Bt Research 2024, Vol.15, No.1, 30-41 http://microbescipublisher.com/index.php/bt 32 3.2 Soil health and microbial activity The impact of Bt transgenic crops on soil health and microbial activity has been extensively studied. Bt crops have been found to affect soil enzyme activity and microbial community structure to some extent (Figure 1). Although most studies have found these effects to be temporary and inconsistent, a few have recorded significant impacts, particularly under long-term cultivation conditions. The residues of Bt crops have notably affected soil microorganisms, necessitating further research to assess their long-term ecological impacts (Li et al., 2022; Lebedev et al., 2022). Studies on the soil incubation of Cry1Ac protein have shown no adverse effects on soil microbial communities, with no significant changes in the diversity and population of bacteria, fungi, and archaea within 100 days (Zhao et al., 2018). A global meta-analysis of soil enzyme activity found that certain enzymes, such as dehydrogenase and urease, increased in activity under Bt crop cultivation, while others, such as neutral phosphatase, decreased. The response ratio of soil enzymes was greater with the incorporation of Bt residues than without (Li et al., 2019). Figure 1 Potential impact of transgenic plants on soil quality indicators (Adopted from Lebedev et al., 2022) Figure 1 from Lebedev et al. (2022) illustrates the potential impacts of transgenic plants on soil quality indicators. The figure emphasizes how root exudates and plant residues from Bt crops can alter soil microbial communities and enzyme activity. It highlights the complexity of soil-plant interactions, showing that changes in soil enzyme activity and microbial biomass are influenced by various biotic and abiotic factors. This detailed description aids in understanding the multifaceted impacts of Bt crops on soil health, stressing the need for integrated management practices to mitigate any adverse effects on soil ecosystems. 3.3 Non-target organisms The potential effects of Bt crops on non-target organisms, including beneficial insects and soil organisms, have been a major focus of biosafety assessments. A comprehensive review of 76 articles on non-target plant-associated insects and soil organisms found no significant harmful impacts from approved GM events, although critical risk assessments are still recommended before commercialization (Yaqoob et al., 2016). Additionally, studies on the rhizosphere of transgenic rice indicated no significant changes in the population and activity of soil organisms such as bacteria, fungi, and nematodes, nor in the physicochemical properties of the soil (Sahoo et al., 2015). These results are supported by findings that Bt crops do not significantly alter the microbial communities in the
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