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

为了获得提高日本南部地区热带禾本科植物越冬能力的基础资料，进行了一些调查。所得结果总结如下。从10月到次年4月，黍属、狼尾草属和狗尾草属8种禾本科植物群体光合能力的时程变化规律不同。但3月以前光合能力变化的水平或格局的种间差异与3月上旬开始的春季再生初期光合能力的种间差异没有必然的联系。春返青初期植物光合能力与光合速率受抑制程度明显相关，在秋季或冬季期间遮光或落叶。抑制越强，春季光合能力越低。然而，在Rhodesgrass和Makarikarigrasss中，没有观察到在前两种草中看到的这种关系。后两种禾本科牧草的越冬分蘖数百分率均以前者为高。由此推断，在再生期，以光合作用为主的储备物质的数量，前者比后者更容易限制分蘖的早期生长速度，因此，对于越冬能力强的禾本科植物，如鸭茅和百喜草，低温期的光合速率影响其春季再生的光合能力。

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.