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

摘要

Napier grass (Pennisetum purpureum) is known as a species with high productivity of biomass and high water use efficiency. In this study, the water transport and leaf photosynthesis of the species was studied using cv. Merkeron grown in different environments. Differences in photosynthesis and transpiration were measured directly after excision of various plant parts. During the measuring of rates of leaf photosynthesis (Pn) and transpiration (Tr), the excision of a lower part of the leaf blade caused the rates to rise temporarily, and especially large increases were observed in leaves subjected to drought stresses. The rise of Pn depended on the increases in stomatal and mesophyll conductances. No responses in Pn and Tr were detected by excisingany parts of plant below the sheath joint of the measuring leaf, but excision of the leaf sheath caused increases in both rates. It is suggested that the leaf sheath joint may have a role in controlling or preventing transpiration. Contrary to this, in shade-grown plants the photosynthetic and transpiration rates were increased by rhizome excision. Napier grass is considered to have a high sensitivity to water movement within the plant and a unique morphological mechanism to conserve the use of water.