[Radial growth response of Populus euphratica to climate change in the Cele desert oasis ecotone, China]. / ç­–å‹’æ²™æ¼ ç»¿æ´²è¿‡æ¸¡å¸¦èƒ¡æ¨å¾„å‘ç”Ÿé•¿å¯¹æ°”å€™å˜åŒ–çš„å“åº”.

Populus euphratica is an important tree species in the arid regions of Northwest China, which is sensitive to climate changes. Climate of the Northwest China is changing to be "warm and humid", but how it would affect the regional forest growth is not clear. In this study, the radial growth response of P. euphratica to major climatic factors and their temporal changes during 1984-2021 were analyzed by using dendrochronology method in the desert oasis ecotone of Cele in the southern Tarim basin. The results showed that tree-ring width index of P. euphratica had a significant negative correlation with temperature in September of the previous year, and in February and May of current year, had significant positive correlation with precipitation in September of previous year and March and May of current year, and had significant positive correlations with SPEI in February and May of current year. The relationships between tree-ring width index and combined month climatic factors were more obvious. The results of moving correlation analysis showed that the correlation between tree-ring width index and temperature in the growing season tended to be strengthened in recent years, while the correlation between tree-ring width index and precipitation, SPEI tended to be declined or remain stable. The variations of the relationships between tree-ring width index and combined month climatic factors were more obvious compared that with single month. Current regional climate is conducive to the growth and development, as well as the improvement of ecological shelter function of P. euphratica forest in the desert oasis ecotone of Cele.

Density functional theory studies on hydroxylamine mechanism of cyclohexanone ammoximation on titanium silicalite-1 catalyst.

The hydroxylamine mechanism of cyclohexanone ammoximation on defective titanium active site of titanium silicalite-1 (TS-1) was simulated using two-layer ONIOM (M062X/6-31G**:PM6) method. A new energy favorable reaction route was found, which contained two parts: (1) the catalytic oxidation of adsorbed NH3 to form hydroxylamine using the Ti-OOH as an active oxidant formed by reacting H2O2 with the defective Ti active site; (2) the subsequent noncatalytic oximation of desorbed hydroxylamine and cyclohexanone out of TS-1 pores to form cyclohexanone oxime. In the catalytic formation of hydroxylamine on the Ti active site of TS-1, the proposed mechanism of two-step single-proton transfer aided by a lattice oxygen atom bonded to Ti atom need a lower reaction energy than the mechanism proposed before. In the subsequent noncatalytic oximation of hydroxylamine and cyclohexanone, which contained two elementary reaction steps in total, the mechanisms of one-step double-proton transfer in the first elementary reaction step and the subsequent one-step three-proton transfer for the second elementary reaction step were proposed, in which the solvent water molecules played a very important role in assisting and stabilizing the proton transfer processes.