Measuring plant water use: What does the phytometer method determine? In hydrological investigations, the phytometer (potted-plant) method is typically used to measure which component of the hydrologic cycle?

Introduction / Context:
Separating evaporation and transpiration is important for water balance studies, irrigation planning, and ecohydrology. The phytometer, which uses living plants in controlled containers, provides a direct way to quantify plant water use.

Given Data / Assumptions:

• Plants are grown in pots (lysimeters or phytometers) with known soil and drainage conditions.
• Weight or volume changes reflect water consumption by plants, after accounting for precipitation and percolation.
• Environmental factors (radiation, humidity, wind) are recorded to interpret results.

Concept / Approach:

Transpiration is the flux of water vapor from plant stomata. In a phytometer, changes in mass (or water balance) over time indicate the water transpired by the plant. With proper controls (bare-soil pots), researchers may also separate soil evaporation to estimate evapotranspiration partitioning.

Step-by-Step Solution:

Verification / Alternative check:

Comparisons with porometer or sap-flow techniques often align in trends, validating the phytometer as a classical method for transpiration quantification.

Why Other Options Are Wrong:

• Interception: Measured with canopy collectors or throughfall gauges, not phytometers.
• Evaporation from open water: Determined by pan evaporimeters or energy balance over water bodies.
• Infiltration capacity: Estimated with infiltrometers or infiltration tests in soil.
• None of these: Incorrect because phytometers target plant transpiration.

Common Pitfalls:

• Neglecting drainage or percolation losses, which biases transpiration estimates.
• Failing to use bare-soil control pots to separate soil evaporation from plant transpiration.

Final Answer:

Transpiration from vegetation.