## 4 Discussion
Additionally, heightened CO\({}_{2}\) levels can activate aerobic respiration to eliminate surplus CO\({}_{2}\), potentially enhancing ATP production and the generation of respiratory metabolites. When analyzing the relationship between differential metabolites and differentially expressed genes, we found that for the same metabolite, multiple genes had significant positive and negative correlations; these genes with positive and negative regulatory relationships may have some regulatory relationship between them, which would require further research to confirm. Furthermore, the same gene can also regulate different metabolites. The genes TRINITY_DN8959_c0_g4 and TRINITY_DN8383_c0_g1 had significant correlations with D-xylitol, guanosine, and 3-hydroxybutyric acid, 4-[(E)-2-(3,5-dimethylphenyl)]ether]phenol, methylsuccinic acid, and succinic acid but had negative correlations with folic acid and polyphobilinogen. Interestingly, the metabolites D-xylitol, guanosine, and 3-hydroxybutyric acid, had the same genes (none of these genes had annotated information) associated with them. 3-hydroxybutyrate (3-HB), as a very important metabolite, is found in animals, bacteria, and plants. It is well known that in animals, 3-HB is formed as a product of the normal metabolism of fatty acid oxidation and can therefore be used as an energy source in the absence of sufficient blood glucose. In microorganisms, 3-HB mainly serves as a substrate for the synthesis of polyhydroxybutyrate (PHB), which is a reserve material [57]. However, some fungi have shown the ability to cause PHB degradation [58]. Recent studies have shown that in plants, 3-HB acts as a regulatory molecule that most likely influences the expression of genes involved in DNA methylation, thereby altering DNA methylation levels. Additionally, in animals, 3-HB is not only an intermediate metabolite but also an important regulatory molecule that can influence gene expression, lipid metabolism, neuronal function, and overall metabolic rate [59]. The significant increase in the content of pyruvate acid and methylglutaric suggests that the synthesis of terpenoids in Caoyuanheimo-1 (_Agaricus_ sp.) may be related to the accumulation of these two substances. Terpenoids in fungi are generally synthesized in the mevalonate pathway (MVA) [60; 61]. Some studies have indicated that the composition of triterpenes contents changes during the fruiting of _Ganoderma lucidum_ and that triterpene is synthesized based on acetyl CoA from central carbohydrate catabolism [62]. The MVA is the synthesis of isoprene pyrophosphate and dimethylallyl pyrophosphate from acetyl CoA in eukaryotes. These two conclusions do not contradict each other. The content of 11 terpenids also consistently increased as the fruiting body matured. Therefore, triterpenes may be associated with the fructification of edible mushrooms [63]. Two types of terpenoids had lower contents in the young period compared with the primordium period. These two types of terpenoids may be metabolized during the young fruiting period and may be involved in the growth and development process. Three terpenoids also had the lowest contents during the ripe fruiting period, which was also observed in _Ganoderma lucidum_[62], indicating that all three terpenoids may be synthesized or metabolized throughout the entire growth and development process; this lays the foundation for the excavation of terpenoids in fungal mycelia. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/horticulturalvae10050469/s1](https://www.mdpi.com/article/10.3390/horticulturalvae10050469/s1)]([https://www.mdpi.com/article/10.3390/horticulturalvae10050469/s1](https://www.mdpi.com/article/10.3390/horticulturalvae10050469/s1)); Figure S1. Metabolome PCA analysis of HY and HZ (a), HY and HC (b), and HZ and HC (c). Figure S2. Statistics for the transcripts and unigenes in the transcriptome data. Figure S3. Transcriptome PCA analysis of HY, HZ, and HC. Figure S4.