Stimulating effect of increasing N fertilization on plant growth and rhizosphere microbial activity at low levels of N2O emissions

Abstract

A greenhouse experiment was conducted to assess the short-term effects of nitrogen (N) addition on plant growth, rhizosphere microbial activity, and N₂O emissions. Nitrogen was applied to lettuce plants once the roots had occupied the entire volume of the pots, ensuring that the whole soil volume could be considered rhizosphere soil. The hypothesis tested was that adding a low amount of plant-available nitrogen to the rhizosphere would increase plant root growth and root-associated microbial activity with minimal N₂O emissions. Conversely, when the nitrogen availability exceeds the demands of the plant-soil system, it decreases root and microbial growth while increasing N₂O emissions. Results indicated that nitrogen applied at rates of 0–100 mg N kg⁻¹ was efficiently utilized by plants, supporting the growth of both aboveground and belowground plant biomass and microbial biomass. Notably, the addition of nitrogen did not increase N₂O production. These findings suggest that dense root systems can efficiently utilize relatively high amounts of nitrogen.