Rice production plays a crucial role ia the food supply of China and a better understanding of the changes in paddy soil fertility and the management effects is of practical importance for increasing rice productivity...Rice production plays a crucial role ia the food supply of China and a better understanding of the changes in paddy soil fertility and the management effects is of practical importance for increasing rice productivity. In this study, field sampling in a typical red soil region of subtropical China, Jiangxi Province, was used to observe changes in the soil physical, chemical,and biological properties in a cultivation chronosequence of paddy fields. After cultivation, clay (＜ 0.002 mm) content in the soil, which was 39% in the original uncultivated wasteland, decreased to 17% in the 80-year paddy field, while silt(0.02-0.002 mm) content increased. Additionally, macroporosity increased and pore shapes became more homogeneous.Soil pH generally increased. Soil organic C and total N contents of the 0-10 cm layer increased from 4.58 and 0.39 g kg-1to 19.6 and 1.62 g kg-1, respectively, in the paddy fields after 30-year cultivation and then remained stable. Soil total P content increased from 0.5 to 1.3 g kg-1 after 3 years of rice cultivation, indicating that application of phosphate fertilizer could accelerate phosphorous accumulation in the soil. Total K content in the 0-10 cm soil layer for the 80-year paddy field decreased by 28% compared to that of the uncultivated wasteland land. Total Fe and free Fe contents declined with years of cultivation. The bacterial population increased and urease activity noticeably intensified after years of cultivation.In this chronosequence it appeared that it took 30 years to increase soil fertility to a relatively constant value that was seen after 80 years of cultivation.展开更多
Mangroves are special woody plant communities in the intertidal zone of tropical and subtropical coasts. They prove to be a natural microorganisms and new metabolites storage. In the study of mangrove endophytic fungi...Mangroves are special woody plant communities in the intertidal zone of tropical and subtropical coasts. They prove to be a natural microorganisms and new metabolites storage. In the study of mangrove endophytic fungi metabolites, four new compounds, Compounds 1, 2, 3 and 4, as well as a known octaketide, oytosporone B (5), are isolated from an endophytic fungus, Dothiorella sp., HTF3. They all show cytotoxic activities. The elucidation of these structures is mainly based on 1D/ 2D NMR and ESI-MS spectral analyses.展开更多
The authors compute the quasiconvex envelope of certain functions defined on the space M,.mn of real m x n matrices via a homogeneous function on Mmn - They also deduce Invariance properties for various convex envelop...The authors compute the quasiconvex envelope of certain functions defined on the space M,.mn of real m x n matrices via a homogeneous function on Mmn - They also deduce Invariance properties for various convex envelopes from corresponding invariance properties satisfied by a function. Some applications related in particular to nonlinear elasticity arc given.展开更多
文摘Rice production plays a crucial role ia the food supply of China and a better understanding of the changes in paddy soil fertility and the management effects is of practical importance for increasing rice productivity. In this study, field sampling in a typical red soil region of subtropical China, Jiangxi Province, was used to observe changes in the soil physical, chemical,and biological properties in a cultivation chronosequence of paddy fields. After cultivation, clay (＜ 0.002 mm) content in the soil, which was 39% in the original uncultivated wasteland, decreased to 17% in the 80-year paddy field, while silt(0.02-0.002 mm) content increased. Additionally, macroporosity increased and pore shapes became more homogeneous.Soil pH generally increased. Soil organic C and total N contents of the 0-10 cm layer increased from 4.58 and 0.39 g kg-1to 19.6 and 1.62 g kg-1, respectively, in the paddy fields after 30-year cultivation and then remained stable. Soil total P content increased from 0.5 to 1.3 g kg-1 after 3 years of rice cultivation, indicating that application of phosphate fertilizer could accelerate phosphorous accumulation in the soil. Total K content in the 0-10 cm soil layer for the 80-year paddy field decreased by 28% compared to that of the uncultivated wasteland land. Total Fe and free Fe contents declined with years of cultivation. The bacterial population increased and urease activity noticeably intensified after years of cultivation.In this chronosequence it appeared that it took 30 years to increase soil fertility to a relatively constant value that was seen after 80 years of cultivation.
文摘Mangroves are special woody plant communities in the intertidal zone of tropical and subtropical coasts. They prove to be a natural microorganisms and new metabolites storage. In the study of mangrove endophytic fungi metabolites, four new compounds, Compounds 1, 2, 3 and 4, as well as a known octaketide, oytosporone B (5), are isolated from an endophytic fungus, Dothiorella sp., HTF3. They all show cytotoxic activities. The elucidation of these structures is mainly based on 1D/ 2D NMR and ESI-MS spectral analyses.
文摘The authors compute the quasiconvex envelope of certain functions defined on the space M,.mn of real m x n matrices via a homogeneous function on Mmn - They also deduce Invariance properties for various convex envelopes from corresponding invariance properties satisfied by a function. Some applications related in particular to nonlinear elasticity arc given.
