The Importance of Short-Term Ultraviolet-B Radiation in Biomass and Photosynthetic Productivity of Eichhornia Crassipes (Mart.) Solms

The current study was designed to test the concerning strategy of water hyacinth (Eichhornia crassipes (Mart.) Solms) to UV-B. In this study, we evaluated the short-term effect of UV-B radiation (short-term UV-B radiation, S-UV-B) on water hyacinth under the natural conditions of Nanjing, China (118°46′E, 32°24′N, 30 m above sea level) with supplemental ultraviolet-B (12 W m−2 above ambient). The growth characteristics and the photosynthetic performance of water hyacinth leaves exposed to UV-B were assessed by measuring net photosynthetic rate, the specific fluorescence parameters including maximal fluorescence (Fm), efficiency of photosystem II (Fv/Fm), and JIP-test parameters. Water hyacinth was tolerant to 1-h UV-B doses over 25 days, maintaining a stable dry weight after treatment. Conversely, plants showed elongation of roots and a decrease in ramet numbers. These changes in growth were closely related to a physiological protection strategy consisting of a higher ability to dissipate extra light energy, strong antioxidative abilities, higher phosphoenolpyruvate carboxylase (PEPC) activity, and stable ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity, as indicated by the stable net photosynthetic rate and reduced inhibition of reactive oxygen species content. After the 3-h dose of UV-B, dry weight decreased significantly, as the above-mentioned protective strategy could not cope with the oxidative damage arising from these treatments. The study concludes that S-UV-B is a potent stimulating factor in increasing the concentrations of defense compounds and antioxidants in water hyacinth to optimize its performance under stress.