Insights on the role of vegetation on nitrogen cycling in effluent irrigated lands

This work investigated the effect of plant species (Eucalyptus camaldulensis vs Arundo donax) on N-turnover during land application of pre-treated municipal wastewater. The study was carried out in 40-L pots under field conditions and revealed strong effects of plant species on N uptake, potential nitrification rate (PNR), and gaseous losses of N. E. camaldulensis accumulated 38% more N in its biomass than A. donax. With regard to the soil N, there was no effect of plant species on total Kjeldahl N content. The lower PNR measured in pots planted with A. donax could not be explained by differences in archaeal or bacterial amoA gene copies; suggesting that plant species affected the activity of nitrifiers.The loads of NH4+-N applied were not found to have delayed the oxidation of NH4+-N, despite the differences in PNR, as indicated by soil solution and soil NH4+-N concentrations in the rhizosphere of the two plant species throughout the period of the study. However, decreased concentrations of NO3−-N were measured in the pots planted with A. donax from the end of June onwards. This finding implies increased losses of N through denitrification and reveals a direct effect of plant species on the activity of denitrifiers since differences in copy numbers of denitrification genes (nirK, nirS, nosZ) were observed only early in the season. Our findings reveal a critical role of plant species on N cycling in terrestrial environments with important implications for the management/restoration of N-polluted areas, such as riparian zones, and for land treatment systems and constructed wetlands.

► Our findings revealed an effect of plant species on the nitrification rate.
► Our data also reveal a potential role of archaeal ammonia oxidizers in ammonia oxidation.
► nosZ gene copies occurred at significantly lower numbers compared to nirK and nirS.
► Our findings have important implications for the management/restoration of N-polluted areas.