In this article, we discuss the effect of salinity on the viability and decomposition of Eichhornia crassipes plant under normal photoperiod, dark condition and physiological response. Highest concentration of total organic carbon (27.43 mg C l -1 ) was recorded in 15 psu salinity after 45 days. The TOC output was more in case of leaf (3.6 mg C l -1 ) than petiole (2.39 mg C l -1 ) under dark condition, after 21 days in freshwater. Salt stress was found to enhance the superoxide dismutase activity at 20 psu in both leaf and petiole. Enzyme activity declined when salt-stressed plants were transferred to nutrient enriched freshwater. This indicated that 20 psu could be a plant's salt tolerance limit. The potential transfer test conducted in this study showed that Eichorrnia introduction through shipping activities is less likely.Keywords: Eichhornia crassipes, salinity stress, superoxide dismutase, total organic carbon.EICHHORNIA CRASSIPES (Mart.) Solms (water hyacinth) is an invasive aquatic macrophyte. The ability of the plant to flourish in any condition has made it a noxious and invasive weed in tropical and subtropical regions 1,2 . The plant has a wide range of tolerance to temperature, lighting conditions, pH, drought resistance and salinity 1,3 . The backwaters in Cochin including Cochin Port area, KeralaIndia, become infested by this plant during monsoon when the sluice gates of Thannermukkom salt-water barrier are opened. The sluice gates prevent the E. crassipes plants growing upstream to move downstream. As a consequence, the plant is subjected to a varying range of salinities both in the upstream and downstream areas. The high salinity condition affects the plant and it starts decaying. Further, these plants are also subjected to physical damage, breaking into pieces, due to movement of mechanized boats, trawlers and ships in the area. The dead plants generate detrital matter, which is a major organic source in an aquatic system. The extent of detritus decomposition depends on the type of metabolic activities taking place in the system 4 . During decomposition of the plants, three main types of microbial activity occuraerobic, facultative anaerobic and anaerobic. Besides these, various factors both external and biochemical are also involved in the process of decomposition 4-6 , biotic and abiotic 7,8 . However, some authors have indicated that tissue chemistry influences the decomposition process more than environmental conditions 3,9,10 . Earlier decomposition studies on E. crassipes showed that physical leaching and biological degradation are the two principal processes involved [11][12][13] . Litter decomposition is also influenced by nutrient concentration 14 , water salinity 15 and seasonal periodicity 16 . The sudden appearance of E. crassipes during monsoon in the Port area and its subsequent disappearance, add to the complexity of the ecosystem. It therefore, becomes imperative to investigate the organic matter supply to ecosystem due to plant decomposition. In view of the perennial E. crassip...
