Effect of pattern of water supply on Vicia faba L. 3. Plant water relations, expansive growth and stomatal reactions.

Abstract

Faba beans cv. Minica, Wierboon, Kristall, Felix, Optica and Alfred grown in the field in the Netherlands were irrigated to near field capacity, or water stressed, between the onset of flowering and the end of the growing season. Leaf water potential ( psi ), osmotic potential ( pi ) and turgor (P) were linearly related to leaf relative water content (RWC) with no significant differences between cultivars. At full turgor, pi hardly differed between water supply treatments, and the slopes of pi vs. RWC were not significantly different between treatments, indicating the absence of osmotic adjustment. Water supply did not affect the slope of P vs. RWC, and it was concluded that the faba bean cultivars lacked mechanisms to keep P high during water stress. Internode growth during flowering was 2-3 times greater in the well watered than in the stressed treatment. In greenhouse studies with cv. Minica, vegetative growth decreased linearly with decreasing P. Maximum stomatal conductance in the field decreased with psi from an estimated maximum level of 1.0 s/cm (at full turgidity and light intensity >800 micro E/msuperscript 2 per s), following a negative exponential curve. It was concluded that vegetative (expansive) growth decreases faster with decreasing P or psi than the stomatal conductance (and most probably faster than the rate of photosynthesis). It is suggested that this result may help to explain the positive effect of mild water stress on reproductive growth in faba beans. (Abstract retrieved from CAB Abstracts by CABI’s permission)