Stem Water Potential Measurements Research Articles

In Situ Psychrometry For Measuring Cut Flower Water Status

Abstract Mature potted rose bushes and cut rose blooms (Rosa hybrida ‘Samantha’) were used to assess the reliability of in situ stem psychrometers for measuring the water potential of these plant systems. Concurrent measurements of adjacent leaf water potential using a pressure bomb were correlated with the psychrometer measurements. The plants were subjected to a series of drought and rehydration cycles in order to exhibit a wide range of water potential (— 0.1 to —1.8 MPa). The results closely followed a 1:1 correlation. The psychrometer installations on intact rose bush stems produced reliable measurements of stem water potential for up to 6 weeks. The technique described is a nondestructive means to monitor the water status of intact plants or cut flowers continuously in response to management practices, storage and shipping techniques, or methods to enhance keeping quality.

Hydraulic Characteristics of Mountain Ash (Eucalyptus regnans F. Muell.) Derived From in situ Measurements of Stem Water Potential

An osmotic tensiometer has been successfully used for in situ measurements of stem water potential, Ψst, in mountain ash. During spring and early summer when soils were saturated, fluctuations in Ψst, at a given height in different trees were very similar. When Ψst, values were measured at different positions around the circumference of individual trees during late summer, considerable variation between the different positions was recorded. The data at this time also suggest that night temperatures above 17°C can lead to stomatal opening, but this was not confirmed by direct measurement. Possible reasons for apparent discrepancies between leaf and stem water potential measurements are discussed. The time lag between vapour pressure deficit and Ψst was around 2 h whenΨst values were high, but fell to 10 min or less for Ψst values below about - 1.2 MPa. Analysing this time lag in terms of a resistance-capacitance model of water flow made it possible to estimate the storage-to-vessel transfer resistance as 1.7 × 107 Pa s m3 kg-1.

Measurement of Stem Water Potential of Young Plants Using a Hygrometer Attached to the Stem

A simple method was developed for the continuous non-destructive measurement of plant stem water potential. It consists of exposing a small section of stem vascular tissue and attaching to it a standard commercially available dewpoint hygrometer. Excellent agreement was found between water potential determined by this method, and that measured with a pressure-chamber on leaves covered with aluminium foil. Stem water potentials responded within minutes to changes in radiation and transpiration. Resistance to water uptake was found to be independent of the rate of transpiration.