Regulation of nitrogen acquisition in vegetables by different impacts on autotrophic and heterotrophic nitrification

Aims The understanding of the interactions between N transformations and N uptake by plants in greenhouse soils with large N accumulation is still not clear. The aim is to understand the plant- soil interactions (vegetables) on N transformations with respect to N supply. Methods N-15 tracing studies were conducted in two greenhouse soils to simultaneously quantify soil gross N transformation and plant N uptake rates using the Ntrace(plant) tool. Results There were significant feedbacks between vegetable N uptake and soil gross N transformation rates in the rhizospheric soil, whether soil N accumulation occurred or not. Plant NO3- uptake rates (U-NO3) were higher than the NH4+ uptake rates (U-NH4), which is consistent with the NO3--preference of the vegetable plants studied. While U-NH4 was still responsible for 6-49% of total N uptake rates, significantly negative relationships between U-NH4 and NH4+ immobilization rate and autotrophic nitrification rate (O-NH4) were observed. O-NH4 was significantly inhibited in the presence of plants and decreased with time. O-NH4 (1.11 mg N kg(-1) d(-1)) was much lower than U-NO3 (8.29 mg N kg(-1) d(-1)) in the presence of plants. However, heterotrophic nitrification rate (O-Nrec), which ranged from 0.10 to 8.11 mg N kg(-1) d(-1) was significantly stimulated and was responsible for 5-97% of NO3- production in all plant treatments, providing additional NO3- to meet N requirements of plants and microorganisms. Conclusions The management of organic N fertilizers should be improved to stimulate inorganic N production via heterotrophic nitrification in greenhouse cultivation.

Automated summary

The study revealed significant feedback between vegetable N uptake and soil gross N transformation rates. Plant NO3- uptake rates were higher than NH4+ uptake rates, while NH4+ uptake still accounted for a portion of total N uptake. Additionally, heterotrophic nitrification rate was stimulated and played a significant role in NO3- production in plant treatments.