Photosynthetic characteristics and water use efficiency of three coastal dune plants

To clarify the ecophysiological characteristics of plants growing on a coastal dune, net photosynthetic rate (Pn) and leaf conductance (g1) of three perennial species in Japanese coastal regions,Ischaemum anthephoroides (C₄),Carex kobomugi (C₃) andCalystegia soldanella (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 μll⁻¹ intercellular CO₂ concentration (C ₁), and itsPn was not light-saturated at a high photosynthetically active photon flux density (PPFD) of 1000 μmol m⁻²s⁻¹. This C₄ species showed a high optimal leaf temperature forPn (35°C) and a lowg1 (0.1 mol H₂O m⁻²s⁻¹), permitting maintenance of the highest water use efficiency (WUE, the ratio ofPn to transpiration rate (Tr)) in the field among the three species. At light saturation,C. soldanella had the lowestPn andg1 and a similar carboxylation efficiency related toC ₁ (Pn/C₁ ratio) asCarex kobomugi. Calystegia soldanella also had a high optimal temperature forPn (30°C), and achieved higherWUE thanCarex kobomugi, as a result of efficient stomatal regulation. In contrast, at the optimum temperatureC. kobomugi had a highPn comparable toI. anthephoroides due to a highg1 of 0.3 mol H₂O m⁻²s⁻¹, but with high temperature treatmentsPn andg1 were significantly decreased.C. kobomugi always had the lowestWUE among the three species in the field. It is therefore clear thatI. anthephoroides is a heat-resistant species,Calystegia soldanella is a heat-enduring species andCarex kobomugi is a heat-evading species due to its eraly phenology.