# Effects of Climate Conditions before Harvest Date on Edamame Metabolome
## 3 Discussion  
Plants display a higher metabolic plasticity in response to the environment since, unlike animals, they cannot take shelter. Therefore, plants biosynthesize various metabolites in response to stress. It has been reported that environmental conditions, such as temperature and light intensity, affect the amount of metabolites in plants [25; 26; 27; 28; 29]. Most reports have focused on secondary metabolites, such as flavonoids and terpenoids; however, the effects of environmental conditions on the number of primary metabolites, such as sugars and organic acids, that are important for the quality of agricultural products, have also been investigated. The effects of temperature, ultraviolet radiation, and sunlight duration on fruit quality and composition were studied using nine strawberry varieties grown at three different altitudes [30]. They reported a correlation between the phenylpropanol amount and sunshine duration. Moreover, the pH value, which is thought to be caused by the sugar amount and organic acid amount in fruit, changes depending on the light intensity and temperature. A previous study reported that differences in light-shielding conditions in a greenhouse and a field affected the amounts of sugars, amino acids, and organic acids contained in maize [31]. However, these previous studies compared climate conditions and metabolite amounts over a long period before harvest and did not investigate the more detailed changes in climate conditions. In the present study, we focused on the weather conditions for one to nine days before harvesting. We found that minute changes in climate conditions before the harvest date affected the amount of metabolites related to the quality of agricultural products. Specifically, an accumulated sunshine duration and average temperature in the several days before harvest were positively correlated with some amino acids and negatively correlated with organic acid and the nucleotide amount in edamame (Figure 3). This may be true not only for edamame but also for other agricultural products. The quality of agricultural products varies depending on the year of harvest. In the case of wine, the year of production is important in addition to the brewery and grape variety. However, there are few studies on the annual changes in low-molecular-weight compounds contained in agricultural products. A study that examined the leaf area, leaf dry weight, plant height, and chlorophyll amount in 12 shortgrass species over a 4-year period found that these traits had a large influence depending on the year, although the detailed reason was not clarified [32]. It is also known that the sterol composition contained in dandelion leaves changes depending on the amount of sunlight and temperature [33]. A previous study aimed to evaluate the use of organic fertilizers by examining the amount of \(\delta^{15}\)N contained in tea leaves over multiple years [34]. Our comparative analysis of meteorological conditions and edamame metabolites over a 6-year period suggested that the sunshine duration and average temperature have a significant influence on the amount of some compounds in edamame (Figures 4-6). Amino acids are abundant in edamame and are involved in its flavor [9; 35; 36]. We found that the amino acid amount in edamame was affected by the sunlight duration and average temperature up to the day before harvest. Proline (Pro) has been reported to accumulate in plants in response to stresses, such as heat and drought, and it is also known that Pro application confers tolerance to these stresses in plants [37; 38; 39; 40]. In this study, the amount of Pro in edamame also increased with increases in the sunlight duration and average temperature (Tables 1 and 2). A long sunshine duration and high average temperatures can cause heat stress and drought stress to edamame plants. The edamame used in this study may also have been subjected to these stresses, depending on the conditions of sunlight duration and average temperature.