Quantitative analysis of the isoflavone content and biological growth of soybean (Glycine max L.) at elevated temperature, CO2 level and N application
Authors: Kim Seung‐Hyun , Jung Woo‐Suk , Ahn Joung‐Kuk , Kim Jin‐Ae , Chung Ill‐Min 
Published: August 2005

Effects of ambient and elevated CO2 levels (360 and 650 µmol mol−1 respectively), ambient and high (5 °C above ambient) temperatures and their interactions with N application on soybean (Glycine max L.) were studied in 2001. Overall, total isoflavones in whole soybean seeds were highest (1383.0 µg g−1) in the elevated CO2 (AE) treatment without N application and lowest (414.1 µg g−1) in the elevated temperature (EA) treatment with N application. Malonylgenistin (449.2 µg g−1) and malonyldaidzin (435.9 µg g−1) concentrations in the AE treatment without N application were highest among the 12 individual isoflavones, while aglycon and acetyl conjugates showed lower concentrations (below 10 µg g−1) than glucoside and malonyl conjugates in all treatments. Overall, N application had no effect on total isoflavone concentration, while both temperature and CO2 level had a higher effect on increasing isoflavones, including aglycon and acetyl conjugates (P = 0.001). In the biological growth analysis, total dry weight was highest (100.9 g) in the elevated temperature and CO2 (EE) treatment with N application, while leaf area was more affected by CO2 than by temperature and increased with N application. There were larger numbers of pods (99) and seeds (176) per plant in the EE treatment with N application, and generally the AE treatment showed a greater increase in 100‐seed weight (g per 100 seeds) and in pods and seeds per plant than other treatments. Overall, total dry weight was highly affected (P = 0.001) by three main factors, temperature, CO2 and N application, but the interactions temperature × N and temperature × CO2× N did not affect total dry weight. Also, total dry weight tended to increase with increasing numbers of pods (r2 = 0.93***) and seeds (r2 = 0.93***) and larger leaf area (r2 = 0.85***). In addition, numbers of pods and seeds were significantly affected (P = 0.01–0.001) by temperature, CO2 and temperature × CO2. Generally, elevated CO2 and temperature did not affect N, P and K concentrations in the seeds but did decrease the concentrations of Ca and Mg, which were increased in the AE treatment. Among the nutrients, Ca and Mg were highly correlated with temperature and CO2 level. N concentration in the seeds increased with applied N and in particular showed a high increase with elevated temperature and ambient CO2 (EA treatment). The variation in isoflavones was correlated with temperature (r2 = −0.70**) and CO2 (r2 = 0.67**), while N application was not correlated with isoflavone concentration. Also, Ca (r2 = −0.85***) and Mg (r2 = −0.57*) in the seeds were correlated with variation in isoflavones. This indicated that isoflavones were in higher concentrations under conditions of low temperature and increasing CO2, which also resulted in low Ca and Mg concentrations in the seeds. The results of this study suggest that the long‐term adaptation of the soybean to growth at elevated CO2 level and high temperature might potentially increase its isoflavone content, growth and yield. Copyright © 2005 Society of Chemical Industry