Optimal root oxygen release from two macrophytes Saururus cernuus L. and Pistia stratiotes L. varies with light and temperature in simulated constructed wetlands microcosms

Abstract

Different environmental factors influence photosynthesis, transpiration, stomatal conductance, and oxygen released from macrophytes' roots. We measured several physiological parameters of Saururus cernuus L. (Lizard's Tail) and Pistia stratiotes L. (Water Cabbage) by exposing the plants to various controlled environmental conditions. The oxygen released from the plant roots was also used to treat the chemical and biological oxygen demand in wastewater in microcosms. This work determined that photosynthetic rate and oxygen release were dependent not only on the plant species but also on the light intensity exposed. The highest rate of photosynthesis differed considerably between the two plants, as S. cernuus required more light intensity than P. stratiotes. Maximum root oxygen release was at peak photosynthesis, thus correlated with light intensity. The temperature had an effect on stomatal conductance, photosynthesis rate, and transpiration rate was affected by the wind speed. For the highest stomatal conductance and photosynthesis, P. stratiotes required a higher temperature than S. cernuus. Stomatal conductance also influenced the oxygen released from plant roots. Furthermore, a relationship was determined between physiological processes and their potential to release oxygen from the roots where the reduction in COD and BOD measured at the end of the experiment was largely attributed to the oxygen that the macrophytes added to the substrate through their roots. The results of this study provide a good benchmark for plant scientists to predict the physiological processes of plants in response to different environmental conditions to control the negative impacts of harsh environmental conditions on plants' ability to release oxygen in their rhizosphere and to improve the efficiency of CW.