Comparison of Growth Feature and Drought Tolerance between Two High Productive Species,Kenaf (Hibicus cannabinus, C3-plant) and Napiergrass (Pennisetum purpureum, C4-plant)

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Kenaf(Hibicus Cannabibus) and napiergrass (Pennisetum purpureum) are known as C3- and C4-plant species with a high biomass productivity and drought tolerance, respectively. Their growth features and photosynthetic responces to mild and severe drought treatments were investigated in pot cultivations. The results obtained were as follows: 1) The biomass production of kenaf was large, almost similar to that of napiegrass. THe CO2 exchange rate (CER) and stomatal conductance (Gs) of kenaf were high and stable during the sunshine time, while those parameters of napiegrass had a decreasing tendency toward the afternoon. 2) CER, Gs and mesophyll conductance (Gm) in both species were depressed ni the drought treatments. C4-plants are known to have a high tolerance to droughts, but here in kenaf, CER showed a less depression compared to the drought treatments ans its recovery was incomplete. 3) The drought treatnent did not strongly affected the maximum quantum yields in photosystem Ⅱ(Fv/Fm) in both species, but had a significant effect on the quantum yield (Φe) in the stable photosynthetic condition. The depression of Φe was singificantly larger in napiegrass, and its recovery by re-watering was poor. The high tolerability and quick recovely in kenaf is presumed to depend on photorespiration, by which the excessive in leaves was effectively disspirated to prptect the photosynthetic apparatus.
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