Dissolved organic nitrogen （DON） represents a significant pool of soluble nitrogen （N） in soil ecosystems. Soil samples under three different horticultural management practices were collected from the Xiaxiyang Or...Dissolved organic nitrogen （DON） represents a significant pool of soluble nitrogen （N） in soil ecosystems. Soil samples under three different horticultural management practices were collected from the Xiaxiyang Organic Vegetable and Fruit Farm, Shanghai, China, to investigate the dynamics of N speciation during 2 months of aerobic incubation, to compare the effects of different soils on the mineralization of ^14C-labeled amino acids and peptides, and to determine which of the pathways in the decomposition and subsequent ammonification and nitrification of organic N represented a significant blockage in soil N supply. The dynamics of N speciation was found to be significantly affected by mineralization and immobilization. DON, total free amino acids, and NH^＋-N were maintained at very low levels and did not accumulate, whereas NO3^--N gradually accumulated in these soils. The conversion of insoluble organic N to low-molecular-weight （LMW） DON represented a main constraint to N supply, while conversions of LMW DON to NH4^＋-N and NH4^＋-N to NO3^--N did not. Free amino acids and peptides were rapidly mineralized in the soils by the microbial community and consequently did not accumulate in soil. Turnover rates of the additional amino acids and peptides were soil-dependent and generally followed the order of organic soil 〉 transitional soil 〉 conventional soil. The turnover of high-molecular-weight DON was very slow and represented the major DON loss. Further studies are needed to investigate the pathways and bottlenecks of organic N degradation.展开更多
How to model the permeability evolution of rock subjected to liquid nitrogen cooling is a key issue. This paper proposes a simple but practical method to study the permeability evolution of rocks subject to liquid nit...How to model the permeability evolution of rock subjected to liquid nitrogen cooling is a key issue. This paper proposes a simple but practical method to study the permeability evolution of rocks subject to liquid nitrogen cooling. FLAC with FISH function was employed to numerically model the rock behavior under cooling. The enhanced perme- ability of the volumetric strain was defined, and the permeability was directly evaluated based on element＇s volumetric strain. Detailed procedures for implementing the evolution model of permeability in this paper were presented. A case study was carried out to simulate a coal bed where liquid nitrogen was injected in the bore hole. And a semi-submerged test of liquid nitrogen was performed. The method to model the permeability evolution of rocks subject to liquid nitrogen shock in this paper was proved to be right by the test results. This simulation results are discussed with the hope to provide some insight into understanding the nitrogen cooling practice.展开更多
基金Project supported by the National High Technology Research and Development Program (863 program) of China(No. 2006AA10A311)the National Natural Science Foundation of China (No. 40901124)the Shanghai Leading Aca-demic Discipline Program,China (No. B209)
文摘Dissolved organic nitrogen （DON） represents a significant pool of soluble nitrogen （N） in soil ecosystems. Soil samples under three different horticultural management practices were collected from the Xiaxiyang Organic Vegetable and Fruit Farm, Shanghai, China, to investigate the dynamics of N speciation during 2 months of aerobic incubation, to compare the effects of different soils on the mineralization of ^14C-labeled amino acids and peptides, and to determine which of the pathways in the decomposition and subsequent ammonification and nitrification of organic N represented a significant blockage in soil N supply. The dynamics of N speciation was found to be significantly affected by mineralization and immobilization. DON, total free amino acids, and NH^＋-N were maintained at very low levels and did not accumulate, whereas NO3^--N gradually accumulated in these soils. The conversion of insoluble organic N to low-molecular-weight （LMW） DON represented a main constraint to N supply, while conversions of LMW DON to NH4^＋-N and NH4^＋-N to NO3^--N did not. Free amino acids and peptides were rapidly mineralized in the soils by the microbial community and consequently did not accumulate in soil. Turnover rates of the additional amino acids and peptides were soil-dependent and generally followed the order of organic soil 〉 transitional soil 〉 conventional soil. The turnover of high-molecular-weight DON was very slow and represented the major DON loss. Further studies are needed to investigate the pathways and bottlenecks of organic N degradation.
文摘How to model the permeability evolution of rock subjected to liquid nitrogen cooling is a key issue. This paper proposes a simple but practical method to study the permeability evolution of rocks subject to liquid nitrogen cooling. FLAC with FISH function was employed to numerically model the rock behavior under cooling. The enhanced perme- ability of the volumetric strain was defined, and the permeability was directly evaluated based on element＇s volumetric strain. Detailed procedures for implementing the evolution model of permeability in this paper were presented. A case study was carried out to simulate a coal bed where liquid nitrogen was injected in the bore hole. And a semi-submerged test of liquid nitrogen was performed. The method to model the permeability evolution of rocks subject to liquid nitrogen shock in this paper was proved to be right by the test results. This simulation results are discussed with the hope to provide some insight into understanding the nitrogen cooling practice.
