GROWTH AND PHOTOSYNTHESIS OF THREE AZOLLA SPECIES IN RESPONSE TO IRRADIANCE

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Physiological studies of Azolla (azolla) species in relation to comparative responses to environment are limited. In this study, growth, carbon dioxide exchange rate (CER) and evapotranspiration (ET) were measured in Azolla caroliniana, A. microphylla and A. pinnata mats grown in a greenhouse at 100, 65, and 35% of ambient light levels. Although A. caroliniana had higher frond area index (FAI) and specific frond area, its CER per unit frond weight was significantly lower than A. microphylla and A. pinnata at a photosynthetic photon flux density (PPFD) of 300μmol m^<-2> s^<-1> probably due to mutual shading; at 1300 μmol m^<-2> s^<-1>, however, the differences in CERs among the species were not significant. At any given PPFD, CER per unit weight decreased in the order A. caroliniana>A. microphylla>A. pinnata, and with increasing biomass per unit area from 500 to 1500g m^<-2>. ET of the azolla canopy was more closely related to FAI than to CER. The results indicate that A. caroliniana, which has a lower optimun FAI than A. microphylla, needs to be more frequently harvested to maximise biomass production. Measurements on biomass mats of azolla provided realistic estimates of CER, but in in-situ measurements of ET, evaporation appeared to be a significant component at low growth light levels.
九州大学の論文