Soil Fauna Accelerate Litter Decomposition of Cry1Ac Transgenic Maize Independently of Microbial α-Diversity: A Multi-Year, Multi-Region Field Study

The return of Bt transgenic maize litter to farmland may affect soil fauna and litter decomposition. From 2015 to 2018, we carried out a multi-year, multi-region litterbag experiment in three major maize-growing regions of China using Cry1Ac transgenic maize Bt-799 and its non-transgenic hybrid. We used litterbags with mesh sizes of 5, 2, and 0.02 mm to control soil fauna access. Soil fauna communities and litter decomposition rates were examined in all regions, and bacterial and fungal communities were additionally examined in the third year at Gongzhuling. The results showed that the introduction of Bt gene had no significant effect on soil fauna community composition, microbial α-diversity, or litter decomposition. Decomposition rates were significantly higher in large- and medium-mesh litterbags than in small-mesh litterbags across all regions and years, demonstrating that soil fauna substantially accelerated litter decomposition. Soil fauna abundance was significantly positively correlated with decomposition rate (r = 0.847, p < 0.001), whereas maize variety and microbial α-diversity indices showed no significant correlation. These findings indicate that soil fauna promote litter decomposition of Cry1Ac transgenic maize, with no detectable association with microbial α-diversity, and that the Bt gene has no detectable effect on the measured soil biological processes.