## 3 Results and Discussion
### Determination of Microbial Community Structure
Among the storage conditions under quasi-low temperature, horizontal ventilation, and nitrogen gas atmosphere and normal temperature, vertical ventilation, and nitrogen gas atmosphere, the relative abundance of _Aspergillus_ was relatively high, the values of which were 7.81% and 16.02%. Therefore, the highest mycotoxins in rice grains stored under normal temperature, vertical ventilation, and nitrogen gas atmosphere may be due to the highest relative abundance of _Aspergillus_. The quality of rice is affected by some toxigenic fungi such as _Penicillium_, _Aspergillus_, _Fusarium_, and _Alternaria_[54]. Among fungal genera, aflatoxin B1 produced by _Aspergillus flavus_ in _Aspergillus_ has the highest toxicity. _Aspergillus flavus_ can produce aflatoxin B1, which has strong carcinogenicity and teratogenicity and seriouslyaffects the health and safety of mammals [55]. Meanwhile, rice infected by _Aspergillus flavus_ is common, which will cause dry matter loss and quality deterioration. This may also be the reason for the low content of starch and protein composition in rice grains stored under normal temperature, vertical ventilation, and nitrogen gas atmosphere. In addition, environmental factors such as temperature, humidity, etc., play determinate roles in the growth of fungi. In the three storage conditions, the relative abundance of _Aspergillus_ (1.64%) and _Penicillium_ (0.01%) is the lowest in rice grains stored under the condition of normal temperature, horizontal ventilation, and nitrogen gas atmosphere. It was indicated that horizontal ventilation could lower the temperature more than vertical ventilation, thereby inhibiting the growth of harmful fungal generally. The temperature and humidity changes in horizontal ventilation are faster than that in vertical ventilation with a better cooling effect [56]. Therefore, horizontal ventilation should be preferred in the actual storage of rice grains. Figure 3: Bacterial and fungal community structures of rice grain samples in different storage environments. The Chao 1 index and Shannon index of bacteria (**A**) and fungi (**B**). Principal coordinates analysis (PCoA) of the bacterial (**C**) and fungal community (**D**) based on Bray–Curtis distance. Relative abundance of bacteria (**E**) and fungi (**F**). RA: room temperature, horizontal ventilation, nitrogen gas atmosphere; RB: room temperature, vertical ventilation, nitrogen gas atmosphere; RC: quasi-low temperature, horizontal ventilation, nitrogen gas atmosphere. To investigate the similarities and differences in microbial communities among rice grains stored under three different conditions, Venn diagrams were constructed (Figure 4A,B). The Venn diagrams showed that the number of shared bacterial ASVs in the three storage conditions was 424 and the common fungal ASVs in the three storage conditions was 141. The rice grains stored under the condition of normal temperature, horizontal ventilation, and nitrogen gas atmosphere contained the most unique ASVs in the bacterial community, which included 1901 ASVs. The rice grains stored under the condition of normal temperature, vertical ventilation, and nitrogen gas atmosphere contained the most unique ASVs in the fungal community, which included 550 ASVs. The common and unique representative genera of rice grains under the three storage conditions were detected (Figure 4A,B). The unique genera of rice grains stored under the condition of normal temperature, vertical ventilation, and nitrogen gas atmosphere were the greatest, with their unique bacterial genera including _Steptomyces, Pseudorhodolanes,_ etc., and their unique fungal genera including _Pencilillium, Stemplyilium_, etc. (Figure A3). It was suggested that the storage condition of normal temperature, vertical ventilation, and nitrogen gas atmosphere was more suitable for microbial growth.