## 3 Results and Discussion
### Determination of Microbial Community Structure  
A total of 1,177,974 and 1,306,651 partial 16S rRNA and ITS rRNA gene sequences were generated from the 13 rice grain samples, respectively. To compare the richness and diversity of the microbial communities between the rice grains stored under these three storage conditions, Shannon and Chao 1 indices were investigated (Figure 3A,B). The results showed that Shannon (bacteria: 9.16 \(\pm\) 0.22, fungi: 4.00 \(\pm\) 0.78) and Chao 1 (bacteria: 2663.16 \(\pm\) 143.44, fungi: 324.58 \(\pm\) 263.57) indices of bacteria and fungi communities of the rice grains stored under the condition of normal temperature, vertical ventilation, and nitrogen gas atmosphere were highest among the three groups. It was indicated that in rice grains stored under this condition, elevated microbial activity can contribute to increased external and internal damage, as it becomes more frequent. Principal coordinate analysis (PCoA) was conducted using a Bray-Curtis distance matrix to assess the bacterial and fungal communities' similarity of rice grains stored under different conditions (Figure 3C,D). The results revealed that the microbial composition in rice grains stored under the condition of normal temperature, horizontal ventilation, and nitrogen gas atmosphere and quasi-low temperature, horizontal ventilation, and nitrogen gas atmosphere exhibited similarities, while the rice grains stored under the condition of normal temperature, vertical ventilation, and nitrogen gas atmosphere displayed distinct differences from the other two storage conditions. A total of 45 bacteria phyla and 5 fungi phyla were identified in the rice grain samples, among which Proteobacteria (average relative abundance: 52.44%), _Firmicutes_ (25.95%), _Acidobacteriota_ (5.89%), _Bacteroidota_ (4.70%), and _Actinobacteriota_ (4.64%) in bacteria and _Ascomycota_ (73.06%) and _Basidiumcyota_ (26.31%) in fungi were dominant, with relative abundance greater than 2% (Figure A4). A total of 854 bacteria genera and 368 fungal genera were detected at the genus level, which further revealed differences in the microbial composition among the three storage conditions. _Pantoea_, _Allorhizobium-Neorhizobium-Parahizobium-Rhizobium, Lactobacillus_, and _Pseudocitrobacter_ were the most dominant bacterial genera in the rice grain sample. The main genera detected from the microbial community in this study were consistent with previous studies [48]. The relative abundance of _Lactobacillus_ (20.47%) and _Alternaria_ (26.04%) was highest in the rice grains stored under the condition of normal temperature, horizontal ventilation, and nitrogen gas atmosphere compared with the other two storage conditions (Figure 3E,F). _Lactobacillus_ spp. could produce lactic acid, which is often used to ferment food and could also be used as a bacterial inoculant to produce silage and inhibit molds, _Escherichia coli_, etc. [49]. _Alternaria_ is frequently isolated from plants [50]. The highest relative abundance of _Pantoea_ (14.34%) and _Moesziomyes_ (28.72%) was detected in rice grains stored under the condition of normal temperature, vertical ventilation, and nitrogen gas atmosphere storage (Figure 3E,F). _Pantoea_ might cause leaf blight disease, which becomes a devastating problem in rice agroecosystems [51]. _Moesziomyes_ is often found to parasitize various plants without plant pathogenicity [52]. The relative abundance of _Pantoea_ (35.03%) and _Phaeosphaeria_ (31.21%) was highest in rice grains stored under quasi-low temperature, horizontal ventilation, and nitrogen gas atmosphere (Figure 3E,F). _Phaeosphaeria_ often causes leaf spot disease in tropical and subtropical maize [53]. The high relative abundance of _Pantoea_ and _Phaeosphaeria_ might cause the degradation of rice grains' quality. Although several types of microorganisms can be detected, the majority of them are harmless. Some typical filamentous fungi are mainly harmful to rice grains' quality.