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Free-living diazotrophs play a critical role in nitrogen (N) supply to ecosystems. Land-use change and plant rhizosphere are two important factors influencing diazotroph populations, but their relative strength in determining the soil diazotrophic community is still unclear, especially in acidic soils. One natural vegetation (the dominant species is green foxtail) and three agricultural land-uses (maize, peanut and soybean, respectively) widely distributed in the acidic soil region of southern China were selected. Bulk and rhizosphere soils were collected from every land-use, and their properties were determined. Quantitative PCR and high-throughput sequencing were applied to investigate soil diazotrophic abundance, diversity and community composition. Land use conversion from natural vegetation to different agricultural land-uses significantly reduced diazotroph abundances in bulk soils, however, the rhizosphere had a positive effect on the abundances in agricultural land-uses. Statistical analysis showed that the rhizosphere exerted a stronger effect on diazotroph abundance than land-use change. Converting natural vegetation to agricultural land-uses also decreased diazotroph richness and land-use types differed significantly in community composition, but plant rhizosphere did not cause these effects. In particular, the community variations in leguminous plants were more distinct than maize. Land-use change also influenced some topological properties of the community network. In acidic soil, land-use change has noticeable effects on the richness and composition of diazotrophic community than the rhizosphere. The rhizosphere, however, has a more obvious effect in increasing the abundance of the diazotrophs. These results highlight the critical role of land-use change in manipulating soil diazotrophic community composition.

Although phosphorus (P) availability and plant cultivation affect diazotrophic populations, studies often consider individual factors rather than their combined effects. Their relative importance to diazotrophs remains poorly understood, especially in acidic soils with P deficiency. It is hypothesized that the influences of P fertilization and plant cultivation on diazotrophic communities differ in acidic soils. The objectives were to investigate these influences and identify the key determining factors. Maize was grown in an acidic soil that was supplemented with 0, 20, and 50 mg P kg− 1 for 42 days. Maize biomasses, plant nutrient contents, and soil physicochemical properties were determined. Based on the nifH gene, the abundances and community compositions of diazotrophs in the different plant/soil compartments (bulk soils, rhizosphere soils, and roots) were respectively investigated using quantitative PCR and high-throughput sequencing. P fertilization significantly improved the diazotrophic abundances in the bulk and rhizosphere soils, but not in the roots. The plant/soil compartments had stronger effects on the abundance and diversity of diazotrophs than did P fertilization. Furthermore, the plant/soil compartments influenced diazotrophic community composition, but P fertilization did not. However, in the same sampling site, P fertilization caused community variations in the bulk and rhizosphere soils, rather than in the roots. Although P fertilization affected the abundances and compositions of diazotrophic communities in the bulk and rhizosphere soils, the plant/soil compartments resulting from maize cultivation had more noticeable effects than did P fertilization. These findings improved the understanding of biological nitrogen fixation in acidic soils.

In acidic soil, plant aluminum (Al) tolerance and nitrogen (N) fertilizer form play the important roles in influencing plant growth. Diazotrophs as plant growth promoting rhizobacteria can contribute to plant available N, but the response to plant growth differences resulting from plant Al tolerance or N fertilizer form in acidic soil is poorly understood. Here, we investigated this response. Three maize cultivars with different Al-tolerance levels were grown in an acidic soil that was added with nitrate (NO3−-N) or ammonium (NH4+-N) fertilizers. After 42 days, maize biomasses and root morphologies as well as the physicochemical properties of bulk and rhizosphere soils were determined. Based on nifH gene, soil diazotroph abundance was determined by quantitative RT-PCR and community composition was assayed using high-throughput sequencing. For the same maize cultivar, application of NO3−-N fertilizer relative to NH4+-N fertilizer increased maize biomass, root length, root surface area, and rhizosphere pH, but not significantly affect rhizosphere nifH copy number and community composition. The nifH copy numbers did not show significant differences among rhizosphere samples of three maize cultivars, but community composition was obviously different between Al-tolerant and Al-sensitive cultivars. In acidic soil, maize cultivars depending on Al tolerance altered rhizosphere diazotrophic community composition, but this effect seemed to be not susceptible to N fertilizer forms.

Igneous intrusions may contain sufficient heat that can have an effect on the generation of hydrocarbons from the source rock. This model is tested in the Yingtai Fault Depression of the southern Songliao Basin, where intrusive rocks are abundant. A heat conduction model and kinetic models of hydrocarbon generation are calibrated by using the hydrocarbon yield data from pyrolysis experiment and vitrinite reflectance values of source rocks adjacent to intrusive rocks. Our analysis shows that the intrusive rock contributes to the hydrocarbon generated from organic matter in the neighboring rock nearby the intrusive rock. For instance, as the distance to the contact surface is decreased, the maturity of the organic matter of neighboring rock increases gradually, H/C and TOC decreases gradually. The results have revealed that the extents affected by intrusive rocks with different thicknesses at various initial temperatures are basically not more than twice of the thickness of the intrusive rock. For multiple intrusive rocks, the extent and the degree of the thermal effect during a contemporaneous emplacement and emplacement at different stages are obviously different. The extent and degree of the thermal effect during contemporaneous emplacement are normally large. The degrees of thermal effect are different for neighboring rocks with different initial maturity, which is affected by the intrusive rock with the same parameters (such as thickness or initial temperature). Setting 0.9 % as the maturity (Ro) limit, at maturity less than 0.9 %, the Ro thermal effect (increment amount of Ro) increases as the initial maturity of the neighboring rock rises. At maturity of more than 0.9 %, it decreases as the initial maturity of neighboring rock rises. The results of the geological application have shown that the hydrocarbon generation history of source rock in an area with intrusive rocks can be solved effectively by an integrated use of the heat conduction model and the kinetic model of hydrocarbon generation.

Using polymer-derived technology, continuous high-temperature resistant Si-Al-C fibers were prepared by one step method, which included melt-spinning of polyaluminocarbosilane (PACS), curing of continuous PACS fibers, and sintering of the cured products. The results show that the average diameter and tensile strength of continuous Si-Al-C fibers are 11 to 12 μm and 1.8 to 2.0 GPa, respectively. The chemical formula of Si-Al-C fibers is SiC1.01O0.0400Al0.024, which is nearly stoichometric. The fibers are mainly composed of β-SiC crystalline, small amount of α-SiC, and amorphous SiC. Continuous Si-Al-C fibers exhibit excellent thermal stability. When the fibers were exposed in argon for 1 h, the tensile strength did not decrease until 1500°C. After heat treatment at 1800°C in argon for 1 h, the fibers maintained about 80% of the initial strength. It was higher than that of Nicalon and Hi-Nicalon fibers.

The high-temperature resistant Si–Al–C–(O) fibers were prepared through polymer-derived method using continuous polyaluminocarbosilane (PACS) fibers. Evolutions of the crystallization during the pyrolysis of the Si–Al–C–(O) precursor fibers were investigated by a series analysis. The structure of the fibers transforms from organic state to inorganic state and the crystalline phases appear during the pyrolysis. The β-SiC crystallite size increases when the temperature is higher than 1,300 °C. At the same time, the α-SiC appears. At 1,600 and 1,800 °C, the grain size of β-SiC of the fibers is 15.4 and 22.1 nm, respectively. The growth of β-SiC and the appearing of α-SiC have a great influence on the properties of the fibers. The change of the tensile strength of the pyrolysis products is divided into three stages with the growth of the crystal. The tensile strength of the Si-Al-C fibers is higher than 1.9 GPa.

To the Editor: Paroxysmal supraventricular tachycardia (PSVT) is a common arrhythmia characterized with sudden onset of regular and narrow QRS complex tachycardia. P6 (Neiguan) is a well-known acupoint lessening postoperative nausea and vomiting (PONV) [1]. Here, we present a case of PSVT successfully terminated by P6 acupressure during anesthesia. A 51-year-old woman underwent titanium plate removal surgery with spinal anesthesia. Preoperative 12-lead electrocardiogram (ECG) showed sinus rhythm and normal heart rate (Supplementary Fig. 1). Spinal anesthesia was performed with ropivacaine 15 mg, and adequate anesthesia was controlled at the L1 level. When the supine posture was changed to Trendelenburg position, she complained of chest tightness. Her BP was 131/84 mmHg. The ECG showed a narrow complex tachycardia with heart rate of 138–160 beats per minute and absence of P waves. ST depression with 3 mm is also noted in lead II (Supplementary Fig. 2). A diagnosis of PSVT was made. Immediate management included changing to supine posture, carotid sinus massage, and slight ocular compression, but these interventions failed. Just before adenosine (50 lg/kg) was given intravenously, P6 acupressure was suggested. Obtaining the patient’s permission, P6 acupressure was performed with the thumb for continuous compression at the acupoint. To our surprise, her heart rate dropped to 76 bpm in 5 s, and the ECG converted to sinus rhythm from then on (Supplementary Fig. 3). No further episodes of PSVT occurred, and she was discharged home 5 days later. P6 stimulation was reported to reduce heart rate through increasing vagal modulation [2]. Compared with vagal stimulation maneuvers and anti-arrhythmic drugs, P6 acupressure is relative safe and easy to perform. Further confirmation should include randomized controlled clinical studies.