Characterization of Carbon Assimilation Rate, Stomatal Conductance and Transpiration Rate for Eight Proteaceae Species

To gather some data adaptable for the cultivation of Proteaceae in southwestern Japan, the leafgas exchange characteristics of the potted plants were monitored under artificial light and natural environmental conditions. Under artificial light, photosynthetic measurements of 1-year-old seedlings of Banksia speciosa, Protea compacta, P. cynaroides, P. longifolia, P. macrocephala, P. neriifolia, P. repens, and Telopea speciosissima revealed that B. speciosa had the highest assimilation rate (8.81μmol·m-2·sec-1), while T. speciosissima had the lowest (1.39μmol·m-2·sec-1) with a chlorophyll content of 317.66 mg·m-2. The seasonal and diurnal patterns in carbon assimilation under field conditions from May 1998 to April 1999 were obtained for B. speciosa, P. compacta, P. cynaroides, P. macrocephala, and T. speciosissima. Seasonal trends in the assimilation rate (Anet) varied substantially among the species, but they can be divided into 3 types : 1) A decline in the assimilation rate in summer and winter and an increase in spring and autumn (B. speciosa and P. macrocephala), 2) a decline in the assimilation rate in winter and an increase in summer and autumn (P. compacta and T. speciosissima juvenile and mature) and 3) a small fluctuating assimilation rate throughout the year (P. cynaroides). A decrease in dark respiration occurred in all species in summer. Small differences were observed in the diurnal gas exchange patterns between autumn (November 1998) and spring (April 1999). In autumn, the diurnal curve was similar for all species, with a peak around 09 : 00-10 : 00 for each physiological parameter. A significant linear relationship exists between the assimilation rate and the natural log-transformed values of stomatal conductance. B. speciosa exhibited a steeper slope than did the other species, suggesting that additional factors besides stomatal conductance are involved in causing this more efficient carbon gain.