Short communicationEffects of inorganic nitrogen form on growth, morphology, N uptake, and nutrient allocation in hybrid Napier grass (Pennisetum purpureum × Pennisetum americanum cv. Pakchong1)

Plant cultivars with high biomass production may have a high potential for being used in integrated water treatment and plant production system. The highly productive hybrid Napier grass cultivar, Pennisetum purpureum × Pennisetum americanum cv. Pakchong1, may be a candidate species for being used in such systems. We studied the effects of inorganic nitrogen form (NH4+, NH4NO3 or NO3−) on growth, morphology, N uptake, water content and mineral allocation in this species under hydroponic conditions at equimolar concentrations (500 μmol N L−1). Generally, the N-form significantly affected growth, biomass allocation and tissue nutrient and mineral composition of the plants. The hybrid Napier grass grew better on NH4+ compared to NO3−, and the plants supplied with NH4+ contained three times more chlorophylls than plants supplied with NO3− alone or NO3− combined with NH4+. The morphology of the plants was, however, not affected by N source, except for the shoot to root ratio, which was lower in NH4+-fed plants. The relative water content of the leaves was lowest in the NH4+-fed plants, but the transpiration rate was not affected, indicating that NH4+ nutrition and the associated low tissue concentration of K had negative effects on the water use efficiency of the plants.The study suggests that this hybrid Napier grass cultivar may be a new candidate species for use in integrated water treatment and plant production systems.