Diversity and assembly of active bacteria and their potential function along soil aggregates in a paddy field.

Numerous studies have found that soil microbiomes differ at the aggregate level indicating they provide spatially heterogeneous habitats for microbial communities to develop. However, an understanding of the assembly processes and the functional profile of microbes at the aggregate level remain largely rudimentary, particularly for those active members in soil aggregates. In this study, we investigated the diversity, co-occurrence network, assembly process and predictive functional profile of active bacteria in aggregates of different sizes using H218O-based DNA stable isotope probing (SIP) and 16S rRNA gene sequencing. Most of the bacterial reads were active with 91 % of total reads incorporating labelled water during the incubation. The active microbial community belonged mostly of Proteobacteria and Actinobacteria, with a relative abundance of 55.32 % and 28.12 %, respectively. Assembly processes of the active bacteria were more stochastic than total bacteria, while the assembly processes of total bacteria were more influenced by deterministic processes. Furthermore, many functional profiles such as environmental information processing increased in active bacteria (19.39 %) compared to total bacteria (11.22 %). After incubation, the diversity and relative abundance of active bacteria of certain phyla increased, such as Proteobacteria (50.70 % to 59.95 %), Gemmatimonadetes (2.63 % to 4.11 %), and Bacteroidetes (1.50 % to 2.84 %). In small macroaggregates (SMA: 0.25-2 mm), the active bacterial community and its assembly processes differed from that of other soil aggregates (MA: microaggregates, <0.25 mm; LMA: large macroaggregates, 2-4 mm). For functional profiles, the relative abundance of important functions, such as amino acid metabolism, signal transduction and cell motility, increased with incubation days and/or in SMA compared to other aggregates. This study provides robust evidence that the community of active bacteria and its assembly processes in soil aggregates differed from total bacteria, and suggests the importance of dominant active bacteria (such as Proteobacteria) for the predicted functional profiles in the soil ecosystem.

Experimental Study on Conductivity Anisotropy of Limestone Considering the Bedding Directional Effect in the Whole Process of Uniaxial Compression.

Experimental studies were conducted on the changes of the potential differences in different directions during the uniaxial compression on limestone samples parallel and normal to the bedding plane. In the test, electric current was supplied at both ends of the samples, and concurrent measurement was conducted in four measuring lines at a 45-degree angle to each other. First, the change laws of the potential differences in different directions and the similarities and differences of rock samples were summarized. In regards to the uniaxial compression properties and crack growth, the above-mentioned similarities and differences were further analyzed. Then, the anisotropy factor was introduced to further explore the response characteristics. It was found that the anisotropic changes of rock samples went through three stages during the uniaxial compression process, providing a reference for describing the properties in different failure stages of rock samples and obtaining precursory information about the fracture. Besides, the relationship between the peak stress and initial potential difference in a direction normal to the current direction was obtained by means of data fitting, providing a new method of predicting the uniaxial compressive strength of rock samples. According to the preceding analysis, this paper studied rock anisotropy by considering the bedding directional effect in terms of conductivity and provided a reference for subsequent study on rock materials' properties and engineering practices.