Abstract
Information about evaporation and transpiration fluxes is vital for water budgets, modeling of water flows and climate, as well as for assessing the hydrological impact of land management practices. Under natural conditions, these fluxes are difficult to measure accurately, which results in large measurement inaccuracies. These inaccuracies can be reduced in controlled experiments. We present a device that is especially useful for transpiration studies conducted in large and/or heavy containers where weighing becomes too cumbersome or expensive. With our device we set a water table and control soil moisture of potted small trees by periodically replenishing soil water consumed by the tree, thereby measuring the inflow volume, which represent whole-tree transpiration. The device is made of inexpensive, easily available and durable materials and can be used for in- and outdoor experiments. Data acquisition is fast and easy. The mean measurement error of the device is 4.5% (±3.2% SD) for refill (i.e., transpiration) volumes of 1.5 L or larger. For a transpiring surface of 3 m², this amount is equal to an accuracy of 0.02 mm. Validation on field data showed that transpiration measured by the device is comparable to transpiration measured by gravimetric changes.
Highlights
Transpiration (T) involves the transport of soil water through plants and its subsequent loss by evaporation through their stomata
When soil water is consumed by vegetation, upward capillary flow causes a drawdown of the water level at the bottom of the container, as well as in the water supply device
We evaluated whether tree transpiration measured by the device yields comparable results as when measured with a weighing balance
Summary
Transpiration (T) involves the transport of soil water through plants and its subsequent loss by evaporation through their stomata. T together with evaporation (E) from soil (Es ) and wet vegetation canopy (interception Ei ) forms evapotranspiration (ET). ET is the driving component of earth surface-plant-atmosphere water fluxes [1]. E and T can occur simultaneously and are both controlled by solar radiation, temperature, wind velocity, and vapor pressure gradient. These factors determine the amount of energy available for vaporization and the removal of water vapor from the evaporating surface. T and E can be both limited by a lack of available soil moisture and are influenced by plant characteristics and plant density
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