To calculate the transpiration of plants, it is necessary to know the actual stomata resistance.
The stomata are active components of the plant system and react on environmental impacts such as solar input, air temperature and water availability in the soil.

ENVI-met provides two methods for calculating the stomata resistance: A simple approach based on the work of Deardorff (1978) and a very sophisticated approach called A-gs model following the work of Jacobs (1994) (for exact references please refer to the papers available on the UNCONVERTED WINHELP MACRO:! ExecFile(“www.envi-met.com”)ENVI-met webpage)

The Deardorff approach scales an explicitly given maximum value of the stomata resistance with respect to the solar input and the water availability whereas the A-gs model calculates the photosynthesis rate of the plant and concludes from that to the C02 demand and finally to the state of the stomata.

We recommend the use of the A-gs model as it is more plant physiologically based than the Deardorff model.

To choose the model, use the [PLANTMODEL] section:

00: [PLANTMODEL] _____________Settings for plant model
01: Stomata res. approach (1=Deardorff, 2=A-gs)  =2
02: Background CO2 concentration [ppm]           =350

What do the lines mean?

01: Stomata res. approach (Default 2, A-gs)

Select the stomata resistance model to be used in the simulation.

02: Background CO2 concentration [ppm] (Default 350 ppm)

Sets the background CO2 concentration. Only needed for the A-gs model.
Remark: If other sources in the model are of the CO2 type, they will add up to the CO2 concentration.

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