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Climate warming and fertilization schemes have had widespread impacts on both above- and belowground bioprocess in natural and agricultural ecosystems, especially those in sensitive and fragile areas such as the Tibetan Plateau. In this study, we evaluated the effects of amendment of different forms of nitrogen (N) on the microbial community in typical Tibetan grassland soils under ambient conditions and conditions that mimic future effects from global warming. Both high-throughput 16S rRNA gene sequencing and functional gene microarray technology were used to detect the responses of microbial phylogenetic and functional compositions to N amendment and elevated temperature. Our results indicated that sodium nitrate and ammonium sulfate divergently shaped the microbial community composition at ambient temperature. Sodium nitrate decreased the abundance of genes involved in N cycling and carbon (C) decomposition, while ammonium sulfate had no significant effect. However, these distinct effects could be overrode by elevated temperature, where it was observed that both N amendment increased the abundance of N cycling and C decomposition genes. This indicates that future warming may "mask" the effects of amendment of different forms of N in alpine grassland. It may give a new perspective for N amendment in future warming scenario.