The effects of long-term NaCl and KCl treatment on plant growth and antioxidative responses were investigated in Chenopodium album, a salt-resistant species widely distributed in semi-arid and light-saline areas of Xinjiang, China. Growth parameters [plant height, branch number, leaf morphology and chlorophyll (Chl) content],

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Chenopodium album  L., a salt-tolerant species that is widely distributed in the semi-arid areas of Xinjiang, China, produces numerous dimorphic seeds (black and brown). To investigate the effects of three salts (NaCl, KCl, and CaCl2, which constitute the main salt cations in the soil in semi-arid areas) on seed germination and seedling survival of C. album, seeds were germinated in different salinity treatments: 0, 100, 200, and 250 mmol·L–1 of NaCl or KCl; or, 300 and 400 mmol·L–1 NaCl or KCl, each amended with CaCl2 (0, 2.5, 5.0, 7.5, and 10.0 mmol·L–1). Results showed that the brown seeds were more salt tolerant, and a higher percentage germinated than black seeds in the different salinity treatments. The percentage of germinating of black seeds could be significantly improved, when under saline conditions, by the synergetic action of ethephon (C2H6ClO3P) and KNO3. The addition of low concentrations of CaCl2 improved seed germination for seeds exposed to 300 mmol·L–1 NaCl or KCl, and the alleviating effects were stronger for the brown than for the black seeds. Seedling survival could also be enhanced by the addtion of CaCl2. These results suggest that the dimorphic seeds of C. album exhibit different germination patterns under different salinity conditions, and that the diversity in salt tolerance of dimorphic seeds enables C. album to adapt to semi-arid areas successfully. The physiological mechanism by which CaCl2 enhances the germination of dimorphic seeds requires further study.

To identify genes expression in Chenopodium album exposed to NaCl stress and screen ESTs related to salt stress, a subtractive suppression hybridization (SSH) library of C. album under salt stress was constructed in the present study. Random EST sequencing produced 825 high-quality ESTs with GenBank ID GE746311-GE747007, which had 301 bp of average size and were clustered into 88 contigs and 550 singletons. They were classified into 12 categories according to their function annotations. 635 ESTs (76.97%) showed similarities to gene sequences in the non-redundancy database, while 190 ESTs (23.03%) showed low or no similarities. The transcriptional profiles of 56 ESTs randomly selected from 347 unknown or novel ESTs of SSH library under varying NaCl concentration and at different time points were analyzed. The results indicated that a high proportion of tested ESTs were activated by salt stress. Four in 56 ESTs responded to NaCl were also enhanced in expression level when exposed to ABA and PEG stresses. The above four ESTs were validated by northern blotting which was consistent with the results of RT-PCR. The results suggested that genes corresponded to these ESTs might be involved in stress response or regulation. The complete sequences and detailed function of these ESTs need to be further studied.

To understand the characteristics of variation in porosity and permeability, the physical properties of the shale reservoir under different stress conditions play an important role in guiding shale gas production. With the shale of the Wufeng–Longmaxi Formation in the south of the Sichuan Basin as the research object, stress-dependent porosity and permeability test, high-pressure mercury injection, and scanning electron microscope test were performed in this study to thoroughly analyze the variation in physical properties of different shale lithofacies with effective stress. Besides, the stress sensitivity of different lithofacies reservoirs was evaluated by using parameters such as pore compressibility coefficient (PCC) and porosity sensitivity exponent (PSE), while the optimized support vector machine (SVM) algorithm was adopted to predict the coefficient of reservoir porosity sensitivity. According to the research results, the porosity and permeability of shale reservoirs decline as a negative exponential function. When the effective stress falls below 15 MPa, the damage rate of permeability/porosity increases rapidly with the rise of effective stress. By contrast, the permeability curvature of the shale reservoirs plunges with the rise of effective stress. It was discovered that a higher siliceous content results in a higher permeability curvature of shale, indicating the greater stress sensitivity of the reservoir. The ratio of matrix porosity to microfracture porosity determines the PSE, which is relatively low, and low aspect ratio pores contribute to high porosity compressibility and stress sensitivity. Young’s modulus shows a negative correlation with pore compressibility and a positive correlation with Poisson’s ratio. High clay minerals have a large number of low aspect ratio pores and a low elastic modulus, which leads to both high PCC and low PSE. Based on the principal component analysis, a multiclassification SVM model was established to predict the PSE, revealing that the accuracy of the sigmoid, radial basis function (RBF), and linear kernel function is consistently above 70%. According to error analysis, the accuracy can exceed 80% with the RBF kernel function and appropriate penalty factor. The research results serve to advance the research on the parameters related to overburden pressure, porosity, and permeability. Moreover, the optimized SVM algorithm is applied to make a classification prediction, which provides a reference for shale reservoir exploration and development both in theory and practice.