We have investigated unlignified tension wood and normally lignified wood celluloses inPopulus maximowiczii with particular reference to the composition of two crystalline phases I/I (triclinic/ monoclinic). Four independent techniques, which enable us to detect the two phases, CP/MAS13C NMR, Fourier transform infrared microscopy, selected-area electron diffraction, and X-ray diffraction were applied. Because of the low crystallinity of wood celluloses, particularly in the case of celluloses in the lignified cell wall, no single method was decisive enough to be able to determine the composition of the two phases as one can with highly crystalline materials. The I dominant structure (monoclinic crystal type) was, however, preferred for both tension and normal wood celluloses. 相似文献
A new compound of 4,4'-diamino-N,N'-diethyl bisbenzenesulfamide (C18H26N4O4S2,Fw = 426.55) has been synthesized and its structure was determined by X-ray crystallography method. The crystal belongs to the monoclinic system, space group P21/c with a = 10.0623(9), b =13.6759(13), c =15.5309(14) (A),β = 100.482(2)°, V= 2101.6(3)(A)3, Dc = 1.348 g/cm3, F(000) = 904,μ = 0.285 mm-1, Z = 4, the final R = 0.0512 and wR = 0.1363 for 3485 observed reflections with I >2σ(Ⅰ). The structure of the title compound is pseudo secondary axisymmetric, and the two sulfamide-groups show distorted tetrahedral configurations. 相似文献
Floristic composition, community structure and soil moisture and nutrient contents in abandoned fields of different ages were analyzed to clarify the regenerative aspects of succession as a tool for vegetation restoration. The results indicated that secondary succession in this region can be interpreted as an auto-succession: there are main changes in species-relative abundance and species turnover. Annual or biennial species (e.g. Artemisia scoparia), acted as pioneers and strongly dominated the early stages. Then, they underwent a progressive decline, while forbs (e.g. Artemisia sacrorum) and grasses (e.g. Xanthium sibiricum) had their peak abundance at intermediate stages. Dwarf shrubs (e.g. Lespedeza dahurica) and short rhizome grass (e.g. Bothriochloa ischaemum) appeared at mid-succession stage and gradually increased in abundance during succession, becoming dominant at late stages. The first axis of detrended correspondence canonical analysis arranged the sites according to their fallow time, indicating a successional sere. The second axis, associated with diverging pathways of regeneration, correlated with topographic factors and soil moisture and nutrition. Structural divergence between plots increased as succession went on, attained the highest at the mid-succession stage, decreased at the late stage.
Soil moisture and available phosphorus content decreased steadily with field age after their abandonment, whereas pools of organic matter, total and available nitrogen, potassium and total phosphorus increased with field age. The pace and direction of recovery of native vegetation and natural soil properties in these abandoned fields resembled classic old-field succession, which is a form of secondary succession that often serves as a template for guiding restoration efforts. Interface between the abandoned field soil and plant system was crucial to the above process. Our current study supported the generally accepted hypothesis in the succession literature. 相似文献