Water Transport in Impaired Leaf Vein Systems

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Abstract
The subject of our investigation was the water regime of broad bean leaves (Vicia faba L.), especially after having mechanically severed parts of the leaf blade and the leaf venation. Under moderate conditions, 18 ‐ 22 °C temperature and 50 ‐ 70 % relative humidity, the leaves remained viable even after extensive damage. Only if more than 90 % of the xylem cross sectional area of a leaf was severed, the leaf wilted. Lesser damage to the xylem cross‐sectional area only resulted in a reduced rate of transpiration and assimilation, compared to intact leaves. The cuts in larger veins were bypassed into small or even very small veins, as shown by xylem transport of dyes. In intact leaves, small veins have a negligible task in long‐distance transport. Here, however, transport velocity in small veins was severalfold increased compared to the measurement of transport velocity in veins of the same size in intact leaves. Thereby, water transport to leaf areas distal from the cut was ensured.

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