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Abstract. Large portions of Mars' surface are covered with deposits of fine, homogeneous, weathered dusty-soil material. Nanophase iron oxides, silicate mineralolds, and salts prevail in the soil. The mode of formation of this somewhat peculiar type of soil is still far from being clear. One scenario suggests that weathering took place during early epochs when Mars may have been "warm and wet." The properties of the soil are not easily reconciled wi.'th this scenario. We propose another possible scenario that attributes, in part, the peculiar nature of the Martian dust and soft to a relatively "young" weathering product formed during the last few hundreds of millions of years in a process that involves acidic volatiles. We tested this hypothesis in an experimental study of the first step of acidolytic weathering of a partly palagonitized VOlcanic tephra of hawaiitic lava origin, using sulfi•c, hydrochloric and nitric acids and their mixtures. The tephra effectively "neutralize" the added acidity. The protonic acidity added to the tephra attacks the primary-minerals, releasing Fe, A1, and Mg, which control the pH, acting as Lewis-acid species of varying acid strengths. The full mount of acidity added to the tephra is stored in it, but only a very small fraction is preserved as the original protonic acidity. The majority of the added sulfate and chloride were present as salts and easily solubilized minerals. Well-crystallized sulfate salt minerals of aluminum and calcium were detected by powder X ray diffractomen, whereas secondary magnesium and iron minerals were not detected, due probably to lack of crystallinity. The presence of gyps m (CaSO4'2H20) and alunogen (A12(SO4)3'17H20) is probably responsible for the observed increased hygroscopicity of the acidified tephra and their tendency. to form hardened crusts. We suggest that if this mechanism is of importance on Mars, then the chemically weathered component of the Martian soil consists of a salt-rich mineral mixture containing the salts of the anionicligands SO4 and C1 resulting from volafiles emitted from volcanoes during more recent eruptions (up to 109 years B.P.). The lack of liquid water on Mars surface during that time slowed or halted mineralogical evolution into highly crystallized minerals having large mineral grains. The chemically weathered components are mixed wi.th _the products of physical weathering. The recently formed soil may cover and coat more evolved, hydrothermally modified, mineral deposits formed in earlier epochs Of Mars.

The intestinal barrier integrity is essential for the absorption of nutrients and health in humans and animals. Dysfunction of the mucosal barrier is associated with increased gut permeability and development of multiple gastrointestinal diseases. Recent studies highlighted a critical role for glutamine, which had been traditionally considered as a nutritionally non-essential amino acid, in activating the mammalian target of rapamycin cell signaling in enterocytes. In addition, glutamine has been reported to enhance intestinal and whole-body growth, to promote enterocyte proliferation and survival, and to regulate intestinal barrier function in injury, infection, weaning stress, and other catabolic conditions. Mechanistically, these effects were mediated by maintaining the intracellular redox status and regulating expression of genes associated with various signaling pathways. Furthermore, glutamine stimulates growth of the small intestinal mucosa in young animals and also enhances ion transport by the gut in neonates and adults. Growing evidence supports the notion that glutamine is a nutritionally essential amino acid for neonates and a conditionally essential amino acid for adults. Thus, as a functional amino acid with multiple key physiological roles, glutamine holds great promise in protecting the gut from atrophy and injury under various stress conditions in mammals and other animals.

Due to the different degrees of controls exerted by biological and geochemical processes, climate changes are suggested to uncouple biogeochemical C, N and P cycles, influencing biomass accumulation, decomposition and storage in terrestrial ecosystems. However, the possible extent of such disruption in grassland ecosystems remains unclear, especially in China’s steppes which have undergone rapid climate changes with increasing drought and warming predicted moving forward in these dryland ecosystems. Here, we assess how soil C-N-P stoichiometry is affected by climatic change along a 3500-km temperate climate transect in Inner Mongolia, China. Our results reveal that the soil from more arid and warmer sites are associated with lower soil organic C, total N and P. The ratios of both soil C:P and N:P decrease, but soil C:N increases with increasing aridity and temperature, indicating the predicted decreases in precipitation and warming for most of the temperate grassland region could lead to a soil C-N-P decoupling that may reduce plant growth and production in arid ecosystems. Soil pH, mainly reflecting long-term climate change in our sites, also contributes to the changing soil C-N-P stoichiometry, indicating the collective influences of climate and soil type on the shape of soil C-N-P balance.