The growth responses of the hygro-halophyte A. portulacoides to salinity appear largely to depend on changes in its rate of photosynthetic gas exchange. Photosynthesis appears to be limited mainly through stomatal conductance and hence intercellular CO(2) concentration, rather than by effects on PSII; moderate salinity might stimulate carboxylation capacity. This is in contrast to more extreme halophytes, for which an ability to maintain leaf area can partially offset declining rates of carbon assimilation at high salinity.

Rice is the most important food crop in the world and is a primary source of food for more than half of the world population. However, salinity is considered the most common abiotic stress reducing its productivity. Soil salinity inhibits photosynthetic processes, which can induce an over-reduction of the reaction centres in photosystem II (PSII), damaging the photosynthetic machinery. The arbuscular mycorrhizal (AM) symbiosis may improve host plant tolerance to salinity, but it is not clear how the AM symbiosis affects the plant photosynthetic capacity, particularly the efficiency of PSII. This study aimed at determining the influence of the AM symbiosis on the performance of PSII in rice plants subjected to salinity. Photosynthetic activity, plant gas-exchange parameters, accumulation of photosynthetic pigments and rubisco activity and gene expression were also measured in order to analyse comprehensively the response of the photosynthetic processes to AM symbiosis and salinity. Results showed that the AM symbiosis enhanced the actual quantum yield of PSII photochemistry and reduced the quantum yield of non-photochemical quenching in rice plants subjected to salinity. AM rice plants maintained higher net photosynthetic rate, stomatal conductance and transpiration rate than nonAM plants. Thus, we propose that AM rice plants had a higher photochemical efficiency for CO2 fixation and solar energy utilization and this increases plant salt tolerance by preventing the injury to the photosystems reaction centres and by allowing a better utilization of light energy in photochemical processes. All these processes translated into higher photosynthetic and rubisco activities in AM rice plants and improved plant biomass production under salinity.

Halophytes that are capable of tolerating a wide range of salinity may grow best at intermediate salinities, but the physiological mechanisms underlying positive growth responses to salinity are not clear. This work investigated the growth of Arthrocnemum macrostachyum (Moric) C. Koch (a halophytic C3 shrub) over a wide range of salinities, and the extent to which its responses can be explained by photosynthetic physiology. Growth, gas exchange and chlorophyll fluorescence characteristics of plants were examined in a glasshouse experiment; tissue concentrations of photosynthetic pigments, ash, sodium, potassium, calcium and nitrogen were also determined. Plants showed marked stimulation of growth by salt, with a broad optimum of 171-510 mm NaCl for relative growth rate (RGR). Stimulation of RGR appeared to depend mainly on an increase in specific shoot area, whereas reduced RGR at high salinity (1030 mm) could be attributed to a combination of lower unit shoot (leaf) rate and lower shoot mass fraction. The non-saline treatment plants had the greatest fraction of non-photosynthetic, atrophied surface area. However, net photosynthesis (A) was also stimulated by NaCl, with an optimum of c. 510 mm NaCl. The responses of A to salinity could be accounted for largely by limitation by stomatal conductance (Gs) and intercellular CO(2) concentration (Ci). Even the most hypersaline treatment apparently had no effect on photosystem II (PSII) function, and this resistance could be an important strategy for this halophyte in saline soils. In contrast, Fv/Fm indicated that absence of salt represents an environmental stress for A. macrostachyum and this could be a contributory factor to salt stimulation of A. Notwithstanding the importance of the ability to develop and maintain assimilatory surface area under saline conditions, stimulatory effects on A also appear to be part of a suite of halophytic adaptations in this plant.

Sarcocornia fruticosa (L.) A.J. Scott is found in coastal marshes of south-west Spain, growing under a very wide range of interstitial soil salinity from 10 mM up to nearly 1000 mM. A glasshouse experiment was designed to investigate the effect of this range of salinities on the morphology and the photosynthetic apparatus of S. fruticosa by measuring growth rate, photosynthetic and non-photosynthetic area, atrophy of distal branch ends, water status, chlorophyll fluorescence parameters, gas exchange and photosynthetic pigment concentrations. The long-term effects of salinity on the growth of S. fruticosa were mainly determined by the extent of photosynthetic area rather than the variations in net photosynthetic rate. Photosynthetic area was reduced at 1030 mM as a result of a decrease in the length of the photosynthetic portions. This was induced by fewer internodes and, at salinities lower than 510 mM, smaller internode diameter. Net photosynthetic rate increased as the quantum efficiency of photosystem II decreased in the different salinity treatments, which means that the plant could be increasing photorespiration and/or using cyclic electron transport as additional photoprotective mechanisms. The recorded drop in net photosynthetic rate at higher salinities appeared to be due to a reduction in stomatal conductance. The results indicate that S. fruticosa is capable of tolerating very high and continued exposure to salt, showing its greatest growth rate at 510 mM NaCl.

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Endophytic bacterial population was isolated from Spartina maritima tissues, a heavy metal bioaccumulator cordgrass growing in the estuaries of Tinto, Odiel, and Piedras River (south west Spain), one of the most polluted areas in the world. Strains were identified and ability to tolerate salt and heavy metals along with plant growth promoting and enzymatic properties were analyzed. A high proportion of these bacteria were resistant toward one or several heavy metals and metalloids including As, Cu, and Zn, the most abundant in plant tissues and soil. These strains also exhibited multiple enzymatic properties as amylase, cellulase, chitinase, protease and lipase, as well as plant growth promoting properties, including nitrogen fixation, phosphates solubilization, and production of indole-3-acetic acid (IAA), siderophores and 1-aminocyclopropane-1-carboxylate (ACC) deaminase. The best performing strains (Micrococcus yunnanensis SMJ12, Vibrio sagamiensis SMJ18, and Salinicola peritrichatus SMJ30) were selected and tested as a consortium by inoculating S. maritima wild plantlets in greenhouse conditions along with wild polluted soil. After 30 days, bacterial inoculation improved plant photosynthetic traits and favored intrinsic water use efficiency. However, far from stimulating plant metal uptake, endophytic inoculation lessened metal accumulation in above and belowground tissues. These results suggest that inoculation of S. maritima with indigenous metal-resistant endophytes could mean a useful approach in order to accelerate both adaption and growth of this indigenous cordgrass in polluted estuaries in restorative operations, but may not be suitable for rhizoaccumulation purposes.

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Summary1 This account reviews information on all aspects of the biology of Sarcocornia perennis that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles : distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history, and conservation. Sarcocornia perennis is a spreading, jointed-stemmed, halophyte that differs from the closely related Salicornia in being a shrubby perennial and in aspects of inflorescence structure. In Britain, it is found mainly on the coasts of south-east England, on gravelly or sandy foreshores, and well-drained sediments of tidal salt marshes. 3 Sarcocornia perennis occurs relatively low in the tidal frame but only in well-drained situations, as seedling establishment and long-term survival are intolerant of highly reducing surface sediments. It has a role in the early stages of salt-marsh succession, sometimes as the primary colonist on sandy substrates. In southern Europe, its invasion may be facilitated by the raised clonal tussocks of Spartina maritima , a primary colonist; subsequently, S. perennis dominates the tussocks and supports their rapid radial and upward growth by trapping silt. Pollen flow from the high marsh species Sarcocornia fruticosa may allow invasion by hybrids between the two species. 4 Hybridization between the diploid S. perennis and octaploid S. fruticosa in southwest Spain has been confirmed by analysis of random amplified DNA (RAPDs). This has also clarified the relationship between the two subspecies present there (the widely distributed ssp. perennis and the more upright, rigid Iberian endemic ssp. alpini (Lag.) Castroviejo). 5 Sarcocornia perennis maintains low water potentials and a positive carbon balance under highly saline conditions. Salinity treatment had no effect on the efficiency of Photosystem II (Fv/Fm). Total germination was also unaffected by salinity up to 2%, although above this it was progressively inhibited; the reduction in germination at Correspondence: A.J. Davy (e-mail a.davy@uea.ac.uk) *Abbreviated references are used for many standard works: see Journal of Ecology (1975), 63, 335-344. Nomenclature of vascular plants follows Flora Europaea and, where different, Stace (1997).