Gas exchange of Typha orientalis presl. communities in artificial ponds

Large field chambers were used for measuring the net carbon dioxide exchange of vigorously growing communities of Typha orientalis Presl. Uptake was greatest at the beginning of summer, when that of a community with leaf area index 6.8 reached almost 6 g CO 2 m −2 (water surface area) h −1. In a second community with LAI 4.8 maximum uptake was 3.8 g CO 2 m −2 h −1. In both communities there was a marked decline in uptake over the middle part of each day: uptake also declined quite rapidly as the communities aged. Maximum dry weight increases of 30 and 24 g m −2 24 h −1 for the 2 communities, respectively, were calculated from day-time net assimilation and night-time respiration. Measurements of maximum water loss from the first community showed a water-use efficiency of 7.86, which declined as the summer progressed. The photosynthetic performance of the Typha communities was similar to that of some well-irrigated C 3 crop plants grown in a similar climate.