Soil salinization is a growing concern that degrades soil quality and inhibits agricultural productivity. Miscanthus species have received wide attention because of their high calorific potential, their value as an energy plant, and their ability to maintain high biomass accumulation. However, most studies focused on the biochemical and physiological responses to salt stress while neglecting the osmotic adjustment processes and the contribution of both organic and inorganic substances to these processes. This study evaluates the response mechanism of Miscanthus sinensis to salt stress (0-300 mM of NaCl) by evaluating the growth and photosynthetic parameters, photosynthetic response to light, and contribution of organic and inorganic substances to osmotic potential. The results revealed that M. sinensis adopted Na + compartmentalization and reallocation of biomass to the aboveground parts to mitigate the negative impact of salinity stress. Specifically, Na+ accumulated more in the root and leaf, with an increment magnitude of 75.4-173.9 and 56.7-217.1 times, respectively. This was supported by the changing trend of the stem/leaf ratio (25.1 %-55.9 %) compared to the root/shoot ratio (12.3 %-18.3 %). Also, salt-induced stress decreased the leaf's water content and water use efficiency as a result of low intracellular osmosis, and to mitigate osmotic damage, M. sinensis enhanced the accumulation of proline. These results offer theoretical and scientific insights into managing the cultivation and improving the yield of M. sinensis and other energy herbaceous plants in saline soils.

Biostimulants such as ascorbic acid, known as vitamin C, have been reported to have numerous positive roles in plant tolerance to abiotic stresses. However, little is known about the biostimulant effects of ascorbic acid on alfalfa (Medicago sativa). Accordingly, a pot experiment was conducted to investigate the effects of 1 mM ascorbic acid, applied as foliar spray, on the salt tolerance of a Moroccan alfalfa population Demnate 201. One month-old M. sativa seedlings were exposed to 200 mM NaCl for four weeks with or without 1 mM of exogenous ascorbic acid treatment. The results showed that salinity stress significantly (p < 0.001) reduced plant biomass, disturbed photosynthesis-related parameters and induced oxidative stress. However, ascorbic acid foliar spray counteracted the observed negative effects of salinity. It significantly (p < 0.001) improved plant growth and photosynthetic parameters. Besides, stress indicators, including Na+ in shoot and root, hydrogen peroxide and electrolyte leakage, were significantly reduced by 42%, 29%, 12% and 34%, respectively, in treated and salt-stressed alfalfa plants. Interestingly, the decrease in oxidative stress markers was positively correlated to the ability of ascorbic acid to induce the accumulation of flavonoids and to increase the antioxidant activity of guaiacol peroxidase. Furthermore, compatible solutes, such as proline and soluble sugars, were found higher especially in salt-stressed alfalfa plants treated with 1 mM ascorbic acid. Our findings showed that ascorbic acid supply could be an eco-friendly and sustainable technique to mitigate the toxic effect of salt and could improve alfalfa forage production when grown in salt-affected soils.

The mechanism of perchlorate resistance of the desert cyanobacterium Chroococcidiopsis sp. CCMEE 029 was investigated by assessing whether the pathways associated with its desiccation tolerance might play a role against the destabilizing effects of this chaotropic agent. During 3 weeks of growth in the presence of 2.4 mM perchlorate, an upregulation of trehalose and sucrose biosynthetic pathways was detected. This suggested that in response to the water stress triggered by perchlorate salts, these two compatible solutes play a role in the stabilization of macromolecules and membranes as they do in response to dehydration. During the perchlorate exposure, the production of oxidizing species was observed by using an oxidant-sensing fluorochrome and determining the expression of the antioxidant defense genes, namely superoxide dismutases and catalases, while the presence of oxidative DNA damage was highlighted by the over-expression of genes of the base excision repair. The involvement of desiccation-tolerance mechanisms in the perchlorate resistance of this desert cyanobacterium is interesting since, so far, chaotropic-tolerant bacteria have been identified among halophiles. Hence, it is anticipated that desert microorganisms might possess an unrevealed capability of adapting to perchlorate concentrations exceeding those naturally occurring in dry environments. Furthermore, in the endeavor of supporting future human outposts on Mars, the identified mechanisms might contribute to enhance the perchlorate resistance of microorganisms relevant for biologically driven utilization of the perchlorate-rich soil of the red planet.

During winter when the active layer of Arctic and alpine soils is below 0 degrees C, soil microbes are alive but metabolizing slowly, presumably in contact with unfrozen water. This unfrozen water is at the same negative chemical potential as the ice. While both the hydrostatic and the osmotic components of the chemical potential will contribute to this negative value, we argue that the osmotic component (osmotic potential) is the significant contributor. Hence, the soil microorganisms need to be at least halotolerant and psychrotolerant to survive in seasonally frozen soils. The low osmotic potential of unfrozen soil water will lead to the withdrawal of cell water, unless balanced by accumulation of compatible solutes. Many microbes appear to survive this dehydration, since microbial biomass in some situations is high, and rising, in winter. In late winter however, before the soil temperature rises above zero, there can be a considerable decline in soil microbial biomass due to the loss of compatible solutes from viable cells or to cell rupture. This decline may be caused by changes in the physical state of the system, specifically by sudden fluxes of melt water down channels in frozen soil, rapidly raising the chemical potential. The dehydrated cells may be unable to accommodate a rapid rise in osmotic potential so that cell membranes rupture and cells lyse. The exhaustion of soluble substrates released from senescing plant and microbial tissues in autumn and winter may also limit microbial growth, while in addition the rising temperatures may terminate a winter bloom of psychrophiles. Climate change is predicted to cause a decline in plant production in these northern soils, due to summer drought and to an increase in freeze-thaw cycles. Both of these may be expected to reduce soil microbial biomass in late winter. After lysis of microbial cells this biomass provides nutrients for plant growth in early spring. These feedbacks in turn, could affect herbivory and production at higher trophic levels. (C) 2009 Elsevier Ltd. All rights reserved.