Molecular Soil Biology 2024, Vol.15, No.1, 17-27 http://bioscipublisher.com/index.php/msb 18 remediation, identifies key microbial taxa and functional traits that contribute to the resilience and effectiveness of SynComs in saline-alkali soils, and discusses the challenges and future directions for researching and applying SynComs in agricultural practices. By integrating insights from multiple studies, this paper aims to explore the potential of engineered synthetic microbial communities (SynComs) in restoring soil health in saline-alkali environments, and to provide a roadmap for future research and practical applications to enhance soil health, improve crop productivity, and contribute to sustainable agricultural practices in saline-alkali environments. 1 Overview of Alkaline Soils 1.1 Characteristics and formation of saline-alkali soils Saline-alkali soils are characterized by high concentrations of soluble salts and exchangeable sodium, which lead to elevated soil pH and poor soil structure. These soils typically form in arid and semi-arid regions where evaporation exceeds precipitation, causing salts to accumulate in the soil profile. The primary salts found in saline-alkali soils include sodium chloride, sodium sulfate, and sodium carbonate. The formation of these soils is often exacerbated by poor irrigation practices, inadequate drainage, and the use of saline water for irrigation (Shi et al., 2019). 1.2 Impact of salinity and alkalinity on soil health and crop productivity High salinity and alkalinity adversely affect soil health by disrupting soil structure, reducing soil permeability, and impairing nutrient availability. These conditions lead to poor soil aeration and water infiltration, which in turn hinder root growth and microbial activity. Crop productivity is significantly reduced in saline-alkali soils due to osmotic stress, ion toxicity, and nutrient imbalances. For instance, high sodium levels can displace essential nutrients like potassium and calcium, leading to deficiencies that affect plant growth and yield (Cui et al., 2020; Lu et al., 2020). Additionally, salinity and alkalinity can alter the composition and function of soil microbial communities, further impacting soil health and plant productivity (Liu et al., 2020; Wang et al., 2020b). 1.3 Traditional methods of managing saline-alkali soils and their limitations Traditional methods for managing saline-alkali soils include leaching, gypsum application, and the use of salt-tolerant crop varieties. Leaching involves the application of large volumes of water to flush salts from the root zone, but this method is often limited by water availability and the risk of groundwater contamination. Gypsum application helps to displace sodium ions with calcium ions, improving soil structure and reducing alkalinity. However, the effectiveness of gypsum is limited in soils with high levels of sodium carbonate, and its application can be cost-prohibitive (Huang et al., 2020; Wang et al., 2020b). The use of salt-tolerant crop varieties can provide some relief, but breeding programs have struggled to develop varieties that can thrive in highly saline-alkali conditions (Qin et al., 2016). These traditional methods often provide only temporary relief and do not address the underlying causes of soil salinization and alkalization, necessitating the exploration of more sustainable and innovative strategies (Zhou et al., 2022). 2 Engineered Synthetic Microbial Communities (SynComs) 2.1 Definition and principles of SynComs Engineered Synthetic Microbial Communities (SynComs) are artificially designed consortia of microorganisms that are tailored to perform specific functions within an ecosystem. These communities are constructed using principles of synthetic biology and genetic engineering to enhance or introduce desired traits in microbial populations. The primary goal of SynComs is to leverage the synergistic interactions among different microbial species to achieve outcomes that are difficult to accomplish with single-species cultures (Figure 1). In the context of soil health restoration, SynComs can be designed to improve nutrient cycling, enhance plant growth, and mitigate the adverse effects of soil salinization and alkalization (Wang et al., 2019). Arnault et al. (2024) conducted a series of meticulously designed experiments to explore and optimize the role of synthetic microbial communities (SynComs) in plant-microbe interactions. The study investigated the effects of mass and surface sterilization on seed colonization, the impact of soil and seed community coalescence on the rhizosphere, and the influence of SynCom composition on strain selection. By measuring the microbial
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