Primordial nitrification processes have been studied extensively using geochemical approaches, but the biological origination of nitrification remains unclear. Ammonia-oxidizing archaea (AOA) are widely distributed nitrifiers and implement the rate-limiting step in nitrification. They are hypothesized to have been important players in the global nitrogen cycle in Earth’s early history. We performed systematic phylogenomic and marker gene analyses to elucidate the diversification timeline of AOA evolution. Our results suggested that the AOA ancestor experienced terrestrial geothermal environments at ∼1,165 Ma (1,928-880 Ma), and gradually evolved into mesophilic soil at ∼652 Ma (767-554 Ma) before diversifying into marine settings at ∼509 Ma (629-412 Ma) and later into shallow and deep oceans, respectively. Corroborated by geochemical evidence and modeling, the timing of key diversification nodes can be linked to the global magmatism and glaciation associated with the assembly and breakup of the supercontinent Rodinia, and the later oxygenation of the deep ocean. Results of this integrated study shed light on the geological forces that may have shaped the evolutionary pathways of the AOA, which played an important role in the ancient global nitrogen cycle.

Temperature, nutrients, and salinity are among the important factors constraining the distribution and abundance of microorganisms in the ocean. Marine Group II (MGII) belonging to Euryarchaeota commonly dominates the planktonic archaeal community in shallow water and Marine Group I (MGI, now is called Thaumarchaeota) in deeper water in global oceans. Results of quantitative PCR (qPCR) and 454 sequencing in our study, however, showed the dominance of MGII in planktonic archaea throughout the water column of the northeastern South China Sea (SCS) that is characterized by strong water mixing. The abundance of ammonia-oxidizing archaea (AOA) representing the main group of Thaumarchaeota in deeper water in the northeastern SCS was significantly lower than in other oceanic regions. Phylogenetic analysis showed that the top operational taxonomic units (OTUs) of the MGII occurring predominantly below 200 m depth may be unique in the northeastern SCS based on the observation that they are distantly related to known sequences (identity ranging from 90–94%). The abundance of MGII was also significantly correlated with total bacteria in the whole column, which may indicate that MGII and bacteria may have similar physiological or biochemical properties or responses to environmental variation. This study provides valuable information about the dominance of MGII over AOA in both shallow and deep water in the northeastern SCS and highlights the need for comprehensive studies integrating physical, chemical, and microbial oceanography.

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Two computer models of concrete frame with staircase were made and the seismic-performance of the models in elastic-phase was calculated by adopting base shear method, spectrum analysis by ETABS. The results show that including staircase into models will change the seismic performance of frame structure significantly. The paper proposes that the computer model with staircase and the response spectrum analysis should be used firstly in the seismic design of concrete frame with staircase.

To solve the fabrication problems of traditional precast shear walls caused by too many connections joints, a new type of precast shear wall with unconnected vertically distributed reinforcements and concealed bracings is developed in this paper. Four full-scale shear walls, including one cast-in-place specimen and three precast specimens, were tested under low-cycle lateral loading conditions to evaluate the seismic performance of the new type of precast shear wall. The test results showed that the loading capacity and energy dissipation of the new type of precast shear wall were comparable to those of the cast-in-place specimen; however, the failure mode was similar to the damage mechanism of an infilled wall frame, not the traditional bending-shear mode of shear walls. Then, a new strut-and-tie model considering dowel action was proposed for this new type of precast shear wall. Finally, a parametric study was conducted by finite element analysis to determine a reasonable value of the effective strength coefficient for the strut-and-tie model. Good agreement was achieved between the test and model results.