Determination of the Seasonal Changes of the Biological Nitrogen-Fixation Activity of Different Plants in the Xilingoule Grassland Inner Mongolia THE DIVERSITY OF DOMINANT SOYBEAN RHIZOBIUM TYPE IN CHINESE SOILS AND ITS SYMBIOTIC CHARACTERISTIC WTIH HOST ENHANCING EFFECT OF MANNITOL ON NITROGEN FIXATION ACTIVITY IN ANABAENA UNDER OSMOTIC STRESS Inh ibiting Effect of Assoc ia tive Nitrogen-f ixa tionBacter ia on Bacter ia W ilt D isea se of Euca lyptus The Influence of High Temperature and Drought on the Growth, Nodulation and Nitrogen-Fixation of Alnus cremastogyne in Different Kinds of Soils