Molecular Soil Biology 2024, Vol.15, No.1, 17-27 http://bioscipublisher.com/index.php/msb 21 Coker et al., 2022) In summary, the strategic design and application of SynComs hold significant promise for the restoration of soil health in saline-alkali environments. By leveraging advanced techniques in synthetic biology and genetic engineering, SynComs can be tailored to enhance microbial diversity, target specific soil health issues, and provide sustainable solutions for soil remediation. Coker et al. (2022) explored strategies to maximize the diversity of synthetic microbial communities (SynComs) by systematically adjusting the initial community proportions. The study utilized various starting ratios to analyze how these adjustments impact the overall microbial diversity and community structure. Shannon diversity index measurements combined at two and six days demonstrated the significant effects of initial proportions on community diversity. Principal Component Analysis (PCA) of robust Aitchison distances provided insights into the structural differences between communities at different starting ratios. Furthermore, the analysis compared sequencing reads under PMA and mock-treated conditions, revealing statistically significant differences. The taxonomic composition heatmap after 16 hours of growth highlighted the dynamic changes in community structure based on initial ratios. These findings underscore the importance of initial community composition in influencing SynCom diversity, offering valuable strategies for optimizing microbial communities for applications in agriculture and ecosystem management. 3 Mechanisms of SynComs in Soil Health Restoration 3.1 Biological pathways involved in the detoxification of saline-alkali soils Synthetic microbial communities (SynComs) play a crucial role in the detoxification of saline-alkali soils through various biological pathways. One significant mechanism is the enhancement of antioxidant enzyme activities, which helps in mitigating oxidative stress caused by high salinity and alkalinity. For instance, the overexpression of specific genes such as ChbZIP1 in plants has been shown to upregulate antioxidant enzymes like GPX1, DOX1, and CAT2, thereby enhancing the plant's tolerance to alkali stress (Qu et al., 2021). Additionally, SynComs can influence the microbial community structure, promoting the growth of haloalkaliphilic taxa that are better adapted to saline-alkali conditions, thus aiding in the detoxification process (Wang et al., 2019). 3.2 Enhancement of nutrient cycling and soil structure by SynComs SynComs contribute significantly to nutrient cycling and the improvement of soil structure in saline-alkali environments. The application of organic amendments such as vermicompost and humic acid fertilizers has been shown to enhance soil aggregate stability and microstructure, which in turn improves soil permeability and salt leaching (Liu et al., 2020). These amendments also stimulate the microbial community involved in nitrogen cycling, increasing the abundance of nitrifying bacteria and reducing nitrogen losses through denitrification processes. Furthermore, SynComs can enhance enzyme activities such as catalase, urease, and alkaline phosphatase, which are crucial for nutrient cycling and overall soil health. 3.3 Interaction between SynComs and native soil microbiota The interaction between SynComs and native soil microbiota is a key factor in the successful restoration of saline-alkali soils. SynComs are designed to complement and enhance the existing microbial communities, promoting beneficial interactions that improve soil health. For example, SynComs can enhance the diversity and richness of native bacterial communities, leading to a more resilient and stable soil microbiome (Shi et al., 2019). Additionally, the introduction of SynComs can alter the microbial network interactions, strengthening the adaptability of the soil microbiome to saline-alkali stress (Martins et al., 2023). This synergistic interaction between SynComs and native microbiota is essential for the long-term sustainability of soil health restoration efforts. 3.4 Potential for long-term soil health improvement The potential for long-term soil health improvement through the use of SynComs is promising, given their ability to provide consistent and stable benefits under various environmental conditions. SynComs are engineered to possess traits that ensure robust colonization and persistence in the soil, which is crucial for maintaining their
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