Strategies for adaptation of Suaeda physophora, Haloxylon ammodendron and Haloxylon persicum to a saline environment during seed-germination stage

BACKGROUND AND AIMS: Germination is very important for plant establishment in arid regions. The strategies taken by halophytes during the seed germination stage to adapt to saline environments in an arid zone were investigated in Suaeda physophora (euhalophyte), Haloxylon ammodendron (xero-halophyte) and Haloxylon persicum (xerophyte). METHODS: Seeds of S. physophora, H. ammodendron and H. persicum were exposed to a range of iso-osmotic NaCl and PEG solutions. Seed germination in, and recovery germination from, high NaCl were recorded. The effects of iso-osmotic NaCl and PEG on seed water uptake and changes in ion content were measured. In addition, the structure of seeds and Na+ distribution in the seed coat and embryos of dry seeds were investigated. KEY RESULTS: The relative increase in fresh weight of germinating seeds was markedly reduced in -2.24 MPa PEG compared with that in -2.24 MPa NaCl, while the opposite trend was found in concentration of K+ during the initial 9 h for all species. Haloxylon ammodendron and S. physophora had a higher recovery germination from -3.13 MPa NaCl compared with H. persicum. Seeds of all species had no endosperm. More Na+ was compartmentalized in the seed coats of the two halophytic species compared with that in the xerophyte H. persicum. CONCLUSIONS: The effect of NaCl on seed germination was due to both osmotic stress and ion toxicity for the three species. High soil salinity and a high content of Na+ in seeds may induce more seeds to remain ungerminated in S. physophora and H. ammodendron. Morphological structure and adaptation to salinity during seed germination may determine the geographical distribution of H. ammodendron and S. physophora in certain saline regions.     

Effect of salinity on seed germination,ion content and photosynthesis of cotyledons in halophytes or xerophyte growing in Central Asia

Aims We investigated the impact of salinity on seed germination, chlorophyll content, chloroplast structure and photosynthesis of the green embryos in desiccated seeds of the xerophyte Haloxylon persicum, xero-halophyte Haloxylon ammodendron and euhalophyte Suaeda physophora.Methods Seeds of H. persicum, H. ammodendron and S. physophora were collected from natural environment in Fukang, Xinjiang province. Pretreatment with 700 mM NaCl was carried out to stimulate the natural 'seed priming'; we analyzed the joint effect of salinity and different species on germination physiology and cotyledonal structure and photosynthetic function changes during germination and recovery stage.Important findings We found that seeds did not suffer ion toxicity for the two halophytes H. ammodendron and S. physophora, as evidenced by the high final germination after ungerminated seeds pretreated with 700 mM NaCl were transferred to distilled water, but the final germination of the xerophyte H. persicum was significantly lower than that of control. The Na + concentration in embryos increased under salinity for all species, while K + concentration decreased by salinity only for H. persicum and H. ammodendron, i.e. the concentration of K + in embryos of H. persicum and H. ammodendron decreased by 36% and 46%, respectively. For all species, whether dry intact seeds or cotyledons of dry seeds imbibed in deionized water and NaCl solution, had high chlorophyll content. Treatment with NaCl also caused chloroplast thylakoids to swell and chlorophyll content to decrease in seeds of H. persicum, but no significant change was observed in the more salt-tolerant species S. physophora and H. ammodendron. Fluorescence measurement showed that 700 mM NaCl decreased the Fv/Fm ratio of cotyledons in seeds for all species, especially for H. persicum and H. ammodendron. Photosynthetic oxygen releasing was detected from the seeds that were moistened with distilled water and 700 mM NaCl for 6 or 24 h and from the seeds that were initially moistened with 700 mM NaCl in darkness for 10 days, then transferred to distilled water for another 6 and 24 h. The results indicated that the chlorophyll in cotyledon of desiccated seed had photosynthetic function in early germination stage, even under high-saline condition. In addition, the photosynthesis of chlorophyll in the embryonic cotyledons of desiccated seeds during germination was similar to that in leaves of young seedlings for all species. In conclusion, the chloroplasts of the two halophytes were more salt resistant compared with the xerophyte H. persicum. The photosynthetic function of chlorophyll in cotyledons of mature seeds may be ecologically important for seedling development in early stage for plants growing in extremely saline or arid environments.     

Accumulation of inorganic and organic osmolytes and their role in osmotic adjustment in NaCl-stressed vetiver grass seedlings

The accumulation of inorganic and organic osmolytes and their role in osmotic adjustment were investigated in roots and leaves of vetiver grass (Vetiveria zizanioides) seedlings stressed with 100, 200, and 300 mM NaCl for 9 days. The results showed that, although the contents of inorganic (K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl⁻, NO₃⁻, SO₄²⁻ and H₂PO₃⁻)) and organic (soluble sugar, organic acids, and free amino acids) osmolytes all increased with NaCl concentration, the contribution of inorganic ions (mainly Na⁺, K⁺, and Cl⁻) to osmotic adjustment was higher (71.50–80.56% of total) than that of organic solutes (19.43–28.50%). The contribution of inorganic ions increased and that of organic solutes decreased in roots with the enhanced NaCl concentration, whereas the case in leaves was opposite. On the other hand, the osmotic adjustment was only effective for vetiver grass seedlings under moderate saline stress (less than 200 mM NaCl).     

Effects of saline‐waterlogging and dryness/moist alternations on seed germination of halophyte and xerophyte

In arid zones, precipitation distribution is extremely uneven, with saline‐waterlogging and dry–moist cycles appearing frequently, which negatively impact on seed germination and seedling establishment. The responses of two halophytes, Suaeda physophora and Haloxylon ammodendron, and a xerophyte, Haloxylon persicum, to saline‐waterlogging and dry–moist cycles were studied. The results showed that aeration increased seed germination for all species when seeds were submerged in NaCl, especially for xerophyte. Compared with S. physophora and H. ammodendron, seed germination, recovery germination, and total germination of H. persicum were much lower when seeds were submerged in 700 mm NaCl, especially for the recovery germination and total germination of nongerminated seeds when the seeds were desiccated and then transferred to distilled water. However, when the seeds were submerged in 700 mm NaCl with aeration, the seed germination, recovery germination, and total germination of nongerminated seeds transferred to distilled water increased dramatically for H. persicum. No adverse effect of desiccation was found on those values of nongerminated seeds pretreated in NaCl with or without aeration for the two halophytes. In conclusion, seeds of the two halophytes were more tolerant to waterlogging and dry–moist cycles than seeds of the xerophyte during emergence under saline conditions; these traits may be important for halophytes to survive extreme saline environments during the seed germination stage.     

Chlorophyll in desiccated seeds of a euhalophyte, Suaeda physophora, and its significancy in plant adaptation to salinity during germination

The seed cotyledons of a euhalophyte, Suaeda physophora, were found to be dark green. The pigment extracted from the cotyledons was proved to be chlorophyll for the absorption spectra curve of extracts the same as that for leaves. Photosynthetic oxygen-exchanging could be detected after the seeds were moistened for 6 h. Microstructure of organelles in cotyledons of ungerminated seeds was detected by transmission electron microscopy. Histochemical pigmentation was used to investigate the degree of damage on the membrane of radicles. A xerophyte, Haloxylon persicum, whose cotyledons of desiccated seeds also contain chlorophyll was used as a comparative species. The results showed that S. physophora maintained the ultra-structure of chloroplasts, the integrity of plasma membranes of radicles kept much better than that of H. persicum, which showed the great adaptability to salinity of the euhalophyte even at the seed-germination stage. Seeds were incubated in 0 and 700 mmol/L NaCl for 10 days in darkness at 20 ℃ , then ungerminated seeds in NaCl solution were transferred to deionised water and reincubated for another 8 days and was recorded the germination recovery. Dry seeds moistened with deionised water germinated gradually in the dark and germination was maximal after 3 or 4 d. Seeds at 700 mmol/L NaCl for 10 d and transferred back to deionised water germinated abruptly, most seeds germinated in one day and photosynthesis was also detected. It is concluded that recovery germination of S. physophora ensured the seeds could germinate rapidly after salinity declines, for example under the mild but transitory favorable edaphic condition in early spring. Photosynthesis function in seeds might also promoted radicle growth and seedling establishment.     

盐胁迫下盐地碱蓬体内无机离子含量分布特点的研究

用不同浓度NaCl溶液处理盐地碱蓬（Suaeda salsa)植株后,测定并比较老叶、幼叶及根部的无机离子含量和对K的选择性,叶片及根部的Na^ 、Cl^-含量随盐度的增加而升高,且累积趋势相似,盐胁迫下根部Na^ 、Cl^-及总离子含量（K^ 、Na^ 、Ca^2 ,NO3^-,Cl^-)明显低于叶片,说明盐地碱蓬地盐胁迫下,以叶片优先积累大量离子（如Na^ ,Cl^-) 为其适应特征。NaCl处理下,叶片的K^ ,Ca^2 含量低于对照,但随盐度的增加保持相对稳定,而根部K^ 含量,K/Na比、对K的选择性则高于叶片,这对盐胁迫下地上部的K^ 亏缺有一定补偿作用。低盐度处理（100mmol/LNaCl)促进NO3^-的吸收,另外随盐度的增加,叶片渗透势下降,渗透调节能力增强,幼叶渗透势低于老叶,但渗透调节能力相同。     

OSMOTIC ADJUSTMENT OF PLANTS TO SALINE MEDIA. II. DYNAMIC PHASE

Bernstein , Leon . (U. S. Salinity Lab., Riverside, Calif.) Osmotic adjustment of plants to saline media. II. Dynamic phase. Amer. Jour. Bot. 50(4): 360–370. Illus. 1963.—The time-course of osmotic adjustment in bean and pepper plants to increased salinity of the medium was determined by periodic sampling of plants following salt additions to the medium. Bean plants adjusted to increases of 1 atm OP within a day, the adjustment in roots occurring primarily at night following salt addition at 6 pm , whereas leaves and stems made most of their adjustment in the daytime. Pepper plants did not adjust completely to 1.5 atm NaCl additions in 48 hr, but OP increased by about the same amount in both species (0.5—1.0 atm per day). Diurnal fluctuations in OP of leaves and stems of both species and in roots of pepper were matched by parallel fluctuations in K concentrations. Added NaCl caused increased concentrations of K in leaves and stems which were more or less replaced by more slowly absorbed ions, Ca and Mg in bean leaves and Na in bean stems. Other salts produced comparable immediate effects on K level, but K was replaced more rapidly if the cation added was readily accumulated by the bean (Ca). In roots, Na uptake predominated if Na salts were added but K uptake was important on the CaCl₂ treatment. The K effects suggest a passive distribution of K between the cell and the medium.     

盐胁迫下囊果碱蓬出苗状况及苗期抗盐性

研究了盐胁迫对囊果碱蓬出苗、幼苗生长、离子积累以及光合放氧速率的影响.囊果碱蓬生长的最适盐浓度在200 mmol/L NaCl左右.高浓度NaCl(400 mmol/L和600 mmol/L)没有显著降低其出苗率,200 mmol/L NaCl对出苗率具有促进作用.400 mmol/L和600 mmol/L NaCl显著降低了光合放氧速率.囊果碱蓬在高浓度NaCl处理下能够维持叶片较高的K+/Na+ 及含水量可能是其适应高盐生境的重要机制.     

Effects of NO 3 − -N on the growth and salinity tolerance of Tamarix laxa Willd

The influence of NO ₃ ^? -N on growth and osmotic adjustment was studied in Tamarix laxa Willd., a halophyte with salt glands on its twigs. Seedlings of T. laxa Willd. were exposed to 1 mM (control) or 300 mM NaCl, with 0.05, 1 or 10 mM NO ₃ ^? -N for 24 days. The relative growth rate of seedlings at 300 mM NaCl was lower than that of control plants at all NO ₃ ^? -N levels, but the concentrations of organic N and total N in the twigs did not differ between the two NaCl treatments. Increasing NO ₃ ^? supply under 300 mM NaCl improved the growth of T. laxa, indicating that NO ₃ ^? played positive roles in improving salt resistance of the plant. The twigs of T. laxa Willd. accumulated mainly inorganic ions, especially Na⁺ and Cl^?, to lower osmotic potential (Ψs): the contributions of Na⁺ and Cl^? to Ψs were estimated at 31% and 27% respectively, at the highest levels of supply of both NaCl and NO ₃ ^? -N. The estimated contribution of NO ₃ ^? -N to Ψs was as high as 20% in the twigs in these conditions, indicating that NO ₃ ^? was also involved in osmotic adjustment in the twigs. Furthermore, increases in tissue NO ₃ ^? were accompanied by decreases in tissue Cl^? and proline under 300 mM NaCl. The estimated contribution of proline to Ψs declined as with NO ₃ ^? -N supply increased from 1 to 10 mM, while the contributions of nitrate to Ψs were enhanced under 300 mM NaCl. This suggested that higher accumulation of nitrate in the vacuole alleviated the effects of salinity stress on the plant by balancing the osmotic potential. In conclusion, NO ₃ ^? -N played both nutritional and osmotic roles in T. laxa Willd. in saline conditions.     

Extension growth of Impatiens glandulifera at low irradiance: importance of nitrate and potassium accumulation

BACKGROUND AND AIMS: The summer annual Impatiens glandulifera can reach 3 m in height within deciduous woodland. The primary objective was to determine if NO(3)(-) accumulation, and hence its osmotic effect, is an important physiological mechanism allowing Impatiens to achieve substantial height under low irradiance. METHODS: Stem extension, concentrations of K(+) and NO(3)(-) in leaves and concentrations of K(+), NO(3)(-) and other inorganic anions, malate, sugars, total N and total osmoticum in stem were measured in I. glandulifera sampled at different irradiance levels in deciduous woodland and in a glasshouse. Also, the energetic costs, as absorbed photons, of generating osmolarity in stem cell vacuoles with KNO(3), K(2)malate or hexose sugar were determined. KEY RESULTS: Results were similar in the woodland and glasshouse. At 50-100 % relative irradiance (Ir; open ground PAR = 100 % Ir) and 2-10 % Ir, plant height increased from 7-14 cm to 130-154 cm in 64-67 d. Leaf and stem NO(3)(-) concentrations were negligible at 50-100 % Ir while K(+), malate(2-) and sugars, respectively, accounted for 33.2-50.1 %, 19.3-20.8 % and 2.0-2.6 % of total osmoticum in stems. At 2-10 % Ir, NO(3)(-) concentrations were four to eight times greater in stems than leaves. Here, NO(3)(-) constituted 26.7-34.3 % of the total osmotic concentration in the stem and NO(3)(-)-N constituted 69-81 % of total N in stem tissue. Also at 2-10 % Ir, K(+) comprised 44.9-45.9 % and malate plus sugars 2.2-3.1 % of total osmotic concentration. The energy cost of osmoticum as KNO(3) was calculated as less than half that of malate and less than one-seventh that for hexose. Further calculations suggest that use of KNO(3), K(2)malate or glucose as osmoticum at low irradiance would, respectively, cost approx. 7 %, 16 % and 50 % of the total construction cost of the stem. CONCLUSIONS: It is concluded that accumulation of NO(3)(-) in place of organic molecules in stems is an important mechanism allowing I. glandulifera to achieve substantial height at low irradiance.     

Photosynthetic limitations of a halophyte sea aster (Aster tripolium L) under water stress and NaCl stress

To understand the mechanisms of salt tolerance in a halophyte, sea aster ( Aster tripolium L.), we studied the changes of water relation and the factors of photosynthetic limitation under water stress and 300 mM NaCl stress. The contents of Na(+) and Cl(-) were highest in NaCl-stressed leaves. Leaf osmotic potentials ( Psi(s)) were decreased by both stress treatments, whereas leaf turgor pressure ( Psi(t)) was maintained under NaCl stress. Decrease in Psi(s) without any loss of Psi(t) accounted for osmotic adjustment using Na(+) and Cl(-) accumulated under NaCl stress. Stress treatments affected photosynthesis, and stomatal limitation was higher under water stress than under NaCl stress. Additionally, maximum CO(2) fixation rate and O(2) evolution rate decreased only under water stress, indicating irreversible damage to photosynthetic systems, mainly by dehydration. Water stress severely affected the water relation and photosynthetic capacity. On the other hand, turgid leaves under NaCl stress have dehydration tolerance due to maintenance of Psi(t) and photosynthetic activity. These results show that sea aster might not suffer from tissue dehydration in highly salinized environments. We conclude that the adaptation of sea aster to salinity may be accomplished by osmotic adjustment using accumulated Na(+) and Cl(-), and that this plant has typical halophyte characteristics, but not drought tolerance.     

氮和钙交互作用对番茄氮素吸收的影响

以沈阳草甸土为栽培基质,采用二次D-饱和最优设计,进行番茄N、Ca两因素效应的盆栽试验,结果表明,在本试验条件下,番茄茎、叶、果实中氮素含量随生育期的进展而下降,氮肥对番茄果实中NO3^--N含量影响呈直线正效应,但各处理番茄果实中NO3^--N含量均不超过可生食标准．适量施用钙肥有利于控制果实中NO3^--N含量,氮肥对番茄植株地上部分和果实中N含量影响均符合报酬递减律．氮肥和钙肥对番茄N素积累符合报酬递减律;番茄从开花期到果实膨大期属N素最大效应期．番茄叶片硝酸还原酶活性受氮素影响较大．N、Ca配合施用,有利于提高番茄叶片硝酸还原酶活性,钙素可降低硝酸还原酶活性,土壤中NO3^--N含量和电导率EC值均随氮肥施用增加而提高。     

NaCl处理对盐地碱蓬开花及Na＋、K＋含量的影响

为探讨盐地碱蓬（Suaeda salsa）开花与盐的关系, 研究了1 （对照）、200和400 mmol·L-1 NaCl处理对盐地碱蓬不同分枝和单株开花数目、叶片和茎及花器官中的Na＋、K＋含量及Na＋/K＋比的影响。结果表明： 与对照相比, 200 mmol·L-1 NaCl处理下盐地碱蓬分枝及单株开花数目增加最显著, 单株开花数目增加了69.90%, 花器官中的Na＋含量、Na＋/K＋比分别增加了1.41倍和1.77倍, 而一级叶片的Na＋含量、Na＋/K＋比分别增加了3.96倍和4.96倍, 茎中Na＋含量、Na＋/K＋比分别增加了7.00倍和12.39倍。400 mmol·L-1 NaCl处理下, 单株开花数目增加了19.00%, 花器官中的Na＋含量、Na＋/K＋比分别增加了2.09倍和3.21倍, 而一级叶片的Na＋含量、Na＋/K＋比分别增加了4.28倍和6.50倍, 茎中Na＋含量、Na＋/K＋比分别增加了7.65和15.40倍。这些结果表明, NaCl处理下真盐生植物盐地碱蓬可能通过把Na＋区域化到茎叶而动员其中的K＋到花器官中维持花器官中合适的Na＋/K＋比而促进开花。     

NaCl胁迫对小黄花菜生长及相关生理指标的影响

为探讨小黄花菜的耐盐机理,选育良好的耐盐植物以缓解土壤盐渍化问题,该文选取小黄花菜(Hemerocallis minor)为试材,采用砂培法,研究不同浓度Na Cl(50、100、150、200、250 mmol·L~(-1))胁迫对小黄花菜的生长性状、细胞质膜透性和有机渗透调节物质含量等的影响。结果表明:(1)小黄花菜在100～150mmol·L~(-1)Na Cl胁迫时,损害初步显现,但不影响其存活;在Nacl浓度为200 mmol·L~(-1)以上时,小黄花菜生长被显著抑制,造成根系不发育、叶片受害、植株干物质积累显著不足,严重影响其生存状态。(2)在50～150mmol·L~(-1)盐渍环境下,叶片膜透性、MDA含量增幅较小,该浓度范围的Na Cl胁迫造成的膜脂损伤有限; 200mmol·L~(-1)以上浓度的Na Cl胁迫使得小黄花菜叶片的离子平衡无法继续维持,膜的选择透性丧失。(3)随着Na Cl浓度的增加,叶片中脯氨酸含量显著增加;在50～100 mmol·L~(-1)Nacl胁迫下,叶片可溶性糖含量在胁迫初期有所增加,在15 d时达到最大,胁迫后期开始下降;叶片中可溶性蛋白含量的变幅较为平缓,说明小黄花菜的主要渗透调节物质不是可溶性蛋白。该研究发现通过提高叶片膜透性,促进自身有机渗透调节物质的合成,能够在一定程度上缓解盐渍对植株的侵害,使得小黄花菜能够在50～100 mmol·L~(-1)的盐碱环境下正常生长。     

Effect of salinity on osmotic adjustment,proline accumulation and possible role of ornithine-δ-aminotransferase in proline biosynthesis in <Emphasis Type="Italic">Cakile maritima</Emphasis>

The short time response to salt stress was studied in Cakile maritima. Plants were exposed to different salt concentrations (0, 100, 200 and 400 mM NaCl) and harvested after 4, 24, 72 and 168 h of treatment. Before harvesting plants, tissue hydration, osmotic potential, inorganic and organic solute contents, and ornithine-δ-aminotransferase activity were measured. Plants of C. maritima maintained turgor and tissue hydration at low osmotic potential mainly at 400 mM NaCl. The results showed that, in leaves and stems, Na⁺ content increased significantly after the first 4 h of treatment. However, in roots, the increase of Na⁺ content remained relatively unchanged with increasing salt. The K⁺ content decreased sharply at 200 and 400 mM NaCl with treatment duration. This decrease was more pronounced in roots. The content of proline and amino acids increased with increasing salinity and treatment duration. These results indicated that the accumulation of inorganic and organic compounds was a central adaptive mechanism by which C. maritima maintained intracellular ionic balance under saline conditions. However, their percentage contribution to total osmotic adjustment varies from organ to organ; for example, Na⁺ accumulation mainly contributes in osmotic adjustment of stem tissue (60%). Proline contribution to osmotic adjustment reached 36% in roots. In all organs, proline as well as δ-OAT activity increased with salt concentration and treatment duration. Under normal growth conditions, δ-OAT is mainly involved in the mobilization of nitrogen required for plant growth. However, the highly significant positive correlation between proline and δ-OAT activity under salt-stress conditions suggests that ornithine pathway contributed to proline synthesis.     

Ecophysiological responses of the euhalophyte Suaeda salsa to the interactive effects of salinity and nitrate availability

Effects of salinity and nitrate nitrogen (NO₃⁻-N) on ion accumulation and chlorophyll fluorescence were monitored for two populations of Suaeda salsa grown from seeds in a greenhouse experiment. One population inhabits the intertidal zone and the other occurs on inland saline soils. Ion contents in soils and in leaves of the two populations were also investigated in field. In the greenhouse, seedlings were exposed to a NaCl concentration of 0.6 and 35.1 ppt, with 0.1 or 5 mM NO₃⁻-N treatments for 20 days. The contents of Na⁺ and Cl⁻ were higher, but NO₃⁻ was lower in soils of the intertidal zone than at the inland site. In the field, ion concentrations and the estimated contribution of these ions to osmotic potential in leaves showed no difference between the two populations, except that the estimated contribution of Na⁺ to osmotic potential in leaves of the intertidal population was lower than that in the inland population. In the greenhouse, in contrast, the concentration of Cl⁻ was lower, but NO₃⁻ concentration and the estimated contribution of NO₃⁻ to osmotic potential were higher, in the leaves of plants from the intertidal zone. Salinity had no effect on the maximal efficiency of PSII photochemistry (Fv/Fm) and the actual PSII efficiency (ΦPSII). The results indicated that S. salsa from the intertidal zone was better able to regulate Cl⁻ to a lower level, and accumulate NO₃⁻ even with low soil NO₃⁻ concentrations. Tolerance of the PSII machinery to high salinity stress may be an important characteristic for the studied species supporting growth in highly saline environments.     

盐胁迫下盐芥渗透调节物质的积累及其渗透调节作用

用含有NaCl0、50、100、200、300、400mmol/L的Hoagland培养液处理盐芥幼苗一定时间后,分别测定其根和叶含水量、渗透势、几种无机和有机渗透调节物质含量,并计算了渗透调节物质在不同条件下的计算渗透势值(COP).结果表明:随盐处理浓度的增加,盐芥根和叶的含水量和渗透势逐渐降低;Na 和Cl-是根和叶积累的无机渗透调节物质;SS、OA和FAA是根积累的有机渗透调节物质,Pro是叶和根积累的有机渗透调节物质.Na X-ray微区分析表明液泡是积累Na 的主要部位.     

The role of cotyledons in the establishment of Suaeda physophora seedlings

The role of cotyledons in seedling establishment of the euhalophyte Suaeda physophora under non-saline and saline conditions (addition of 1 mM or 400 mM NaCl) was investigated. Survival and fresh and dry weights were greater for seedlings grown in the light (12-h light/12-h dark) than in the dark (24-h dark). The shading of cotyledons tended to decrease shoot height, shoot organic dry weight, number of leaves, and survival of seedlings regardless of NaCl treatment, but the effect of cotyledon shading was greater with 400 mM NaCl. Concentrations of Na⁺ were higher in cotyledons than in leaves, regardless of NaCl treatment. The K⁺/Na⁺ ratio was lower in cotyledons than in leaves for seedlings treated with 1 mM NaCl but not for seedlings treated with 400 mM NaCl. Addition of 400 mM NaCl decreased oxygen production in cotyledons but especially in leaves. These results are consistent with the hypothesis that, by generating oxygen via photosynthesis and by compartmentalizing Na⁺, cotyledons are crucial for the establishment of S. physophora seedlings in saline environments.     

Ecophysiological responses of the euhalophyte Suaeda salsa to the interactive effects of salinity and nitrate availability

Effects of salinity and nitrate nitrogen (NO₃⁻-N) on ion accumulation and chlorophyll fluorescence were monitored for two populations of Suaeda salsa grown from seeds in a greenhouse experiment. One population inhabits the intertidal zone and the other occurs on inland saline soils. Ion contents in soils and in leaves of the two populations were also investigated in field. In the greenhouse, seedlings were exposed to a NaCl concentration of 0.6 and 35.1 ppt, with 0.1 or 5 mM NO₃⁻-N treatments for 20 days. The contents of Na⁺ and Cl⁻ were higher, but NO₃⁻ was lower in soils of the intertidal zone than at the inland site. In the field, ion concentrations and the estimated contribution of these ions to osmotic potential in leaves showed no difference between the two populations, except that the estimated contribution of Na⁺ to osmotic potential in leaves of the intertidal population was lower than that in the inland population. In the greenhouse, in contrast, the concentration of Cl⁻ was lower, but NO₃⁻ concentration and the estimated contribution of NO₃⁻ to osmotic potential were higher, in the leaves of plants from the intertidal zone. Salinity had no effect on the maximal efficiency of PSII photochemistry (Fv/Fm) and the actual PSII efficiency (ΦPSII). The results indicated that S. salsa from the intertidal zone was better able to regulate Cl⁻ to a lower level, and accumulate NO₃⁻ even with low soil NO₃⁻ concentrations. Tolerance of the PSII machinery to high salinity stress may be an important characteristic for the studied species supporting growth in highly saline environments.     

抗旱性不同的小麦叶片的渗透调节与水分状况的关系

两年的试验结果表明：在土壤水分胁迫下抗旱性强的小麦品种叶片的相对含水量和水势均高于抗旱性弱的品种;渗透势与水势为线性关系,水势每变动一个单位,渗透势变动0.71- 0.93个单位;渗透势与相对含水量的对数化关系为两条直线组成的一条折线,第一条直线渗透势的下降完全由渗透调节引起;第二条直线渗透势下降主要是细胞失水浓缩的结果。渗透调节能力为：秦麦3号>昌乐5号>山农587>济南13>烟农15>鲁麦5号。