# Effects of Different Planting Environments on the Fragrance of _Dalixiang_ (_Oryza sativa_ L.)
## 1 Introduction  
Rice is a staple food for nearly one-third of the global population. With consumers' ever-increasing demands for rice quality, fragrant rice has been gradually gaining popularity in the worldwide rice trading market. Typically, its price is approximately twice that of ordinary rice [1, 2]. Research indicates that 2-acetyl-1-pyrroline (2 AP) is the primary compound conferring fragrance to rice [2, 3]. [PERSON] et al. [4] have demonstrated that when thebetaine aldehyde dehydrogenase gene (_OsBadh2_) mutates, resulting in a non-functional truncated betaine aldehyde dehydrogenase (BADH2) protein, \(\gamma\)-aminobutyraldehyde (GAB-ald) cannot be converted into \(\gamma\)-aminobutyric acid (GABA). Instead, it spontaneously cyclizes to form delta1-pyrroline, which then gives rise to 2 AP through a series of reactions. Moreover, methylglyoxal (MG), another key substrate in 2 AP biosynthesis, is generated during the process where the enzyme encoded by the triose phosphate isomerase gene (_OsTPI_) catalyzes the conversion of glycerol-3-phosphate to dihydroxyacetone phosphate. MG provides an acetyl group to react with delta1-pyrroline via acetylation to form 2 AP [5; 6]. Meanwhile, the glycerol-3-phosphate dehydrogenase gene (_OsGAPDH_), its corresponding enzyme, and pyruvate are also significantly associated with the biosynthesis of MG [5]. [PERSON] et al. [7] and [PERSON] et al. [8] have further discovered that proline, ornithine, and glutamic acid likely act as crucial precursor substances in the 2 AP biosynthesis pathway. Through the catalysis of the respective enzymes encoded by the proline dehydrogenase (_OsProDH_), ornithine aminotransferase (_OsOAT_), and delta1-pyrroline-5-carboxylic acid synthetase (_OsP5 CS_) genes, they are transformed into delta1-pyrroline-5-carboxylic acid (P5C), which is then further converted into 2 AP. Apart from genetic factors, the fragrance of fragrant rice is also influenced by cultivation environment, farming practices, and fertilization methods. [PERSON] et al. [9] have found that in regions with low precipitation, the 2 AP content in the grains of fragrant rice cultivars increases significantly, thereby enhancing the fragrance. [PERSON] et al. [10] have also reported that the 2 AP content in fragrant rice grown at high altitudes is relatively high. Within a certain range, higher levels of nitrogen, total potassium, available potassium, zinc, total phosphorus, available phosphorus, and organic matter in soil nutrients can effectively boost the 2 AP content in fragrant rice, thus enhancing its aroma [11; 12; 13; 14]. Soil nutrients exert a significant regulatory effect on the synthesis of 2-acetyl-1-pyrroline (2 AP) in rice. The accumulation of 2 AP in rice is comprehensively affected by key nutrients such as nitrogen, phosphorus, and potassium, as well as soil moisture conditions. Studies suggest that an appropriate amount of nitrogen fertilizer can promote 2 AP synthesis, yet excessive nitrogen application inhibits its accumulation. This might be attributed to the enhanced protein synthesis and intensified metabolic competition induced by excessive nitrogen [15]. A proper ratio of phosphorus and potassium is equally vital. Phosphorus fertilizer plays a particularly prominent role in elevating the 2 AP content, while potassium fertilizer indirectly promotes the formation of aroma precursor substances by regulating enzyme activity [16; 17]. Additionally, there exists a positive correlation between soil organic matter content and 2 AP. Returning straw to the field or applying organic fertilizers can increase soil active organic carbon and microbial activity, accelerating the conversion of precursor substances and thus increasing the 2 AP content [18]. Trace elements such as zinc and iron also impact on the aroma synthesis pathway by participating in key enzymatic reactions [17; 18; 19]. _Dalxiang_ is a high-quality rice variety developed by the Guizhou Rice Research Institute through indica-japonic hybridization.