Daily embolism and refilling of root xylem vessels in three dicotyledonous crop plants

Embolisms were observed directly in the xylem vessels of roots of field-grown buckwheat (Fagopyrum esculentum Moench.), sunflower (Helianthus annuus L.) and soybean (Glycine max (L.) Men.) by cryo-microscopy. No vessels were embolized at dawn, but in all three species some embolisms had formed by 0900 hours, The percentage of vessels embolized reached 40-60 % between 0900 and 1200 hours, then declined to near 0 % by sunset. The plants were still transpiring when embolisms were refilling. There was no correlation of percentage embolism with rate of transpiration, but a small positive correlation with balance pressure. Daily embolism and refilling of root vessels were observed previously in maize, and also appear to be a normal process in dicotyledonous crop plants. ((C) Inra/Elsevier, Paris.).