TEMS variables

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Plant stomatal maximum conductance

Definition Stomatal conductance maximum is a numerical measure of the maximum rate of passage of either water vapour or carbon dioxide through the stomata, or small pores, of the plant.

Rationale The maximum stomatal conductance is a key parameter of the rate of carbon assimilation and transpiration from vegetation. It is needed for biogeochemical, hydrological and plant production modelling. It is anticipated that it will change as a consequence of elevated carbon dioxide and possibly changes in the climate. It is measured at saturating levels of sunlight, in the absence of water stress.

Users Biogeochemical modellers, and GCM and NWP modellers.

Measurement method Tiers 1-3: field measurements using standard techniques;

Tier 5: estimated using optical remote-sensing measurements.

Units of measure mole H2O/m2/sec

Frequency of measurement Once every decade.

Spatial resolution Tiers 1, 2, 3 and 4

Accuracy/precision required ± 10%

Associated measurements Leaf area, Leaf N, temperature and PAR at the time of measurement, and species composition and cover type.

Present status Stomatal conductance is a widely measured parameter using established instrumentation but it is still not globally and routinely observed.

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R and D needed None

Copyright © 2001 GTOS. Global Terrestrial Observing System ··· last updated: February 2001