Studies on the ecology and geographical distribution of C3 and C4 grasses. III. Geographical distribution of C3 and C4 grasses in relation to climatic conditions in Indian-subcontinent.

Abstract

In the previous papers, the authors have reported on the compositions of C3 and C4 species in the grass flora of Japan, and also in subtropical and tropical regions of South East Asia, in which we attempted to clarify the geographical distribution of C3 and C4 species with special reference to climatic conditions and altitudinal cline of the grass flora of tropical South East Asia and discussed its ecological significance. In the present study, the geographical distribution of C3 and C4 species in the grass flora of Indian subcontinent was critically investigated in relation to the climatic conditions. The results obtained are as follows : 1) A highly negative correlation exists between the percent of C4 grasses and annual rainfall in each subdivisional region in Indian subcontinent. In dry regions, however, a predominant occurrence of C4 grasses was noted, often attaining 100%. 2) Due to a relative increase of the Festucoideae grasses in the regions of Northwest-, North- and Himal-India, there occurs no conspicuous relationship between the percent of C4 grasses and annual rainfall. However, disregarding the Festucoideae, we can recognize a theoretically expected trend between the relative abundance of C4 grasses and annual rain fall. 3) The relative abundance of the species belonging to Eragrostoideae increases with decreasing annual rainfall, and/or declines drastically with increasing rainfall. Under the wet conditions with more than 1200 mm annual rainfall, the percent of Eragrostoideae species decreases to a certain low level, ca. 20%. 4) The percent of Aristida species increases with decreasing annual rainfall, and/or declines drastically with increasing rainfall. The highest subdivisional percent of Aristida species can be recognized in the Indian-desert (ca. 10%), but the lowest in the regions of South India, Ceylon and East India (ca. 1%). 5) The percent of the Panicoideae increases in response to the increase in annual rainfall with favourable temperature regime, but seems to attain a saturated level under the conditions with more than 1200 mm annual rainfall. 6) The relative abundance of C3 species belonging to the subfamily Bambusoideae, Oryzoideae and Arundionoideae is correlated most highly with annual rainfall. 7) The relative abundance of C4 grasses in the grass flora of a certain region is determined directly by the number of C4 species present in that region under consideration, but also indirectly by the number of total C3 species present there.