Different sensitivity of Phragmites australis and Glyceria maxima to high availability of ammonium-N

Abstract

The ability to cope with NH 4 +-N was studied in the littoral helophytes Phragmites australis and Glyceria maxima, species commonly occupying fertile habitats rich in NH 4 + and often used in artificial wetlands. In the present study, Glyceria growth rate was reduced by 16% at 179 μM NH 4 +-N, and the biomass production was reduced by 47% at 3700 μM NH 4 +-N compared to NO 3 −-N. Similar responses were not found in Phragmites. The amounts (mg g −1 dry wt) of starch and total non-structural carbohydrates (TNC) in rhizomes were significantly lower in NH 4 + (8.9; 12.2 starch; 20.1; 41.9 TNC) compared to NO 3 − treated plants (28.0; 15.6 starch; 58.5; 56.3 TNC) in Phragmites and Glyceria, respectively. In addition, Glyceria showed lower amounts (mg g −1 dry wt) of soluble sugars, TNC, K +, and Mg 2+ in roots under NH 4 + (5.6; 14.3; 20.6; 1.9) compared to NO 3 − nutrition (11.6; 19.9; 37.9; 2.9, for soluble sugars, TNC, K +, and Mg 2+, respectively), while root internal levels of NH 4 + and Ca 2+ (0.29; 4.6 mg g −1 dry wt, mean of both treatments) were only slightly affected. In Phragmites, no changes in soluble sugars, TNC, Ca 2+, K +, and Mg 2+ contents of roots (7.3; 14.9; 5.1; 17.3; 2.6 mg g −1 dry wt, means of both treatments) were found in response to treatments. The results, therefore, indicate a more pronounced tolerance towards high NH 4 + supply in Phragmites compared to Glyceria, although the former may be susceptible to starch exhaustion in NH 4 +-N nutrition. In contrast, Glyceria's ability to colonize fertile habitats rich in NH 4 + is probably related to the avoidance strategy due to shallow rooting or to the previously described ability to cope with high NH 4 + levels when P availability is high and NO 3 − is also provided.