Water Stress and Leaf Growth of Field Beans (Vicia faba L.) in the Field: Leaf Number and Total Leaf Area

The leaf area growth of field beans grown under covers in the field was measured non-destructively on plants subjected to three different degrees of soil water stress by means of drying cycles of different lengths in 1974 and 1975. After a period of 46 days the total leaf area of the well-watered plants was about double that of the non-watered ones. The total leaf area at the final-sampling and the mean plant water potential during the observation period were linearly related with highly significant correlation coefficients (0·96 in 1974 and 0·86 in 1975). The differences between treatments in total leaf area were mainly produced by the mechanisms determining leaf size rather than those associated with leaf production and maintenance, namely leaf production, unfolding and death. In neither year was leaf production or unfolding sensitive to water stress before flowering. Plant water potential (ψ) exerted a cumulative long term effect on these two mechanisms. The threshold values of ψ for reducing the rates of leaf production and unfolding were more negative in the drier year (1975). Leaf death was affected by drought earlier than leaf production and unfolding.