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Thèse--Sc. nat.--Caen, 1971. N°: 41. / L'Article principal se rapportant à la thèse, extrait de Oecologia plantarum. N° 6, 1971, pp. 227-245. est conservé sous la cote: [4° THS. Pièce. 299.

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It has been demonstrated the technical feasibility of using seawater and other saline water for irrigation. Through the use of saline water for irrigation, highly salt-tolerant crops could greatly increase global agriculture. Brackish water and seawater from different sources are available in areas suitable for production of salt-tolerant crops. Dwarf glasswort Salicornia bigelovii Torr. (Chenopodiaceae), is a leafless, succulent, small-seeded, annual saltmarsh plant, with potential as a saline water crop. It is also a potential oilseed, forage, biomass crop, and a promising carbon sequestration plant. In the first chapter of this document we describe a study where we grew Salicornia bigelovii from seedlings, in saline, drying soils in a greenhouse experiment. The effects of drought and salinity stress were additive. Optimal growth and water use efficiency coincided at 0.35-0.53 M NaCl. The plants were tolerant of high salinity but exhibited little drought tolerance. Salicornia bigelovii plants varied little in their uptake of Na+ for osmotic adjustment, with final Na+ contents of 18% on a dry mass basis. Both growth and water use efficiency of Salicornia bigelovii were affected by salinity. Also, Na+, the primary cation involved in osmotic adjustment of this species, apparently stimulates growth by mechanisms apart from its role as an osmoticum. In the second chapter of this dissertation we developed a research study where we evaluated the production and osmotic adjustment of two S. bigelovii lines (Texas and Florida), plants were grown in pot in a green house and irrigated with water treated with three different levels of NaCl (5 ppt, 15 ppt and 30 ppt) combined with inorganic fertilizer. At the end of the experiment sixty plants from each line were measured for height, biomass, seed yield, seed size, dry matter yield, and tissue osmolarity. There was no significant difference among groups in plant height, or final biomass either in salinity irrigation treatments, or S. bigelovii lines. Tissue osmolarity differed among salinity treatments but not among S. bigelovii lines. The highest tissue osmolarity value was 1192 mM kg-1 found at the treatment 30ppt in the Florida line. Total biomass production was 12 000 kg/Ha.

The halophyte Mesembryanthemum crystallinum L. accumulates high concentrations of NaCl (up to 1 M) in its leaf cells as a response to soil salinity. While there is evidence that vacuolar sodium transport is mediated by a tonoplast Na⁺/H⁺ antiporter (Barkla ^{et al.}, 1995), little is known about the transport of Cl^- transport into the vacuole. So far, it has been uncertain whether secondary active transport (e.g. H⁺/C1^- antiporter) is involved or whether a passive mechanism (Cl^- channel) is sufficient to mediate Cl^- accumulation in the vacuole of M.crystallinum. This thesis describes the use of tonoplast vesicles from leaf mesophyll cells of M. crystallinum to study vacuolar Cl^- transport. Cl^- uptake into the vesicles was measured using the Cl^--sensitive fluorescent dye lucigenin (N/N'-dimethyl-9,9'-bisacridinium dinitrate). This work was complemented by a patch-clamp study of ionic currents of leaf-mesophyll vacuoles from M.crystallinum. Cl^- transport into tonoplast vesicles showed saturation-type kinetics with an apparent Km between 10 and 36 mM and a maximum initial change of the intravesicular Cl^- concentration of 4.8 mM min^-, corresponding to an estimated Cl^- flux of 31 nmol m² s^-¹. Vacuolar chloride transport was not affected by sulphate, malate, or nitrate, indicating a high specificity of this transport process for chloride over other anions. By imposing insidepositive membrane potentials using a K⁺/valinomycin clamp revealed a sigmoidal voltagedependent relationship with the steepest increase in vacuolar Cl^- uptake around +30 mV. Only under severe salt treatment with 500 mM NaCl for 3 weeks did 9-week-old M. crystallinum plants show a significant increase (63%) of vacuolar C^- uptake, along with an increased V-type H⁺-ATPase hydrolytic activity (up to 65%). The apparent K_m of vacuolar Cl^- uptake was also increased from 27 mM to 44 mM under these conditions. An inside-acid pH gradient, generated by a K⁺/nigericin clamp, reduced the initial rate of chloride transport into tonoplast vesicles of M.crystallinum. External Cl^-, in contrast to external Na⁺ , did not dissipate an inside-acidic ΔpH generated by various techniques. This is strong evidence against a proton-driven antiport mechanism. The patch-clamp study of ionic currents of whole vacuoles and excised vacuolar membrane patches from M.crystallinum. leaf-mesophyll cells revealed a number of cation channels. At cytosolic free Ca ²⁺ concentrations of 1μM and above, ubiquitous slow-vacuolar type cation currents could be observed. In excised patches, eleven different single channel types, with conductances ranging from 2 up to 200 pS, could be described. However, no clear Cl^-conductance could be identified. The lack of observed vacuolar Cl^- channel activities is discussed in the light of possible lack of Cl^--channel activation due to the loss of a cytosolic factor. The results obtained from the biochemical work on tonoplast vesicles support the hypothesis that a passive transport mechanism (i.e. channel) is sufficient to mediate vacuolar chloride transport in M.crystallinum. The observed upregulation of vacuolar Cl^- transport under severe salt stress shows that it plays an important role in the salt adaptation of this halophytic plant.

Aspects of salt tolerance of Salicornia pacifica were investigated. Survival of this plant in a saline environment is due to many interacting factors. A soil pH of 7.5 to 8.0 +- 0.2 and a constant sub-surface soil moisture level of 25 to 35% are necessary for plant survival. A fluctuating lower soil moisture leevel and higher pH favor etablishment of Distichlis stricta. The ion content in S. pacifica remained constant despite increased moisture stress throughout the growing season due to accumulation of salts which were significantly higher in the surface soil layers than in the subsurface layers around the roots. High salt concentrations in the soil are diluted by winter precipitation which allows for germination of seeds of S. pacifica. The seeds contain a seed coat inhibitor which appears to be sodium chloride. The seeds require a light stimuli for germination. Each internode of the plant was found to be osmotically independent. Chloride ions were distributed in each tissue, cell, and oganelle. The most likely inference about salt tolerance in S. pacifica is that sensitive enzyme systems are protected from the harmful efects of salt by other proteins of the cell.

Based upon literature search, field investigation, examination of the halophyte collection at the Environmental Research Laboratory in Tucson, Arizona, and an expert survey, 97 salt-tolerant plants have been identified for the use as landscape plants. The plants were screened at salinity levels between 5 and 40 ppt which are critical for plant survival. The globally gathered data revealed information about landscape criteria, such as aesthetic value, climate amelioration, soil stabilization, color, form and drought tolerance, which were organized into architectural, engineering and design categories. These landscape halophytes range from herbaceous ground covers to woody trees. The data were filed in a computer data base, including detailed information about the description and performance of every plant, habitat requirements, maintenance, landscape values and economic uses. The data base, which is continually up-dated, is a search-type, which functions as an information storage system and is designed to provide plant selection by needed characteristics or intended use.

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Stable chlorine isotopes are useful geochemical tracers in processes involving the formation and evolution of evaporitic halite. Halite and dissolved chloride in groundwater that has interacted with halite in arid non-marine basins has a delta Cl-37 range of 0 +/- 3 parts per thousand, far greater than the range for marine evaporites. Basins characterized by high positive (-1 to +3 parts per thousand), near-0%, and negative (-0.3 to -2.6%) are documented. Halite in weathered crusts of sedimentary rocks has delta Cl-37 values as high as +5.6 parts per thousand. Salt-excluding halophyte plants excrete salt with a delta Cl-37 range of -2.1 to -0.8%. Differentiated rock chloride sources exist, e.g. in granitoid micas, but cannot provide sufficient chloride to account for the observed data. Single-pass application of known fractionating mechanisms, equilibrium salt-crystal interaction and disequilibrium diffusive transport, cannot account for the large ranges of delta Cl-37. Cumulative fractionation as a result of multiple wetting-drying cycles in vadose playas that produce halite crusts can produce observed positive delta Cl-37 values in hundreds to thousands of cycles. Diffusive isotope fractionation as a result of multiple wetting-drying cycles operating at a spatial scale of 1-10 cm can produce high delta Cl-37 values in residual halite. Chloride in rainwater is subject to complex fractionation, but develops negative delta Cl-37 values in certain situations; such may explain halite deposits with bulk negative delta Cl-37 values. Future field studies will benefit from a better understanding of hydrology and rainwater chemistry, and systematic collection of data for both Cl and Br.

Gold and nickel mining are a common land use in the semiarid Eastern Goldfields region of Western Australia,, A frequent outcome of mining activity is highly saline landforms that result from the widespread use of hypersaline (> 50 g L(subscript)-1 NaCl) groundwater for mineral processing and hydraulic tailings reclamation, and from saline horizons in soils, subsoils and mullock. Under State government legislation, all mined land must be rehabilitated to a stable and sustainable landform at the completion of mining activities.There was little land rehabilitation carried out in the mining industry until the mid1980s. At that time, legislation was introduced and, in due course, guidelines were issued on recommended approaches to rehabilitation. Today, rehabilitation of disturbed areas is usually integrated into the mining program and has become the rule rather than the exception. There has, however, been limited innovation in recent years and the established methods are not suitable for every land rehabilitation scenario, especially those where very high salinity is an important factor. The aims of this thesis were to make a contribution towards a better understanding of the ecology of halophytes suitable for use in revegetation and the likely physical requirements for their sustainable establishment on post-mining landforms.In terms of germination, many of the halophytes currently used for rehabilitation of saline substrates are well suited in that they are able to germinate in solutions of up to 20 g L(subscript)-1 NaCl. Furthermore, when higher salinities are encountered, seed dormancy is induced until salinity is reduced to a level at which germination can occur. There were differences observed between germination of annual and perennial chenopods that reflected their successional roles where annual chenopods tend to have a higher salt tolerance and germinate more ++ / rapidly. I developed a tolerance index to enable different germination responses to be readily compared. Values for the tolerance index ranged from 5.7 to 25.3 for the halophytic species compared with a value of 0.2 for the glycophytic Secale cereale. Values for saltbushes (Atriplex) and bluebushes (Maireana) ranged from 6.5 to 9.8 while values for samphires (Halosarcia) were higher (10.7-17.4).Germination and early growth of taxa in the succulent genus, Halosarcia, were also studied. Though a member of the Chenopodiaceae, with a number of species occurring commonly throughout the region, Halosarcia spp. are not widely used in rehabilitation. This is in part attributable to the poor level of knowledge of germination and growth characteristics compared with saltbushes and bluebushes, many of which are widely used. Two species studied, H. halocnemoides subsp. halocnemoides and H. pruinosa, are more salt-tolerant for germination than some other chenopods more widely used. Furthermore, in terms of their early growth, each taxon continued to grow in salinities up to 40 g L(subscript)-1 NaCl, although root .Production and mass were reduced at that concentration. Another taxon, H. pergranulata subsp. pergranulata, was found to have a partial physical dormancy attributable to the testa, a phenomenon rare among halophytes. Dormancy was alleviated by scarification but was most effective where this occurred near the micropyle.Field trials were conducted to assess methods of rehabilitating severely salt-affected surfaces (EC(subscript)e > 50 dS m(subscript)-1). In the initial trial, a number of surface treatments, including ripping, rock mulching and mounding, were shown to reduce soil EC, in loam soils over a long period of time (seven years) compared with the control. In a subsequent trial, the use of good quality waste water, in conjunction with ponding banks, strongly ++ / promoted the establishment of vegetation by supplementing soil moisture and enhancing soil P although a reduction in soil EC(subscript)e was not observed. The depth and duration of ponding influenced the species that established and the cover achieved. Methods by which a soil cover could be established over hypersaline tailings surfaces were also investigated. The absence of a capillary break layer resulted in severe salinisation (EC(subscript)e > 100 dS m(subscript)-1) of a non-saline clay loam soil cover and likely severe difficulties in establishing and maintaining vegetation on the cover. Two types of capillary break layer, a synthetic membrane and a layer of coarse iron fayalite granules (nickel slag), were both effective at preventing the capillary rise of salts into the soil cover.The physical and biological characteristics of the shores of Lake Lefroy, a large salt lake in the Eastern Goldfields region, were analysed using multivariate techniques.Physical characteristics were strongly influenced by the orientation of the shore relation to the predominant winds, and by depth to the saline groundwater table. Plant species were distributed in zones across the lake shores with small changes in elevation resulting in substantial changes in species distributions. Those plant species occurring at the lowest elevations (Zone I), including Halosarcia spp., exhibited a very high tolerance of saline soil and groundwater through an ability to accumulate Na+ and Cl- and make the necessary osmotic adjustments, and a capacity to tolerance high groundwater levels. Under certain conditions, the lake shore environment could be a useful model for a rehabilitated landform.