Citation: Szili-Kovács, T.; Takács, T. Advanced Research of Rhizosphere Microbial Activity. Agriculture 2023, 13, 911. https://doi.org/10.3390/ agriculture13040911 Received: 14 April 2023 Revised: 18 April 2023 Accepted: 19 April 2023 Published: 21 April 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). agriculture Editorial Advanced Research of Rhizosphere Microbial Activity Tibor Szili-Kovács * and Tünde Takács * Centre for Agricultural Research, Institute for Soil Sciences, Herman O. út 15., 1022 Budapest, Hungary * Correspondence: szili-kovacs.tibor@atk.hu (T.S.-K.); takacs.tunde@atk.hu (T.T.) Soils are generally considered a complex and largely unexplored vital “black box” with thousands of microorganism taxa in their networks. The declaration of the “International Decade of Soils” (2015–2024) has drawn attention to the soil as one of the most important natural resources, as well as highlighting uses of soil and the global problem of soil degradation [1]. All soil functions play an important role in everyday human life. The genetic and functional diversity of soil microorganisms is crucial for conserving soil health and functions. Studies on the soil microbial communities of the rhizosphere are essential for developing environmentally friendly practices and agricultural management, soil awareness, sustainability, and security. According to recent publications, theinteraction between soil microbes and plants could be much more complex than previously thought. The concept of the rhizosphere originated with Hiltner’s work dating back to the beginning of the 20th century [2]. A volume of soil, which was influenced by roots and inhabited by soil microorganisms quite different from the surrounding soil, was conceived and named the rhizosphere. The interface between the roots and the soil is complex, delineated by uncertain boundaries that can change over space and time. The rhizosphere is one of the most significant hotspots in soils and harbors large numbers of microbial species belonging to archaea, bacteria, and fungi [3]. Plants have direct and indirect effects on soil fauna and microorganisms by releasing root exudates and litter deposition serving carbon and energy sources for heterotrophic organisms; meanwhile, they have the selective power to shape microbial communities around the root system and on the root surface, which is called the rhizoplane. Microbial activity in the rhizosphere can be one or two orders of magnitude higher than that of the surrounding bulk soil [4]. Moreover, it is a very dynamic and sensitive system. Microbes in the rhizosphere can aid plant nutrition, water uptake, and plant growth promotion by hormone and siderophore production and protect plants against pathogenic microbes, while in certain conditions some of them become pathogenic too. Climate change, land use change, and different management options are challenges to evaluating soil health in connection with plant–microbe interactions [5]. In this Special Issue, 10 papers were selected and accepted for publication. Most papers focus on rhizosphere microbiome (fungi or bacteria) analysis by DNA amplicon sequencing. Some of these papers used isolation techniques to select and check microbes with plant growth promotion and plant pathogenic defense abilities in order to develop potential biofertilizers. Two papers focused on arbuscular mycorrhizal fungi (AMF), another on nitrifying bacteria and archaea in the rhizosphere, and another on one bacillus strain preselected and thoroughly investigated by genome mining to reveal all functional abilities that may be important for plant-growth-promoting (PGP) properties. Plants can regulate the composition of the rhizosphere microorganism community. For many hundreds of years, medicinal plants have been used not only for human medicine but also for protection against soil pathogens. The sensitivity of soil fungi to secondary plant metabolites changes with the compound produced by the plant species. When investigating the rhizosphere soils of five medicinal plant species—Origanum syriacum, Salvia fructicosa, Teucrium capitatum, Myrtus communis, and Pistacia lentiscus—significant differences were found both in the function and in the taxonomical composition of the Agriculture 2023, 13, 911. https://doi.org/10.3390/agriculture13040911 https://www.mdpi.com/journal/agriculture