分类: 生物学 >> 生态学 提交时间: 2023-05-11 合作期刊: 《干旱区科学》
摘要:Variations of precipitation have great impacts on soil carbon cycle and decomposition of soil organic matter. Soil bacteria are crucial participants in regulating these ecological processes and vulnerable to altered precipitation. Studying the impacts of altered precipitation on soil bacterial community structure can provide a novel insight into the potential impacts of altered precipitation on soil carbon cycle and carbon storage of grassland. Therefore, soil bacterial community structure under a precipitation manipulation experiment was researched in a semi-arid desert grassland in Chinese Loess Plateau. Five precipitation levels, i.e., control, reduced and increased precipitation by 40% and 20%, respectively (referred here as CK, DP40, DP20, IP40, and IP20) were set. The results showed that soil bacterial alpha diversity and rare bacteria significantly changed with altered precipitation, but the dominant bacteria and soil bacterial beta diversity did not change, which may be ascribed to the ecological strategy of soil bacteria. The linear discriminate analysis (LDA) effect size (LEfSe) method found that major response patterns of soil bacteria to altered precipitation were resource-limited and drought-tolerant populations. In addition, increasing precipitation greatly promoted inter-species competition, while decreasing precipitation highly facilitated inter-species cooperation. These changes in species interaction can promote different distribution ratios of bacterial populations under different precipitation conditions. In structural equation model (SEM) analysis, with changes in precipitation, plant growth characteristics were found to be drivers of soil bacterial community composition, while soil properties were not. In conclusion, our results indicated that in desert grassland ecosystem, the sensitive of soil rare bacteria to altered precipitation was stronger than that of dominant taxa, which may be related to the ecological strategy of bacteria, species interaction, and precipitation-induced variations of plant growth characteristics.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: In this article, a composite film from polyimide and thermally exfoliated graphene was prepared through in situ polymer- ization, and the weight percent of thermally exfoliated graphene with respect to the polyimide monomers was 5 wt %. The film was carbonized at 1000 C for 1 h and then heat-treated at various temperatures up to 2100 C. For comparison, the corresponding pure polyimide film was also prepared and heat-treated at the same condition. It was found that the addition of graphene could effectively prevent the polyimide film from shrinking in the direction parallel to the film surface during the heat treatment. Furthermore, the results of density, X-ray diffraction, shrinkage in the direction perpendicular to the film surface and scanning electron microscopy revealed that the graphitization process of the polyimide could be accelerated by addition of graphene obviously. In view of the above phenomena, a reasonable explanation was presented. VC 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41274.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: Ultrathin carbon foams with the thickness about 24 mm were fabricated by the pyrolysis of polyimide/ graphene composite foams. The addition of graphene was verified to stabilize the porous structure of the foams and accelerate their graphitization process simultaneously. Consequently, the well-defined carbon foams exhibited much higher electromagnetic interference (EMI) shielding effectiveness (SE) up to 24 dB over the frequency range of 8e12 GHz, in comparison with the non-foamed counterparts. The possible mechanism behind the phenomenon was attributed to their enhanced microwave absorption via the internal multiple scattering and reflections. Moreover, the SE could be further improved to 43 and 51 dB by increasing the sample thickness gradually to 51 and 73 mm, respectively. The carbon foams with high thermal stability are very promising in the fabrication of ultrathin EMI shields for thermally harsh applications.