To clarify the ecophysiological characteristics of plants growing on a coastal dune net photosynthetic rate (Pn) and leaf conductance (gl) of three perennial species in Japanese coastal regions, Ischaemum anthephoroides (C4), Carex kobomugi (C3) and Calystegia solclanella (C3), were compared under controlled environmental conditions and field conditions at the kado-ori coast at Ohno Village, Ibaraki. I. anthephoroides achieved photosynthetic CO2 saturation at ca. 100 micromol/mol intercellular C02 concentration (Ci), and its Pn was not light-saturated at a high photosynthetically active photon flux density (PPFD) of 1000 micromol/m2/s. This C4 species showed a high optimal leaf temperature for Pn (35 degC) and a low gl (0.1 mol H2O/m2/s), permitting maintenance of the highest water use efficiency (WUE, the ratio of Pn to transpiration rate (Tr)) in the field among the three species. At light saturation, Calystegia soldanella had the lowest Pn and gl and a similar carboxylation efficiency related to Ci (Pn/Ci ratio) as Carex kobomugi. Calystegia soldanella also had a high optimal temperature for Pn (30 degC), and achieved higher WUE than Carex kobomugi, as a result of efficient stomatal regulation. In contrast, at the optimum temperature, Carex kobomugi had a high Pn comparable to I. anthephoroides due to a high gl of 0.3 mol H2O/m2/s, but with high temperature treatments Pn and gl were significantly decreased. Carex kobomugi always had the lowest WUE among the three species in the field. It is therefore clear that I. anthephoroides is a heat-resistant species, Calystegia soldanella is a heat-enduring species and Carex kobomugi is a heat-evading species due to its early phenology.

Key words : Coastal dune plants ; Leaf conductance; Net photosynthetic rate; Temperature; Water use efficiency.