Functional Niche Under Abiotic Stress 15 Anish Kumar Sharma, Vishal Singh Negi, Archana Negi, Bharat Sinh Solanki, and Khyati Harkhani Abstract The ecosystem functioning of any functional niche is largely dependent on the structure and organization of the inhabiting microbial communities. The micro- bial communities often display dynamic organization which is under constant exposure to diverse abiotic stress conditions. Such stress conditions play a major role in shaping and influencing the microbial community organization and its diversity. Microorganisms, which represent the earliest life forms, have undergone the longest evolutionary period resulting in the acquisition and devel- opment of capabilities to withstand extreme stress conditions. Besides their resilience nature against various abiotic stress conditions, microbes also display adaptability by rapid mutation to counter the stress conditions. As different microbes have different capabilities to tolerate any stress condition, the stress condition often favors the enrichment of microbes which display tolerance to the exposed condition. In this chapter, we summarized various abiotic stress conditions, including temperature, salt, drought, waterlogging, and metal toxicity stress, and how they influence the structure and diversity of the inhabiting microbial community structure and diversity. Various mechanisms employed by microorganisms to withstand these abiotic stress conditions are also described in the chapter. Keywords Niche · Abiotic stress · Salt · Temperature · Drought · Waterlogging · Heavy metal toxicity A. K. Sharma (*) · V. S. Negi · A. Negi · B. S. Solanki · K. Harkhani School of Sciences, P P Savani University, Surat, Gujarat, India e-mail: anish.sharma@ppsu.ac.in # The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021 M. Nath et al. (eds.), Microbial Metatranscriptomics Belowground, https://doi.org/10.1007/978-981-15-9758-9_15 311