Studies on growth and distribution of Na+, K+ and Cl− in soybean varieties differing in salt tolerance

Soybean plants, varieties “Lee”, “Jackson” and “Bragg” were grown in solution culture at various salinity levels. A NaCl concentration of 10 mM was already inhibitory to growth of “Jackson”; growth of “Lee”, however, was only reduced at a salt concentration of 50 mM or higher. The moderately salt tolerant variety “Lee” efficiently excluded Cl^? from the leaves up to about 50 mM NaCl in the medium, but showed high Cl^? contents in the root; exclusion of Na⁺ from the leaves was also apparent in this variety. On the other hand, the salt sensitive variety “Jackson” did not have the capacity for exclusion of Cl^? and Na⁺. The physiological behaviour of the variety “Bragg” resembled that of “Jackson”. It is suggested that the exclusion of Cl^? and Na⁺ from the leaves in the soybean variety “Lee” is regulated by the root.     

Short-term studies on the uptake and transport of Cl− by soybean cultivars differing in salt tolerance

Short-term tracer experiments (³⁶Cl) were conducted with the differentially salt susceptible soybean cultivars “Lee” (moderately tolerant) and “Jackson” (sensitive) to elucidate the pattern of Cl^? uptake and translocation in relation to the physiology of salt tolerance. Rates of Cl^? uptake by excised roots of “Jackson” were much greater in the lower (0.1–0.5 mM NaCl) and particularly in the higher concentration range than by the more tolerant cultivar. The transfer rate to the shoot was significantly higher in “Jackson” than in “Lee” and increased with time of treatment. The cultivar “Lee” translocated a relatively high amount of Cl^? during the onset of salt treatment, but in contrast to “Jackson” was then able to slow down Cl^? translocation into the shoot to a degree about proportional to the increment of dry matter. In experiments on secondary translocation both cultivars extruded substantial amounts of ³⁶Cl^? to the nutrient solution during the period in inactive solution with constant salinity following labeling. Possibly, some Cl^? that had moved into the leaves during labeling was retranslocated and extruded via the roots. The absolute efflux rate was presumably greater for “Jackson” than for “Lee” although it appeared not efficient enough to compensate for the high rate of influx into the root. After 5–6 days of secondary translocation a lesser amount of Cl^? was shifted from the root to the shoot in “Lee” as compared with “Jackson”. Chloride accumulation in the upper root and lower stem, similar to that reported for Na⁺ in several Na⁺ excluding species, was not observed. From the results it may be concluded that the cultivar “Jackson” cannot sufficiently control the uptake of Cl^? and its translocation, particularly into the mature leaves; this contributes causally to the development of severe injury under continuous salt stress.     

Influence of extreme K:Na ratios and high substrate salinity on plant metabolism of crops differing in salt tolerance

Mineral regulation of two soybean varieties Jackson and Lee was investigated in long term water culture experiments using saline solutions. The effects of extreme K:Na ratios using chloride and sulfate as counterions were studied in the early stages of salinity.

The growth rates of both varieties were not affected by salinization. A K⁺ stimulated, intensive acropetal Cl^‐ translocation was observed in the salt sensitive variety Jackson. The varieties did not differ in Na⁺ translocation and in the suppression of Ca²⁺ and Mg²⁺ in the leaves. But the effect of the nature of salinization indicates already differences in Na uptake and translocation of the cultivars.

The avoidance of Cl^‐, but also of Ha⁺, in connection with influences of the resulting ionic imbalance on metabolic pathways are probably the most causative factors for the different tolerance to salinity of the two soybean varieties.     

Influence of extreme K:Na ratios and high substrate salinity on plant metabolism of crops differing in salt tolerance

Abstract

Ion‐specific initial salt effects due to supply of extreme K⁺, Na⁺, Cl or SO₄ ^2‐ combinations were studied on the carbohydrate pattern as well as on the activity of amylases, phosphorylase and invertase of two soybean varieties, Jackson and the more tolerant Lee.

Reducing sugars were little affected. Salinity increased leaf sucrose more in Jackson than in Lee, and more due to Cl^? than to SO₄ ^2‐ supply. Salinity increased the higher level of root sucrose in Lee less than the lower sucrose level in Jackson, independent of the nature of salination. Salinity increased leaf starch more in Jackson than in Lee. KCl increased leaf starch of Jackson most, Na₂SO₄. least. KCl increased leaf starch of Lee more than NaCl, while K₂SO₄ and Na₂SO₄ tended to decrease leaf starch. Only KCl stimulated amylases and phosphorylase in leaves of Jackson. Salinity changed amylases according to the starch content in leaves of Lee, while phosphorylase decreased independent of the ion combination supplied. Salinity decreased invertase in leaves of Jackson, it affected invertase in Lee only little.

It is suggested that the carbohydrate metabolism dependent and independent of ionic regulation contribute to physiological salt tolerance mechanisms of soybean varieties.     

Auswirkungen hoher NaCl-Konzentration im Nährmedium auf die Transpiration,den Abscisinsäure-, Cytokinin- und Prolingehalt zweier Sojabohnensorten

Effect of high NaCl concentration in the nutrient medium on transpiration, abscisic acid, cytokinin and proline content of two soybean varieties With the differentially salt-sensitive soybean varieties ?Lee”? and ?Jackson”? the effect of salinization on transpiration, Cl^? and Na⁺ accumulation, and on abscisic acid (ABA), cytokinin and proline content was investigated. Salinization with 75 mM NaCl in the nutrient medium drastically inhibited the transpiration (about 40%) of both varieties but more so with the variety ?Jackson”?. Nevertheless this variety translocated substantially more Cl^? into the shoot than ?Lee”?. However, ?Lee”? accumulated more Cl^? into the roots and thus was able to effectively protect the shoot against a toxic Cl^? concentration. The Na⁺ distribution in the roots and shoots was nearly the same in both varieties. The ABA content of the leaves of both varieties increased 5-fold to 1200 ng × g^? dry weight after 48 h of salt stress. About the same time transpiration of the salt-stressed plants reached a minimum. Between 48 and 168 h the ABA content of ?Lee”? dropped to about half. The ABA level in ?Jackson”? remained higher which indicated that the shoot was stressed more intensely and/or longer. The results do not imply a causal relationship between the ABA concentration in the leaves and the exclusion of C1^? from the shoot of ?Lee”?. The cytokinin concentration of the two soybean varieties was not significantly affected by salinization. The proline content in the leaves increased markedly with salt stress in both varieties but much more so in ?Jackson”?. Proline content in the leaves increased from about 1.8 μmoles × g^?1 dr. w. before salt stress to 24.7 μmoles × g^?1 dr. w. after 168 h of stress. However, the proline concentration dropped to nearly the initial level within 48 h after a 120 h salt stress treatment was discontinued and the plants were returned to a control solution. In ?Lee”? salinization only doubled the amount of proline found initially. The highest value was observed after 120 h of salinization.     

盐胁迫下柚实生苗生长、矿质营养及离子吸收特性研究

以坪山柚为材料,对盐胁迫下实生苗生长、矿质营养及离子吸收特性进行了研究。结果表明,沙培30d,80～200mmol/L盐胁迫,随盐浓度提高,坪山柚实生苗株高、叶面积、地上部干重和根部干重明显降低。溶液培养8d,坪山柚实生苗地上部及根Na+、Cl-含量随盐浓度的增加而增加,根及地上部K+、Ca2+、Mg2+以及P和Mn含量下降,Fe、Zn、Cu含量的变化因器官而异。其中,地上部Fe含量对盐胁迫敏感,可作为柚耐盐性鉴定指标。40mmol/L盐胁迫,坪山柚地上部K+/Na+、Ca2+/Na+、Mg2+/Na+值均显著下降,且Mg2+/Na+值+/Na+值>1;浓度≥160mmol/L盐胁迫,K+/Na+值+吸收、运转效率比Cl-高。     

Effects of NaCl and silicon on ion distribution in the roots,shoots and leaves of two alfalfa cultivars with different salt tolerance

Abstract

The effects of exogenous NaCl and silicon on ion distribution were investigated in two alfalfa (Medicago sativa. L.) cultivars: the high salt tolerant Zhongmu No. 1 and the low salt tolerant Defor. The cultivars were grown in a hydroponic system with a control (that had neither NaCl nor Si added), a Si treatment (1 mmol L^?1 Si), a NaCl treatment (120 mmol L^?1 NaCl), and a Si and NaCl treatment (120 mmol L^?1 NaCl + 1 mmol L^?1 Si). After 15 days of the NaCl and Si treatments, four plants of the cultivars were removed and divided into root, shoot and leaf parts for Na⁺, K⁺, Ca²⁺, Mg²⁺, Fe³⁺, Mn²⁺, Cu²⁺ and Zn²⁺ content measurements. Compared with the NaCl treatment, the added Si significantly decreased Na⁺ content in the roots, but notably increased K⁺ contents in the shoots and leaves of the high salt tolerant Zhongmu No.1 cultivar. Applying Si to both cultivars under NaCl stress did not significantly affect the Fe³⁺, Mg²⁺ and Zn²⁺ contents in the roots, shoots and leaves of Defor and the roots and shoots of Zhongmu No.1, but increased the Ca²⁺ content in the roots of Zhongmu No.1 and the Mn²⁺ contents in the shoots and leaves of both cultivars, while it decreased the Ca²⁺ and Cu²⁺ contents of the shoots and leaves of both cultivars under salt stress. Salt stress decreased the K⁺, Ca²⁺, Mg²⁺ and Cu²⁺ contents in plants, but significantly increased Zn²⁺ content in the roots, shoots and leaves and Mn²⁺ content in the shoots of both cultivars when Si was not applied. Thus, salt affects not only the macronutrient distribution but also the micronutrient distribution in alfalfa plants, while silicon could alter the distributions of Na⁺ and some trophic ions in the roots, shoots and leaves of plants to improve the salt tolerance.     

运东近滨海地区燕麦秸秆盐分积累与改良盐碱地潜力分析

为探明燕麦在运东滨海盐碱地区秸秆盐分积累特点以及改良盐碱地的潜力,选用"坝莜1号"、"白燕2号"和"花早2号"燕麦,采用单因素随机区组试验,以品种和土壤含盐量作为因素,进行了2组田间试验,测得燕麦的生物量、秸秆离子浓度和积累量及秸秆与土壤离子浓度比值。研究结果显示,"坝莜1号"燕麦开花-灌浆至成熟期整株生物量从2.9 t·hm-2增加至3.8 t·hm-2,延迟20 d收获则减少至2.5 t·hm-2。"白燕2号"在低土壤盐分浓度(1.0 g·kg-1左右)下的生物量(3.1 t·hm-2)显著大于中浓度(2.0 g·kg-1左右,1.7 t·hm-2)和高浓度(3.0 g·kg-1左右,0.4 t·hm-2)下的生物量。中等土壤盐分浓度下"坝莜1号"的生物量(3.8 t·hm-2)显著高于"白燕2号"(3.1t·hm-2)和"花早2号"(2.2 t·hm-2)。"坝莜1号"秸秆中Na+、K+浓度从开花到成熟均显著增加,而Mg2+、Ca2+和Cl-则显著降低。延迟20 d收获,除Ca2+外,其他离子浓度均显著降低。随着土壤盐分的升高,"白燕2号"秸秆Na+、Mg2+、Ca2+和Cl-浓度显著升高,而K+显著下降。3个品种的Na+、K+和Mg2+之间存在显著差异,而Cl-和Ca2+浓度无显著差异。燕麦秸秆中Cl-浓度最高,K+和Na+基本相当,均高于Mg2+和Ca2+。"坝莜1号"秸秆中Na+、K+、Mg2+、Cl-积累量成熟期最高,延迟收获20 d后积累量均显著降低。"白燕2号"秸秆Na+、K+、Mg2+、Ca2+、Cl-积累量随土壤盐分升高显著下降。除Ca2+外,Na+、K+、Mg2+、Cl-积累量品种之间差异显著。"坝莜1号"秸秆与土壤离子浓度比值中,Na++K+最大(46~63),其次是Cl-(30~46)、Mg2+(24~30)和Ca2+(3~15);延迟收获后Na++K+和Cl-秸秆与土壤浓度比值显著下降,Mg2+比值无显著变化,Ca2+比值显著升高。随着土壤盐分升高"白燕2号"秸秆与土壤Na++K+和Cl-浓度比值显著下降,Ca2+无显著变化。秸秆与土壤离子浓度比值在品种之间存在显著差异。燕麦理论上具有改良盐碱地的潜力,但收获时间和土壤盐分均会显著地影响燕麦生物量、离子浓度和积累量,从而影响燕麦改良盐碱地的效果。     

Effect of grafting on the growth and ion concentrations of cucumber seedlings under NaCl stress

Abstract

To assess whether grafting raised the salt tolerance of cucumber seedlings by limiting transport of Na⁺ to the leaf and to test whether the salt tolerance of grafted plants was affected by the shoot genotype, two cucumber cultivars (“Jinchun No. 2”, a relatively salt-sensitive cultivar, and “Zaoduojia”, a relative salt-tolerant cultivar) were grafted onto rootstock pumpkin (Cucurbita moschata Duch. cv. “Chaojiquanwang”, a salt-tolerant cultivar). Ungrafted plants were used as controls. The effects of grafting on plant growth and ion concentrations were investigated under NaCl stress. Reductions in the shoot and root dry weights, leaf area and stem diameter of grafted plants were lower and concentrations of K⁺ and Cl^? in the leaves were higher than those of ungrafted plants under the same NaCl stress. The Na⁺ concentration and Na⁺/K⁺ ratio in scion leaves and in the stems of grafted plants were lower, whereas those in rootstock stems and roots were higher than in ungrafted plants under the same NaCl stress. Shoot and root dry weight, leaf area and stem diameter were negatively correlated with leaf Na⁺ concentrations and Na⁺/K⁺ ratio, but were positively correlated with leaf K⁺ concentrations. The Na⁺ concentrations and Na⁺/K⁺ ratio were lower, whereas the K⁺ concentrations in the leaves of grafted “Zaoduojia” plants were higher than those in grafted “Jinchun No. 2” plants under the same NaCl stress. The reductions in leaf area and stem diameter of grafted “Jinchun No. 2” plants were more severe than those of grafted “Zaoduojia” plants. These results indicate that: (1) the higher salt tolerance of grafted cucumber seedlings is associated with lower Na⁺ concentrations and Na⁺/K⁺ ratio and higher K⁺ concentrations in the leaves, (2) grafting improved the salt tolerance of cucumber seedlings by limiting the transport of Na⁺ to the leaves, (3) the salt tolerance of grafted cucumber seedlings is related to the shoot genotype.     

Soil salt and NaCl have different effects on seed germination of the halophyte Suaeda salsa

Seed germination is a key life‐history stage of halophytes. Most studies on seed germination of halophytes have focused on the effects of a single salt, while little information is available on the effects of mixed salt in the natural habitat. Due to the contribution of multiple ions in saline soil, we hypothesized that the effect of mixed salt on seed germination will differ from that of a single salt and the mechanism of how germination is affected will differ as well. The effects of mixed salt and NaCl on germination, water imbibition, and ionic concentrations of seeds of Suaeda salsa (L.) Pall. were compared at various salinity levels. Germination percentage (GP) and rate (GR) decreased with increasing salinity level, regardless of salt type. There was no difference in GP or GR between mixed salt and NaCl when the salinity level was below 20 dS m^?1. Above 20 dS m^?1, GP and GR in NaCl were lower than those in mixed salt. At the same salinity level, Na⁺ concentration in seeds was higher in NaCl than that in mixed salt, but the reverse was true for Ca²⁺ and Mg²⁺ concentrations. Imbibition rate for seeds in NaCl was lower than that in mixed salt at the same salinity level. Addition of Ca²⁺ and Mg²⁺ alleviated the inhibition of NaCl on seed germination. In conclusion, our results suggest that the effects of soil salts and NaCl on seed germination are different, and using NaCl instead of soil salt might not be realistic to show the effect of saline stress on seed germination of halophytes in the natural habitat.     

Comparison of the response of ion distribution in the tissues and cells of the succulent plants Aloe vera and Salicornia europaea to saline stress

There exists a great variability among plant species regarding their sensitivity and resistance to high salinity in soil, and most often this variability is related with the ability of a particular plant species to regulate ion homeostasis and transport. In this study, we have investigated the effects of NaCl on growth rate, water status, and ion distribution in different cells and tissues of two succulent plants, Aloe vera and Salicornia europaea. Our results showed that the growth of A. vera seedlings was significantly decreased in response to salinity. However, the growth of S. europaea seedlings was greatly stimulated by high concentrations of NaCl. Under saline conditions, S. europaea seedlings maintained K⁺ and Ca²⁺ uptake in roots and showed a higher root‐to‐shoot flux of Na⁺ and Cl^– as compared to A. vera. Despite great accumulation of Na⁺ and Cl^– in photosynthetically active shoot cells in S. europaea, its growth was enhanced, indicating S. europaea is capable of compartmentalizing salt ions in the vacuoles of shoot cells. Aloe vera seedlings, however, showed a low transport rate of Na⁺ and Cl^– to leaves and suppressed uptake of K⁺ and Ca²⁺ in roots during NaCl treatment. Our results also implicate that A. vera may be able to accumulate Na⁺ and Cl^– in the metabolically inactive aqueous cells in leaves and, as a result, the plant can survive and can maintain growth under saline conditions.     

Wirkung einer Abscisinsäure-Applikation auf die Cl−Translokation in Sojabohnen bei niedriger und hoher Besalzung des Nährmediums

Effect of abscisic acid in the root medium on Cl^? translocation in soybeans under low and high salt conditions With soybeans of the varieties ?Lee”? and ?Jackson”? the effect of abscisic acid (ABA) applied to the root medium in different concentrations (10^?4, 10^?5 and 10^?6M) on Cl^? translocation was investigated. Under low salt conditions (0,5 mM NaCl) ABA, depending on its concentration, strongly decreased Cl^? translocation to the shoot. At the highest ABA concentration, within 24 h the Cl^? content of the shoots was reduced to about 40 % of the control, the Cl^? accumulation within the roots was reduced about 25 %. However, the 10^?5 and the 10^?6M ABA treatment increased Cl^? accumulation in the roots but decreased Cl^? translocation to the shoot. Under high salt conditions (75 mM NaCI) ABA had no measureable effect on CI- translocation to the shoot. It was found that the genetic mechanism responsible for high CI- accumulation within the roots of ?Lee”? and high CI- translocation to the shoot of ?Jackson”? was not affected by ABA. ABA strongly inhibited transpiration. High ABA concentration in combination with low salt treatment decreased the transpiration rate up to 50 % of the control. ABA also inhibited transpiration under high salt conditions. This result is discussed considering the fact, that ABA added to the highly saline nutrient solution did not decrease the CI- translocation to the shoot. An investigation using ¹⁴C-ABA showed, the radioactive substance was taken up by the roots and translocated to the shoot independently from the salt treatment. The metabolism of the radioactive substance was different for roots and leaves. However, no difference could be observed by comparing the two soybeans varieties with or without salt treatment.     

Is the salt tolerance of maize related to sodium exclusion? I. Preliminary screening of seven cultivars

Maize (Zea mays L.) plants in the early stage of development were treated with 80 mM sodium chloride (NaCl) with or without supplemental calcium (Ca²⁺) (8.75 mM) for a seven day period. The effects of salinity on dry matter production and shoot and root concentrations of sodium (Na⁺), Ca²⁺, and potassium (K⁺) were measured for seven Pioneer maize cultivars. Salinity significantly reduced total dry weight, leaf area, and shoot and root dry weight below control levels. For all seven cultivars, Na⁺concentrations were reduced and leaf area was significantly increased by supplementing salinized nutrient solutions with 8.75 mM calcium chloride (CaCl₂). The two cultivars with the lowest shoot and root Na⁺ concentrations under NaCl‐salinity showed the greatest increases in total, shoot and root dry weights with the addition of supplemental Ca. Shoot fresh weight/dry weight ratios for all cultivars were decreased significantly by both salinity treatments, but supplemental Ca²⁺ increased the ratio relative to salinity treatments without supplemental Ca. Root fresh weight/dry weight ratios were decreased only by salinity treatments with supplemental Ca. With NaCl‐salinity, cultivars which had lower shoot and root Na⁺ concentrations were found to be more salt sensitive and had significantly lower amounts of dry matter production than those cultivars which had higher shoot and root Na⁺ concentrations. It was concluded that Na⁺ exclusion from the shoot was not correlated with and was an unreliable indicator of salt tolerance for maize.     

不同矿化度咸水灌溉对小麦产量和生理特性的影响

为充分利用河北低平原区蕴藏丰富的咸水资源,缓解淡水资源匮乏的矛盾,在连续定位灌溉田间试验的基础上,采用裂区设计,以灌溉水矿化度作为主处理,以不同小麦品种作为副处理,研究了不同矿化度梯度咸水灌溉对小麦产量、叶片相对电导率、丙二醛(MDA)含量、脯氨酸(Pro)含量以及叶片Na+、K+、Ca2+及K+/Na+等指标的影响及其与品种耐盐性的关系。研究结果表明,随灌溉水矿化度的增加叶片的细胞膜透性增强,同时膜脂氧化产物MDA增加、渗透调节物质脯氨酸增多、叶片中Na+累积增多,而高矿化度下Ca2+和K+/Na+比值明显降低;从品种的产量和耐盐指数来看,"石家庄8号"较"衡4399"表现较强的耐盐特性。从生理指标来看,"石家庄8号"较"衡4399"细胞膜更稳定,"衡4399"用2 g.L 1以上咸水灌溉其膜透性显著增加,而"石家庄8号"需要4 g.L 1以上咸水灌溉膜透性才显著提高。另外"石家庄8号"的耐盐性还与其维持较高的K+和较低的脯氨酸水平以及较高的K+/Na+比值有关,而与Na+、Ca2+绝对含量关系不明显。从MDA来看,返青期和孕穗期"石家庄8号"较"衡4399"水平低,但到抽穗期和灌浆期其积累量较"衡4399"反而要高。灌溉水的矿化度超过4 g.L 1时,两个小麦品种产量明显降低但耐盐性强的"石家庄8号"减产幅度相对较小。因此咸水灌溉小麦品种选择十分重要,从作物耐盐性和产量考虑,多年连续灌溉咸水的矿化度不宜超过4 g.L 1。     

EFFECT OF PACLOBUTRAZOL AND PUTRESCINE ON ANTIOXIDANT ENZYMES ACTIVITY AND NUTRIENTS CONTENT IN SALT TOLERANT CITRUS ROOTSTOCK SOUR ORANGE UNDER SODIUM CHLORIDE STRESS

The effects of paclobutrazol (PBZ) and putrescine (Put) on antioxidant enzymes activity, proline contents and nutrients uptake were studied on salt tolerant citrus rootstock sour orange. Six-month-old nucellar seedlings grown in pots and subjected to three levels of PBZ and two levels each of salinity and Put for 90 days. Seedlings treated with PBZ or Put alone or in combination had higher anti-oxidant enzymes activities, accumulation of proline and nutrients contents like potassium (K⁺) and calcium (Ca²⁺) under both saline and non-saline conditions. Further, application of PBZ or Put alone or in combination also reduced the accumulation of both Na⁺ and Cl^? ions in leaves and roots in NaCl stressed seedlings. A combined application of 250 mg L^?1 PBZ and 50 mg L^?1 Put proved to be more effective in improving proline and Ca²⁺ content and restricting accumulation of Na⁺ ions in leaf tissues.     

Sodium‐calcium interactions with growth,water, and photosynthetic parameters in salt‐treated beans

Calcium (Ca²⁺) amelioration of the plant's growth response to salinity depends on genetic factors. In this work, supplemental Ca²⁺ did not improve growth in Phaseolus vulgaris L. cv. Contender under high‐saline conditions and negatively affected several physiological parameters in nonsalinized plants. The response to supplemental Ca²⁺ was examined using plants grown in 25% modified Hoagland solution at different Na⁺ : Ca²⁺ ratios. In control plants (1 mM Ca²⁺; 1 mM Na⁺) surplus Ca²⁺ (4 or 10 mM) was associated with stomatal closure, decrease of hydraulic conductivity, sap flow, leaf specific dry weight, leaf K⁺ and leaf Mg²⁺ concentrations, and inhibition of CO₂ assimilation. Leaf water content was enhanced, while water‐use efficiency and dry matter were unaffected during the 15 d experimental period. The Ca²⁺ effect was not cation‐specific since similar results were found in plants supplied with high external Mg²⁺ or with a combination of Ca²⁺ and Mg²⁺. Relative to control plants, salinization (50 and 100 mM NaCl) caused a decrease in dry matter, hydraulic conductivity, sap flow, leaf Mg²⁺ activity, and inhibition of stomatal opening and CO₂ assimilation. However, NaCl (50 and 100 mM NaCl) enhanced leaf K⁺ concentration and water‐use efficiency. At 100 mM NaCl, leaf water content also significantly increased. Supplemental Ca²⁺ had no amelioration effect on the salt‐stress response of this bean cultivar. In contrast, the 50 mM–NaCl treatment improved stomatal conductance and CO₂‐assimilation rate in plants exposed to the highest Ca²⁺ concentration (10 mM). Phaseolus vulgaris is classified as a very NaCl‐sensitive species. The similarities in the effects caused by supplemental Ca²⁺, supplemental Mg²⁺, and NaCl salinity suggest that P. vulgaris cv. Contender has a high non‐ion‐specific salt sensitivity. On the other hand, the improvement in gas‐exchange parameters in Ca²⁺‐supplemented plants by high NaCl could be the result of specific Na⁺‐triggered responses, such as an increase in the concentration of K⁺ in the leaves.     

Time sequence studies on uptake and distribution of Na+ and Cl– in diplachne fusca (Kallar grass) grown in NaCl

Abstract

The time sequence of uptake and distribution of labelled Na and Cl^– in osmotically adjusted “Kallar”; grass was studied at low (10 mM) and moderately high salinity (100 mM) in nutrient solutions. Increasing NaCl raised the concentrations of Na⁺ and Cl^– in the tissue of tops and roots but had little or no effect on plant growth. On the leaves no toxic symptoms were obvious, not even in plants grown at salt stress of 200 mM NaCl. In all treatments, the young and the old leaves extruded 30–60% and 30–70% of their total Na⁺ and Cl^–. As the amounts of Na⁺ and Cl^– in the tissue increased with time, their extrusion also increased, however, as a proportion of the total Na⁺ and Cl^– it did not change much with time. Autoradiographs revealed that the extruded salts were distributed equally on the upper and lower surface of all leaves, parallel to veins. There seemed to be a more intense distribution of Na⁺ and Cl^– in the leaf sheaths as well as in the apical region of the roots. However, the net transfer rates, even after only 6 hours of uptake, did not indicate a strong retention mechanism in the roots.     

NaCl胁迫下甜瓜幼苗离子吸收特性研究

以厚皮甜瓜黄河蜜和薄皮甜瓜白沙蜜为试材,在人工控制条件下,研究了NaCl胁迫对甜瓜幼苗Na+、K+、Ca2+和Cl-吸收与分配的影响。结果表明,随NaCl浓度的增加,两个甜瓜品种各器官中Na+和Cl-含量均逐渐增加,K+含量逐渐减少,叶片中Ca2+含量逐渐降低,而根中的 Ca2+含量逐步增加;各器官中Na+/K+和叶片中Na+/ Ca2+逐渐增加;SK、Na 和SCa、Na逐步下降。NaCl胁迫下,黄河蜜叶片和茎中Na+ 积累和叶、茎、根中Cl-积累及K+ 、Ca2+ 降低幅度均明显低于白沙蜜;黄河蜜对K+ 和Ca2+的选择吸收和运输能力受胁迫的影响小于白沙蜜。表明厚皮甜瓜黄河蜜比薄皮甜瓜白沙蜜具有更强的耐盐性和盐适应性。     

Edaphic characterization and soil ionic composition influencing plant zonation in a semiarid Mediterranean salt marsh

Soil characteristics and plant zonation were studied in a semiarid Mediterranean salt marsh in SE Spain. According to topographic sequences and plants distribution, two transects were established from the border of La Mata lagoon to the upland vegetation limit and soils were described and analysed. Regularly spaced plots were established in these transects in accordance with the stands of vegetation and surface soil samples were taken every 2 months for 2 years. The following edaphic factors were determined: soil moisture content, pH and concentration of Cl⁻, SO₄²⁻, Ca²⁺, Mg²⁺, Na⁺ and K⁺ in the saturation extract. In addition, the groundwater level was measured and the duration of the flooding periods established in each plot. Soil–plant relationships were studied by means of canonical correspondence analysis. Based on rainfall data for the study period, dry and wet seasons were separated and the habitats of the plant communities were compared for salt quantity and quality independently for each season. Soils were classified, according to FAO (1998), as Hypercalcic, Sodic and Mollic Solonchaks and Hypercalcic Sodic Calcisols. The most important variables which explained plant zonation were: the flooding period, total salinity, minimum Ca²⁺/Na⁺ ratio and the mean sodium adsorption ratio. When the habitats of the main plant communities were compared, differences in salt quantity, quality and seasonal variations were found. Two chenopod shrubs, Arthrocnemum macrostachyum and Sarcocornia fruticosa, predominated in the most saline areas. More pronounced seasonal variations in soil salinity were found in the A. macrostachyum zone than in the Sarcocornia fruticosa zone. The highest value for K⁺/Na⁺ and Ca²⁺/Na⁺ ratios were measured in the Suaeda vera stand. The Lygeum spartum zone was distinguished by the high Ca²⁺/Na⁺ and Ca²⁺/Mg²⁺ ratios in the wet period. Among the rushes, Schoenus nigricans predominated in the less saline areas, where the K⁺/Na⁺ ratio was higher and the Ca²⁺/Na⁺ ratio lower than where Juncus maritimus predominated. Limonium cossonianum communities occupied an intermediate position with respect to soil salinity, between the chenopod shrubs and the other communities.Our results suggest that salt marsh plant zonation is influenced by temporal and spatial edaphic gradients which must be jointly considered if soil–plant relationships in saline soils are to be fully understood.