The near-zero-magnetic field alters microbial community structure and ecological functions in mangroves

The geomagnetic field is a fundamental environmental factor, yet the effects of its absence-termed the near-zero-magnetic field (NZMF) on microbial communities and associated ecological functions remain poorly understood. To address this, we conducted for the first time a 30-day NZMF incubation experiment using sediments and three microorganisms isolated from mangrove ecosystems. They were exposed to two magnetic conditions: the natural geomagnetic field and a near-zero-magnetic field (<3 nT), achieved using a specially designed magnetic shielding device. We analyzed the changes in microbial community composition, co-occurrence networks, and ecological functions. Our findings showed that while the overall prokaryotic and eukaryotic microbial diversity remained unaffected, NZMF exposure significantly stimulated the growth of specific taxa such as Geobacter and methanogenic archaea. Microbial co-occurrence networks revealed a reduction in inter-taxa connections under NZMF. Furthermore, NZMF significantly altered the activity of key biogeochemical enzymes, reducing the content of available potassium and organic matter, and suppressing xylosidase activity, while enhancing the activity of leucine aminopeptidase and urease. Together, these results demonstrated that NZMF could reshape microbial community structure and key ecological functions, despite minimal shifts in overall diversity. These findings highlight the importance of geomagnetic fields as an underappreciated environmental factor and underscore the need for further research into the biogeochemical and biological implications of magnetic field variations.