Effect of NH 4+/NO 3− availability on nitrate reductase activity and nitrogen accumulation in wetland helophytes Phragmites australis and Glyceria maxima

Abstract

The effect of NH 4 +/NO 3 − availability on nitrate reductase (NR) activity in Phragmites australis and Glyceria maxima was studied in sand and water cultures with the goal to characterise the relationship between NR activity and NO 3 − availability in the rhizosphere and to describe the extent to which NH 4 + suppresses the utilization of NO 3 − in wetland plants. The NR activity data showed that both wetland helophytes are able to utilize NO 3 −. This finding was further supported by sufficient growth observed under the strict NO 3 − nutrition. The distribution of NR activity within plant tissues differed between species. Phragmites was proved to be preferential leaf NO 3 − reducer with high NR activity in leaves (NR max > 6.5 μmol NO 2 − g dry wt −1 h −1) under all N treatments, and therefore Phragmites seems to be good indicator of NO 3 − availability in flooded sediment. In the case of Glyceria the contribution of roots to plant NO 3 − reduction was higher, especially in sand culture. Glyceria also tended to accumulate NO 3 − in non-reduced form, showing generally lower leaf NR activity levels. Thus, the NR activity does not necessarily correspond with plant ability to take up NO 3 − and grow under NO 3 −-N source. Moreover, the species differed significantly in the content of compounds interfering with NR activity estimation. Glyceria, but not Phragmites, contained cyanogenic glycosides releasing cyanide, the potent NR inhibitor. It clearly shows that the use of NR activity as a marker of NO 3 − utilization in individual plant species is impossible without the precise method optimisation.