Partial root-zone drying irrigation improves intrinsic water-use efficiency and maintains high photosynthesis by uncoupling stomatal and mesophyll conductance in cotton leaves

Partial root-zone drying irrigation (PRD) can improve water-use efficiency (WUE) without reductions in photosynthesis; however, the mechanism by which this is attained is unclear. To amend that, PRD conditions were simulated by polyethylene glycol 6000 in a root-splitting system and the effects of PRD on cotton growth were studied. Results showed that PRD decreased stomatal conductance (gs) but increased mesophyll conductance (gm). Due to the contrasting effects on gs and gm, net photosynthetic rate (AN) remained unaffected, while the enhanced gm/gs ratio facilitated a larger intrinsic WUE. Further analyses indicated that PRD-induced reduction of gs was related to decreased stomatal size and stomatal pore area in adaxial and abaxial surface which was ascribed to lower pore length and width. PRD-induced variation of gm was ascribed to the reduced liquid-phase resistance, due to increases in chloroplast area facing to intercellular airspaces and the ratio of chloroplast surface area to total mesophyll cell area exposed to intercellular airspaces, as well as to decreases in the distance between cell wall and chloroplast, and between adjacent chloroplasts. The above results demonstrate that PRD, through alterations to stomatal and mesophyll structures, decoupled gs and gm responses, which ultimately increased intrinsic WUE and maintained AN.

Trehalose-6-phosphate synthase 8 increases photosynthesis and seed yield in Brassica napus

Trehalose-6-phosphate (T6P) functions as a vital proxy for assessing carbohydrate status in plants. While class II T6P synthases (TPS) do not exhibit TPS activity, they are believed to play pivotal regulatory roles in trehalose metabolism. However, their precise functions in carbon metabolism and crop yield have remained largely unknown. Here, BnaC02.TPS8, a class II TPS gene, is shown to be specifically expressed in mature leaves and the developing pod walls of Brassica napus. Overexpression of BnaC02.TPS8 increased photosynthesis and the accumulation of sugars, starch, and biomass compared to wild type. Metabolomic analysis of BnaC02.TPS8 overexpressing lines and CRISPR/Cas9 mutants indicated that BnaC02.TPS8 enhanced the partitioning of photoassimilate into starch and sucrose, as opposed to glycolytic intermediates and organic acids, which might be associated with TPS activity. Furthermore, the overexpression of BnaC02.TPS8 not only increased seed yield but also enhanced seed oil accumulation and improved the oil fatty acid composition in B. napus under both high nitrogen (N) and low N conditions in the field. These results highlight the role of class II TPS in impacting photosynthesis and seed yield of B. napus, and BnaC02.TPS8 emerges as a promising target for improving B. napus seed yield.

Leaf Traits Explain the Growth Variation and Nitrogen Response of Eucalyptus urophylla × Eucalyptus grandis and Dalbergia odorifera in Mixed Culture

Mixed cultivation with legumes may alleviate the nitrogen (N) limitation of monoculture Eucalyptus. However, how leaf functional traits respond to N in mixed cultivation with legumes and how they affect tree growth are unclear. Thus, this study investigated the response of leaf functional traits of Eucalyptus urophylla × Eucalyptus grandis (E. urophylla × E. grandis) and Dalbergia odorifera (D. odorifera) to mixed culture and N application, as well as the regulatory pathways of key traits on seedling growth. In this study, a pot-controlled experiment was set up, and seedling growth indicators, leaf physiology, morphological parameters, and N content were collected and analyzed after 180 days of N application treatment. The results indicated that mixed culture improved the N absorption and photosynthetic rate of E. urophylla × E. grandis, further promoting seedling growth but inhibiting the photosynthetic process of D. odorifera, reducing its growth and biomass. Redundancy analysis and path analysis revealed that leaf nitrogen content, pigment content, and photosynthesis-related physiological indicators were the traits most directly related to seedling growth and biomass accumulation, with the net photosynthetic rate explaining 50.9% and 55.8% of the variation in growth indicators for E. urophylla × E. grandis and D. odorifera, respectively. Additionally, leaf morphological traits are related to the trade-off strategy exhibited by E. urophylla × E. grandis and D. odorifera based on N competition. This study demonstrated that physiological traits related to photosynthesis are reliable predictors of N nutrition and tree growth in mixed stands, while leaf morphological traits reflect the resource trade-off strategies of different tree species.

Integrating Chlorophyll a Fluorescence and Enzymatic Profiling to Reveal the Wheat Responses to Nano-ZnO Stress

It has been shown that increased concentrations of zinc oxide nanoparticles (nano-ZnO) in the soil are harmful to plant growth. However, the sensitivity of different wheat cultivars to nano-ZnO stress is still unclear. To detect the physiological response process of wheat varieties with different tolerance to nano-ZnO stress, four wheat cultivars (viz., cv. TS1, ZM18, JM22, and LM6) with different responses to nano-ZnO stress were selected, depending on previous nano-ZnO stress trials with 120 wheat cultivars in China. The results found that nano-ZnO exposure reduced chlorophyll concentrations and photosynthetic electron transport efficiency, along with the depressed carbohydrate metabolism enzyme activities, and limited plant growth. Meanwhile, the genotypic variation in photosynthetic carbon assimilation under nano-ZnO stress was found in wheat plants. Wheat cv. JM22 and LM6 possessed relatively lower Zn concentrations and higher leaf nitrogen per area, less reductions in their net photosynthetic rate, a maximum quantum yield of the PS II (Fv/Fm), electron transport flux per cross-section (ETo/CSm), trapped energy flux per cross-section (TRo/CSm), and total soluble sugar and sucrose concentrations under nano-ZnO stress, showing a better tolerance to nano-ZnO stress than wheat cv. TS1 and ZM18. In addition, the chlorophyll a fluorescence parameters Fv/Fm, ETo/CSm, and TRo/CSm could be used to rapidly screen wheat varieties resistant to nano-ZnO stress. The results here provide a new approach for solving the issues of crop yield decline in regions polluted by heavy metal nanoparticles and promoting the sustainable utilization of farmland with heavy metal pollution.

Different Physiological Responses to Continuous Drought between Seedlings and Younger Individuals of Haloxylon ammodendron

Drought is an important environmental factor that influences physiological processes in plants; however, few studies have examined the physiological mechanisms underlying plants' responses to continuous drought. In this study, the seedlings and younger individuals of Haloxylon ammodendron were experimentally planted in the southern part of the Gurbantunggut Desert. We measured their photosynthetic traits, functional traits and non-structural carbohydrate contents (NSCs) in order to assess the effects of continuous drought (at 15-day and 30-day drought points) on the plants' physiological responses. The results showed that at the 15-day (15 d) drought point, the leaf light-saturated net photosynthetic rate (An) values of both the seedlings and the younger individuals were decreased (by -68.9% and -45.2%, respectively). The intrinsic water use efficiency (iWUE) of the seedlings was significantly lower than that of the control group (-52.2%), but there was no diffenrence of iWUE observed in younger individuals. At the 30-day (30 d) drought point, a decrease in the An (-129.8%) of the seedlings was induced via biochemical inhibition, with a lower potential maximum photochemical rate (Fv/Fm, 0.42) compared with the control group, while a decrease in the An (-52.3%) of the younger individuals was induced due to lower stomatal conductance (gs, -50.5%). Our results indicated that prolonged drought induced a greater risk of seedling mortality as the relatively limited ability of stomatal regulation may increase the possibility of massive embolism, resulting in hydraulic failure.

Enhancing alfalfa photosynthetic performance through arbuscular mycorrhizal fungi inoculation across varied phosphorus application levels

This study evaluated the effects of arbuscular mycorrhizal fungi inoculation on the growth and photosynthetic performance of alfalfa under different phosphorus application levels. This experiment adopts two-factors completely random design, and sets four levels of fungi application: single inoculation with Funneliformis mosseae (Fm, T1), single inoculation with Glomus etunicatum (Ge, T2) and mixed inoculation with Funneliformis mosseae × Glomus etunicatum (Fm×Ge, T3) and treatment uninfected fungus (CK, T0). Four phosphorus application levels were set under the fungi application level: P2O5 0 (P0), 50 (P1), 100 (P2) and 150 (P3) mg·kg-1. There were 16 treatments for fungus phosphorus interaction. The strain was placed 5 cm below the surface of the flowerpot soil, and the phosphate fertilizer was dissolved in water and applied at one time. The results showed that the intercellular CO2 concentration (Ci) of alfalfa decreased at first and then increased with the increase of phosphorus application, except for light use efficiency (LUE) and leaf instantaneous water use efficiency (WUE), other indicators showed the opposite trend. The effect of mixed inoculation (T3) was significantly better than that of non-inoculation (T0) (p < 0.05). Pearson correlation analysis showed that Ci was significantly negatively correlated with alfalfa leaf transpiration rate (Tr) and WUE (p < 0.05), and was extremely significantly negatively correlated with other indicators (p < 0.01). The other indexes were positively correlated (p < 0.05). This may be mainly because the factors affecting plant photosynthesis are non-stomatal factors. Through the comprehensive analysis of membership function, the indexes of alfalfa under different treatments were comprehensively ranked, and the top three were: T3P2>T3P1>T1P2. Therefore, when the phosphorus treatment was 100 mg·kg-1, the mixed inoculation of Funneliformis mosseae and Glomus etunicatum had the best effect, which was conducive to improving the photosynthetic efficiency of alfalfa, increasing the dry matter yield, and improving the economic benefits of local alfalfa in Xinjiang. In future studies, the anatomical structure and photosynthetic performance of alfalfa leaves and stems should be combined to clarify the synergistic mechanism of the anatomical structure and photosynthetic performance of alfalfa.

Effects of Cadmium, Thallium, and Vanadium on Photosynthetic Parameters of Three Chili Pepper (Capsicum annuum L.) Varieties

Photosynthesis is a crucial process supporting life on Earth. However, unfavorable environmental conditions including toxic metals may limit the photosynthetic efficiency of plants, and the responses to those challenges may vary among genotypes. In this study, we evaluated photosynthetic parameters of the chili pepper varieties Jalapeño, Poblano, and Serrano exposed to Cd (0, 5, 10 µM), Tl (0, 6, 12 nM), and V (0, 0.75, 1.5 µM). Metals were added to the nutrient solution for 60 days. Stomatal conductance (Gs), transpiration rate (Tr), net photosynthetic rate (Pn), intercellular CO2 concentration (Ci), instantaneous carboxylation efficiency (Pn/Ci), instantaneous water use efficiency (instWUE), and intrinsic water use efficiency (iWUE) were recorded. Mean Pn increased with 12 nM Tl in Serrano and with 0.75 µM V in Poblano. Tl and V increased mean Tr in all three cultivars, while Cd reduced it in Jalapeño and Serrano. Gs was reduced in Jalapeño and Poblano with 5 µM Cd, and 0.75 µM V increased it in Serrano. Ci increased in Poblano with 6 nM Tl, while 12 nM Tl reduced it in Serrano. Mean instWUE increased in Poblano with 10 µM Cd and 0.75 µM V, and in Serrano with 12 nM Tl, while 6 nM Tl reduced it in Poblano and Serrano. Mean iWUE increased in Jalapeño and Poblano with 5 µM Cd, in Serrano with 12 nM Tl, and in Jalapeño with 1.5 µM V; it was reduced with 6 nM Tl in Poblano and Serrano. Pn/Ci increased in Serrano with 5 µM Cd, in Jalapeño with 6 nM Tl, and in Poblano with 0.75 µM V. Interestingly, Tl stimulated six and inhibited five of the seven photosynthetic variables measured, while Cd enhanced three and decreased two variables, and V stimulated five variables, with none inhibited, all as compared to the respective controls. We conclude that Cd, Tl, and V may inhibit or stimulate photosynthetic parameters depending on the genotype and the doses applied.

Corrigendum: Retrieving rice (Oryza sativa L.) net photosynthetic rate from UAV multispectral images based on machine learning methods

[This corrects the article DOI: 10.3389/fpls.2022.1088499.].

Retrieving rice (Oryza sativa L.) net photosynthetic rate from UAV multispectral images based on machine learning methods

Photosynthesis is the key physiological activity in the process of crop growth and plays an irreplaceable role in carbon assimilation and yield formation. This study extracted rice (Oryza sativa L.) canopy reflectance based on the UAV multispectral images and analyzed the correlation between 25 vegetation indices (VIs), three textural indices (TIs), and net photosynthetic rate (Pn) at different growth stages. Linear regression (LR), support vector regression (SVR), gradient boosting decision tree (GBDT), random forest (RF), and multilayer perceptron neural network (MLP) models were employed for Pn estimation, and the modeling accuracy was compared under the input condition of VIs, VIs combined with TIs, and fusion of VIs and TIs with plant height (PH) and SPAD. The results showed that VIs and TIs generally had the relatively best correlation with Pn at the jointing-booting stage and the number of VIs with significant correlation (p< 0.05) was the largest. Therefore, the employed models could achieve the highest overall accuracy [coefficient of determination (R ²) of 0.383-0.938]. However, as the growth stage progressed, the correlation gradually weakened and resulted in accuracy decrease (R ² of 0.258-0.928 and 0.125-0.863 at the heading-flowering and ripening stages, respectively). Among the tested models, GBDT and RF models could attain the best performance based on only VIs input (with R ² ranging from 0.863 to 0.938 and from 0.815 to 0.872, respectively). Furthermore, the fusion input of VIs, TIs with PH, and SPAD could more effectively improve the model accuracy (R ² increased by 0.049-0.249, 0.063-0.470, and 0.113-0.471, respectively, for three growth stages) compared with the input combination of VIs and TIs (R ² increased by 0.015-0.090, 0.001-0.139, and 0.023-0.114). Therefore, the GBDT and RF model with fused input could be highly recommended for rice Pn estimation and the methods could also provide reference for Pn monitoring and further yield prediction at field scale.

Dissection of Hyperspectral Reflectance to Estimate Photosynthetic Characteristics in Upland Cotton (Gossypium hirsutum L.) under Different Nitrogen Fertilizer Application Based on Machine Learning Algorithms

Hyperspectral technology has enabled rapid and efficient nitrogen monitoring in crops. However, most approaches involve direct monitoring of nitrogen content or physiological and biochemical indicators directly related to nitrogen, which cannot reflect the overall plant nutritional status. Two important photosynthetic traits, the fraction of absorbed photosynthetically active radiation (FAPAR) and the net photosynthetic rate (Pn), were previously shown to respond positively to nitrogen changes. Here, Pn and FAPAR were used for correlation analysis with hyperspectral data to establish a relationship between nitrogen status and hyperspectral characteristics through photosynthetic traits. Using principal component and band autocorrelation analyses of the original spectral reflectance, two band positions (350-450 and 600-750 nm) sensitive to nitrogen changes were obtained. The performances of four machine learning algorithm models based on six forms of hyperspectral transformations showed that the light gradient boosting machine (LightGBM) model based on the hyperspectral first derivative could better invert the Pn of function-leaves in cotton, and the random forest (RF) model based on hyperspectral first derivative could better invert the FAPAR of the cotton canopy. These results provide advanced metrics for non-destructive tracking of cotton nitrogen status, which can be used to diagnose nitrogen nutrition and cotton growth status in large farms.

Improvement of Photosynthesis by Biochar and Vermicompost to Enhance Tomato (Solanum lycopersicum L.) Yield under Greenhouse Conditions

Chlorophyll fluorescence is an important tool in the study of photosynthesis and its effect on the physiological indicators of crop growth is worth exploring. The trial was conducted to investigate the effect of biochar (CK, 0%; BA₃, 3%; BA₅, 5%; by mass of soil) and vermicompost (VA₃, 3%; VA₅, 5%) on photosynthesis, chlorophyll fluorescence, and tomato yield under greenhouse condition. Results revealed that photosynthetic parameters and chlorophyll fluorescence traits of BA₃, VA₃, BA₅, and VA₅ were significantly higher than those of CK, and the improvement of vermicompost was more effective than biochar at the same application rate. VA₃ treatment had the highest net photosynthetic rate (Pn), intercellular CO₂ concentration (Ci), variable fluorescence (Fv), maximum fluorescence (Fm), PSII maximum photochemical efficiency (Fv/Fm), PSII potential photochemical activity (Fv/Fo), absorption flux per cross section (CS; ABC/CSm), trapped energy flux per CS (TRo/CSm), and electron transport flux per CS (ETo/CSm), which increased by 49%, 65%, 17%, 12%, 4%, 25%, 10%, 15%, and 30%, respectively, compared with CK. The study also found that BA and VA rates could effectively improve tomato yield and water use efficiency (WUE). The yield under BA₃, VA₃, BA₅, and VA₅ treatments was 21%, 33%, 23%, and 25% higher than that under CK, and the WUE increased from 31.2 kg·m^-3 under CK to 41.4 kg·m^-3 under VA₃. Pearson correlation analysis indicated that the increment of photosynthesis showed a highly significant correlation with Fv/Fo, ABC/CSm, TRo/CSm, and ETo/CSm and enhanced the light energy absorbed, trapped, and transported per CS of plant leaves, thereby contributing to the increase in tomato yield. Therefore, for one-season tomato production, the application of 3% vermicompost was considered economical with regard to improving photosynthesis, enhancing WUE, and increasing tomato yield.

The relationship between the main leaf traits and photosynthetic physiological characteristics of Phragmites australis under different habitats of a salt marsh in Qinwangchuan, China

Plant leaf morphological and photosynthetic physiological characteristics are key functional traits in the adaptability of plants to heterogeneous environments. Analysis of the correlation between leaf morphological traits and photosynthetic physiological characteristics of salt marsh plants is helpful to deepen our understanding of how salt marsh plants adjust their leaf structure and function to adapt to their environment. However, there have been few studies on the relationship between leaf morphology and photosynthetic physiological characteristics of plants in inland salt marshes under a habitat gradient. A Phragmites australis community was divided into three plots based on differences in the wetland habitat conditions: a remote water area (plot I, 400-550 m from the water margin), a middle water area (plot II, 200-350 m from the water margin) and a near water area (plot III, 0-150 m from the water margin). The relationship between leaf morphological traits and photosynthetic physiological parameters of P. australis in heterogeneous habitats was studied. The results showed that as the habitat conditions changed from plot I to plot III, the soil characteristics, above-ground characteristics of the community and the photosynthetically active radiation changed significantly (P < 0.05). Besides, there was a highly significant positive correlation (P < 0.01) between leaf dry weight (LDW) and net photosynthetic rate (P _n), the effective quantum yield of PSII photochemistry (Y(II), actual photochemical efficiency of PSII) and photochemical quenching (QP); and between leaf area and P _n, Y(II) and QP in the three habitats. Moreover, in plot I, P. australis tended to have small and thick leaves with a low LDW and specific leaf area. In plot III, leaves were large and thin to adapt to the change in habitat conditions. This study provides a scientific theoretical basis for understanding the ecological adaptation strategies of plants in the harsh environment of an inland salt marsh and the conservation and management of wetland plants.

Transcriptome analysis and mining of genes related to shade tolerance in foxtail millet (Setaria italica (L.) P. Beauv.)

A stereo interplanting system with foxtail millet beneath chestnut trees is an effective planting method to raise the utilization of land in chestnut orchards, increase yields and improve quality of chestnut nuts. Consequently, exploration of genes involved in shade tolerance response in foxtail millet and breeding shade-tolerant varieties have become urgent issues. In this study, RNA-seq of leaf samples from two shade-tolerant varieties and three shade-intolerant varieties of foxtail millet at the booting stage was performed. Comparisons between the varieties revealed that 70 genes were commonly differentially expressed. Moreover, the ratio of net photosynthetic rate under shaded environment to that under light environment could be used as an indicator of shade tolerance. Subsequently, weighted gene co-expression network analysis was employed to construct a co-expression network and modules were correlated with this ratio. A total of 375 genes were identified as potentially relevant to shade tolerance, among which nine genes were also present in the 70 differentially expressed genes, which implied that they were good candidates for genes involved in shade tolerance. Our results provide valuable resources for elucidation of the molecular mechanisms underlying shade tolerance and will contribute to breeding of shade-tolerant foxtail millet that are adapted to the shaded environment under chestnut trees.

[Attapulgite can improve yield and total ferulic acid content of Angelica sinensis by adjusting source-sink relationship]

Attapulgite(ATP), as a fertilizer slow-release agent and soil conditioner, has shown remarkable effect in improving the utilization rate of fertilizer and the yield and quality of agricultural products and Chinese medicinal materials. This study aims to explore the effect of ATP on the growth and root quality of Angelica sinensis. To be specific, Mingui 1 was used, and through the pot(soil culture) experiment in the Dao-di producing area, the effects of conventional chemical fertilizer added with ATP on the morphology, photosynthesis, soil respiration, and content of ferulic acid and volatile oil in roots of Mingui 1 were detected. The underlying mechanism was discussed from the perspective of source-sink relationship. The results showed that ATP, via the fertilizer slow-release effect, could meet the needs of A. sinensis for nutrients at the root expansion stage, improve the net photosynthetic rate of leaves and aboveground biomass of plants, and promote the transfer and accumulation of nutrients from the aboveground part(source) to the underground root(sink) in advance during the dry matter accumulation period of roots, so as to improve the root weight per plant. ATP can increase the content of total ferulic acid(the sum of free ferulic acid and coniferyl ferulate), the main effective component of Angelicae Sinensis Radix, by promoting the synthesis of ferulic acid in the roots and the transformation to coniferyl ferulate. However, it had little effect on the content of volatile oil. ATP had certain influence on soil respiration, which needs to be further explored from root activity, rhizosphere microorganisms, and soil microorganisms. This study can lay a basis for soil remediation and improvement and ecological cultivation of A. sinensis.

Post-flowering Soil Waterlogging Curtails Grain Yield Formation by Restricting Assimilates Supplies to Developing Grains

Soil waterlogging is among the major factors limiting the grain yield of winter wheat crops in many parts of the world, including the middle and lower reaches of the Yangtze River China. In a field study, we investigated the relationship between leaf physiology and grain development under a varying duration of post-flowering waterlogging. A winter wheat cultivar Ningmai 13 was exposed to soil waterlogging for 0 (W0), 3 (W3), 6 (W6), and 9 d (W9) at anthesis. Increasing waterlogging duration significantly reduced flag leaf SPAD (soil plant analysis development) values and net photosynthetic rate (Pn). There was a linear reduction in flag leaf Pn and SPAD as plant growth progressed under all treatments; however, the speed of damage was greater in the waterlogged leaves. For example, compared with their respective control (W0), flag leaves of W9 treatment have experienced 46% more reduction in Pn at 21 d after anthesis (DAA) than at 7 DAA. Increasing waterlogging duration also induced oxidative damage in flag leaves, measured as malondialdehyde (MDA) contents. The capacity to overcome this oxidative damage was limited by the poor performance of antioxidant enzymes in wheat leaves. Inhibited leaf Pn and capacity to sustain assimilate synthesis under waterlogged environments reduced grain development. Compared with W0, W6 and W9 plants experienced a 20 and 22% reduction in thousand grain weight (TGW) in response to W6 and W9, respectively at 7 DAA and 11 and 19%, respectively at 28 DAA. Sustained waterlogging also significantly reduced grain number per spike and final grain yield. Averaged across two years of study, W9 plants produced 28% lesser final grain yield than W0 plants. Our study suggested that wheat crops are highly sensitive to soil waterlogging during reproductive and grain filling phases due to their poor capacity to recover from oxidative injury to photosynthesis. Management strategies such as planting time, fertilization and genotype selection should be considered for the areas experiencing frequent waterlogging problems.

Effects of Low-Temperature Stress during the Anther Differentiation Period on Winter Wheat Photosynthetic Performance and Spike-Setting Characteristics

Climate change has caused frequent extreme low-temperature events to threaten global food security. Spring low-temperature stress is one of the major limiting factors for high and stable yields of wheat. We used two wheat varieties differing in spring cold-sensitivity (cold-tolerant variety Yannong 19 and cold-sensitive variety Xinmai 26) to examine the effects of low-temperature stress during the anther differentiation period on wheat photosynthetic performance and spike-setting characteristics. Low-temperature stress was simulated in a climate box at -2 °C, 0 °C or 2 °C (night) and 15 °C (day) for 24 h, 48 h or 72 h. With the extension of the treatment time and the decrease of temperature, the photosynthetic rate, stomatal conductance and transpiration rate of wheat leaves gradually decreased. All treatments except -2 °C for 72 h recovered slowly within 7-15 days after treatment. Low-temperature stress greatly reduced grains per spikelet, 1000-grain weight and yield per plant. By analyzing the spikelets in different stalk locations (upper, middle and lower), we found that the number of upper spikelets was significantly less than lower and middle spikelets after low-temperature stress. The sterile grain of upper spikelets (Xinmai 26, for example) can reach 100% at -2 °C for 48 h and 72 h, and the yield loss rate was 90.52% at 2 °C for 24 h, which was much higher than for the lower spikelets (60.73%) and middle spikelets (50.94%). Overall, these findings suggest that low-temperature stress during the anther differentiation period alters the photosynthetic activity involved in the accumulation of dry matter in wheat, which leads to delaying young spike growth, especially for upper spikelets, and ultimately in a decrease in yield.

Effect of Foliar Fertigation of Chitosan Nanoparticles on Cadmium Accumulation and Toxicity in Solanum lycopersicum

Simple Summary

The experiment conducted on Solanum lycopersicum provided an insight about Cd uptake, and the way a Solanum lycopersicum changes its physiological, biochemical and morphological responses when CTS-NPs are administered against Cd. As an effective important polymer, CTS-NPs enhanced the plant biomass, SPAD index, photosynthetic rate, and protein content in the Solanum lycopersicum plants grown in Cd stress, as a study herein. Addition of CTS-NPs reduced Cd accumulation by increasing the nutrient uptake. Furthermore, CTS-NPs treatment enhances tolerance to Cd stress through hampering ROS production accompanied by H₂O₂ activity, through reducing the peroxidation of lipids by minimizing MDA content, and through improving enzymatic (CAT, POX, SOD), non-enzymatic (GSH and AsA), and osmoprotectants (proline) antioxidant contents that are considered as a first line of defense to protect plants from stress.

Abstract

Cadmium (Cd) stress is increasing at a high pace and is polluting the agricultural land. As a result, it affects animals and the human population via entering into the food chain. The aim of this work is to evaluate the possibility of amelioration of Cd stress through chitosan nanoparticles (CTS-NPs). After 15 days of sowing (DAS), Solanum lycopersicum seedlings were transplanted into maintained pots (20 in number). Cadmium (0.8 mM) was providing in the soil as CdCl₂·2.5H₂O at the time of transplanting; however, CTS-NPs (100 µg/mL) were given through foliar spray at 25 DAS. Data procured from the present experiment suggests that Cd toxicity considerably reduces the plant morphology, chlorophyll fluorescence, in addition to photosynthetic efficiency, antioxidant enzyme activity and protein content. However, foliar application of CTS-NPs was effective in increasing the shoot dry weight (38%), net photosynthetic rate (45%) and SPAD index (40%), while a decrease in malondialdehyde (24%) and hydrogen peroxide (20%) was observed at the 30 DAS stage as compared to control plants. On behalf of the current results, it is demonstrated that foliar treatment of CTS-NPs might be an efficient approach to ameliorate the toxic effects of Cd.

Optimal Design of Plant Canopy Based on Light Interception: A Case Study With Loquat

Canopy architecture determines the light distribution and light interception in the canopy. Reasonable shaping and pruning can optimize tree structure; maximize the utilization of land, space and light energy; and lay the foundation for achieving early fruiting, high yield, health and longevity. Due to the complexity of loquat canopy architecture and the multi-year period of tree growth, the variables needed for experiments in canopy type training are hardly accessible through field measurements. In this paper, we concentrated on exploring the relationship between branching angle and light interception using a three-dimensional (3D) canopy model in loquat (Eriobotrya japonica Lindl). First, detailed 3D models of loquat trees were built by integrating branch and organ models. Second, the morphological models of different loquat trees were constructed by interactive editing. Third, the 3D individual-tree modeling software LSTree integrated with the OpenGL shadow technique, a radiosity model and a modified rectangular hyperbola model was used to calculate the silhouette to total area ratio, the distribution of photosynthetically active radiation within canopies and the net photosynthetic rate, respectively. Finally, the influence of loquat tree organ organization on the light interception of the trees was analyzed with different parameters. If the single branch angle between the level 2 scaffold branch and trunk is approximately 15° and the angles among the level 2 scaffold branches range from 60 to 90°, then a better light distribution can be obtained. The results showed that the branching angle has a significant impact on light interception, which is useful for grower manipulation of trees, e.g., shoot bending (scaffold branch angle). Based on this conclusion, a reasonable tree structure was selected for intercepting light. This quantitative simulation and analytical method provides a new digital and visual method that can aid in the design of tree architecture.

Reversible colour change in leaves enhances pollinator attraction and reproductive success in Saururus chinensis (Saururaceae)

Background and Aims

Although there has been much experimental work on leaf colour change associated with selection generated by abiotic environmental factors and antagonists, the role of leaf colour change in pollinator attraction has been largely ignored. We tested whether whitening of the apical leaves subtending the inflorescences of Saururus chinensis during flowering enhances pollinator attraction, and whether re-greening of the white leaves after flowering increases carbon assimilation and promotes seed development.

Methods

White leaves were removed or covered, and the effects of these manipulations on pollinator visitation and subsequent reproductive success were assessed. The net photosynthetic rates of leaves of different colour were measured and their photosynthetic contributions to seed development were evaluated.

Key Results

Saururus chinensis is able to self-pollinate autonomously, but depends largely on flies for pollination. White leaves had different reflectance spectra from green leaves, and white leaves attracted significantly more pollinators and led to significantly higher fruit and seed set. Although leaf whitening resulted in a reduction in photosynthetic capacity, it translated into only a small decrease in seed mass. When leaves had turned back from white to green after flowering their photosynthetic capacity was similar to that of 'normal' green leaves and promoted seed development.

Conclusions

The reversible leaf colour change in S. chinensis appears to be adaptive because it enhances pollination success during flowering, with a small photosynthetic cost, while re-greening of these leaves after flowering helps to meet the carbon requirements for seed development.

Morphological, Photosynthetic, and Physiological Responses of Rapeseed Leaf to Different Combinations of Red and Blue Lights at the Rosette Stage

Rapeseed (Brassica napus L.) is sensitive to light quality. The factory production of rapeseed seedlings for vegetable use and for transplanting in the field requires an investigation of the responses of rapeseed to light quality. This study evaluated the responses of the leaf of rapeseed (cv. "Zhongshuang 11") to different ratios of red-photonflux (RPF) and blue-photonflux (BPF) from light emitting diodes (LEDs). The treatments were set as monochromatic lights, including 100R:0B% and 0R:100B%, and compound lights (CLs), including 75R:25B%, 50R:50B%, and 25R:75B%. The total photonflux in all of the treatments was set as 550 μmolm(-2)s(-1). With an increase of BPF, the rapeseed leaves changed from wrinkled blades and down-rolled margins to flat blades and slightly up-rolled margins, and the compact degree of palisade tissue increased. One layer of the cells of palisade tissue was present under 100R:0B%, whereas two layers were present under the other treatments. Compared to 100R:0B%, 0R:100B% enhanced the indexes of leaf thickness, leaf mass per area (LMA), stomatal density, chlorophyll (Chl) content per weight and photosynthetic capacity (P max), and the CLs with high BPF ratios enhanced these indexes. However, the 100R:0B% and CLs with high RPF ratios enhanced the net photosynthetic rate (P n). The leaves under the CLs showed growth vigor, whereas the leaves under 100R:0B% or 0R:100B% were stressed with a low F v/F m (photosynthetic maximum quantum yield) and a high content of [Formula: see text] and H2O2. The top second leaves under 100R:0B% or 0R:100B% showed stress resistance responses with a high activity of antioxidase, but the top third leaves showed irreversible damage and inactivity of antioxidase. Our results showed that the rapeseed leaves grown under 0R:100B% or CLs with a high BPF ratio showed higher ability to utilize high photonflux, while the leaves grown under 100R:0B% or CLs with a low BPF ratio showed higher efficiency in utilizing low photonflux. Under different R:B photonflux ratios, red and blue lights may play mutual roles in P n. When the blue light dominated, the P n showed a B-preference. When the red light dominated, the P n showed an R-preference. Furthermore, CLs were suitable for the P n of rapeseed seedlings.

[Optimal model of photosynthesis-light response curve in canopy of planted Larix olgensis tree.]

Rectangle hyperbola model (RH), nonrectangle hyperbola model (NRH), exponential model (EM), modified rectangle hyperbola model (MRH), and modified exponential model (MEM) were applied respectively for modeling the photosynthesis-light response curves (PLC) based on four types of curves (photosynthesis-light response curve of inhibition, PLC_i, photosynthesis-light response curve of saturation, PLC_s, photosynthesis-light response curve of unsaturation, PLC_u andphotosynthesis-light response curve in weak light, PLC_w) in canopy of 15 years old planted Larix olgensis tree in the Maoershan Forest Farm, Heilongjiang Province. The major photosynthetic physiological indexes including maximum net photosynthetic rate (P_{n max}), dark respiration rate (R_d), light compensation point (LCP), light saturation point at saturated light intensity (LSP) and apparent quantum yield (AQY) were calculated. All the five candidate models were comprehensively compared by the model goodness-of-fit and the precision estimations of photosynthetic physiological indexes in the four types of curves. The results showed that MEM model was only suitable for fitting the PLC_i. MRH model showed the best goodness-of-fit for PLC_i and PLC_s(R_a²was 0.9986 and 0.9978, respectively). Meanwhile, NRH model expressed the best fitting result in PLC_u and PLC_w (R_a² was 0.9996 and 0.9963, respectively). MRH had the lowest mean absolute value of relative error (MAPE) when evaluating P_{n max} in different types of curves (0.1%<MAPE<0.7%), but its precision estimation for LCP was relatively worse (2.5%<MAPE<9.4%). NRH model exhibited more accurate estimation for LCP of PLC_s and PLC_u, as well as R_d of PLC_u(MAPE was 1.8%, 0.1%, and 3.9%, respectively). RH model represented better prediction effect for LCP of PLC_i and R_d of PLC_s(MAPE was 1.0% and 2.7%, respectively). EM was more sui-table for estimating LCP of PLC_w(MAPE was 0.2%). Comprehensive analysis showed that MRH model not only proved well model goodness-of-fit and accurate estimation of photosynthetic physiological indexes, but also showed the highest stability when fitting different types of curves. As a result, MRH model was finally selected as the optimal canopy photosynthesis-light response model of planted L. olgensis tree.

Physio-biochemical and morphological characters of halophyte legume shrub, Acacia ampliceps seedlings in response to salt stress under greenhouse

Acacia ampliceps (salt wattle), a leguminous shrub, has been introduced in salt-affected areas in the northeast of Thailand for the remediation of saline soils. However, the defense mechanisms underlying salt tolerance A. ampliceps are unknown. We investigated various physio-biochemical and morphological attributes of A. ampliceps in response to varying levels of salt treatment (200-600 mM NaCl). Seedlings of A. ampliceps (25 ± 2 cm in plant height) raised from seeds were treated with 200 mM (mild stress), 400 and 600 mM (extreme stress) of salt treatment (NaCl) under greenhouse conditions. Na(+) and Ca(2+) contents in the leaf tissues increased significantly under salt treatment, whereas K(+) content declined in salt-stressed plants. Free proline and soluble sugar contents in plants grown under extreme salt stress (600 mM NaCl) for 9 days significantly increased by 28.7 (53.33 μmol g(-1) FW) and 3.2 (42.11 mg g(-1) DW) folds, respectively over the control, thereby playing a major role as osmotic adjustment. Na(+) enrichment in the phyllode tissues of salt-stressed seedlings positively related to total chlorophyll (TC) degradation (R (2) = 0.72). Photosynthetic pigments and chlorophyll fluorescence in salt-stressed plants increased under mild salt stress (200 mM NaCl). However, these declined under high levels of salinity (400-600 mM NaCl), consequently resulting in a reduced net photosynthetic rate (R (2) = 0.81) and plant dry weight (R (2) = 0.91). The study concludes that A. ampliceps has an osmotic adjustment and Na(+) compartmentation as effective salt defense mechanisms, and thus it could be an excellent species to grow in salt-affected soils.

Hydrogen peroxide regulated photosynthesis in C4-pepc transgenic rice

In this study, we investigated the photosynthetic physiological basis in 'PC' transgenic rice (Oryza sativa L.), showing high-level expression of the gene encoding C4 phosphoenolpyruvate carboxylase (pepc), by hydrogen peroxide (H2O2). The C4-PEPC gene (pepc) from maize in the transgenic rice plants was checked by PCR. Comparison of yield components and photosynthetic indices between PC and untransformed wild-type (WT) plants indicated that increased yield in PC was associated with higher net photosynthetic rate and higher activities of phosphoenolpyruvate carboxylase (PEPC). Both PC and WT plants were treated with 1 mmol L(-1) abscisic acid (ABA), 0.04% 1-butanol (BA), 2 mmol L(-1) neomycin (NS), or 2 mmol L(-1) diphenyleneiodonium chloride (DPI) to investigate the relationship between photosynthesis and levels of H2O2 and phosphatidic acid. In both PC and WT, ABA induced H2O2 generation and simultaneous decrease in stomatal conductance (g(s)). PC plants treated with BA showed decreased H2O2 content and strongly increased g(s) within 2 h of treatment. Similar results were observed in response to DPI treatment in PC. However, WT did not observe the decrease of H2O2 during the treatments of BA and DPI. The reduced H2O2 content in PC caused by BA treatment differed to that induced by DPI because BA did not inhibit NADPH oxidase activities. While BA induced a larger PEPC activity in PC, and higher catalase activity as well. These results indicated that the regulation of endogenous H2O2 metabolism of PC could be helpful for enhancing photosynthetic capability.

Significant relationships among frost tolerance and net photosynthetic rate, water use efficiency and dehydrin accumulation in cold-treated winter oilseed rapes

Five winter oilseed rape cultivars (Benefit, Californium, Cortes, Ladoga, Navajo) were subjected to 30 days of cold treatment (4 °C) to examine the effect of cold on acquired frost tolerance (FT), dehydrin (DHN) content, and photosynthesis-related parameters. The main aim of this study was to determine whether there are relationships between FT (expressed as LT50 values) and the other parameters measured in the cultivars. While the cultivar Benefit accumulated two types of DHNs (D45 and D35), the other cultivars accumulated three additional DHNs (D97, D47, and D37). The similar-sized DHNs (D45 and D47) were the most abundant; the others exhibited significantly lower accumulations. The highest correlations were detected between LT50 and DHN accumulation (r=-0.815), intrinsic water use efficiency (WUEi; r=-0.643), net photosynthetic rate (r=-0.628), stomatal conductance (r=0.511), and intracellular/intercellular CO2 concentration (r=0.505). Those cultivars that exhibited higher Pn rate in cold (and further a significant increase in WUEi) had higher levels of DHNs and also higher FT. No significant correlation was observed between LT50 and E, PRI, or NDVI. Overall, we have shown the selected physiological parameters to be able to distinguish different FT cultivars of winter oilseed rape.

Impaired leaf CO2 diffusion mediates Cd-induced inhibition of photosynthesis in the Zn/Cd hyperaccumulator Picris divaricata

Mechanisms of cadmium (Cd)-induced inhibition of photosynthesis in the Zn/Cd hyperaccumulator Picris divaricata were investigated using photosynthesis limitation analysis. P. divaricata seedlings were grown in nutrient solution containing 0, 5, 10, 25, 50, or 75 μM Cd for 2 weeks. Total limitations to photosynthesis (TL) increased from 0% at 5 μM Cd to 68.8% at 75 μM Cd. CO2 diffusional limitation (DL) made the largest contribution to TL, accounting for 93-98% of TL in the three highest Cd treatments, compared to just 2-7% of TL attributable to biochemical limitation (BL). Microscopic imaging revealed significantly decreased stomatal density and mesophyll thickness in the three highest Cd treatments. Chlorophyll fluorescence parameters related to photosynthetic biochemistry (Fv/Fm, NPQ, ΦPSII, and qP) were not significantly decreased by increased Cd supply. Our results suggest that increased DL in leaves is the main cause of Cd-induced inhibition of photosynthesis in P. divaricata, possibly due to suppressed function of mesophyll and stomata. Analysis of chlorophyll fluorescence showed that Cd supply had little effect on photochemistry parameters, suggesting that the PSII reaction centers are not a main target of Cd inhibition of photosynthesis in P. divaricata.

Growth and survival of Halimione portulacoides stem cuttings in heavy metal contaminated soils

The halophytic shrub Halimione portulacoides demonstrates a high tolerance to heavy metal contamination and a capacity for accumulating metals within its tissues. On the Iberian Peninsula, this species has colonized habitats with high levels of metal pollution. The aim of this study is to analyze the response of H. portulacoides stem cuttings to this pollution. Growth, photosynthesis and metal uptake were examined in H. portulacoides through an experiment in which stem cuttings were replanted in metal-contaminated soil. This condition decreased growth and lowered both photosynthetic rate and stomatal conductance. Reduced photosynthetic performance was largely due to the reduced concentration of photosynthetic pigments. Despite these responses, there was some important evidence suggesting the phytoremediatory potential of Halimione stem cuttings. The results of our study indicate that this salt-marsh shrub may represent a biotool of value in the restoration of polluted areas.

Growth and photosynthetic responses to copper in wild grapevine

The present study evaluates the tolerance and accumulation potential of Vitis vinifera ssp. sylvestris under moderate and high external Cu levels. A greenhouse experiment was conducted in order to investigate the effects of a range of external Cu concentrations (0-23mmolL(-1)) on growth and photosynthetic performance by measuring gas exchange, chlorophyll fluorescence parameters and photosynthetic pigments. We also measured the total copper, nitrogen, phosphorus, sulphur, calcium, magnesium, iron, potassium and sodium concentrations in the plant tissues. All the experimental plants survived even with external Cu concentrations as high as 23mmolL(-1) (1500mg Cu L(-1)), although the excess of metal resulted in a biomass reduction of 35%. The effects of Cu on growth were linked to a reduction in net photosynthesis, which may be related to the effect of the high concentration of the metal on photosynthetic electron transport. V. vinifera ssp. sylvestris survived with leaf Cu concentrations as high as 80mgkg(-1) DW and growth parameters were unaffected by leaf tissue concentrations of 35mg Cu kg(-1) DW. The results of our study indicate that plants of V. vinifera ssp. sylvestris from the studied population are more tolerant to Cu than the commercial varieties of grapevine that have been studied in the literature, and could constitute a basis for the genetic improvement of Cu tolerance in grapevine.

Overexpression of tomato enhancer of SOS3-1 (LeENH1) in tobacco enhanced salinity tolerance by excluding Na+ from the cytosol

The salt overly sensitive pathway has an important function in plant salinity tolerance. The enhancer of SOS3-1 (ENH1) participates in a new salinity stress pathway with SOS2 but without SOS3. To investigate the physiological effects and functional mechanism of ENH1 under salt stress, ENH1 was isolated from tomato and overexpressed in tobacco. Under salt stress, the sprouting percentage, fresh weight, and dry weight of transgenic plants were higher than those of wild-type (WT) plants. Under salt stress, the chlorophyll content, net photosynthetic rate, and maximal photochemical efficiency of PSII in transgenic plants decreased more slowly than those in WT plants. The overexpression of LeENH1 in tobacco excluded Na(+) from the cytosol and retained high K(+) levels in the cytosol to reestablish ion homeostasis. Higher thylakoid-bound ascorbate peroxidase activity and lower reactive oxygen species levels were found in transgenic plants under salt stress.

Abscisic acid and aldehyde oxidase activity in maize ear leaf and grain relative to post-flowering photosynthetic capacity and grain-filling rate under different water/nitrogen treatments

This study investigated changes in leaf abscisic acid (ABA) concentrations and grain ABA concentrations in two maize cultivars and analyzed the following relationships under different water/nitrogen treatments: leaf ABA concentrations and photosynthetic parameters; leaf ABA concentrations and grain ABA concentrations; leaf/grain ABA concentrations and grain-filling parameters; and aldehyde oxidase (AO, EC 1.2.3.1) activities and ABA concentrations. The ear leaf average AO activities and ABA concentrations were lower in the controlled release urea treatments compared with the conventional urea treatments. The average AO activities in the grains were higher in the controlled release urea treatments, and the ABA concentrations were significantly increased at 11-30 DAF. The Pn and ABA concentrations in ear leaves were negatively correlated. And the Gmean were positively correlated with the grain ABA concentrations at 11-30 DAF and negatively correlated with the leaf ABA concentrations at 20 and 40-50 DAF. The grain ABA concentrations and leaf ABA concentrations were positively correlated. Thus, the Gmean were closely related to the AO activities and to the ear leaf and grain ABA concentrations. As compared to other treatments, the subsoiling and controlled release urea treatment promoted the uptake of water and nitrogen by maize, increased the photosynthetic capacity of the ear leaves, increased the grain-filling rate, and improved the movement of photosynthetic assimilates toward the developing grains. In the cultivar Z958, higher ABA concentrations in grains at 11-30 DAF and lower ABA concentrations in ear leaves during the late grain-filling stage, resulted in higher grain-filling rate and increased accumulation of photosynthetic products (relative to the cultivar D3).

Overexpression of a tomato carotenoid ε-hydroxylase gene alleviates sensitivity to chilling stress in transgenic tobacco

Chilling is one of the most serious environmental stresses that disrupt the metabolic balance of cells and enhance the production of reactive oxygen species (ROS). Lutein plays important roles in dissipating excess excitation energy and eliminating ROS to maintain the normal physiological function of cells. A tomato carotenoid epsilon-ring hydroxylase gene (LeLUT1) was isolated, and the LeLUT1-GFP fusion protein was localized in the chloroplast of Arabidopsis mesophyll protoplast. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis indicated that the expression of LeLUT1 was the highest in the leaves and was down-regulated by various abiotic stresses in tomato. The transgenic tobacco plants overexpressing LeLUT1 had higher lutein content, which was decreased in cold condition. Under chilling stress, the non-photochemical quenching (NPQ) values were higher in the transgenic plants than in the wild type (WT) plants. Compared with the WT plants, the transgenic plants showed lower levels of hydrogen peroxide (H2O2), superoxide radical (O2(·-)), relative electrical conductivity, and malondialdehyde content (MDA), and relatively higher values of maximal photochemical efficiency of photosystem II (Fv/Fm), oxidizable P700 of PSI, and net photosynthetic rate (Pn). Therefore, the transgenic seedlings were less suppressed in growth and lost less cotyledon chlorophyll than the WT seedlings. These results suggested that the overexpression of LeLUT1 had a key function in alleviating photoinhibition and photooxidation, and decreased the sensitivity of photosynthesis to chilling stress.

Enhanced salt resistance in apple plants overexpressing a Malus vacuolar Na+/H+ antiporter gene is associated with differences in stomatal behavior and photosynthesis

High salinity is a major abiotic factor that limits crop production. The dwarfing apple rootstock M.26 is sensitive to such stress. To obtain an apple that is adaptable to saline soils, we transformed this rootstock with a vacuolar Na(+)/H(+) antiporter, MdNHX1. Differences in salt tolerance between transgenic and wild-type (WT) rootstocks were examined under field conditions. We also compared differences when 'Naganofuji No. 2' apple was grafted onto these transgenic or WT rootstocks. Plants on the transgenic rootstocks grew well during 60 d of mild stress (100 mM NaCl) while the WT exhibited chlorosis, inhibited growth and even death. Compared with the untreated control, the stomatal density was greater in both non-grafted and grafted WT plants exposed to 200 mM NaCl. In contrast, that density was significantly decreased in leaves from grafted transgenic plants. At 200 mM NaCl, net photosynthesis, stomatal conductance, intercellular CO2 concentration, and chlorophyll contents were markedly reduced in the WT, whereas the declines in those values were only minor in similarly stressed transgenic plants. Therefore, we conclude that overexpressing plants utilize a better protective mechanism for retaining higher photosynthetic capacity. Furthermore, this contrast in tolerance and adaptability to stress is linked to differences in stomatal behavior and photosynthetic rates.

Coronatine enhances drought tolerance via improving antioxidative capacity to maintaining higher photosynthetic performance in soybean

Coronatine (COR), a structural and functional mimic of jasmonates, is involved in a wide array of effects on plant development and defence responses. This study was conducted to explore the role of exogenously applied COR in alleviating the adversities of drought stress in soybean. COR treatment markedly increased the activities of antioxidant enzymes and proline content, and reduced the accumulation of malondialdehyde and hydrogen peroxide under drought stress. Thus, COR-treated plants had higher leaf relative water content and lower electrolye leakage, which led to higher chlorophyll content, activities of RuBPCase and PEPCase, and net photosynthetic rate compared to control plants exposed to drought. COR also increased maximal efficiency of PS II photochemical reaction and photochemical quenching coefficient, but decreased non-photochemical quenching coefficient. These beneficial effects led to enhanced photosynthetic performance and the translocation of assimilated (14)C which promoted growth and accumulation of dry biomass in COR-treated soybean plants subjected to drought. Interestingly, COR application did not affect the growth and biomass accumulation under well-watered condition. These results suggested the involvement of COR on improving drought tolerance in soybean by modulating antioxidant systems and membrane stability to maintain higher photosynthetic performance.

Gas exchange variability and water use efficiency of thirty landraces of rice still under cultivation in Kumaun region of the Indian Central Himalaya

Gas exchange characteristics of thirty landraces of rice (Oryza sativa L.) along with an introduced variety VL-206 (recommended high yielding variety for rainfed uplands of the Indian Central Himalaya, ICH), grown in earthen pots and kept in the open at the Institute nursery at Kosi (1150m amsl, 79°38'10″E and 29°38'15″N) were studied. The photosynthetic rate (Pn) and other related parameters were found to vary considerably among landraces. Based on the comparison of Pn of landraces with that of VL-206, these were categorized into two groups: i) high (〉6.0 µmol m(-2)s(-1)), and ii) low (<6.0 µmol m(-2)s(-1)) Pn groups. Overall the landraces belonging to the high Pn group (Saurajubawan, Syaudhan and Taichin) which had higher stomatal conductance (gs), transpiration rate (E), water use efficiency (WUE), mesophyll efficiency (low Ci/gs ratio) and chlorophyll (Chl) content in comparison to landraces in the low Pn group. However, significant differences were not found in the intercellular CO2 concentration (Ci) between landraces belonging to the high and low Pn groups. Differences among landraces were found with regard to dark respiration; landraces with low Pn respired proportionately more of the carbon fixed than those of high Pn group. Based on the studied gas exchange characteristics Saurajubawan, Syaudhan and Taichin, local landraces of rice, may be identified as potential cultivars with high Pn and WUE.