Seasonal dynamics of soil microorganisms and soil nutrients in fast-growing Populus plantation forests of different ages in Yili, Xinjiang, China Effects of simulated nitrogen deposition on temperature sensitivity of soil respiration components in Populus L. plantations in a riparian zone of the Yangtze River Effects of simulated nitrogen deposition on the each component of soil respiration in the Populus L. plantations in a riparian zone of the mid-lower Yangtze River COMPARISON OF DIFFERENT INTERCROPPING WAYS OF POPLAR PLANTATION IN SAND LAND OF THE YELLOW RIVER ORIGINAL COURSE