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The isotopic ratio of
13
C to
12
C in plant tissue is less than the isotopic ratio of
13
C to
12
C in the
atmosphere, indicating that plants discriminate against
13
C during photosynthesis. Variation in
discrimination against
13
C during photosynthesis is due to both stomatal limitations and enzymatic
processes. Carbon isotope discrimination provides an integrated measure of water-use efficiency,
samples are easily collected, and processed, and large numbers of samples may be collected in
diverse environments.
Stomata play an important role in both the CO2 assimilation and water relations of trees. Therefore,
stomatal traits have been suggested as criteria for selection of clones or genotypes which are more
productive and have larger water-use efficiency (WUE) than others.
Both CO2 uptake and water losses are affected by stomatal dimensions and aperture. Consequently,
stomatal traits such as stomatal density, length and responsiveness are considered key determinants
of plant growth and water balance.
In this work we are trying to analyse the stomatal number and usage of l2C and l3C carbon from
environment in 15 different accessions of Urginea indica and Urginea wightii. This work can help us
to distinguish the Urginea indica and U.wightii accessions that are more mesophytic and tend to
develop xerophytic characteristics.
In most of the dry land accessions or rock and hilly environment habituated accessions of U.indica
showed low values of 13C and their water usage is also less in them showing low stomatal numbets,
indicating low utilisation of 13C which is a tendency of dry land or xerophytic adaptation or C-4
pathway.
In those Urginea accessions that grow with moderate and more water ( high rainfall) have more
number of stomata and the values of 13C is high. This is an indication of mesophytic habitat
because it shows the tendency towards C -3 plants.
Key words: Carbon discrimination, Water use efficiency ( WUE), C-4 pathway, Urginea indica , Urginia wightii