Growth Characteristics and Physiological Responses of Soybean (Glycine max L.) under Excessive Soil Moisture Stress

Due to global climate change and poor drainage soil characteristic in paddy fields, soybeans which are one of main upland crops in Korea are prone to get stressed by excessive soil moisture during cultivation. Excessive soil moisture stress causes poor growth, yield loss, and disease to soybeans. In order to prevent damages by excessive soil moisture stress, it is important to understand responses of soybeans under excessive soil moisture condition. Therefore, this study investigated morphological and physiological responses of soybeans by excessive soil moisture at various growth stages; V2, R1, R3, R5 and whole growing period. Soybeans were planted and characteristics of photosynthesis, chlorophyll fluorescence and 1-Aminocyclopropane-1-carboxilic acid (ACC) were measured from leaves after excessive soil moisture treatment. After harvest, growth and yield components were measured. As a result, soybean showed the smallest stalk height from soybeans which had excessive soil moisture at V2 and whole growing period. On the other hand, the greatest yield loss occurred when excessive soil moisture applied at R5, while the smallest at R2 and whole growing period. Soybean leaves showed the smallest photosynthetic rate and stomatal conductance under excessive soil moisture condition. These decline continued at least 1 week and restored to the values of photosynthetic rate and stomatal conductance from soybeans with no stress. Soybeans under excessive soil moisture exhibited greater ACC values than one of no stress. These increment of ACC continued 2 weeks and diminished. Soybeans treated with excessive soil moisture at V2, R1, R3 and whole growing period had decrease in photosynthetic rate and increase in ACC values. These results can indicate that changes of ACC contents in soybean leaves may be used as indicator of excessive soil moisture stress.