Manganese as an ecological factor in salt marshes

The plant available manganese concentration (Mn²⁺) of salt-marsh sediments was compared to that of acidic and neutral soils. The mean soil-manganese concentration was higher in the top 1 cm of salt-marsh soil than in the neutral soil and comparable to that of the acidic soil (0–5 cm). A peak in the soil-manganese concentration in the upper marsh was observed one week after the spring tide but this effect was not evident in the lower marsh. Despite these differences, there was no correlation between mean manganese concentration and position on the marsh.The response to manganese of salt-marsh halophytes was studied by measuring growth and root elongation in a range of Mn²⁺ concentrations with and without sodium chloride. Although there was a differential response to manganese between salt-marsh species, manganese resistance was not related to position on the marsh. Most of the species investigated were tolerant of Mn²⁺ at concentrations higher than normally recommended for plant growth. Moreover a salt-marsh ecotype of Festuca rubra was found to have a higher manganese resistance than an inland ecotype of the same species.When sodium chloride was included in the growth medium, salt-marsh plants had a greatly increased resistance to manganese associated with a reduced uptake. This effect is reflected in the tissue-manganese concentration which was lower than in Deschampsia flexuosa although both groups of plants were exposed to a similar range of Mn²⁺ concentrations. It is concluded that sodium chloride markedly reduces the phytotoxicity of manganese in salt marshes.Nomenclature following Clapham, Tutin & Warburg (1968). Flora of the British Isles.The work was carried out while one of us (C. E. Singer) was in receipt of an SERC studentship, which is gratefully acknowledged.     

Response of mesquite to nitrate and salinity in a simulated phreatic environment: Water use,dry matter and mineral nutrient accumulation

Mesquite plants (Prosopis glandulosa var. Torreyana) were grown in 2-m long columns 20 cm in diameter, and provided with a constant, stable ground water source 10 cm above the sealed base of the column. Ground water contained 0, 1 or 5 mM nitrate, or a mixed salt solution (1.4, 2.8, or 5.6 dS m^-1) with the ionic ratios of ground water found in a field stand of Prosopis at Harper's Well (2.8 dS m^-1). Water uptake in the highly salinized columns began to decrease relative to low salt columns when soil salinity probes 30 cm above the column base read approximately 28 dS m^-1, a potential threshold for mesquite salt tolerance. Prosopis growth increased with increasing nitrate, and decreased with increasing salinity. Water use efficiency was little affected by treatment, averaging approximately 2 g dry matter L^-1 water used. Most fine roots were recovered from a zone about 25 cm above the ground water surface where water content and aeration appeared to be optimal for root growth. Root-shoot ratio was little affected by nitrate, but increased slightly with increasing salinity. Plant tissue P concentrations tended to increase with increasing salinity and decrease with increasing N, approaching potentially deficient foliage concentrations at 5 mM nitrate. The whole-plant leaf samples increased in sodium concentration both with added salt and with added nitrate. Foliar manganese concentrations increased with increasing salt in the absence of nitrate. Concentrations of sodium in leaves were low (<10 g kg^-1), considering the high salt concentrations in the ground water. Prosopis appears to exclude sodium very effectively, especially from its younger leaves. Although Prosopis is highly salt tolerant, the degree to which it utilizes soil nitrate in place of biologically fixed N may lower its salinity tolerance and affect its nutrient relations in phreatic environments.     

Cellular and whole plant responses ofVigna radiata to NaCl stress

The effect of different NaCl regimes was examined on the growth and ion accumulation in whole plants and callus cultures ofVigna radiata. Whole plants grown in sand culture were watered with Hoagland's solution supplemented with 0–350 mol m⁻³ of NaCl. Callus cultures were initiated from leaves of 7-d old seedlings of the same seed stock and grown in modified PC-L2 medium containing the same levels of NaCl as in Hoagland's solution. Callus showed the same tolerance to salt as did the whole plant suggesting thatV. radiata appears to have a mechanism(s) for salt tolerance which operates at the cellular level. Ion analysis of whole plant showed that root sodium concentrations of the tolerant cultivar G-65 was much higher while shoot sodium was much less than those of salt sensitive cultivar ML-1. Callus cultures of cv. G-65 also accumulated higher Na⁺ levels. Thus, the greater salt tolerance of cv. G-65 was associated with the control of sodium accumulation at the shoot or cellular level. Communicated by J. POSPíŠILOVá     

Calcium and Salt Toleration by Bean Plants

The role of calcium in the salt relations of the bean plant, Phaseolus vulgaris, was examined. Brittle wax bush bean plants were cultured in nutrient solutions containing 50 mM NaCl. In the absence of added calcium the plants showed a general breakdown of the roots. A low concentration of calcium in the nutrient solution (0.1 mM) prevented this. Without added calcium the plants absorbed and translocated sodium at such a rate that high concentrations of it built up in the leaves within two days. With increasing concentrations of calcium in the nutrient solution the leaves contained progressively less sodium, and at 3 mM CaSO₄ the concentrations of sodium in the leaves was equal to that of the control plants grown without addition of salt. Even after both roots and stems had reached a high concentration of sodium, the leaves of plants grown in the presence of adequate concentrations of calcium contained little sodium.     

Foliar and root absorption of Na+ and Cl− in maize and barley: Implications for salt tolerance screening and the use of saline sprinkler irrigation

Above-canopy sprinkler irrigation with saline water favours the absorption of salts by wetted leaves and this can cause a yield reduction additional to that which occurs in salt-affected soils. Outdoor pot experiments with both sprinkler and drip irrigation systems were conducted to determine foliar ion accumulation and performance of maize and barley plants exposed to four treatments: nonsaline control (C), salt applied only to the soil (S), salt applied only to the foliage (F) and salt applied to both the soil and to the foliage (F+S). The EC of the saline solution employed for maize in 1993 was 4.2 dS m^–1 (30 mM NaCl and 2.8 mM CaCl₂) and for barley in 1994, 9.6 dS m^–1 (47 mM NaCl and 23.5 mM CaCl₂). The soil surface of all pots was covered so that in the F treatment the soil was not salinized by the saline sprinkling and drip irrigation supplied nutrients in either fresh (treatments C and F) or saline water (treatments S and F+S).Saline sprinkling increased leaf sap Na⁺ concentrations much more than did soil salinity, especially in maize, even though the saline sprinkling was given only two or three times per week for 30 min, whereas the roots of plants grown in saline soil were continuously exposed to salinity. By contrast, leaf sap Cl^– concentrations were increased similarly by saline sprinkling and soil salinity in maize, and more by saline sprinkling than saline soil in barley. It is concluded that barley leaves, and to a greater extent maize leaves, lack the ability to selectively exclude Na⁺ when sprinkler irrigated with saline water. Moreover, maize leaves selectively absorbed Na⁺ over Cl^– whereas barley leaves showed no selectivity. When foliar and root absorption processes were operating together (F+S treatment) maize and barley leaves accumulated 11–14% less Na⁺ and Cl^– than the sum of individual absorption processes (treatment F plus treatment S) indicating a slight interaction between the absorption processes. Vegetative biomass at maturity and cumulative plant water use were significantly reduced by saline sprinkling. In maize, reductions in biomass and plant water use relative to the control were of similar magnitude for plants exposed only to saline sprinkling, or only to soil salinity; whereas in barley, saline sprinkling was more detrimental than was soil salinity. We suggest that crops that are salt tolerant because they possess root systems which efficiently restrict Na⁺ and Cl^– transport to the shoot, may not exhibit the same tolerance in sprinkler systems which wet the foliage with saline water. ei]T J Flowers     

Arbuscular mycorrhizal fungi enhance root cadmium and copper accumulation in the roots of the salt marsh plant Aster tripolium L.

It is known that vegetation plays an important role in the retention of heavy metals in salt marshes by taking up and accumulating the metals. In this study, we investigated whether arbuscular mycorrhizal fungi (AMF) increase Cd and Cu uptake and accumulation in the root system of the salt marsh species Aster tripolium L., and whether indigenous AMF isolated from polluted salt marshes have higher capacity to resist and alleviate metal stress in A. tripolium than isolates of the same species originated from non-polluted sites. Plants inoculated with Glomus geosporum, either isolated from a polluted salt marsh site (PL isolate) or from a non-polluted site (NP isolate), and non-mycorrhizal (NM) plants were compared in a pot experiment at four different Cd and Cu concentrations. Cd had no effect in root colonization, whereas high concentrations of Cu decreased colonization level in plants inoculated with the NP isolate. AM colonization did not increase plant dry weight or P concentration but influenced root Cd and Cu concentrations. Inoculation with PL and NP isolates enhanced root Cd and Cu concentrations, especially at highest metal addition levels, as compared to NM plants, without increasing shoot Cd and Cu concentrations. There was no evidence of intraspecific variation in the effects between AMF isolated from polluted and non-polluted sites, since there were no differences between plants inoculated with PL or NP isolate in any of the tested plant variables. The results of this study showed that AMF enhance metal accumulation in the root system of A. tripolium, suggesting a contribution of AMF to the sink of metals within vegetation in the salt marshes.     

Boron and calcium increasePisum sativum seed germination and seedling development under salt stress

A beneficial effect of B and Ca application on symbiotic interaction between legume and rhizobia under saline conditions has recently been shown, suggesting conventional agricultural practices to increase crop salt tolerance. However, nothing is known about application of both nutrients on early events of legume development under salt stress, prior to the establishment of a symbiotic interaction. Therefore, the effects of different levels of B (from 9.3 to 93μM B) and Ca (from 0.68 to 5.44 mM Ca) on seed germination, root elongation, plant development, and mineral composition of pea (Pisum sativum L. cv. Argona) grown under 0 to 150 mM NaCl, were analysed. Development of plants previously germinated in the presence of salt was more impaired than that of plants put under salt stress once seeds were germinated. A NaCl concentration of 75 mM and 150 mM inhibited pea seed germination and seedling growth. The addition of either extra B or extra Ca to the germination solution prevented the reduction caused by 75 mM NaCl but not that of 150 mM NaCl. However, root elongation and plant development under salt stress (75 mM NaCl) was enhanced only by addition of both B and Ca. When plants were cultivated in the absence of external N, N content in roots and shoots originating from seeds was diminished by salt and enhanced by B and Ca, suggesting a role of these nutrients in remobilisation of seed nutrient stores. Salinity also led to an extremely high concentration of Na⁺ ions, and to a decrease of B and Ca concentrations. This can be overcome by addition of both nutrients, increasing salt tolerance of developing pea plants. The necessity of nutritional studies to increase crop production in saline soils is discussed and proposed.     

REGULATION OF NaCl IN JAUMEA CARNOSA (ASTERACEAE), A SALT MARSH SPECIES,AND ITS EFFECT ON LEAF SUCCULENCE

A salt marsh species, Jaumea carnosa, was used in hydroponic experiments to test the effects of increasing NaCl concentrations on leaf succulence and plant accumulations of K, Ca, Mg, Na and Cl. A nested experimental design was used with four salinity levels. Plants were grown in full Hoagland's solution plus different amounts of NaCl (0.0–1.2 osmoles). Leaf succulence was measured as percent water content as well as vertical elongation of mesophyll cells. There were no corresponding increases in leaf succulence with increasing concentrations of NaCl in the root zone. Plants receiving aerosol spray (40 mg/dm²/day) did not show significant increases in leaf succulence. Leaf succulence was significantly increased when the plants were removed from the NaCl solutions and placed in non-salinized Hoagland's solution. Osmotic concentrations of cell sap in leaf tissues showed significant increases as NaCl concentrations increased in the root zone. The concentrations of K, Ca and Mg were higher in plants grown without NaCl than in those grown with NaCl. The accumulations of K in the root tissues were always higher than those of the shoot tissues. Although there was a two-fold difference in NaCl concentrations at the highest levels, the concentrations of Na in the shoot tissues were relatively similar. The results of the Cl analyses of shoot tissues showed a similar pattern of regulation of uptake. This regulation of salt uptake may be important in preventing injury by limiting accumulations of salt in plant tissues when growing in soils of high osmotic potentials.     

Influence of salt stress on propagation,growth and nutrient uptake of typical aquatic plant species

Anthropogenic activities and natural causes contribute to an increase in the area and degree of degraded saline wetlands in arid/semi‐arid and coastal regions. The objective of this study was to determine the salt tolerance of the seven aquatic plant species Phragmites australis, Arundo donax, Canna indica, Scirpus validus, Alternanthera philoxeroides, Phyllostachys heteroclada and Potederia cordata during asexual reproduction and continuous growth. The species were exposed to five salinity treatments from 0.3 (control) to 20 dS m^?1 during a 30 day experiment. Data were collected on asexual reproduction and growth, chlorophyll content in leaves, Na⁺ and K⁺ concentrations, total nitrogen (TN) and total phosphorus (TP) concentrations in above‐ground biomass (AGB) and below‐ground biomass (BGB). The results showed that: 1) increase in salinity (especially at a salinity level of EC ≥15 dS m^?1) generally inhibited the capacity for asexual reproduction and reduced the chlorophyll content of leaves; 2) total dry biomass of plants was significantly negatively related to asexual reproduction; 3) species‐specific salt tolerance mechanisms were reflected by the Na⁺ and K⁺ concentrations and Na⁺/K⁺ ratios in different parts of the plants; and 4) the absorption of TN and TP were inhibited at high salinity (i.e. EC = 20 dS m^?1) in AGB and BGB of most tested plant species. However, salinity may enhance plant uptake of TN and TP under certain conditions (e.g. EC at 5, 10 and 15 dS m^?1). In general, as compared to the other species tested, giant reed A. donax and alligator weed A. philoxeroides showed relatively high asexual reproduction and growth capacity under high salt stress, and these species should thus be considered as candidates for restoration of degraded saline wetlands and/or for decontaminating saline wastewater.     

不同强度盐胁迫下AM真菌对羊草生长的影响

不同浓度NaCl盐处理下,AM真菌对羊草(Leymus chinensis)的侵染能力和对植物生长的影响,从植物形态和离子含量角度探讨了AM真菌提高羊草耐盐性的作用机理。结果表明,在高盐胁迫下,AM真菌显著降低了盐胁迫效应,提高了羊草生物量,菌根效应明显。菌根化羊草的根茎比显著增加,并且N、P浓度较高,Na~+和Cl~-离子浓度较低,表明AM真菌即促进羊草对营养元素的吸收,又减少了离子毒害。菌根化羊草的Ca~(2+)和K~+离子浓度,以及P/Na~+和K~+/Na~+比高于非菌根化羊草,表明AM真菌可通过调节渗透势以避免或减缓盐胁迫造成的生理缺水。随着盐胁迫的增加,菌根化羊草对磷的依赖性逐渐转换为对钾的依赖性。研究结果有助于揭示AM真菌提高植物耐盐能力的作用机理,并对应用菌根技术修复盐化草地具有理论指导意义。     

Improved Tolerance of <Emphasis Type="Italic">Acacia nilotica</Emphasis> to Salt Stress by Arbuscular Mycorrhiza, <Emphasis Type="Italic">Glomus fasciculatum</Emphasis> may be Partly Related to Elevated K/Na Ratios in Root and Shoot Tissues

A pot experiment was conducted to examine the effect of arbuscular mycorrhizal fungus, Glomus fasciculatum, and salinity on the growth of Acacia nilotica. Plants were grown in soil under different salinity levels (1.2, 4.0, 6.5, and 9.5 dS m⁻¹). In saline soil, mycorrhizal colonization was higher at 1.2, 4.0, and 6.5 dS m⁻¹ salinity levels in AM-inoculated plants, which decreased as salinity levels further increased (9.5 dS m⁻¹). Mycorrhizal plants maintained greater root and shoot biomass at all salinity levels compared to nonmycorrhizal plants. AM-inoculated plants had higher P, Zn, and Cu concentrations than uninoculated plants. In mycorrhizal plants, nutrient concentrations decreased with the increasing levels of salinity, but were higher than those of the nonmycorrhizal plants. Mycorrhizal plants had greater Na concentration at low salinity levels (1.2, 4.0 dS m⁻¹), which lowered as salinity levels increased (6.5, 9.5 dS m⁻¹), whereas Na concentration increased in control plants. Mycorrhizal plants accumulated a higher concentration of K at all salinity levels. Unlike Na, the uptake of K increased in shoot tissues of mycorrhizal plants with the increasing levels of salinity. Our results indicate that mycorrhizal fungus alleviates deleterious effects of saline soils on plant growth that could be primarily related to improved P nutrition. The improved K/Na ratios in root and shoot tissues of mycorrhizal plants may help in protecting disruption of K-mediated enzymatic processes under salt stress conditions.     

Effects of silicon on enzyme activity and sodium,potassium and calcium concentration in barley under salt stress

Two contrasting barley (Hordeum vulgare L.) cultivars: Kepin No.7 (salt sensitive), and Jian 4 (salt tolerant) were grown in a hydroponics system containing 120 mol m^-3 NaCl only and 120 mol m^-3 NaCl with 1.0 mol m^-3 Si (as potassium silicate). Compared with the plants treated with salt alone, superoxide dismutase (SOD) activity in plant leaves and H⁺-ATPase activity in plant roots increased, and malondialdehyde (MDA) concentration in plant leaves decreased significantly for both cultivars when treated with salt and Si. The addition of Si was also found to reduce sodium but increase potassium concentrations in shoots and roots of salt-stressed barley. Sodium uptake and transport into shoots from roots was greatly inhibited by added Si under salt stress conditions. However, Si addition exhibited little effect on calcium concentrations in shoots of salt-stressed barley. Thus, Si-enhanced salt tolerance is attributed to selective uptake and transport of potassium and sodium by plants. The results of the present study suggest that Si is involved in the metabolic or physiological changes in plants. This revised version was published online in June 2006 with corrections to the Cover Date.     

Response of tomato cultivars to salinity

The responses of five tomato cultivars (L. esculentum Mill) of different degrees of salt tolerance were examined over a range of 0 to 140 mM NaCl applied for 3 and 10 weeks. Judged by both Na and Cl accumulations and maintenance of K, Ca and Mg contents with increasing salinity, the most tolerant cultivars (Pera and GC-72) showed different responses. The greater salt tolerance of cv Pera was associated with a higher Cl and Na accumulation and a lower K content in the shoot than those found in the other cultivars, typical of a halophytic response to salinity. However, the greater salt tolerance of cv GC-72 was associated with a retention of Na and Cl in the root, restriction of their translocation to the shoot and maintenance of potassium selectivity under saline conditions. The salt tolerance mechanisms that operated in the remaining cultivars were similar to that of cv GC-72, as at first they excluded Na and Cl from the shoots, accumulating them in the roots; with longer treatment, the ability to regulate Na and Cl concentrations in the plant was lost only in the most salt sensitive cultivar (Volgogradskij), resulting in a massive influx of both ions into the shoot.The salt sensitivity of some tomato cultivars to salinity could be due to both the toxic effect of Na and Cl ions and nutritional imbalance induced by salinity, as plant growth was inversely correlated with Na and Cl contents and directly correlated with K and Ca contents. This study displays that there is not a single salt tolerance mechanism, since different physiological responses among tomato cultivars have been found.     

Sodium relations in Chenopodiaceae: a comparative approach

Sodium relations of 15 species of Chenopodiaceae were studied in seedlings grown on quartz sand at 10 mol m^?3 of sodium and potassium. Uptake of sodium and potassium into whole plants and shoots was followed over 2 weeks. High alkali ion uptake rates were found in all species. The apparent selectivity of alkali ion uptake showed a continuous variation between species, from nearly perfect sodium exclusion to negligible cation selection. K/Na ratios above 6 were found in the shoots of eight species. For most of these plants above ground sodium concentrations were highest in the hypocotyls. However, in Chenopodium hybridum (shoot K/Na = 10) and C. urbicum (shoot K/Na = 17) above ground sodium concentrations were lowest in hypocotyls and highest in leaves, as in those species accumulating larger amounts of sodium. These differences are discussed with respect to the underlying mechanisms of ion regulation.     

Effect of salinity on mycorrhizal onion and tomato in soil with and without additional phosphate

Summary Vesicular-arbuscular mycorrhizal fungi (VAM) are known to increase plant growth in saline soils. Previous studies, however, have not distinguished whether this growth response is due to enhanced P uptake or a direct mechanism of increased plant salt tolerance by VAM. In a glasshouse experiment onions (Allium cepa L.) were grown in sterilized, low-P sandy loam soil amended with 0, 0.8, 1.6 mmol P kg^–1 soil with and without mycorrhizal inoculum. Pots were irrigated with saline waters having conductivities of 1.0, 2.8, 4.3, and 5.9 dS m^–1. Onion colonized withGlomus deserticola (Trappe, Bloss, and Menge) increased growth from 394% to 100% over non-inoculated control plants when soil P was low ( 0.2 mmol kg^–1 NaHCO₃-extractable P) at soil saturation extract salinities from 1.1 dS m^–1 to 8.8 dS m^–1. When 0.8 and 1.6 mM P was added no dry weight differences due to VAM were observed, however, K and P concentrations were higher in VAM plants in saline treatments.Glomus fasciculatum (Gerdeman and Trappe) andGlomus mosseae (Nicol. and Gerd.) isolates increased growth of VAM tomato 44% to 193% in non-sterilized, saline soil (10 dS m^–1 saturation extract) despite having little effect on growth in less saline conditions when soil P was low. Higher tomato water potentials, along with improved K nutrition by VAM in onion, indicate mechanisms other than increased P nutrition may be important for VAM plants growing under saline stress. These effects appear to be secondary to the effects of VAM on P uptake.     

Salicylic acid differently impacts ethylene and polyamine synthesis in the glycophyte Solanum lycopersicum and the wild‐related halophyte Solanum chilense exposed to mild salt stress

This study aimed to determine the effects of exogenous application of salicylic acid (SA) on the toxic effects of salt in relation to ethylene and polyamine synthesis, and to correlate these traits with the expression of genes involved in ethylene and polyamine metabolism in two tomato species differing in their sensitivity to salt stress, Solanum lycopersicum cv Ailsa Craig and its wild salt‐resistant relative Solanum chilense. In S. chilense, treatment with 125 mM NaCl improved plant growth, increased production of ethylene, endogenous salicylic acid and spermine. The production was related to a modification of expression of genes involved in ethylene and polyamine metabolism. In contrast, salinity decreased plant growth in S. lycopersicum without affecting endogenous ethylene, salicylic or polyamine concentrations. Exogenous application of salicylic acid at 0.01 mM enhanced shoot growth in both species and affected ethylene and polyamine production in S. chilense. Concomitant application of NaCl and salicylic acid improved osmotic adjustment, thus suggesting that salt and SA may act in synergy on osmolyte synthesis. However, the beneficial impact of exogenous application of salicylic acid was mitigated by salt stress since NaCl impaired endogenous SA accumulation in the shoot and salicylic acid did not improve plant growth in salt‐treated plants. Our results thus revealed that both species respond differently to salinity and that salicylic acid, ethylene and polyamine metabolisms are involved in salt resistance in S. chilense.     

Screening sorghum for tolerance to excess manganese in solution culture

This study was conducted to define traits to screen sorghum (Sorghum bicolor L. Moench) genotypes for tolerance to excess Mn. Visual Mn toxicity symptoms, net and total root lengths, shoot and root dry matter yields, and shoot and root Mn concentrations were determined for plants grown in nutrient solutions (pH 4.5) at different levels of Mn (0, 3, 6, 9 and 12 mM above the initial 18 M) to assess plant responses to excess Mn. Dry matter yields showed greatest variability among genotypes, and was an effective trait to evaluate sorghum for tolerance to excess Mn. Reductions in dry matter yields did not occur until Mn levels were above 3 mM. Levels of Mn between 3 and 6 mM could effectively be used to screen sorghum for genotypic differences to excess Mn. Manganese levels above 6 mM were too severe to allow good genotypic differentiation. Of genotypes tested, NB9040 and Wheatland showed good tolerance and SC283 and ICA-Nataima were sensitive to excess Mn.     

Influence of boron and calcium on the tolerance to salinity of nitrogen-fixing pea plants

The effects of different levels of B (from 9.3 to 93 M B) and Ca (from 0.68 to 5.44 mM Ca) on plant development, nitrogen fixation, and mineral composition of pea (Pisum sativum L. cv. Argona) grown in symbiosis with Rhizobium leguminosarum bv. viciae 3841 and under salt stress, were analysed. The addition of extra B and extra Ca to the nutrient solution prevented the reduction caused by 75 mM NaCl of plant growth and the inhibition of nodulation and nitrogen fixation. The number of nodules recovered by the increase of Ca concentration at any B level, but only nodules developed at high B and high Ca concentrations could fix nitrogen. Addition of extra B and Ca during plant growth restored nodule organogenesis and structure, which was absolutely damaged by high salt. The increase in salt tolerance of symbiotic plants mediated by B and Ca can be co-related with the recovery of the contents of some nutrients. Salinity produced a decrease of B and Ca contents both in shoots and in nodulated roots, being increased by the supplement of both elements in the nutrient solution. Salinity also reduced the content in plants of other nutrients important for plant development and particularly for symbiotic nitrogen fixation, as K and Fe. A balanced nutrition of B and Ca (55.8 M B, 2.72 mM Ca) was able to counter-act the deficiency of these nutrients in salt-stressed plants, leading to a huge increase in salinity tolerance of symbiotic pea plants. The necessity of nutritional studies to successfully cultivate legumes in saline soils is discussed and proposed.     

A meta-analysis of arbuscular mycorrhizal effects on plants grown under salt stress

Salt stress limits crop yield and sustainable agriculture in most arid and semiarid regions of the world. Arbuscular mycorrhizal fungi (AMF) are considered bio-ameliorators of soil salinity tolerance in plants. In evaluating AMF as significant predictors of mycorrhizal ecology, precise quantifiable changes in plant biomass and nutrient uptake under salt stress are crucial factors. Therefore, the objective of the present study was to analyze the magnitude of the effects of AMF inoculation on growth and nutrient uptake of plants under salt stress through meta-analyses. For this, data were compared in the context of mycorrhizal host plant species, plant family and functional group, herbaceous vs. woody plants, annual vs. perennial plants, and the level of salinity across 43 studies. Results indicate that, under saline conditions, AMF inoculation significantly increased total, shoot, and root biomass as well as phosphorous (P), nitrogen (N), and potassium (K) uptake. Activities of the antioxidant enzymes superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase also increased significantly in mycorrhizal compared to nonmycorrhizal plants growing under salt stress. In addition, sodium (Na) uptake decreased significantly in mycorrhizal plants, while changes in proline accumulation were not significant. Across most subsets of the data analysis, identities of AMF (Glomus fasciculatum) and host plants (Acacia nilotica, herbs, woody and perennial) were found to be essential in understanding plant responses to salinity stress. For the analyzed dataset, it is concluded that under salt stress, mycorrhizal plants have extensive root traits and mycorrhizal morphological traits which help the uptake of more P and K, together with the enhanced production of antioxidant enzymes resulting in salt stress alleviation and increased plant biomass.     

Varietal differences in physiological and biochemical responses to changes in the ionic environment

Summary Experimental assessment of differences between cultivars of crop species or ecotypes of wild species from different localities in their capacities for ion absorption and transport is made difficult by the problem of obtaining seed material of comparable ionic content. When young seedlings are used this problem is particularly acute if the seeds of the different cultivars have not been raised under identical soil conditions. Propagation of material from ecotypes under controlled conditions is one approach to the solution of this problem. Six maize cultivars have been selected for similarity of phosphate content and the capacity for phosphate absorption from 5 M KH₂PO₄ has been shown to vary by threefold whereas the proportion of the accumulated phosphate that reaches the shoot differs by much less. This level of phosphate supply approached that likely to induce deficiency and when the concentration is reduced to 1 M differences in transport capacity of up to fourfold were observed when the rate of arrival at the tip of the first leaf was continuously monitored. The rapidity with which the transport is shut off by adding 1 mM D(+) mannose to the root environment also varies significantly indicating that sizeable differences in either the accumulation of mannose or the activity of phosphomannoisomerase exist in these cultivars.Ecotypes ofArmeria maritima collected from three sites, inland serpentine, inland mine dumps and coastal salt marsh were maintained as stock plants on the same peat mixture. Samples taken from these stocks were raised on a standard culture solution to provide genetically different material grown under constant conditions. The capacities for ion uptake were shown to differ very considerably and these differences were accentuated when the plants were grown in a range of concentrations of MgSO₄, NaCl and MnSO₄. The absorption of phosphate and its incorporation into nucleic acids were increased temporarily in the presence of 50 mM MgSO₄ but the pattern of these changes was different in the three ecotypes. The absorption of Na, Cl, and Rb was measured after treatment with a range of concentrations of NaCl and the effect of treatment with MnSO₄ on subsequent absorption of Mn and SO₄ was also measured. The coastal plants were significantly more efficient in their absorption of these ions when treated at the lower levels of NaCl (0.5 and 10.0 mM). The short term absorption rates were not reflected in the overall accumulation of sodium over periods of 10 weeks and the coastal plants appeared to reduce the root content of sodium by transfer to the shoot and by increased active pumping to the exterior.