Relations between Photosynthetic Rate during Low Temperature Period and Over-wintering in Tropical Grasses.

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In order to obtain fundamental informations for improving the over-wintering abilities of tropical grasses in southern regions of Japan, some investigations were done. Results obtained were summarized as follows. The patterns of the time course changes of population photosynthetic abilities during the period from October to next April were different among 8 grass species from the genus of Panicum, Pennisetum and Setaria. However, the species differences in the levels or patterns of changes of photosynthetic ability during the period before March were not definitely related to the species differences in the photosynthetic abilities at the early period of spring regrowth which commenced at eraly march.In Dallisgrass and Bahiagrass, the plant photosynthetic ability at the early period of spring regrowth was clearly related to the degree of suppression of photosynthetic rate by shading or defoliation during autumn or winter. The more intense the suppression, the lower was the photosynthetic ability at spring. In Rhodesgrass and Makarikarigrasss, however, such relations as seen in the former two grasses, were not observed. In comprison to the latter two grasses, the percentage of the numbers of tillers surviving throughout the winter, was higher in the formers. From these facts, it was infered that the amount of reserve materials, previously produced mainly by photosynthesis, was more liable to limit the rate of early growth of tillers at the regrowth period in the formers than in the latters.Thus, the photosynthetic rate during the low temperature perid affected the photosynthetic ability at spring regrowth in the grasses with a high over-wintering ability, such as Dallisgrass or Bahiagrass.