,resulting in more carbohydrate accumulation in BN207.Transcriptome analysis revealed that there were several key genes mediating the high photosynthetic efficiency of BN207:Traes CS5 D02 G364100(chlorophyllase),BGI_novel_G006617(lycopeneε-cyclase),Traes CS4 A02 G034800 and Traes CS4 A02 G035100(Zeaxanthin epoxidase),Traes CS6 B02 G122500(light-harvesting complex II chlorophyll a/b binding protein 1).These genes improved the photosynthetic efficiency of BN207 mainly by reducing chlorophyll degradation,promoting carotenoid synthesis,and increasing Lhcb1 protein accumulation.These findings provide important background information for the cultivation of wheat varieties with high photosynthetic efficiency.

Light intensity and hydrogel soil amendment differentially affect growth and photosynthesis of successional tree species

Global climate changes have increased temperatures,radiation indexes,and consequently,irregularities in rainfall in mainly tropical countries,considerably hindering plant establishment in recovering degraded areas.The objective of this study was to evaluate the growth and physiological characteristics of one species of each successional group:pioneer,secondary,and climax when subjected to different light intensities and hydrogel as a soil conditioner during rainy and dry periods.The experiment was conducted in the ecotone between Brazil’s two largest biomes,the Cerrado and the Amazon in the State of Maranh?o.The parameters consisted of three species:Guazuma ulmifolia Lam.(pioneer),Astronium fraxinifolium Schott(secondary),and Cariniana rubra Gardner ex Miers(climax).There were two light intensities:70%and 100%,and two planting conditions:with and without soil conditioner(hydrogel).Gas exchanges were higher during the rainy season;the pioneer and secondary species had greater heights and photosynthetic rates in the dry period;the climax species had the lowest gas exchange and lowest recovery as rainfall resumed.The pioneer and secondary species showed higher physiological plasticity,denoting better adaption to environments with high irradiance.Hydrogel improved the photosynthetic performance of these species in the dry season and in areas with 100%sunlight.

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

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

Exploration of rice yield potential: Decoding agronomic and physiological traits

Rice grain yield is determined by three major"visible"morphological traits:grain weight,grain number per panicle,and effective tiller number,which are affected by a series of"invisible"physiological factors including nutrient use efficiency and photosynthetic efficiency.In the past few decades,substantial progress has been made on elucidating the molecular mechanisms underlying grain yield formation,laying a solid foundation for improving rice yield by molecular breeding.This review outlines our current understanding of the three morphological yield-determining components and summarizes major progress in decoding physiological traits such as nutrient use efficiency and photosynthetic efficiency.It also discusses the integration of current knowledge about yield formation and crop improvement strategies including genome editing with conventional and molecular breeding.

The Growth-Promoting Mechanism of Brevibacillus laterosporus AMCC100017 on Apple Rootstock Malus robusta

Plant growth-promoting rhizobacteria(PGPR) located in rhizobacteria soil are beneficial to plant growth and development. A PGPR strain AMCC100017 of Brevibacillus laterosporus synthesizes the plant hormone IAA in a tryptophan-dependent manner. In this study, the AMCC100017 strain was used to treat Malus robusta, an excellent natural rootstock for apple production, and assess its ability to promote growth. The fresh weight, dry weight, plant height, and lateral root growth of M. robusta were significantly increased with treatment. The presence of the AMCC100017 strain increased IAA content in M. robusta and promoted root secretion of tryptophan. Colonization of the strain in the roots allowed continuous synthesis of IAA and promoted plant growth. In addition, the photosynthetic efficiency in leaves increased after microbial treatment, and the utilization of nitrogen, zinc, iron, copper and magnesium in leaves was increased, which was conducive to photosynthesis.Interestingly, the activities of CAT and SOD, as well as the contents of ROS in plants colonized by AMCC100017 were increased compared to control plants, but the activities of POD and MDA contents were decreased. AMCC100017 strain affected the antioxidant capacity and stress resistance of plants. AMCC100017 strain increased the content of soluble protein and soluble sugar in plants, improved plant metabolic activity and stress resistance. Therefore, AMCC100017 not only increased IAA content and photosynthetic efficiency to promote M. robusta growth, but also affected plant through multiple metabolic pathways.

Comparative Study on Growth Performance of Transgenic(Over-Expressed OsNHX1) and Wild-Type Nipponbare under Different Salinity Regimes

Transgenic Nipponbare which over-expressed a Na＋/H~ antiporter gene OsNHX1 was used to compare its growth performance, water status and photosynthetic efficiency with its wild type under varying salinity regimes. Chlorophyll content, quantum yield and photosynthetic rate were measured to assess the impact of salinity stress on photosynthetic efficiency for transgenic and wild-type Nipponbare. Effects of salinity on water status and gas exchange to both lines were studied by measuring water use efficiency, instantaneous transpiration rate and stomatal conductance. Dry shoot weight and leaf area were determined after three months of growth to assess the impacts of salinity on the growth of those two lines. Our study showed that both lines were affected by salinity stress, however, the transgenic line showed higher photosynthetic efficiency, better utilization of water, and better growth due to low transpiration rate and stomatal conductance. Reduction of photosynthetic efficiency exhibited by the wild-type Nipponbare was correlated to its poor growth under salinity stress.

Leaf area development, dry weight accumulation and solar energy conversion efficiencies of Phaseolus vulgaris L. under different soil moisture levels near Nairobi, Kenya

Leaf area development, dry weight accumulation and solar energy conversion efficiencies of Phaseolus vulgaris L. cv GLP\|2 under two soil moisture levels in two contrasting seasons near Nairobi, Kenya were investigated. The experiment confirms that dry weights and yields of Phaseolus vulgaris are limited by a drought induced decrease in leaf area, leading to less radiation interception as a source for assimilation. However, photosynthetic efficiency in Phaseolus vulgaris also appears to decrease and to contribute to these effects. Finally, an even larger decreases of economic efficiency as obtained in the second season, where stress lasted much later into the season, reveals that such a drought also limits considerably the partitioning and translocation of assimilates to the seeds of Phaseolus vulgaris. The efficiencies obtained are in line with the better literature data for other crops.

Breeding for Parents of Hybrid Rice with Maize pepc Gene

The results of the investigation on transgenic rice with maize C4-specific phosphoenolpyruvate carboxylase (pepc) gene showed that the transgenic rice plants with the maize pepc gene expressed at high level and the maize PEPC expression was inherited in the progenies in a Mendelian manner. The transgenic plants had PEPC activity of more than 10-fold higher than untransformed plants. As compared with untransformed plants, the panicle per plant, spikelet per panicle, 1000-grain weight and grain-weight per plant for transgenic plants increased by 14.9 % , 5.7%, 1.3 % and 13.9 %, respectively. By crossing the maize pepc gene was incorporated into the parents of hybrid rice, which were the photo-sensitive genie male sterile (PGMS) lines of two-line hybrid rice such as Peiai64s, 7001s, 2302s, 2304s and 2306s-1, and the BT type of cytoplas-mic male sterile (CMS) line of three-line hybrid rice such as Shuangjiu A, and restorer lines 5129, Wanjing97 in the spring of 1998. The following progresses were made: (1) The inheritance of the high-level expression of the maize PEPC was stable in different genetic background of rice; (2) PEPC activity of hybrid was the mean of the two parents. Its saturated photosynthetic rate (Pn) rose to 50 % higher than that of the receptor parent. These results demonstrated that it is possible to increase the vigor of the rice plant by transgenic approach with maize pepc gene; (3) The activity of PEPC in leaf could be considered as the major physiological index because the correlation coefficient between PEPC activity and Pn was 0.6470* * ; (4) We have developed three rice lines with maize pepc gene; (5) The selection method of high photosynthetic efficiency rice has been established, which includes soaking seeds into solution of hygromycin phosphotransferase to germinate, tracing the pepc gene by PCR analysis, evaluating the performance of the rice plants in the field and examining PEPC activities and Pn of rice plants with maize pepc gene.

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

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

Influence of ammonium and nitrate supply on growth, nitrate reductase activity and N-use efficiency in a natural hybrid pine and its parents

Selection of tree species with a high capacity to assimilate N and efficiently utilize N resources would facilitate the success of initial tree seedling establishment in infertile soils.The preference for N forms was tested using three pine species(Pinus densata,Pinus tabuliformis and Pinus yunnanensis).Pinus densata is a natural diploid hybrid between P.tabuliformis and P.yunnanensis.Methods Seedlings of three pine species were supplied with nitrate-N,ammonium-N(at two different pH regimes)or combined ammonium and nitrate as a nitrogen source in perlite culture in a controlled environment.Important Findings Seedlings of P.densata had higher total biomass and net photosynthesis when supplied with nitrate-N and ammonium nitrate than with ammonium-N.In parental species,total biomass and net photosynthesis for P.yunnanensis seedlings was higher in ammonium-N than in nitrate-N,whereas the other parental species P.tabuliformis had the highest total biomass among species for all treatments except ammonium with CaCO_(3).Most morphological traits in P.densata seedlings were intermediate between its two parental species.However,N-use efficiency and photosynthetic N-use efficiency of P.densata significantly exceeded both parents when supplied with nitrate-N and ammonium nitrate.The results suggested that the diploid hybrid tree species P.densata has a preference for nitrate and is not well adapted to ammonium-N as a sole nitrogen source regardless of the growth medium pH.Based on changes in environmental conditions,such as predicted future temperature increases in high altitude areas associated with climate change,P.densata is likely to be increasingly competitive and have wide adaptation in high altitude regions.

Tufted Hairgrass(Deschampsia caespitosa)Exhibits a Lower Photosynthetic Plasticity than Antarctic Hairgrass(D.antarctica)

The aim of our work was to assess photosynthetic plasticity of two hairgrass species with different ecological origins （a temperate zone species, Deschampsia caespitosa （L.） Beauv. and an Antarctic species, D. antarctica） and to consider how the anticipated climate change may affect vitality of these plants. Measurements of chlorophyll fluorescence showed that the photosystem Ⅱ （PSⅡ） quantum efficiency of D. caespitosa decreased during 4 d of incubation at 4℃ but it remained stable in D. antarctica. The fluorescence half-rise times were almost always lower in D. caespitosa than in D. antarctica, irrespective of the incubation temperature. These results indicate that the photosynthetic apparatus of D. caespitosa has poorer performance in these conditions. D. caespitosa reached the maximum photosynthesis rate at a higher temperature than D. antarctica although the values obtained at 8 ℃ were similar in both species. The photosynthetic water-use efficiency （photosynthesis-to-transpiration ratio, PIE） emerges as an important factor demonstrating presence of mechanisms which facilitate functioning of a plant in non-optimal conditions. Comparison of the PiE values, which were higher in D. antarctica than in D. caespitosa at low and medium temperatures, confirms a high degree of adjustability of the photosynthetic apparatus in D. antarctica and unveils the lack of such a feature in D. caespitosa.

A near-complete genome assembly of the allotetrapolyploid Cenchrus fungigraminus(JUJUNCAO)provides insights into its evolution and C4 photosynthesis

JUJUNCAO(Cenchrus fungigraminus;2n=4x=28)is a Cenchrus grass with the highest biomass production among cultivated plants,and it can be used for mushroom cultivation,animal feed,and biofuel production.Here,we report a nearly complete genome assembly of JUJUNCAO and reveal that JUJUNCAO is an allopolyploid that originated2.7 million years ago(mya).Its genome consists of two subgenomes,and subgenome A shares high collinear synteny with pearl millet.We also investigated the genome evolution of JUJUNCAO and suggest that the ancestral karyotype of Cenchrus split into the A and B ancestral karyotypes of JUJUNCAO.Comparative transcriptome and DNA methylome analyses revealed functional divergence of homeologous gene pairs between the two subgenomes,which was a further indication of asymmetric DNA methylation.The three types of centromeric repeat in the JUJUNCAO genome(CEN137,CEN148,and CEN156)may have evolved independently within each subgenome,with some introgressions of CEN156 from the B to the A subgenome.We investigated the photosynthetic characteristics of JUJUNCAO,revealing its typical C4 Kranz anatomy and high photosynthetic efficiency.NADP-ME and PEPCK appear to cooperate in the major C4 decarboxylation reaction of JUJUNCAO,which is different from other C4 photosynthetic subtypes and may contribute to its high photosynthetic efficiency and biomass yield.Taken together,our results provide insights into the highly efficient photosynthetic mechanism of JUJUNCAO and provide a valuable reference genome for future genetic and evolutionary studies,as well as genetic improvement of Cenchrus grasses.

Quantitative Trait Loci Mapping of Dark-Induced Senescence in Winter Wheat(Triticum aestivum)

In order to explore the genetics of dark-induced senescence in winter wheat （Triticum aestivum L.）, a quantitative trait loci （QTL） analysis was carried out in a doubled haploid population developed from a cross between the varieties Hanxuan 10 （HX） and Lumai 14 （LM）. The senescence parameters chlorophyll content （Chl a＋b, Chl a, and Chl b）, original fluorescence （Fo）, maximum fluorescence level （Fm）, maximum photochemical efficiency （FvlFm）, and ratio of variable fluorescence to original fluorescence （FvlFo） were evaluated in the second leaf of whole three-leaf seedlings subjected to 7 d of darkness. A total of 43 QTLs were identified that were associated with dark-induced senescence using composite interval mapping. These QTLs were mapped to 20 loci distributed on 11 chromosomes： 1B, 1D, 2A, 2B, 3B, 3D, 5D, 6A, 6B, 7A, and 7B. The phenotypic variation explained by each QTL ranged from 7.5% to 19.4%. Eleven loci coincided with two or more of the analyzed parameters. In addition, 14 loci co-located or were linked with previously reported QTLs regulating flag leaf senescence, tolerance to high light stress, and grain protein content （Gpc）, separately.

Comparison of Responses to Mn Deficiency Between the UK Wheat Genotypes Maris Butler, Paragon and the Australian Wheat Genotype C8MM

Wheat grown in Mn-deficient soil has been widely observed to produce much reduced yields. Breeding for Mn-efficient wheat genotypes adapted to Mn-deficient soils would represent a long-term solution for wheat agronomy. To characterize the physiological basis of Mn efficiency in wheat genotypes would facilitate the breeding programs for producing Mn-efficient wheat. Using a solution culture and a soil culture system in the present study, a Mn-efficient UK wheat genotype Maris Butler and a Mn-inefficient UK wheat genotype Paragon have been compared with a Mn-efficient Australian wheat genotype C8MM in the responses to Mn deficiency in order to characterize the Mn efficiency in these wheat genotypes. Results showed that in solution culture, Marls Butler grown under Mn deficiency had 77% relative dry matter yield of control plants that were grown under Mn sufficiency, whereas CSMM and Paragon had 60% and 58% relative dry matter yield of their respective controls. Results from the soil culture demonstrated that relative dry matter yield remained high for Maris Butler and C8MM （53% and 56%, respectively）, whereas the value for Paragon dropped to 33%. In terms of dry matter yield and photosynthetic efficiency, Maris Butler demonstrated Mn efficiency in both solution culture and soil culture, whereas C8MM showed Mn efficiency only in soil culture. Results also demonstrated that under Mn-depleted supply in soil, plants of C8MM had a significantly higher ability in Mn uptake, whereas plants of Marls Butler showed a higher internal Mn use efficiency in comparison with plants of Paragon. Results from the present study indicate that the ability of C8MM to accumulate higher amounts of Mn is the basis of the improved Mn efficiency of this genotype in comparison with Paragon, and in Marls Butler there is a higher internal use of Mn expressed as an improved photosynthetic efficiency in conferring its Mn efficiency. It is suggested that more than one mechanism has arisen in wheat to confer tolerance to Mn deficiency.

Mediterranean sea cliff plants:morphological and physiological responses to environmental conditions

Aims The plants of Mediterranean sea cliff ecosystems are resistant to several environmental challenges.In this study,six species typical of the coastal rocky cliffs have been analyzed in order to evaluate their diverse morphological and physiological responses to their environment across the seasons,and to examine the strategy of the ecological group to which each species belongs.Since these species are widespread across the Mediterranean region,our aim was also to highlight their ecophysiological features in habitats where the direct influence of the sea is stronger.Methods The selected species are characteristic of the sea cliffs of Elba island(Tyrrhenian sea,Italy):the halophyte Crithmum maritimum,the semideciduous Helichrysum italicum and Lavandula stoechas and the sclerophylls Myrtus communis,Quercus ilex and Rhamnus alaternus.Four morphological traits-canopy height,leaf area,specific leaf area and leaf dry matter content-and two physiological traits-leaf water potential(LWP)and photosynthetic efficiency(PE),measured before the dawn and at midday-were analyzed.Water potential was measured by a pressure chamber and photosynthetic efficiency was determined by the analysis of chlorophyll fluorescence.Plant performance was also evaluated by calculating chronic(PIchr)and dynamic photoinhibition(PIdyn).Important Findings Crithmum maritimum showed high resistance to the recurrent dry periods,because of the high water storage capacity of its leaves and its PE declined markedly only in July,under the harshest climatic conditions.Semideciduous taxa utilize primarily an avoidance strategy,which aims at reducing the overall leaf surface,while sclerophylls mostly show a tolerance strategy towards the prevailing stressors,as demonstrated by LWP and PE,that are lower in the sclerophylls than in the semideciduous taxa during summer,due to osmoregulation and photoinhibition,respectively.Furthermore,variability of physiological parameters was higher in the sclerophylls than in the semideciduous taxa,because the former had to withstand wider oscillations of their LWP and PE.The sclerophyllous taxa underwent a slight loss of PE also in winter,likely owing to the combined action of low temperature and high irradiance.In Mediterranean sea cliff ecosystems,the stressful combination of high irradiance,high temperatures and low rainfall typical of the summer season may have been intensified by the shallow soil which displays a poor water storage capacity.On the other hand,winter stress,caused by high solar radiation and low temperatures,does not seem to seriously affect the performance of the studied species.

Effects of N on Plant Response to Heat-wave:A Field Study with Prairie Vegetation

More intense, more frequent, and longer heat-waves are expected in the future due to global warming, which could have dramatic ecological impacts. Increasing nitrogen （N） availability and its dynamics will likely impact plant responses to heat stress and carbon （C） sequestration in terrestrial ecosystems. This field study examined the effects of N availability on plant response to heat-stress （HS） treatment in naturally-occurring vegetation. HS （5 d at ambient or 40.5 ℃） and N treatments （±N） were applied to 16 1 m^2 plots in restored prairie vegetation dominated by Andropogon gerardii （warm-season C4 grass） and Solidago canadensis （warm-season C3 forb）. Before, during, and after HS, air, canopy, and soil temperature were monitored; net CO2 assimilation （Pn）, quantum yield of photosystem Ⅱ （ФpsⅡ）, stomatal conductance （gs）, and leaf water potential （ψw） of the dominant species and soil respiration （Rsoll） of each plot were measured daily during HS. One week after HS, plots were harvested, and C% and N% were determined for rhizosphere and bulk soil, and above-ground tissue （green/senescent leaf, stem, and flower）. Photosynthetic N-use efficiency （PNUE） and N resorption rate （NRR） were calculated. HS decreased Pn, gs, ψw, and PNUE for both species, and ＋N treatment generally increased these variables （±HS）, but often slowed their post-HS recovery. Aboveground biomass tended to decrease with HS in both species （and for green leaf mass in S. canadensis）, but decrease with ＋N for A. gerardii and increase with ＋N for S. canadensis. For A. gerardii, HS tended to decrease N% in green tissues with ＋N, whereas in S. canadensis, HS increased N% in green leaves. Added N decreased NRR for A. gerardii and HS increased NRR for S. canadensis. These results suggest that heat waves, though transient, could have significant effects on plants, communities, and ecosystem N cycling, and N can influence the effect of heat waves.