SAMSON, N.P. and P. DAYANANDAN.* Dept. of Botany, Madras Christian College, Tambaram, India 600059. - Photosynthetic pathways and ecology of Indian grasses.
The occurrence of C3 and three different subtypes of
C4 photosynthetic pathways in the 1,263 Indian grasses was
surveyed using a combination of taxonomic and anatomical criteria. All
species of the subfamilies Pooideae, Bambusoideae and Oryzoideae are
C3. Some arundinoid and panicoid species are C3
while others are C4. All members of Chloridoideae are
C4. The C3, NADP-ME, NAD-ME and PEP-CK pathways
occur in 536, 504, 132 and 59 species. The all-India C3:
C4 ratio is 3:4. In the high altitude Himalayan region this
ratio is 4:1 while it is 1:4 in the rest of India. Two grass Domains
are recognized: the Temperate Himalayan Domain is dominated by
C3 species, mostly pooids, while the Peninsular Domain has
mostly C4 grasses. A transitional region occurs in
north-east India. Within the C4 species NADP-ME, NAD-ME and
PEP-CK subtypes occur in 8:2:1 ratio. This ratio is characteristic of
Indian C4 grasses in a wide variety of habitats including
the ten Botanical Regions, and also among the endemic species. Cold
temperature favors growth of C3 species; aridity and
salinity promote NAD-ME species, and PEP-CK species are common in
wetlands. These findings are analyzed in relation to the origin of
Indian grass flora, phytogeography and seasonal availability of fodder
for grazing animals.
Key words: ecology, Indain grasses, photosynthetic pathways, Poaceae