On Difference between Tropical and Temperate Grasses in Photosynthetic Rate

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  • 光合成速度における寒地型牧草と暖地型牧草との差異
  • コウゴウセイ ソクド ニ オケル カンチガタ ボクソウ ト ダンチガタ ボクソ

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Abstract

This study was undertaken to investigate the difference between tropical and temperate grasses in photosynthetic rate. The photosynthesis and respiration of an attached leaf were measured in an assimilation chamber (Fig.1) under artificial light condition. The concentration of CO_2 gas in the air was surveyed at the point of entering and leaving of the chamber by means of infra-red gas analyzer. Fourteen temperate and 27 tropical species (including sorghums, corn and African millet) were used. Photosynthesis was measured under light intensities being kept 45 Klx. for temperate and 65 Klx. for tropical species and respiration was measured in darkness. Air temperatures were controlled at 20±0.5℃ for temperate and 35±0.5℃ for tropical species by passing a stream of warm or chilled water through a jaket of the chamber. The experiments were carried out during May in 1975 for temperate species and late June to July in 1976 for tropical species, respectively. The results obtained were summarized as follows. It was quite evident that photosynthetic rate differed sharply between tropical and temperate grasses, being lower in the latter. Most tropical grasses were able to reach about twice as much CO_2 assimilation as the temperate grasses. Especially, dallisgrass, makarikarigrass, green panic, vaseygrass, Rhodesgrass, bahiagrass and grain sorghum showed higher photosynthetic rates (50-55mg CO_2・dm^<-2>・hr^<-1>). Tropical grasses such as Saint Augustine grass, weeping lovegrass, carpetgrass and kikuyugrass, however, showed no more than 27-31mg CO_2・dm^<-2>・hr^<-1>, which value was almost similar to that of smooth bromegrass and tall fescue of temperate grass. From these results, it is suggested that not all of tropical grasses show a high CO_2 assimilation. A significant negative correlation was observed between photosynthetic rate and specific leaf area in temperate grasses and no correlation was found in tropical grasses. Tropical grasses which belong to Panicoideae or Eragrostoideae are superior in photosynthetic activity to temperate grasses of Festucoideae. It is assumed that the species of Panicum, Paspalum and Chloris are superior to the other genera of Panicoideae or Eragrostoideae in photosynthesis. Therefore, it may be concluded that these specific differences in photosynthetic activity are closely associated with taxonomic and evolutionary group of each grass species.

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