Visual estimation of leaf water stress inMercurialis perennis L.

Leaf inclination of three upper leaf pairs of a plant was used as a visual parameter for estimation of leaf (plant) water status inM. perennis. Negative correlation was found between leaf angle and leaf water saturation deficit (WSD). Large angles (between 130 and 80–90°) indicated WSD below approx. 12%, narrow angles expressed negative water balance of the plant and indicated usually strong or moderate water stress. The correlation may be expressed by two regression lines differing in slope. Some differences were observed between three leaf pairs investigated: At the same water deficits, leaves of the first pair (from apex) were inclined to a less degree than leaves of the other two leaf pairs. Leaves of the third pair wilted the most rapidly, therefore their WSD were highest at moderate and strong water stress of the plant. The approximation method tested is suitable for judgment of the plant water status inM. ptrennis and may be used in ecological investigations in forest ecosystems.