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Studies have shown that dissolved organic matters (DOMs) may affect soil nutrient availability to plants due to their effect on microbial communities; however, the relationships of soil DOM-bacterial community-N function in response to root exudates remains poorly understand. Here, we evaluated the DOM composition, bacterial taxonomic variation and nitrogen transformation rates in both acidic and alkaline soils, with or without the typical nitrate preference plant (wheat, Triticum aestivum L.). After 30 days' cultivation, DOM compositions such as sugars, amines, amino acids, organic acid, and ketone were significantly increased in soil with wheat vs. bare soil, and these compounds were mainly involved in nitrogen metabolism pathways. Soil core bacterial abundance was changed while bacterial community diversity decreased in response to wheat planting. Function prediction analysis based on FAPROTAX software showed that the bacterial community were significantly (p < 0.05) affiliated with nitrification and organic compound degradation. Additionally, db-RDA and VPA analysis suggested that the contribution of soil DOM to the variance of bacterial community was stronger than that of soil available nutrients. Furthermore, the N-transformation related bacteria like Burkholderiales and ammonia-oxidizing bacteria (AOB) were positively correlated with soil gross nitrification rate, confirming that the soil N transformation was enhanced in both acidic and alkaline soils. Our results provide insight into how soil DOM affects the community structure and function of bacteria to regulate the process of nitrogen transformation in plant-soil system., Competing Interests: Declaration of competing interest The author(s) declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Aims: Biological nitrification inhibitors (BNIs) can play an important role in inhibiting nitrification and enhancing nitrogen use efficiency (NUE) in agriculture. However, most current BNI studies have been conducted under hydroponics. Genotypic differences in the inhibition of nitrification in soil are still largely unknown. Our main aim was to investigate the regulation of N transformation processes by different rice genotypes with different BNI release potentials on NUE and N loss. Methods: Two rice genotypes, i.e. Wuyujing 3 (WYJ3) and Wuyunjing 7 (WYJ7), reported to have weak and strong BNI capacity, respectively, under hydroponic conditions, and four soils with different pH (i.e. JX (pH 5.09), FJ (pH 6.00), SC1 (pH 7.96) and SC2 (pH 7.94)) were selected for this study. Plant N uptake rates (esp. NH4+ uptake, UNH4) and soil N transformation rates were quantified by 15 N tracing to assess the effects of rice genotypes on nitrification inhibition activity. NUE and N loss were quantified in a separate 15 N-urea labeling experiment. Results: The results showed that the rice genotype with high BNI exudation (i.e. WYJ7) had lower autotrophic nitrification rate (ONH4) and higher UNH4 compared to WYJ3. ONH4 in WYJ7 decreased by 0.05, 0.42, 1.14, and 0.48 mg N kg−1 d−1 compared to WYJ3 for JX, FJ, SC1 and SC2, respectively. The abundance of AOB in soils planted with WYJ7 was lower than in soils planted with WYJ3, which was the most important factor to explain the variation of ONH4. WYJ7 tends to have a relatively higher NUE than WYJ3 in JX, SC1 and SC2. NUE was negatively correlated with ONH4. Conclusion: Our results indicate that some rice genotypes can optimize their N acquisition by regulating soil N transformations (especially nitrification). The development of rice genotypes with strong BNI exudation capacity could be a suitable management practice to increase NUE and yield. [ABSTRACT FROM AUTHOR]

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: 15N tracing studies were conducted in two greenhouse soils to simultaneously quantify soil gross N transformation and plant N uptake rates using the Ntraceplant 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 (UNO3) were higher than the NH4+ uptake rates (UNH4), which is consistent with the NO3−-preference of the vegetable plants studied. While UNH4 was still responsible for 6–49% of total N uptake rates, significantly negative relationships between UNH4 and NH4+ immobilization rate and autotrophic nitrification rate (ONH4) were observed. ONH4 was significantly inhibited in the presence of plants and decreased with time. ONH4 (1.11 mg N kg−1 d−1) was much lower than UNO3 (8.29 mg N kg−1 d−1) in the presence of plants. However, heterotrophic nitrification rate (ONrec), 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. [ABSTRACT FROM AUTHOR]

In the soil N cycle, heterotrophic nitrification is poorly understood. Our understanding of the factors controlling soil heterotrophic nitrification requires support from investigations in the presence of plants. In this study, a series of 15N tracing pot experiments using maize (Zea mays L.) was conducted and the heterotrophic nitrification rate (O Nrec) and maize N uptake rate were estimated using the Ntrace Plant tool to explore the mechanisms that stimulate heterotrophic nitrification by plants. The results showed that the O Nrec (0.79–3.67 mg N kg−1 d−1) was much higher in the presence of maize than in the control (CK, no plants, <0.10 mg N kg−1 d−1). After the maize was removed, the O Nrec decreased significantly, becoming similar to that of CK. These results indicated that the O Nrec was stimulated by the presence of plants. The O Nrec declined rapidly to 0.16 and 0.13 mg N kg−1 d−1 after the maize was covered with a black box for 2 and 4 days (preventing photosynthesis), respectively. Meanwhile, the soil dissolved organic carbon (DOC) concentration decreased significantly after photosynthesis was prevented. Moreover, the O Nrec correlated significantly with the soil DOC content (P < 0.05). These results revealed that root exudates derived from plant photosynthesis were the key factors that altered soil organic matter, thereby accelerating heterotrophic nitrification. We also found that the maize NO 3 − uptake rate correlated significantly and positively with the O Nrec (P < 0.01), suggesting that the stimulation of heterotrophic nitrification by plants played an important role in the supply of NO 3 − to meet the N requirements of maize and microorganisms. • Heterotrophic nitrification is stimulated by the presence of plants. • Root exudates are important in heterotrophic nitrification stimulation. • Symbiotic microorganisms did not affect heterotrophic nitrification. [ABSTRACT FROM AUTHOR]

Plants with ammonium preference are able to exude biological nitrification inhibitors to reduce nitrification keeping the mineral N in NH 4 + form. The question is whether plants with a NO 3 − preference are able to stimulate nitrification to shift mineral N towards NO 3 − production to meet their NO 3 − demand. In this study we attempted to solve this conundrum by conducting 15N tracing studies in a range of soils planted with wheat (Triticum aestivum L.), a typical NO 3 −-preferring crop, to quantify the gross rates of soil N transformations and the plant N uptake rates. Gross N mineralization rates (M) were stimulated by the presence of wheat in all studied soils, improving the mineral N supply. The wheat NH 4 + uptake rates (U NH4) were significantly, positively correlated with M (p < 0.01). The wheat NO 3 − uptake rates (U NO3) were significantly higher than U NH4 confirming the NO 3 − preference of this plant. As NO 3 − production pathways we considered NH 4 + oxidation (O NH4 , the autotrophic pathway) and organic N oxidation to NO 3 −, O Nrec) in this study. The stimulations of O NH4 were only observed in three out of five soils and, except one soil, O NH4 was much lower (average 1.29 mg N kg−1 d−1) than U NO3 (average 7.66 mg N kg−1 d−1) showing that the NO 3 − supply via this pathway was insufficient to meet the plants NO 3 − demand. In these soils, O Nrec was significantly stimulated ranging from 0.86 to 5.52 mg N kg−1 d−1 and was responsible for 34%–74% of NO 3 − production during the 30 days experimental duration. Moreover, U NO3 was significantly, positively correlated with O Nrec (p < 0.05), indicating a direct link between heterotrophic nitrification and plant NO 3 − uptake. One soil (SC2) exhibited a much higher O NH4 (>8.00 mg N kg−1 d−1) and only M was stimulated by the plants presence but not heterotrophic nitrification because the NO 3 − supply via O NH4 was sufficient to meet the plant NO 3 − demand. Heterotrophic nitrification was stimulated by NO 3 − preference plants when NO 3 − supply via oxidation of NH 4 + to NO 3 − was insufficient to meet the NO 3 − requirements. • Interactions between wheat N acquisition and soil N transformations were observed. • Gross N mineralization rates were stimulated by the presence of wheat. • Heterotrophic nitrification was stimulated by wheat when autotrophic nitrification was unable to supply sufficient NO 3 −. [ABSTRACT FROM AUTHOR]