High NH₄⁺ concentrations in water column is taken as one main cause to decline of submersed macrophytes in eutrophic lakes due to its toxic effects on plant, which disturb carbon (C) and nitrogen (N) metabolism greatly, such as depleting carbohydrate reserves and accumulating nitrogenous compounds in plant tissues. However, the toxic effects are species-specific, with some macrophyte species more sensitive to but others tolerant of NH₄⁺ stress, and the underlying mechanism are to be revealed.  

An international group comprised of researchers from Institute of Hydrobiology, Chinese Academy of Sciences and Aarhus University in Denmark addressed this issue based on an acute high NH₄⁺ dosing test and a field lake survey in Lake Erhai. 

They found that the proportional changes in soluble carbohydrate (SC) contents in the leaves and free amino acids (FAA) contents in the stems induced by the NH₄⁺ dosing were closely correlated (positive for SC and negative for FAA) with the colonizing water depths of the plants in Lake Erhai, the plants adaptive to lower light regimes being more efficient in maintaining the SC and FAA homeostasis. These results indicate that conservative carbohydrates metabolism of submersed macrophytes facilitated the plants to colonize to deeper water depths in eutrophic lakes, where low light availability in the water column diminishes carbohydrates production of by the plants.

This work was published online in Freshwater Biology with the title "Linking carbon and nitrogen metabolism to depth distribution of submersed macrophytes in lakes based on high ammonium dosing tests and a field lake survey ". 

Fig.Plots of colonizing depths, PAR requirements and biomass of the 12 species againstSC(F-C)/Cin leaves andFAA(F-C)/Cin stems in response to NH4+fertilization, respectively.