Purslane (Portulaca oleracea L.): A halophytic crop for drainage water reuse systems

Drainage water reuse systems have been proposed for the west side of the San Joaquin Valley of California in order to reduce the volumes of water requiring disposal. Implementation of this system requires development of a cropping system with successively higher salt tolerance. A major limitation is the need to identify alternate species that will be suitable as the final, most salt tolerant crop in the series. These crops must be productive when irrigated with waters that are typically high in sulfate salinity and may be contaminated with potentially toxic trace elements. This study was initiated to evaluate the interactive effects of sulfate salinity and selenium on biomass production and mineral content of purslane (Portulaca oleracea). Plants were grown in greenhouse sand cultures and irrigated four times daily. Treatments consisted of three salinity levels with electrical conductivities (EC_i) of 2.1, 15.2, and 28.5 dS m^–1, and two selenium levels, 0 and 2.3 mg L^–1. In the initial harvests, shoot dry matter was reduced by 15 to 30% at 15.2 dS m^–1 and by 80 to 90% at 28.5 dS m^–1. Regrowth after clipping above the first node was vigorous and biomass from plants irrigated with 15.2 dS m^–1 water was nearly double that from the 2 dS m^–1 treatment. Purslane appears to be an excellent candidate for inclusion in saline drainage water reuse systems. It is (i) highly tolerant of both chloride- and sulfate-dominated salinities, (ii) a moderate selenium accumulator in the sulfate-system, and (iii) a valuable, nutritive vegetable crop for human consumption and for livestock forage.     

Salt stress response in tomato beyond the salinity tolerance threshold

Crop salt tolerance is generally assessed as the relative yield response to increasing root zone salinity, expressed as soil (EC_e) or irrigation water (EC_w) electrical conductivity. Alternatively, the dynamic process of salt accumulation into the shoot relative to the shoot biomass has also been considered as a tolerance index. These relationships are graphically represented by two intersecting linear regions, which identify (1) a specific threshold tolerance, at which yield begins to decrease, and (2) a declining region, which defines the yield reduction rate. Although the salinity threshold is intuitively a critical parameter for establishing plant salt tolerance, we focused our interest on physiological modifications that may occur in the plant at salinity higher than the so-called tolerance threshold. For this purpose, we exposed hydroponically grown tomato plants to eight different salinity levels (EC = 2.5 (non-salinized control); 4.2; 6.0; 7.8; 9.6; 11.4; 13.2; 15.0 dS m⁻¹). Based on biomass production, water relations, leaf ions accumulation, leaf and root abscisic acid and stomatal conductance measurements, we were able to identify a specific EC value (approximately 9.6 dS m⁻¹) at which a sharp increase of the shoot and root ABA levels coincided with (1) a decreased sensitivity of stomatal response to ABA; (2) a different partitioning of Na⁺ ions between young and mature leaves; (3) a remarkable increase of the root-to-shoot ratio. The specificity and functional significance of this response in salt stress adaptation is discussed.     

Salinity-yield response functions of barley genotypes assessed with a triple line source sprinkler system

Evaluation of the salt tolerance of crop cultivars under field conditions is greatly complicated by the typical temporal and spatial variability of soil salinity. We obtained the grain yield – salinity response functions of 124 barley genotypes by growing them in ten salinity treatments imposed by a Triple Line Source Sprinkler (TLS) system during five consecutive years. Additional objectives were to ascertain the consistency and reproducibility over years of these functions, to quantify the deleterious effects of saline sprinkling irrigations, and to assess correlations between salinity tolerance and leaf sap salt concentration. The consistency and reproducibility of the response functions within and between years were adequate (only 8% of the response functions were discarded for statistical reasons). The Y _m (grain yield without salinity) and the EC₅₀ (the EC _e that reduces yield by 50%) estimates were not correlated (P > 0.05) suggesting that the most productive genotypes were not necessarily less salinity tolerant. Y _m was positively and significantly (P < 0.01) correlated with Y₆ and Y₁₂ (fitted grain yields at EC _e values of 6 dS m^-1, and 12 dS m^-1, respectively), indicating that it is a useful statistic in the selection of barley genotypes most productive under medium and high salinities. Foliar salt uptake due to saline sprinkling irrigations decreased the EC₅₀ by around 50% as compared with the salinity tolerance obtained with surface irrigation systems. No consistent relationships were found between either Y _m or EC₅₀ and the leaf sap osmotic potential, Cl, Ca, Na and K concentrations. They could not therefore be used in screening for salinity tolerance of barley. On the basis of the evidence from the present study, Y _m is the best statistic for predicting the most productive barley genotypes in salt-affected soils. This revised version was published online in June 2006 with corrections to the Cover Date.     

Salt tolerance of eggplant

Summary No quantitative information is available regarding the salt tolerance of eggplant (Solanum melongena L.). The present study was conducted over a two-year period in small field plots irrigated by drip, where irrigation frequency was also a variable. The salt tolerance function may be described by the equation Y_r=100–6.9 (EC_e−1.1), where Y_r=relative yield of fruit, EC_e=the mean integrated electrical conductivity at the soil saturation extract, 1.1 dS/m=threshold salinity. Salt was distributed reasonably uniformly within the root zone.     

Effect of saline irrigation on plant water traits,photosynthesis and ionic balance in durum wheat genotypes

In the era of climate change, decreased precipitation and increased evapo-transpiration hampers the yield of several cereal crops along with the soil salinity and poor ground water resource. Wheat being the moderately tolerant crop face many challenges in the arid and semi-arid regions under irrigated agriculture. In view of this, the study was planned to explore the potential of durum wheat genotypes under salinity on the basis of physiological traits. Experiment was designed as RBD in three replications to evaluate 15 wheat genotypes with moderate saline irrigation (EC_iw – 6 dS m⁻¹) and extreme saline irrigation (EC_iw – 10 dS m⁻¹) along with one set of control (Best available water). Different physiological traits such as water potential (ψ_p), osmotic potential (ψ_s), relative water content (RWC), Na⁺ and K⁺ content were recorded in roots as well as shoots at the reproductive stage whereas photosynthetic rate and chlorophyll content were measured in the flag leaves. A significant variability (p < 0.001) was noted among the genotypes under different stress environments and it was observed that durum genotype HI 8728 and HI 8737 showed less reduction in plant water traits (RWC, ψ_p and ψ_s) than the salinity tolerant checks of bread wheat KRL 99 and KRL 3–4. HD 4728 and HI 8708 maintained higher photosynthetic rate as well as higher chlorophyll content under the extreme salinity level of EC_iw – 10 dSm⁻¹. No significant differences were found in root Na⁺ in genotypes KRL 99 (3.17^g), KRL 3–4 (3.34^g) and HI 8737 (3.41^g) while in shoots, lowest accumulation was seen in KRL 99, MACS 3949 and KRL 3–4 at EC_iw – 10 dSm⁻¹. The mean range of K⁺ content was 7.60–9.74% in roots and 4.21–6.61% in shoots under control environment which decreased to 50.77% in roots and 46.05% in shoots under extreme salinity condition of EC_iw – 10 dSm⁻¹. At EC_iw – 10 dSm⁻¹, KRL 99 maintained highest K^+/Na⁺ in both root and shoot followed by KRL 3–4, HI 8737, MACS 3949, HD 4728 in roots and MACS 3949, KRL 3–4, MACS 4020, HD 4758, MACS 3972 and HI 8713 in shoots. The differential response of durum wheat genotypes under salinity particularly for physiological traits, confer their adaptability towards stress environments and exhibit their potential as genetic sources in breeding programs for improving salt stress tolerance.     

Salt Stress Threshold in Millets: Perspective on Cultivation on Marginal Lands for Biomass

Millets hold an immense assurance for food safety and nourishment amid ever-rising agricultural expenses and climate alterations. They are healthful, have supplementary wellbeing profit and need remarkably fewer effort overheads for crop growing. These characters draw attention to millets as a plant of preference for the humankind in the course of emergent alarm about environmental changes. Millets have the prospect to provide biomass and thus bioenergy, reduced carbon emission, carbon footprint and sustainable modern agriculture. As the rate of expansion in budding countries is increasing day by day, the scarcity of energy is a big panic and there is a mounting turn in the direction and rehearsal of waste and biomass as an energy source. Globally, at least 20% of total irrigated land has been injured by salt and 1.5 million hectares is taken away of cultivation every year. Thus, in future, we will have a requirement of efficient crops and utilisation of marginal lands for agriculture. Millet is an answer to the efficient crop. Plants are subjected to various environmental pressures (high/low temperature, heavy metal, salinity, pesticides, etc.) as well as biotic stresses (virus, bacteria, fungi, etc.) and millets are not an exception to it. Millets are categorised as glycophytes and can tolerate average salt threshold of about 6 (EC_e) (dS/m) with some variation from specie to specie. Increase in the salt concentrations can lead to retarded growth and development, thus need for mitigants arise to reduce such stresses. Some mitigants to overcome the stress levels include proline, polyamine and betaines, Na₂SeO₃, H₂S, KNO₃, Mg(NO₃)₂, etc.

     

Biochemical and molecular changes induced by salinity stress in <Emphasis Type="Italic">Oryza sativa</Emphasis> L.

Salinity stress constrains the growth, development, and yield in crops. Rice is an important cereal crop highly affected by salinity. To ensure the agriculture production in salt-affected soils, it is enormously entail to understand the salt adaptation strategies of plants. Salinity directly affects the morphology, physiology, and metabolism of the plants. The current study was carried out to check the influence of different concentrations of sodium chloride on rice cultivar. Higher concentration of the NaCl showed significant reduction in the growth, pigment system, and metabolites in rice cultivars. Salinity also elicited the antioxidant enzymes (CAT, SOD, and POX) response and gene expression. Cell biological studies showed the H₂O₂ production and nuclear fragmentation due to alleviated salinity stress. To delineate the portrayal of antioxidant proteins and autophagy mechanism in salinity stress, the homologs of rice CAT1, Mn-SOD, GPX, ATG1, and ATG6 genes were retrieved from blast search. The real-time PCR analysis showed differential expression of genes and depicts new molecular insight of target genes to understand the salinity stress and autophagy-mediated stress signaling pathways.     

Effects of irrigation frequencies on soil salinity and crop water productivity of fodder maize

This study was carried out at the experimental station of Department of Irrigation and Drainage, Sindh Agriculture University, Tandojam to investigate the effect of different irrigation frequencies on soil salinity and crop productivity. Four irrigation frequencies i.e. Irrigation after 7 days (T1)_, Irrigation after 14 days (T2), Irrigation after 21 days (T3), and Irrigation after 28 days (T4) were applied to fodder maize. The results showed significant effect of treatments on soil salinity. The EC of soil slightly increased under all treatments for all depths as compared to pre-treatments. At treatment T1, the salt amount was most noticeable and the highest EC (1.85) was observed at top surface of soil while the lowest (1.65) EC was observed under T4 at the comparable depth however, EC decreased at deeper depths under all treatments. The pH, SAR and ESP of soil decreased at all treatments however this decrease was more pronounced under T1 as compared to other treatments. The highest SAR was observed under T4 (9.40) while the lowest (8.00) under T1 for the matching depths. Similarly, the highest ESP was observed under T4 (11.40) while the lowest (10.15) under T1 for the similar depths. The results on the analysis of variance were non-significant between soil salinity parameters observed for pre-experiment. However, the results of analysis of variance on pH, EC, SAR and ESP showed significant differences between treatments in the post experiment. The maximum plant height, stem girth, number of leaves per plant and fodder yield were observed when the maize fodder was irrigated with a 7 day frequency and it was followed by other irrigation frequencies. Similarly, crop water productivity was 4.5, 4.2, 3.9 and 3.0 kg m⁻³ under T1, T2, T3, and T4 treatments, respectively. These results revealed that T1 produced the maximum crop water productivity as compared to rest of the treatments. The farming community is thus recommended to apply irrigation, to maize fodder crop, with 7 day frequency in order to get maximum fodder yield.     

Salt tolerance of barley (Hordeum vulgare L.) cultivars at the germination stage: Analysis of the response functions

Two models, initially proposed by Van Genuchten (1983) for evaluating salinity-yield response curves at the adult stage, were applied to study the salinity response of 24 barley cultivars at the germination stage. According to the calculated salinity threshold, EC_t (the solution electrical conductivity, EC, at which germination starts to decrease), and EC₅₀ (the solution EC at which germination is reduced by 50%) parameters, both models give similar results, although model 2, a sigmoid-form curve, fits the observed data slightly better than model 1, a piecewise response function. Also, the results suggest that, for model 1, EC_t seems to be the most reliable parameter for screening barley germplasm because it clearly discriminates the relative salt-tolerance of the studied cultivars and, furthermore, it basically determines their salinity response for the 100 to 50% germination interval. On the other hand, the model 1 s parameter — percent germination decrease per unit salinity increase bove EC_t—is less relevant because of its smaller variation interval and lack of correlation with EC₅₀, indicating that the salinity response of the studied cultivars for the 50% germination value is independent of this parameter.     

Water potential in soil and Atriplex nummularia (phytoremediator halophyte) under drought and salt stresses

Atriplex nummularia is a halophyte widely employed to recover saline soils and was used as a model to evaluate the water potentials in the soil-plant system under drought and salt stresses. Potted plants grown under 70 and 37% of field capacity irrigated with solutions of NaCl and of a mixture of NaCl, KCl, MgCl₂ and CaCl₂ reproducing six electrical conductivity (EC): 0, 5, 10, 20, 30, and 40 dS m^?1. After 100 days, total water (Ψ_{w, plant}) and osmotic (Ψ_{o, plant}) potentials at predawn and midday and Ψ_{o, soil}, matric potential (Ψ_{m, soil}) and Ψ_{w, soil} were determined. The type of ion in the irrigation water did not influence the soil potential, but was altered by EC. The soil Ψ_o component was the largest contributor to Ψ_{w, soil}. Atriplex is surviving ECs close to 40 dS m^?1 due to the decrease in the Ψ_w. The plants reached a Ψ_w of approximately ?8 MPa. The water potentials determined for different moisture levels, EC levels and salt types showed huge importance for the management of this species in semiarid regions and can be used to recover salt affected soils.     

Salinity and crop yield

Thirty crop species provide 90% of our food, most of which display severe yield losses under moderate salinity. Securing and augmenting agricultural yield in times of global warming and population increase is urgent and should, aside from ameliorating saline soils, include attempts to increase crop plant salt tolerance. This short review provides an overview of the processes that limit growth and yield in saline conditions. Yield is reduced if soil salinity surpasses crop‐specific thresholds, with cotton, barley and sugar beet being highly tolerant, while sweet potato, wheat and maize display high sensitivity. Apart from Na⁺, also Cl^?, Mg²⁺, SO₄^2‐ or HCO₃^‐ contribute to salt toxicity. The inhibition of biochemical or physiological processes cause imbalance in metabolism and cell signalling and enhance the production of reactive oxygen species interfering with cell redox and energy state. Plant development and root patterning is disturbed, and this response depends on redox and reactive oxygen species signalling, calcium and plant hormones. The interlink of the physiological understanding of tolerance processes from molecular processes as well as the agronomical techniques for stabilizing growth and yield and their interlinks might help improving our crops for future demand and will provide improvement for cultivating crops in saline environment.     

Characterization of adaptability components of Brazilian isolates of Macrophomina pseudophaseolina

Macrophomina pseudophaseolina is a new Macrophomina species reported on different crop and weed species in Brazil, India and Senegal, but to date there are no studies about its adaptability components. In this work, a collection of 62 M. pseudophaseolina isolates obtained from roots of the weed species Trianthema portulacastrum and Boerhavia diffusa collected in Northeastern Brazil, was used to: (a) study the effect of temperature and salinity on mycelial growth, (b) to determine their sensitivity to the fungicide carbendazim and (c) to assess their aggressiveness on melon and watermelon seedlings. Results showed variability among M. pseudophaseolina isolates. The optimum temperature for mycelial growth ranged between 26.4 and 38.1ºC. NaCl reduced the in vitro growth of all isolates, which were also highly sensitive to the fungicide carbendazim, exhibiting EC₅₀ values ranging from 0.013 to 0.089 mg/L a.i. Disease severity values on melon and watermelon seedlings showed that M. pseudophaseolina isolates were more aggressive in melon than in watermelon. Information about adaptability components of M. pseudophaseolina obtained in this study could be incorporated on breeding programs for melon and watermelon crops.     

Effects of salinity on microbial tolerance to drying and rewetting

Soil salinity and fluctuations in soil matric potential are stressors for soil microorganisms which, in turn, may affect soil organic matter turnover. In response to salinity and low soil water content, many microorganisms accumulate osmolytes. Therefore, it is conceivable that microorganisms in saline soils are more tolerant to drying and rewetting (DRW) stress than those in non-saline soils. An experiment was carried out with three different salinity levels: electrical conductivity (EC_1:5) 0, 2 and 4 dS m^?1 (EC0, EC2, EC4), and two water treatments: a constantly moist control or two DRW cycles. Respiration as an indicator of microbial activity was measured throughout the 59 days of incubation. At the end of the second dry period (day 35) and at the end of the following moist incubation (day 59), microbial biomass and microbial community structure were determined by phospholipid fatty acid (PLFA) analysis. Increasing salinity decreased microbial activity but did not affect its resistance to DRW. On day 59, cumulative respiration decreased in the order EC0 > EC2 > EC4 with no differences between water treatments. Fungal biomass was negatively affected by salinity at the end of the experiment, while bacterial biomass was unaffected. Microbial community structure in moist treatments differed between salinity levels, with EC4 influencing microbial community structure earlier than EC2. The resistance of microbial communities to DRW stress was salt level dependent; only beyond a critical salinity level adaptation to salt stress was able to reduce the impact of water stress on microbial community structure.     

Mini-Review of Knowledge Gaps in Salt Tolerance of Plants Applied to Willows and Poplars

Salt tolerance of agricultural crops has been studied since the 1940, but knowledge regarding salt tolerance of woody crops is still in its initial phase. Salt tolerance of agricultural crops has been expressed as the yield decrease due to a certain salt concentration within the root zone as compared to a non-saline control. The most well-known plant response curve to salinity has been a piece-wise linear regression relating crop yield to root zone salinity. This method used the hypothesis that crops tolerate salt up to a threshold after which their yield decreases approximately linearly. Critique to this method included its lack of sensitivity to dynamic factors such as weather conditions. As a result, other classification indices have been developed, but none is as well accepted as the threshold-slope model. In addition to a mini-review of the key salt tolerance studies, our objective was to classify salt tolerance levels of poplars and willows. Initial classification showed that salt tolerance of these genera ranged from sensitive to moderately tolerant.     

干湿季节下基于遥感和电磁感应技术的塔里木盆地北缘绿洲土壤盐分的空间变异性

土壤盐渍化问题是制约干旱半干旱区植被生长最主要的生态环境地质问题,也是影响绿洲农业生产的障碍性问题.而将遥感与近感技术相结合,是当前评价、监测及预报土壤盐渍化程度的先进方法.以新疆塔里木盆地北缘的渭干河-库车河三角洲绿洲为例,以遥感数据和解译后的电磁感应数据为基础数据源,利用解译后的数据结合GIS和地统计学知识以及野外实测所得到的土壤电导率和盐分资料,分别采用泛克里格(Universal Kriging)、光谱指数回归(Spectral Index Regression)和回归残差泛克里格(Regression-Universal Kriging)3种方法研究了该地区两个关键季节(干季和湿季)土壤盐分的空间变异特征.研究结果表明:研究区的土壤浸提液电导率EC1∶5和土壤盐分呈现显著相关,可以用EC1∶5来代替土壤的全盐量进行分析;电磁感应仪(EM38)所测各季节土壤表观电导率与EC1∶5的相关系数均达到1％显著水平,以表观电导率垂直读数(EMv)和水平读数(EMH)为自变量的多元回归模型拟合效果较好;研究区各季节的表层土壤电导率的空间分布均表现为强相关性,说明土壤采样点间的内部结构性良好,采用能够充分考虑到干旱区表层土壤电导率空间变异的尺度依赖性的球状套合模型,能够更好的拟合土壤表观电导率的空间结构;经过精度比较,回归残差泛克里格法为最优预测方法,这表明将遥感和电磁感应技术相结合,能够有效的提高预测与评估土壤盐分空间分布的精度,为精确地进行土壤盐分预测以及土壤次生盐渍化的防控提供了一定的依据.     

Salinity and salt composition effects on seed germination and root length of four sugar beet cultivars

Salinization is one of the most important factors affecting agricultural land in the world. Salinization occurs naturally in arid and semiarid regions where evaporation is higher than rainfall. Sugar beet yield declines with an increase in salinity, but the sensitivity to salts varies with salt composition in water and sugar beet growth stage. The aim of this study was to determine the effect of water salinity levels and salt composition on germination and seedling root length of four sugar beet cultivars (PP22, IC2, PP36, and 7233). The experiments were undertaken with irrigation water with two salt compositions (NaCl alone and mixture of MgSO₄ + NaCl + Na₂SO₄ + CaCl₂) in three replicates. Thirteen salinity levels with electrical conductivity (EC) of the irrigation water ranging from 0 to 30 dS/m were applied to each cultivar in both experiments. Seed germination percentage and seedling root length growth were determined in 13 days. Statistical analysis revealed that germination and root length were significantly affected by salt composition, cultivars and salinity levels. Regardless of salt composition, seed germination and seedling root length were significantly affected by the irrigation water with EC up to 8 dS/m and 4 dS/m, respectively. Except for cultivar PP22, the adverse effect of salinity of the irrigation water on seed germination and seedling root length was higher for NaCl alone than for the salt mixture, which refers to lower salt stress in field conditions with natural salt composition. Presented at the International Conference on Bioclimatology and Natural Hazards, Poľana nad Detvou, Slovakia, 17–20 September 2007.     

Water relations, nutrient content and developmental responses of Euonymus plants irrigated with water of different degrees of salinity and quality

For 20 weeks, the physiological responses of Euonymus japonica plants to different irrigation sources were studied. Four irrigation treatments were applied at 100 % water holding capacity: control (electrical conductivity (EC) <0.9 dS m^?1); irrigation water normally used in the area (irrigator’s water) IW (EC: 1.7 dS m^?1); NaCl solution, NaCl (EC: 4 dS m^?1); and wastewater, WW (EC: 4 dS m^?1). This was followed by a recovery period of 13 weeks, when all the plants were rewatered with the same amount and quality of irrigation water as the control plants. Despite the differences in the chemical properties of the water used, the plants irrigated with NaCl and WW showed similar alterations in growth and size compared with the control even at the end of the recovery period. Leaf number was affected even when the EC of the irrigation water was of 1.7 dS m^?1 (IW), indicating the salt sensitivity of this parameter. Stomatal conductance (g_s) and photosynthesis (P_n), as well as stem water potential (Ψ_stem), were most affected in plants irrigated with the most saline waters (NaCl and WW). At the end of the experiment the above parameters recovered, while IW plants showed similar values to the control. The higher Na⁺ and Cl⁺ uptake by NaCl and WW plants led them to show osmotic adjustment throughout the experiment. The highest amount of boron found in WW plants did not affect root growth. Wastewater can be used as a water management strategy for ornamental plant production, as long as the water quality is not too saline, since the negative effect of salt on the aesthetic value of plants need to be taken into consideration.     

Interactive effects of NaCl salinity and elevated atmospheric CO2 concentration on growth,photosynthesis, water relations and chemical composition of the potential cash crop halophyte Aster tripolium L.

This study was aimed at obtaining detailed information about the interaction of NaCl-salinity and elevated atmospheric CO₂ concentration in the potential cash crop halophyte Aster tripolium. Plants were irrigated with 5 different salinity levels (0, 25, 50, 75 and 100% sws) under ambient and elevated (520 ppm) CO₂. Under saline conditions leaf water potential decreased to a value below the one of the nutrient solution. Osmotic adjustment was mainly due to the accumulation of sodium and chloride (includer type). However, the salt was unequally distributed within the plants. K/Na selectivity was high in the lateral roots and low in the petioles, so that these organs served as “salt filters” which prevented an excessive salt accumulation and ion toxicity in the leaf blades and in the main root, the storage organ for organic substances. Despite some signs of ion toxicity and nutrial imbalance, these factors do not seem to be predominantly responsible for the limited salinity tolerance of A. tripolium. In order to maintain a positive water balance the salt treated plants increased stomatal resistance. But at the same time stomata closure led to a significant decrease in photosynthesis and thus in WUE. The impaired assimilation rate contributed to the significant growth depression (50% reduction of the maximum yield between 50% and 75% sws), together with the higher energy consumption needed for various salinity tolerance mechanisms, e.g. for an enhanced synthesis of compatible solutes (proline, carbohydrates) and stress-induced proteins. Elevated atmospheric CO₂ concentration led to a significant increase in photosynthesis and in WUE. The latter indicates, together with a higher water potential, that the water relations of the plants had improved. By reducing stomatal resistance energy gain was maximized. The additional supply with energy-rich organic substances was not employed for producing more biomass but for increasing the investment in salinity tolerance mechanisms, e.g. for an enhanced synthesis of proline, carbohydrates and proteins. These mechanisms led to a higher survival rate under saline conditions, i.e. to an improved salt tolerance. The results of the study indicate that A. tripolium is a promising cash crop halophyte which will probably benefit from rising atmospheric CO₂ concentrations in future.     

Agricultural production of halophytes irrigated with seawater

Summary Growing agricultural crops with direct seawater irrigation has progressed within the past few years from the conceptual to the experimental phase. This has been accomplished by selecting halophytes with inherently high salinity tolerance for use as crop plants rather than by increasing the ability of traditional crop plants to tolerate seawater. Some of the halophytes being investigated for use as crops in seawater irrigation scenarios have high nutritional value as forage or fodder crops. Most of them also have high digestibility. The limiting factor in such use is their high salt content, but this limitation can be moderated. However, since seeds of halophytes do not accumulate salt any more than do those of glycophytes, the greatest promise for seawater-irrigated halophytes probably will be as seed crops. The seeds of many halophytes have high protein and oil contents and compare favorably with traditional oilseed crops. Sustained high yields of seed and biomass already have been obtained from some halophytes irrigated with seawater, and within the next few years seawater agriculture should proceed from the experimental to the operational phase.     

Effect of soil salinity on the electro-chemical and chemical kinetics of some plant nutrients in submerged soils

Summary The electro-chemical and chemical kinetics of six California rice soils were significantly influenced by the presence of salts up to an EC of 9 mmhos/cm in saturation extract (EC_e). Subsamples of each soil salinity treatment were incubated for periods up to 10 weeks after flooding. Most of the changes in Eh and pH values took place in the first 3–4 weeks after submergence. Salinity decreased pH values, but slightly increased the redox-potential. Both ammonification and nitrate reduction were significantly decreased, by increasing soil salinity. Salinity up to 9 mmhos/cm did not affect levels of Bray and Kurtz extractable P, but increased the water extractable Ca, Mg, K and Mn. In DTPA extract, salinity in incubated soils had no effect on Zn in 4 soils, but it decreased Fe in acid and neutral soils. Possible explanations for the electro-chemical and chemical kinetic changes due to flooding and salinity are discussed.