Exploring Ammonium Detoxification Mechanism Of Macrophytes Poamogeton Lucens Using Young And Mature Leaves

The decline of submerged macrophyte populations due to nutrient accumulation in freshwater ecosystems has become a significant global problem.Submerged macrophytes are important primary producers and play a crucial role in maintaining the clear state of water in water bodies.The presence of submerged macrophytes influences the community composition of aquatic organisms through their structural roles.Nitrogen is quantitatively the most essential nutrient for plants and a major limiting factor in plant productivity.Macrophytes prefer ammonium to nitrate however,high ammonium in aquatic environment can cause stress on many aquatic plants.Toxicity on aquatic plants caused by excess ammonium in environment has become a hotspot for discussion in recent years.However,previous studies related to ammonium detoxification mechanism have been mainly through species comparison,some mechanisms may be obscured by species diferences.Interestingly,our recent study found that mature leaves of Potamogeton lucens were sensitive to ammonium enrichment,while the young leaves were tolerant.This gave us ideal materials that could be used in study of ammonium detoxification within one species.In this study,we chose the young and mature leaves of P.lucens and the enzyme activities to exploit the possible mechanism of the ammonium detoxification.The results showed that chlorophyll fluorescence and total chlorophyll content decreased in both the young and mature leaves with an increase in ammonium concentration.However,the decrease in mature leaves was more rapid than young leaves.Clutamine synthetase and Glutamate synthase enzyme activities slightly decreased in mature leaves but increased in young leaves.Furthermore,the study recorded an increase of Glutamate dehydrogenase enzyme activities in young leaves and decrease in mature leaves.Free amino acid content increased in both the young and mature leaves,and a decrease of soluble protein content in both the leaves.Starch content in mature leaves decreased significantly with ammonium enrichment,while young leaves increased significantly.Our study revealed that as ammonium stress-tolerant leaves,young leaves of P.lucens had mechanisms including rapid ammonium assimilation through ammonium assimilation enzymes,and carbon metabolism responses that enabled them to achieve detoxification of ammonium,however,this was not the case in mature leaves.Compared to the former studies,our study used the same species therefore gives more convincing evidence on the mechanism of the ammonium detoxification mechanism hence basic in aquatic management and freshwater restorations.