Leaf Water Potential: Comparison of Pressure Chamber and in situ Hygrometer on Five Herbaceous Species1

Abstract

Leaf water potential was measured on the same leaf with an in situ dewpoint hygrometer of the Neumann‐Thurtell design and with a pressure chamber, for potato (Solarium tuberosum ‘Russet Burbank’), sunflower (Helianthus annuus ‘Russian Mammoth’), pepper (Capsicum annuum ‘California Wonder’), soybean (Glycine max ‘Wells’), and oat (Avena sativa ‘Lodi’). On the average the pressure chamber measurement was within 1.5 bars of the in situ potential, although the scatter in the data was large. The comparisons showed a trend in which the pressure chamber gave lower (drier) leaf water potentials than the hygrometer in the high (wet) potential range, and higher potentials than the hygrometer in the dry potential range. This trend was most distinct in sunflowers, soybeans, and oats. Serious error in the pressure chamber measurement can result if evaporative loss of leaf water is not prevented before and during pressurization or if leaves are stored for an extended period between excision and pressurization.