A consideration of the water transport status in napier grass (Pennisetum purpureum Schumach.) based on the temporary rises in leaf photosynthesis and transpiration by plants excision

Napier grass (Pennisetum purpureum Schumach.) is known as a species with hi gh productivity of biomass and high water use efficiency. In this study, th e water transport and leaf photosynthesis of the species, using plants (var . Merkeron) grown in different environments, were discussed on the bases of photosynthetic and transpiratory responses measured directly after excisio ns of various parts of plants. During the measuring of rates of leaf photos ynthesis (Pn) and transpiration (Tr), the excision of a lower part of the l eaf blade allowed the rates to rise temporarily, and especially large incre ases were observed in leaves subjected to drought stresses. The rise of Pn depended on the increases in stomatal and mesophyll conductances. No respon ses in Pn and Tr were detected by excising any parts of plant below the she ath joint of the measuring leaf, but excision of the leaf sheath caused inc reases in both rates. Such parts as the leaf sheath joint seem to have a ro le in controlling or preventing water stream in a plant. Contrary to this, in shade-grown plants the rates increased by rhizome excision. Napier grass is considered to have a high sensitivity to water movement in a plant and a unique morphological mechanism to conserve the use of water.