Biomass, lipid content, and fatty acid composition of freshwater Chlamydomonas mexicana and Scenedesmus obliquus grown under salt stress

Two freshwater microalgae including Chlamydomonas mexicana and Scenedesmus obliquus were grown on Bold Basal Medium (BBM) with different levels of salinity up to 100 mM NaCl. The dry biomass and lipid content of microalgae were improved as the concentration of NaCl increased from 0 to 25 mM. Highest dry weight (0.8 and 0.65 g/L) and lipid content (37 and 34 %) of C. mexicana and S. obliquus, respectively, were obtained in BBM amended with 25 mM NaCl. The fatty acid composition of the investigated species was also improved by the increased NaCl concentration. At 50 mM, NaCl palmitic acid (35 %) and linoleic acid (41 %) were the dominant fatty acids in C. mexicana, while oleic acid (41 %) and α-linolenic acid (20 %) were the major fractions found in S. obliquus.     

Alleviation of the adverse effects of NaCl on germination of maize grains by calcium

The lengths of roots and shoots, fresh and dry matter yield, and the contents of insoluble saccharides and free amino acids were reduced with the rise in NaCl concentration. However, under combination of NaCl with Ca²⁺ ions, these parameters generally raised. Contents of soluble saccharides, proline and quaternary ammonium compounds increased with increasing NaCl concentration, but under addition of CaCl₂ or CaSO₄, contents of these compounds were decreased. Low concentrations of NaCl stimulated soluble proteins, production, but higher concentrations decreased the content of soluble proteins. Addition of Ca²⁺ in the media did not improve the soluble protein production. Insoluble proteins content was increased with the rise of salinity level, but these effects were more pronounced with NaCl and CaCl₂ or CaSO₄ than with NaCl only.     

PSII-efficiency,polysaccharide production,and phenotypic plasticity of Scenedesmus obliquus in response to changes in metabolic carbon flux

To investigate the response of Scenedesmus obliquus to changes in metabolic carbon flux, S. obliquus was cultured in medium with different concentrations of glyoxylate over 9 days. Results showed that growth rates were not affected in the lower concentration glyoxylate (0.25 and 0.5 mM). However, growth rate of S. obliquus was inhibited in the higher concentration glyoxylate (0.85 and 1.25 mM) during the early phase before recovering at higher densities. Changes in growth rates in different glyoxylate concentrations were in line with changes in F_v/F_m and Φ_PSII. Colony formation was observed in S. obliquus in the four glyoxylate treatments. As a consequence, the mean number of cells per particle of S. obliquus in the glyoxylate treatments were significantly higher than those in the control. The total polysaccharide content of S. obliquus cells increased with increased glyoxylate concentrations. The increased glyoxylate-stimulated polysaccharide levels were directly correlated with colony size of S. obliquus.     

Response of barley grains to the interactive e.ect of salinity and salicylic acid

Effect of grain soaking presowing in 1 mM salicylic acid (SA) and NaCl (0, 50, 100, 150 and 200 mM) on barley (Hordeum vulgare cv Gerbel) was studied. Increasing of NaCl level reduced the germination percentage, the growth parameters (fresh and dry weight), potassium, calcium, phosphorus and insoluble sugars content in both shoots and roots of 15-day old seedlings. Leaf relative water content (RWC) and the photosynthetic pigments (Chl a, b and carotenoids) contents also decreased with increasing NaCl concentration. On the other hand, Na, soluble sugars, soluble proteins, free amino acids including proline content and lipid peroxidation level and peroxidase activity were increased in the two plant organs with increasing of NaCl level. Electrolyte leakage from plant leaves was found to increase with salinity level. SA-pretreatment increased the RWC, fresh and dry weights, water, photosynthetic pigments, insolube saccharides, phosphorus content and peroxidase activity in the stressed seedlings. On the contrary, Na⁺, soluble proteins content, lipid peroxidation level, electrolyte leakage were markedly reduced under salt stress with SA than without. Under stress conditions, SA-pretreated plants exhibited less Ca²⁺ and more accumulation of K⁺, and soluble sugars in roots at the expense of these contents in the plant shoots. Exogenous application (Grain soaking presowing) of SA appeared to induce preadaptive response to salt stress leading to promoting protective reactions to the photosynthetic pigments and maintain the membranes integrity in barley plants, which reflected in improving the plant growth.     

Effects of NaCl and Na2CO3 stresses on photosynthetic ability of Chlamydomonas reinhardtii

Chloride and carbonate salts are the main salts causing salinization and widely exist in aquatic environment, so algae may suffer from salinization stress for high water evaporation. In this study, in order to investigate and compare the toxic effects of the two salts on algal photosynthesis, we used NaCl and Na₂CO₃ to stress Chlamydomonas reinhardtii. Under the two salt stresses, the content of O ₂ ^?· and H₂O₂ in the cells was increased significantly, and it was much higher in Na₂CO₃ treatment than in NaCl treatment at the same Na⁺ concentration. The absorbance spectra and 4^th derivative spectra of photosynthetic pigments were declined under 300 mM NaCl and 25 mM Na₂CO₃ stresses, and remarkably changed under 50 mM and 100 mM Na₂CO₃ stresses. When the cells stressed by the two salts, the maximum quantum yield (Fv/Fm), electron transport rate (ETR) and photochemical quenching (qP) were reduced markedly, but the nonphotochemical dissipation (NPQ) was increased markedly. At the same Na⁺ concentration, Na₂CO₃ stress had stronger toxic effects on photosynthetic ability than NaCl stress.     

Antioxidants and unsaturated fatty acids are involved in salt tolerance in peanut

To explore the possible physiological mechanism of salt tolerance in peanut, we investigated the effect of salinity on antioxidant enzyme activity, fatty acid composition, and chlorophyll fluorescence parameters. Seedlings at the initial growth stage had been treated with 0, 100, 150, 200, 250, and 300 mM NaCl for 7 days. Results showed that fresh mass and dry mass decreased with the rise of the NaCl concentration. They decreased significantly when the NaCl concentration was more than 200 mM. The PSII’s highest photochemical efficiency (F _v/F _m) was not affected before treating 250 mM NaCl. However, the PSII (ΦPSII)’s actual photochemical efficiency of decreased after treating 200 mM NaCl. Both the initial fluorescence (F _o) and non-photochemical quenching (NPQ) increased after 200 mM NaCl treatment. PSI oxidoreductive activity (ΔI/I _o) was not affected before 200 mM NaCl. The malondialdehyde (MDA) content increased with the rise of the NaCl concentration. The activities of ascorbate peroxidase (APX) and superoxide dismutase (SOD) activities increased first and then decreased, while the content of H₂O₂ and O ₂ ^?· decreased first and then increased. Treated with 150 mM NaCl, the linolenic acid (18:3) and linoleic acid (18:2) of monogalactosyldiacylglycerols (MGDG), digalactosyldiacylglycerols (DGDG), sulphoquinovosyldiacylglycerols (SQDG) as well as phosphatidylglycerols (PG), the ratio of DGDG/MGDG increased, and the opposite results were obtained with 300 mM NaCl. The double bond index (DBI) of MGDG, DGDG, SQDG, and PG also increased after treating 150 mM NaCl. These conclusions verified that increased unsaturated fatty acid content in membrane lipid of peanut leaves could improve salt tolerance by alleviating photoinhibition of PSII and PSI.     

Effect of NaCl salinity on growth,pigment and mineral element contents,and gas exchange of broad bean and pea plants

Increasing salinity of growth medium induced a reduction in growth and transpiration rate. The concentrations of chlorophylls and carotenoids were increased in most cases in broad bean leaves while in pea plants they remained more or less unchanged with the rise of salinization up to 80mM NaCl. Thereabove a significant decrease in these contents was observed. A stimulation of the net photosynthetic rate of pea was observed at the lowest levels of NaCl but at the highest levels inhibitory effect was recorded. In broad bean all salinization levels inhibited photosynthetic activity, but dark respiration of both plant species was stimulated. The content of Na⁺ in the roots and shoots of both species increased at increasing salinity. In broad bean, Ca²⁺ concentration in shoots and K⁺ and Ca²⁺ contents of roots increased at increasing salinization, while in pea plants, the content of K⁺ and Ca²⁺ was almost unaffected by salinity. Salinity induced an increase in the content of these ions in pea roots. Mg²⁺ content in shoots and roots of both broad bean and pea decreased at increasing salinity except in roots of pea, where it was generally increased.     

Enantioselective toxicological response of the green alga Scenedesmus obliquus to isocarbophos

Chiral compounds usually behave enantioselectively in phyto‐biochemical processes. Isocarbophos (ICP) is a chiral pesticide that is widely used. To evaluate the toxicological response of ICP and its enantiomers to Scenedesmus obliquus, algal growth, total chlorophyll, total soluble protein, and the superoxide anion radicals (O₂^?‐) were investigated. The microalgae were treated with ICP and its enantiomers at 0.01–10 mg/l for 96 h. The growth of S. obliquus was stimulated at low levels of ICP and its enantiomers (0.01–1 mg/l), but all were inhibited at high concentrations (10 mg/l). The total soluble protein content and total chlorophyll content of the tested green alga S. obliquus gradually increased, depending on the growth of algal cells in the medium. Meanwhile, the content of O₂^?‐ was decreased. Interestingly, the cell number and content of the chlorophylls and protein decreased with increasing levels of concentration, whereas O₂^?‐ increased. Our results indicated that enantioselectivity was observed in the dose–response of ICP and its enantiomers in S. obliquus. The high O₂^?‐ level might lead to the death of S. obliquus. The stimulation of growth suggests a regulatory mechanism that is related to the capability of the algae to adapt to the O₂^?‐. Chirality 24:481–485, 2012. © 2012 Wiley Periodicals, Inc.     

Effects of salt-tolerant rootstock grafting on ultrastructure,photosynthetic capacity,and H<Subscript>2</Subscript>O<Subscript>2</Subscript>-scavenging system in chloroplasts of cucumber seedlings under NaCl stress

Plant growth, photosynthetic parameters, chloroplast ultrastructure, and the ascorbate-glutathione cycle system in chloroplasts of self-grafted and rootstock-grafted cucumber leaves were investigated. Grafted plants were grown hydroponically and were exposed to 0, 50, and 100 mM NaCl concentrations for 10 days. Under NaCl stress, the hydrogen peroxide (H₂O₂) content in cucumber chloroplasts increased, the chloroplast ultrastructure was damaged, and the gas stomatal conductance, intercellular CO₂ concentration, as well as shoot dry weight, plant height, stem diameter, leaf area, and leaf relative water content were inhibited, whereas these changes were less severe in rootstock-grafted plants. The activities of ascorbate peroxidase (APX; EC 1.11.1.11), glutathione reductase (GR; EC 1.6.4.2), and dehydroascorbate reductase (DHAR EC 1.8.5.1) were higher in the chloroplasts of rootstock-grafted plants compared with those of self-grafted plants under 50 and 100 mM NaCl. Similar trends were shown in leaf net CO₂ assimilation rate and transpiration rate, as well as reduced glutathione content under 100 mM NaCl. Results suggest that rootstock grafting enhances the H₂O₂-scavenging capacity of the ascorbate–glutathione cycle in cucumber chloroplasts under NaCl stress, thereby protecting the chloroplast structure and improving the photosynthetic performance of cucumber leaves. As a result, cucumber growth is promoted.     

Effect of sodium chloride-induced stress on growth, proline, glycine betaine accumulation, antioxidative defence and bacoside A content in in vitro regenerated shoots of Bacopa monnieri (L.) Pennell

Growth, osmotic adjustment, antioxidant enzyme defense and the principle medicinal component bacoside A were studied in the in vitro raised shoot cultures of Bacopa monnieri, a known medicinal plant, under different concentrations of NaCl [0.0 (control), 50, 100, 150 or 200 mM]. A sharp increase in Na⁺ content was observed at 50 mM NaCl level and it was about 6.4-fold higher when compared with control. While Na⁺ content increased in the shoots with increasing levels of NaCl in the medium, both K⁺ and Ca²⁺ concentrations decreased. Significant reduction was observed in shoot number per culture; shoot length, fresh weight (FW), dry weight (DW) and tissue water content (TWC) when shoots were exposed to increasing NaCl concentrations (50–200 mM) as compared with the control. Decrease in TWC was not significant at higher NaCl level (150 and 200 mM). At 200 mM NaCl, growth of shoots was adversely affected and microshoots died under prolonged stress. Minimum damage to the membrane as assessed by malondialdehyde (MDA) content was noticed in the controls in contrast to sharp increase of it in NaCl-stressed shoots. Higher amounts of free proline, glycinebetaine and total soluble sugars (TSS) accumulated in NaCl-stressed shoots indicating that it is a glycinebetaine accumulator. About 2.11-fold higher H₂O₂ content was observed at 50 mM NaCl as compared with control and it reached up to 7.1-folds more at 200 mM NaCl. Antioxidant enzyme activities (superoxide dismutase, catalase, ascorbate peroxidase and guaiacol peroxidase) also increased with a rise in NaCl level. Increase in bacoside A, a triterpene saponin content was observed only up to 100 mM NaCl level. Higher salt concentrations inhibited the accumulation of bacoside A. It appears from the data that accumulation of osmolytes, ions and elevated activities of antioxidant enzymes play an important role in osmotic adjustment in shoot cultures of Bacopa under salt stress.     

Effects of cadmium and kinetin on chlorophyll content,saccharides and dry matter accumulation in sunflower plants

Cadmium (Cd) and kinetin (Kin) significantly affected the growth and contents of chlorophyll (Chl) and of soluble and reserve (hydrolysable) saccharides in sunflower plants. Cd-treated plants had lower contents of Chl and soluble saccharides and produced less dry matter than control (Cd-untreated) plants. Chla stability to heat (CSI) increased at all Cd concentrations. The same was true for Chlb stability (0–10 μM Cd). Spraying sunflower shoots with Kin solutions counteracted the deleterious effects of Cd. Kin application enhanced the Chla andb contents, Chla/b ratio, content of soluble saccharides and dry matter, and to less extent Chl stability. The relative role of Kin in affecting the parameters tested (as indicated by η² values) was predominant while that of Cd was subsidiary except for Chla stability. The role of Cd×Kin interaction was dominant for hydrolysable saccharides. Hence spraying shoots of plants grown under increasing Cd concentration with Kin can partially alleviate inhibitory effects of cadmium.     

Triadimefon enhances growth and net photosynthetic rate in NaCl stressed plants of Raphanus sativus L.

The effect of sodium chloride and triadimefon (TDM) on the chlorophyll (Chl) content, net photosynthetic rates (P_N), rate of transpiration (E), and intercellular CO₂ concentration (C_i) in Raphanus sativus was studied. The effect of NaCl salinity was partially ameliorated by TDM which caused increase in Chl content, P_N, and C_i. TDM also increased root dry matter production, decreased E, and increased the water use efficiency.     

Changes in dry weight and mineral composition of some oil producing plants over a range of salinity stresses

Using water culture technique, some experiments have been performed to investigate the effect of 60 days salinization treatments (0.0–100 meq 1⁻¹ NaCl) on dry weight and on the content of some nutrient elements (Na, K, Ca, Mg, P, N) in castor bean, sunflower and flax plants. In general the content of sodium increased progressively with the rise of salinity level. The relatively low and moderate salinization levels (20 and 40 meq I⁻¹ NaCl) resulted in a promotion rather than inhibition of the dry weight and in the content of most of the investigated elements in the different organs of the test plants. However with the rise of salinization level from 60 to 100 meq l⁻¹, the dry weight and the content of these nutrient elements were mostly reduced.     

Alleviation of cadmium toxicity on maize seedlings by calcium

The rate of germination, radicle and plumule length, fresh and dry mass of maize seedlings were increased as Ca²⁺ was added to the nutrient solution, which contained different levels of Cd²⁺, especially at low concentration of Ca²⁺ (5 mM) and high concentrations of Cd²⁺ (1.4 and 1.8 mM). The biosynthesis of pigments, respiration rate and content of soluble saccharides in endosperm were reduced sharply as the concentration of Cd²⁺ in the medium increased. This effects was alleviated by Ca²⁺ addition. Cd²⁺ content in seedlings was increased as the Cd²⁺ concentration in medium was increased and decreased sharply as Ca²⁺ was present in the culture medium. The study suggests liming of soil with CaCO₃ to improve the yield of many crops.     

Physiological and proteomic analysis of salinity tolerance of the halotolerant cyanobacterium <Emphasis Type="Italic">Anabaena</Emphasis> sp

The halotolerant cyanobacterium Anabaena sp was grown under NaCl concentration of 0, 170 and 515 mM and physiological and proteomic analysis was performed. At 515 mM NaCl the cyanobacterium showed reduced photosynthetic activities and significant increase in soluble sugar content, proline and SOD activity. On the other hand Anabaena sp grown at 170 mM NaCl showed optimal growth, photosynthetic activities and comparatively low soluble sugar content, proline accumulation and SOD activity. The intracellular Na⁺ content of the cells increased both at 170 and 515 mM NaCl. In contrast, the K⁺ content of the cyanobacterium Anabaena sp remained stable in response to growth at identical concentration of NaCl. While cells grown at 170 mM NaCl showed highest intracellular K⁺/Na⁺ ratio, salinity level of 515 mM NaCl resulted in reduced ratio of K⁺/Na⁺. Proteomic analysis revealed 50 salt-responsive proteins in the cyanobacterium Anabaena sp under salt treatment compared with control. Ten protein spots were subjected to MALDI-TOF–MS/MS analysis and the identified proteins are involved in photosynthesis, protein folding, cell organization and energy metabolism. Differential expression of proteins related to photosynthesis, energy metabolism was observed in Anabaena sp grown at 170 mM NaCl. At 170 mM NaCl increased expression of photosynthesis related proteins and effective osmotic adjustment through increased antioxidant enzymes and modulation of intracellular ions contributed to better salinity tolerance and optimal growth. On the contrary, increased intracellular Na⁺ content coupled with down regulation of photosynthetic and energy related proteins resulted in reduced growth at 515 mM NaCl. Therefore reduced growth at 515 mM NaCl could be due to accumulation of Na⁺ ions and requirement to maintain higher organic osmolytes and antioxidants which is energy intensive. The results thus show that the basis of salt tolerance is different when the halotolerant cyanobacterium Anabaena sp is grown under low and high salinity levels.     

Salicylic Acid (SA) Induced Alterations in Growth,Biochemical Attributes and Antioxidant Enzyme Activity in Faba Bean (<Emphasis Type="Italic">Vicia faba</Emphasis> L.) Seedlings under NaCl Toxicity

In the present study we tried to evaluate the effect of salicylic acid (SA) in alleviating the negative effects of salinity stress. NaCl stress (50 and 100 mM) declines the shoot and root length and maximum decrease was observed at 100 mM concentration of NaCl. Similarly shoot dry weight decreased by 57.14% and root dry weight by 67.24% with 100 mM NaCl stress. The pigments and leaf relative water content (LRWC) were also observed to decline with increase in NaCl concentration. However, supplementation of SA to NaCl stressed seedlings showed enhanced length and dry weight of shoot and root. The pigment and LRWC also increased by the application of SA in the present study. NaCl stress also enhanced proline and glycine betaine (GB) by 3.01 and 2.04 folds, respectively; further enhancement was recorded by the application of SA. Hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) content also showed rise in accumulation, however, seedlings treated with SA and NaCl (100 mM + SA) declines the H₂O₂ accumulation to 1.90 from 2.45 folds and MDA to 1.69 from 2.34 folds over the control. Antioxidants were observed to increase with NaCl concentration and further increase was recorded by the application of SA. Indoleacetic acid (IAA) and indole butyric acid (IBA) decreased by 36.60 and 44.16%, respectively, and ABA increased by 750% with 100 mM NaCl. Addition of SA to NaCl stressed seedlings enhanced the IAA and IBA and decreased the ABA concentration to appreciable level. NaCl is also responsible for the higher accumulation of Na⁺ and Na⁺/K⁺ ratio and decreased uptake of Ca²⁺ and K⁺. Supplementation of SA decreased the Na⁺ accumulation and enhanced the uptake of Ca²⁺ and K⁺ in NaCl stressed seedlings. In conclusion, SA supplementation mitigates the negative effects of NaCl toxicity in faba bean seedlings through the modulation of different osmoprotectants, antioxidants and nutrients uptake.     

Charakterisierung einer Synchronkultur von Scenedesmus obliquus,ihrer potentiellen Photosyntheseleistung und des Photosynthese-Quotienten während des Entwicklungscyclus

Summary Using synchronous cultures, the change in the potential photosynthetic capacity and the behavior of the photosynthetic quotient were investigated during the life cycle of Scenedesmus obliquus, strain D 3. Scenedesmus obliquus was synchronized under a light-dark regime of 14:10 hours. The quality of synchrony was demonstrated by complete synchronization, homogeneity, exponential growth, shortest possible life cycle and non-susceptibility of the life cycle to the synchronizing procedure. Furthermore, the synchronous culture was characterized by determination of cell number, dry weight, packed cell volume, chlorophylls a and b and the carotenoids during the life cycle.The potential photosynthetic capacity (as O₂ evolution) was measured manometrically and polarographically in white light. This capacity increased from the beginning of the light period until the 8th hour and then declined until the 16th hour, that is until just before release of daughter cell. The percentage difference between the maximum and the minimum of the photosynthetic capacity was the same in the light saturating and light limiting region of photosynthesis. — The photosynthetic quotient was measured by means of Warburg's indirect method. It proved to be constant throughout the life cycle under light saturating and light limiting conditions. The ratio of O₂ evolved to CO₂ consumed was just below unity.The results were compared with those of other authors and their significance was discussed. It was concluded that the change in the photosynthetic capacity is inherent in the normal life cycle of green algae and is not a result of the synchronizing light-dark regime.

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Erster Teil einer Habilitationsschrift der Naturwissenschaftlichen Fakultät der Philipps-Universität Marburg. Auszüge dieser Arbeit wurden auf dem International Congress of Photosynthesis Research in Freudenstadt im Juni 1968 vorgetragen.     

Effects of salinity and heat-shock on wheat seedling growth and content of carbohydrates,proteins and amino acids

The effects of salinity (0, 50, 100, 150, and 200 mM NaCl) and heat-shock (42°C) and their interactions on germination, seedling growth, and some relevant metabolic changes of two cultivars (cv. Giza 155 and cv. Stork) of wheat (Triticum vulgaris L.) were studied. Germination studies indicate that plants tolerated salinity up to 100 mM NaCl. The lengths of roots and shoots and their water content, as well as fresh and dry matter yield of cv. Giza 155 seedlings remained more or less unchanged up to 100 mM NaCl and of cv. Stork up to 50 mM NaCl. Salinity induced progressive increase in soluble carbohydrates, soluble proteins and proline in cv. Giza 155 and in soluble proteins, proline and other free amino acids in cv. Stork. However, under the higher salinity levels, in cv. Giza 155 increase in soluble carbohydrates was accompanied by lose in other free amino acids, whereas in cv. Stork an opposite effect was obtained. Heat-shock treatment (42°C for 24 h) induced a significant decrease in the final germination percentage, the shoot and root lengths, fresh matter yield and the water content. The dry matter yield of the two cultivars was considerably increased as compared with the corresponding treatments with NaCl only. Heat-shock treatment resulted in a significant increase, in the amount of soluble carbohydrates and proline in salt treated seedlings of both cultivars. The pattern of changes in amino acids was opposite to that of soluble proteins, indicating that the increase in soluble proteins was at the expense of other amino acids in cv. Giza 155 andvice versa in cv. Stork.     

Salt stress responses of a halophytic grass <Emphasis Type="Italic">Aeluropus lagopoides</Emphasis> and subsequent recovery

To investigate the salt tolerance mechanisms, Aeluropus lagopoides as a halophytic plant was used. Plants were treated with 0, 150, 450, 600, and 750 mM NaCl and harvested at 0, 4, 8, and 10 days after treatment and 1 day and 1 week after recovery. Optimal growth, measured as fresh and dry weights, occurred at 150 mM NaCl, but it was suppressed by 450, 600, and 750 mM NaCl. Recovery significantly increased fresh and dry weights only in 750 mM NaCl-treated plants. Water content was decreased after NaCl treatment and increased after recovery. Na⁺ and proline contents and activity of superoxide dismutase (SOD) were increased after NaCl treatment and decreased after recovery in all treated plants. In contrast, K⁺ content and ascorbate peroxidase activity decreased after NaCl treatment and increased after recovery in all treated plants. Catalase (CAT) was activated only in 750 mM NaCl-treated plants. Total content of soluble protein was slightly changed after NaCl treatment. It was concluded that proline accumulation for osmotic adjustment, SOD activation for O₂^·− scavenging, and CAT activation at the higher level of salt stress to detoxify produced H₂O₂ were main A. lagopoides strategies under salt stress. A. lagopoides salt tolerance was not based on the restriction of Na⁺ uptake.     

Changes in photosynthetic and growth characteristics of Leymus chinensis community along the retrogression on the Songnen grassland in northeastern China

Net photosynthetic rate, stomatal conductance, ratio of sub-stomatal to atmospheric CO₂ concentration, transpiration rate, and water use efficiency changed significantly and assimilation capacity dropped continuously along the salinization and alkalinization process in the afternoon. Assimilation capacity of L. chinensis leaf correlated negatively with the degree of salinization and alkalinization. The photosynthetic characteristics of L. chinensis determined its community formation. By changing the ratio of chlorophyll a/b in leaves and accumulating soluble saccharides in rhizome, L. chinensis could adapt to the saline-alkali condition.