**1. Introduction**

The rhizosphere, the region of soil surrounding plant roots, is a dynamic environment where various interactions between plants and microorganisms occur [1]. Among these interactions, the exchange of nutrients is crucial for plant growth and development. Phosphorus (P) is one of the essential macronutrients for plants known to play a vital role in several physiological processes, including photosynthesis, energy transfer, and nucleic acid synthesis [2]. However, P-availability in the soil is often limited since it is highly reactive and readily forms insoluble compounds unavailable to plants [3]. Plants have evolved various strategies to acquire P from soil to overcome this limitation. These mechanisms involve the secretion of organic acids, enzymes, and other compounds that can solubilize and mineralize P [4] through associations with beneficial microorganisms such as mycorrhizal fungi and rhizobacteria [5].

The interactions between plants and microorganisms in the rhizosphere play a crucial role in regulating P-availability [3]. Microorganisms can contribute to the solubilization and mineralization of P and make it available to plants [6]. Conversely, some microorganisms can immobilize or compete for P and reduce its plant availability [7]. Therefore, understanding the dynamics of plant-microbe interactions in the rhizosphere is essential for improving P-acquisition and enhancing plant growth and yield [8]. Moreover, sustainable agriculture and crop production practices require minimizing chemical fertilizers and enhancing the natural processes of nutrient cycling in soil [9]. Harnessing plant-microbe interactions to optimize P-uptake can reduce the environmental impact of agriculture while improving soil health and crop productivity [10]. Therefore, studying the role of P in plant-microbe interactions in the rhizosphere is critical for developing efficient and sustainable agricultural systems.

This chapter aims to: (i) provide an in-depth analysis of the role of P in plant physiology, growth, and its availability in soil; (ii) discusses P-acquisition and -uptake, its impact on plant metabolism and its influence on plant growth and development; (iii) examines the mechanisms underlying the soil-P acquisition in plants, and the production of phosphatase enzymes, secretion of organic acids, mycorrhizal symbiosis, changes in root morphology, P-use-efficiency, and mobilization and transporters; (iv) explores the impact of P on microbial communities in the rhizosphere and the role it plays in plant-microbe interactions; and (v) highlights the significant implications of P-availability in the rhizosphere for sustainable agriculture and crop production.
