Oxalic acid secretion from roots is considered to be an important mechanism for aluminum (Al) resistance in buckwheat (Fygopyrum esculentum Moench). Nonetheless, only a single Al-resistant buckwheat cultivar was used to investigate the significance of oxalic acid in detoxifying Al. In this study, we investigated two buckwheat cultivars, Jiangxi (Al resistant) and Shanxi (Al sensitive), which showed significant variation in their resistance to Al stress. In the presence of 0 to 100 mM Al, the inhibition of root elongation was greater in Shanxi than that in Jiangxi, and the Al content of root apices (0-10 mm) was much lower in Jiangxi. However, the dependence of oxalic acid secretion on external Al concentration and the time course for secretion were similar in both cultivars. Furthermore, the variation in Al-induced oxalic acid efflux along the root was similar, showing a 10-fold greater efflux from the apical 0-to 5-mm region than from the 5-to 10-mm region. These results suggest that both Shanxi and Jiangxi possess an equal capacity for Al-dependent oxalic acid secretion. Another two potential Al resistance mechanisms, i.e. Al-induced alkalinization of rhizosphere pH and root inorganic phosphate release, were also not involved in their differential Al resistance. However, after longer treatments in Al (10 d), the concentrations of phosphorus and Al in the roots of the Al-resistant cultivar Jiangxi were significantly higher than those in Shanxi. Furthermore, more Al was localized in the cell walls of the resistant cultivar. All these results suggest that while Al-dependent oxalic acid secretion might contribute to the overall high resistance to Al stress of buckwheat, this response cannot explain the variation in tolerance between these two cultivars. We present evidence suggesting the greater Al resistance in buckwheat is further related to the immobilization and detoxification of Al by phosphorus in the root tissues.Ionic aluminum (Al) is highly toxic to plant growth and appears to interfere with a number of physiological and biochemical processes (Rengel, 1992;Kochian, 1995). However, species vary widely in their ability to resist the harmful effect of Al, and significant differences in Al resistance have even been reported between genotypes of the same species (Yang et al., 2005). Over the past few decades, concerted efforts have been made to understand the genetic and physiological basis of Al resistance in many different species. As proposed by Taylor (1991), Al resistance mechanisms can be grouped into two categories. One is based on excluding Al from the root cells, and the other relies on improving the resistance of plants to the Al ions once they enter the cytosol. Among the likely exclusion mechanisms, a role for organic acid efflux has been well documented in several species (Ma, 2000;Ryan et al., 2001;Kochian et al., 2004). Other potential exclusion mechanisms include increases in rhizospheric pH (Degenhardt et al., 1998), phosphate efflux (Pellet et al., 1996), the secretion of proteins to bind Al ...

Iron-deficiency stress of red clover would alter the composition of siderophore-secreting microbes in the rhizosphere, which is probably due to the phenolics secretion of the root, and may in turn help to improve the solubility of Fe in soils and plant Fe nutrition via elevated microbial siderophore secretion.

Aluminium (Al)-induced secretion of organic acids from plant roots is considered a mechanism of Al resistance, but the processes leading to the secretion of organic acids are still unknown. In the present study, a protein-synthesis inhibitor, cycloheximide (CHM), was used to investigate its effect on Al-induced organic acid secretion in a pattern I (rapid exudation of organic acids under Al stress) plant buckwheat ( Fagopyrum esculentum Moench) and a pattern II (exudation of organic acids was delayed by several hours under Al stress) plant Cassia tora L. A dose-response experiment showed that the secretion of oxalate by buckwheat roots was not affected by CHM when added in the range from 0 to 50 µ µ µ µ M , with or without exposure to 100 µ µ µ µ M Al, but the secretion of citrate was completely inhibited by 30 µ µ µ µ M CHM in C. tora . A time-course experiment showed that even prolonged exposure to 20 µ µ µ µ M CHM did not affect oxalate secretion in buckwheat, but significantly inhibited citrate secretion in C. tora . However, citrate synthase (CS) activity in C. tora was not affected during 12 h exposure to 100 µ µ µ µ M Al when compared with that in control roots, although CHM can inhibit CS activity effectively. These results indicated that CS activity was not related to Alregulated citrate efflux in C. tora . The total protein was decreased by 14.0% and 32.3% in C. tora and buckwheat root tip, respectively, after 3-h treatment with 20 µ µ µ µ M CHM. A 3-h pulse with 20 µ µ µ µ M CHM completely inhibited citrate efflux in C. tora during the next 6-h exposure to Al, although a small amount of citrate was exuded after 9-h exposure. However, oxalate efflux in buckwheat was not influenced by a similar treatment. In buckwheat, a 3-h pulse with 100 µ µ µ µ M Al maintained oxalate secretion at a high level during the next 9 h, with or without CHM treatment. Conversely, in C. tora a 6-h pulse with 100 µ µ µ µ M Al induced significant secretion of citrate which was inhibited by the CHM. Taken together, these findings suggest that both de novo synthesis and activation of an anion channel are needed for Al-induced secretion of citrate in C. tora , but in buckwheat the plasma membrane protein responsible for oxalate secretion pre-exists.

Alfalfa (Medicago sativa L.) is an important forage legume in farming and animal husbandry systems. In this study, MiSeq high-throughput sequencing was applied to assess the relationship between bacterial and fungal community structures and alfalfa growth characteristics and soil physical and chemical properties induced by different cultivars alfalfa (Victoria, Kangsai, Aohan) in the grey desert soil. The results showed that the diversity of bacterial and fungal in Victoria was higher, and the bacterial diversity was significantly lower for alfalfa with Aohan than for the others, and the fungal diversity was lower for alfalfa with Kangsai than for the others. Heatmap showed that total nitrogen, fresh weight, pH and organic have significantly affect fungal community structure, whereas pH and organic carbon also significant effects on bacterial community structure. LefSe analysis showed that the growth adaptability of introduced alfalfa is mainly related to fungal and bacterial species, and the beneficial microorganisms with significant differences and relative high abundance are significantly enriched in Victoria. Pathogens with high relative abundance are mainly concentrated in Aohan alfalfa soil. Based on our findings, Victoria is the high-yield alfalfa suitable for planting in gray desert soil, while planting Kangsai and Aohan alfalfa needs probiotic for adjuvant.

Changhua Stone is a rock, composed of clay minerals such as dickites and is also a special secondary quartzite formed by gas liquid metasomatic metamorphism. The article emphasizes its study on rock characteristics, mineral composition, and the causes of formation of Changhua Stone, excluding Changhua Chicken-Blood Stone. By observing petrographical characters of Changhua Stone, analyzing its physical and chemical characters, and testing its geochemical compositions with SEM and X-ray diffraction analysis, the results indicate that the mineral compositions of Changuan Stone are relate to the composition of protolith, the compositions and characters of metasomatic metasomatic fluid, and the conditions of metamorphism, especially the stress and the temperature.