Description:
Understanding of feedbacks between plant N uptake and soil N transformations under various vegetable production systems is of vital importance to enhance vegetable N acquisition and improve N fertilizer management. In this study, a series of 15N tracing pot experiments were conducted under greenhouse (GH) and open-field (OF) conditions, plant N uptake and soil gross N transformation rates were simultaneously quantified using the Ntraceplant tool. The results showed that feedbacks of plant N uptake to soil gross N transformations largely differed between GH and OF. In general, the plant NH4+ and NO3– uptake rates in GH were significantly higher than in OF. The soil mineral N production rates (i.e. the sum of mineralization and heterotrophic nitrification rates) were 1.1-3.9 times lower in GH than OF in the presence of plants. Soil mineral N production rates in GH were reduced under high soil moisture conditions and vegetable activities (especially respiratory activity in rhizosphere, i.e. low aerobic conditions). Compared to OF, the microbial N immobilization rates in GH were 1.6-166.5 times lower in the presence of plants. The lower mineral N production rates and higher plant N uptake rates in GH compared to OF were the most possible reasons for lower microbial N immobilization in GH. This was further supported by significantly positive relationships between microbial N immobilization rates and mineral N production rates. We showed that the soil mineral N supply capacity was weaker in GH than OF in the presence of plants, which was one of the reasons that more N fertilizer was required to meet rapid vegetable growth in greenhouse vegetable production. We also highlighted the importance of water management to improve soil N supply in greenhouse vegetable cultivation