Ammonium and nitrate are both suitable inorganic nitrogen forms for the highly productive wetland grass Arundo donax, a candidate species for wetland paludiculture

The effects of inorganic nitrogen (N) forms (NH4+NO3−or both) at equimolar (0.5 mM) concentrations on growth, biomass allocation, photosynthesis, nitrate reductase activity (NRA) and N uptake rates of Arundo donax were investigated in hydroponic culture. Plants supplied with NH4+, or NH4NO3had significantly higher above-ground biomass, leaf length, shoot number and shoot production rates than NO3−fed plants, whereas the relative growth rates, below-ground biomass, and other plant morphological parameters were indifferent to N nutrition. Leaf photosynthetic pigment concentrations and leaf specific area of NO3−−fed plants were lower than those of plants grown on NH4+, or NH4NO3. In addition, NH4+and NH4NO3fed plants had higher light-saturated rate of photosynthesis and stomatal conductance than NO3−fed plants and there were no differences in leaf dark respiration among N-form treatments. Both leaves and roots of A. donax had NRA, but NRA was much greater in leaves, particularly when plants were fed with NO3−. The N uptake rate of A. donax was greatest when supplied as NH4NO3(1.10 ± 0.34 mg N g−1root DM h−1) although not different from the N uptake rate with NH4+alone (0.61 ± 0.08 mg N g−1root DM h−1), whilst NO3−uptake velocities were similar among N-form treatments. Our results indicate that although some traits perform better in the presence of NH4+, presumably due to lower energetic costs of NH4+uptake, A. donax grows well with either NH4+or NO3−. This reflects its ability to grow well in both wetland and terrestrial soil types, which is an important consideration for its use as a candidate species for paludiculture.