The bacteria that live in natural environments frequently co-exist in complex, spatially structured multispecies biofilm communities where various species interact with each other. High prevalence of synergistic effect on biofilm formation has been gradually found among different bacterial soil isolates in cocultures, which indicates the importance of bacterial interspecific cooperation in multispecies biofilm communities. Meanwhile, spatial organization of bacterial communities is considered to play important roles in shaping the structure and function of multispecies communities, leading to increased fitness during development in natural environments. However, these beneficial interspecific interactions in multispecies biofilms formed on plant hosts and their impacts on plant growth even plant tolerance to environmental stress have not been largely explored yet. In addition, most of what we know about the behaviors and properties of plant-beneficial bacteria comes from studying pure single cultures, overlooking functions and potentials of bacterial consortium when studied as a whole, rather than as individual members. Therefore, exploring emergent properties of multispecies bacterial communities can provide us with new understanding of microbe-plant interactions. Meanwhile, studying micro-scale spatial organization is also key to understanding microbial community behaviors on plant hosts. Here, a four-species biofilm model (Stenotrophomonas rhizophila, Paenibacillus amylolyticus, Microbacterium oxydans and Xanthomonas retroflexus, termed as SPMX) was established on Arabidopsis root to study bacterial consortium impacts on plant drought tolerance and spatial organization of multispecies biofilm during their co-cultivation. The observations from Manuscript I suggest that SPMX remarkably enhanced Arabidopsis plant tolerance to drought in vivo, whereas no drought-tolerant effect was observed when subjected to the individual strains, revealing emergent properties of the SPMX consortium as the underlying cause of the induced drought tolerance. In Manuscript II, more plant-beneficial effects of SPMX were explored. SPMX co-cultured all four together not only promoted seed germination, but also shaped the plant seedling roots in vitro, which may associate with bacterial auxin production when four species were co-cultured together. These findings reveal potential emergent properties of SPMX to promote plant growth, further reflecting the specific functionality and significance of bacterial consortium in ecological systems, especially when interacting with their hosts. Manuscript III focuses on investigating SPMX multispecies biofilm formation and its spatial composition on plant roots over time by combined approaches of visualization using fluorescence in situ hybridization with confocal laser scanning microscopy (FISH CLSM) and 16S rRNA gene amplicon analysis. Differential root colonization patterns between SPMX co-cultures and monocultures showed that SPMX was able to increase root colonization and form multispecies biofilms, structurally different from those formed by individuals. The composition shifts and spatial pattern differences of each species in the SPMX biofilm suggest that weak colonizers when studied in monoculture may play an important role and significantly impact the spatial organization in multispecies biofilm during microbe-plant interactions. The results presented in the manuscripts of this PhD thesis have provided new knowledge of emergent bacterial community properties affecting plant growth and drought tolerance, and have improved our understanding of spatial organization of plant root-associated microbial communities.