page_title: Scholander pressure bomb
section_title: Measurements
hierarchical_section_title: Scholander pressure bomb / Measurements
caption_attribution_description: English: Another common model for pressure bombs. This model uses an analog gauge rather than digital. The top of the canister can be removed and be placed in the groove on the wooden board for sample preparation. The larger steel cylinder is designed for small stems and branches to fit as well as leaves.
context_page_description: A pressure bomb or pressure chamber or Scholander bomb is an instrument that can measure the approximate water potential of plant tissues. A leaf and petiole or stem segment is placed inside a sealed chamber. Pressurized gas is slowly added to the chamber. As the pressure increases at some point the liquid contents of the sample will be forced out of the xylem and will be visible at the cut end of the stem or petiole. The pressure that is required to do so is equal and opposite to the water potential of the sample. Pressure bombs are field portable and mechanically simple, which make them the predominant method for water potential measurements in the fields of plant physiology and ecophysiology.
context_section_description: Several water potential variables can be determined using the pressure bomb analysis.  The most common of which are predawn leaf water potential and midday leaf water potential. Measurements conducted on plants predawn are considered a good representation of the total water status of plant. As no transpiration through stomata should be occurring at night, the plant's water potentials should be in equilibrium across the entire plant and be similar to the water potential of the soil around the roots. Midday leaf water potential is less commonly used as it is more variable and does not correlate well with other physiological measurements of water status. However, midday water potentials can be used to determine times of peak water stress or diurnal changes in plant water status. Additional variables and methods that involve pressure bombs for analysis include: stem conductance, xylem embolisms, and vulnerability curves.
caption: Pressure bomb with cutting board and larger canister
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