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Purpose: Reductive soil disinfestation (RSD) has been widely applied to improve soil degradation, enhancing vegetable N uptake and productivity. However, its effects on interactions between vegetable N uptake and soil gross N transformation remain unclear. Methods: Two degraded vegetable soils were treated with RSD and 15N tracing pot experiments were conducted to quantify the effects of RSD on N cycling in vegetable-soil systems. Results: Vegetable NH4+ and NO3− uptake rates were 1.0–6.5 times higher following RSD than CK, while soil gross N mineralization rates (M) ranged from 0.83–13.00 mg N kg−1 d−1, and were significantly higher than the CK (0.21–8.71 mg N kg−1 d−1). Meanwhile, autotropic nitrification rate (ONH4) increased by 1.7–4.2 following RSD, while NH4+ immobilization rates (INH4) were significantly inhibited by RSD in the presence of planting. This induced a decrease in (ONH4 + INH4)/M, and increases in NH4+ retention times and production rates of soil NO3− following RSD. In addition, RSD improved the overall quality of the degraded soils (increasing the pH, and decreasing EC and NO3− contents as well as pathogen abundance), further promoting vegetable N uptake. Conclusion: RSD promoted vegetable N uptake by regulating soil gross N transformation rates and improving the quality of degraded vegetable soil. However, NO3− production rates were enhanced following RSD, increasing the risk of NO3− leaching and gaseous N losses. N fertilizer management under RSD therefore requires further attention. [ABSTRACT FROM AUTHOR]

Soil organic nitrogen (N) mineralization not only supports ecosystem productivity but also weakens carbon and N accumulation in soils. Recalcitrant (mainly mineral‐associated organic matter) and labile (mainly particulate organic matter) organic materials differ dramatically in nature. Yet, the patterns and drivers of recalcitrant (MNrec) and labile (MNlab) organic N mineralization rates and their consequences on ecosystem N retention are still unclear. By collecting MNrec (299 observations) and MNlab (299 observations) from 57 15N tracing studies, we found that soil pH and total N were the master factors controlling MNrec and MNlab, respectively. This was consistent with the significantly higher rates of MNrec in alkaline soils and of MNlab in natural ecosystems. Interestingly, our analysis revealed that MNrec directly stimulated microbial N immobilization and plant N uptake, while MNlab stimulated the soil gross autotrophic nitrification which discouraged ammonium immobilization and accelerated nitrate production. We also noted that MNrec was more efficient at lower precipitation and higher temperatures due to increased soil pH. In contrast, MNlab was more efficient at higher precipitation and lower temperatures due to increased soil total N. Overall, we suggest that increasing MNrec may lead to a conservative N cycle, improving the ecosystem services and functions, while increasing MNlab may stimulate the potential risk of soil N loss. [ABSTRACT FROM AUTHOR]

Reductive soil disinfestation (RSD) incorporated with sole plant residues or liquid-readily decomposable compounds is an effective management strategy to improve soil health. However, the synthetic effects of RSD incorporated with liquid-readily decomposable compounds and solid plant residues on soil ecosystem services remain unclear. Field experiments were carried out to investigate the effects of untreated soil (CK), RSD incorporated with sawdust (SA), molasses (MO), and their combinations (SA + MO) on the bacterial community and functional composition. The results showed that RSD treatments significantly altered soil bacterial community structure compared to CK treatment. The bacterial community structure and composition in MO and SA + MO treatments were clustered compared to SA treatment. This was mainly attributed to the readily decomposable carbon sources in molasses having a stronger driving force to reshape the soil microbial community during the RSD process. Furthermore, the functional compositions, such as the disinfestation efficiency of F. oxysporum (96.4 − 99.1%), abundances of nitrogen functional genes, soil metabolic activity, and functional diversity, were significantly increased in all of the RSD treatments. The highest disinfestation efficiency and abundances of denitrification (nirS and nrfA) and nitrogen fixation (nifH) genes were observed in SA + MO treatment. Specifically, SA + MO treatment enriched more abundant beneficial genera, e.g., Oxobacter, Paenibacillus, Cohnella, Rummeliibacillus, and Streptomyces, which were significantly and positively linked to disinfestation efficiency, soil metabolic activity, and denitrification processes. Our results indicated that combining RSD practices with liquid-readily decomposable compounds and solid plant residues could effectively improve soil microbial community and functional composition. [ABSTRACT FROM AUTHOR]

Application of reductive soil disinfestation (RSD), biochar, and antagonistic microbes have become increasingly popular strategies in a microbiome-based approach to control soil-borne diseases. The combined effect of these remediation methods on the suppression of cucumber Fusarium wilt associated with microbiota reconstruction, however, is still unknown. In this study, we applied RSD treatment together with biochar and microbial application of Trichoderma and Bacillus spp. in Fusarium-diseased cucumbers to investigate their effects on wilt suppression, soil chemical changes, microbial abundances, and the rhizosphere communities. The results showed that initial RSD treatment followed by biochar amendment (RSD-BC) and combined applications of microbial inoculation and biochar (RSD-SQR-T37-BC) decreased nitrate concentration and raised soil pH, soil organic carbon (SOC), and ammonium in the treated soils. Under RSD, the applications of Bacillus (RSD-SQR), Trichoderma (RSD-T37), and biochar (RSD-BC) suppressed wilt incidence by 26.8%, 37.5%, and 32.5%, respectively, compared to non-RSD treatments. Moreover, RSD-SQR-T37-BC and RSD-T37 caused greater suppressiveness of Fusarium wilt and F. oxysporum by 57.0 and 33.5%, respectively. Rhizosphere beta diversity and alpha diversity revealed a difference between RSD-treated and non-RSD microbial groups. The significant increase in the abundance, richness, and diversity of bacteria, and the decrease in the abundance and diversity of fungi under RSD-induced treatments attributed to the general suppression. Identified bacterial (Bacillus, Pseudoxanthomonas, Flavobacterium, Flavisolibacter, and Arthrobacter) and fungal (Trichoderma, Chaetomium, Cladosporium, Psathyrella, and Westerdykella) genera were likely the potential antagonists of specific disease suppression for their significant increase of abundances under RSD-treated soils and high relative importance in linear models. This study infers that the RSD treatment induces potential synergies with biochar amendment and microbial applications, resulting in enhanced general-to-specific suppression mechanisms by changing the microbial community composition in the cucumber rhizosphere. [ABSTRACT FROM AUTHOR]

Two methodological approaches are commonly used to investigate heterotrophic nitrification (Nith) in soil: process inhibitions and 15N tracing. Although many studies have reported Nith based on 15N tracing approaches, estimates via specific inhibitor are less common. Therefore, we conducted a meta‐analysis to illustrate the similarities and differences of the results of soil Nith between the two approaches. We observed that the average result of gross Nith rate was significantly lower with the 15N tracing approach (1.32 mg N kg−1 day−1) than with the inhibitor approach (3.54 mg N kg−1 day−1) (p < 0.01). Possible explanations include incomplete inhibition of autotrophic nitrification (Nita) due to the adsorption of inhibitors on soil aggregates and the fact that the estimation of Nith via 15N tracing quantifies only the Nith fraction related to organic N oxidation. The results of linear‐mixed models indicated that soil C:N ratio had a significantly positive effect on the difference of Nith estimated via 15N tracing and inhibitor approach, which was also supported by the paired data between natural and C‐ and N‐ manipulated soil. The average contribution of Nith to total nitrification, estimated by the ratio of Nith:(Nith + Nita) or the capacity of NO2−/NO3− production when Nita was inhibited, in the two approaches were not significantly different (34% vs. 33%). While, soil C:N ratio also caused a significantly positive effect on the contribution of Nith to soil total nitrification (p < 0.05). In conclusion, the result of the relative contribution of Nith is less affected by approach than the result of gross Nith rate. In addition, soil C and N substrate availability is likely to be a critical factor affecting the estimation of soil Nith by the two approaches. Highlights: Process inhibitors and 15N tracing are two commonly used methods to quantify soil heterotrophic nitrification (Nith).A meta‐analysis was carried out to compare the results of soil Nith between the two methods.There was a significant difference of the rate of Nith estimated via the two methods, while the contribution of Nith to total nitrification was similar.Soil C and N substrate appeared to influence the estimation of soil Nith via the two approaches. [ABSTRACT FROM AUTHOR]

Reductive soil disinfestation (RSD) is an effective practice to eliminate plant pathogens and improve the soil microbial community. However, little is known about how RSD treatment affects microbial interactions and functions. Previous study has shown that RSD-regulated microbiomes may degenerate after re-planting with former crops, while the effect of planting with different crops is still unclear. Here, the effects of both RSD treatment and succession planting with different crops on microbial community composition, interactions, and functions were investigated. Results showed that RSD treatment improves the soil microbial community, decreases the relative abundance of plant pathogens, and effectively enhances microbial interactions and functions. The microbial network associated with RSD treatment was more complex and connected. The functions of hydrocarbon (C, H), nitrogen (N), and sulfur (S) cycling were significantly increased in RSD-treated soil, while the functions of bacterial and fungal plant pathogens were decreased. Furthermore, the bacterial and fungal communities present in the RSD-treated soil, and soil succession planted with different crops, were found to be significantly different compared to untreated soil. In summary, we report that RSD treatment can improve soil quality by regulating the interactions of microbial communities and multifunctionality. [ABSTRACT FROM AUTHOR]

Reductive soil disinfestation (RSD) is an effective agricultural practice to eliminate soil-borne pathogens that heavily relies on the organic substrate used. However, the influences of combined application of organic residues on disinfestation efficiency, soil microbiomes, and their associated functional characteristics are still not well-characterized. In this work, four treatments, i.e., untreated soil (CK), RSD with 15 t ha−1 sugarcane bagasse (SB), bean dregs (BD), and their combinations (1:1, SB+BD), were conducted to investigate their influence on disinfestation efficiency, microbial functional diversity, community diversity, and composition using Biolog analysis, real-time PCR, and high-throughput sequencing. The SB+BD treatment had synergetic effects on soil microbial activity, metabolic activity, and functional diversity with similar efficacy in pathogen elimination and soil salinization alleviation, as compared to the SB and BD treatments. Moreover, the SB+BD treatment distinctly altered the structure and composition of bacterial and fungal communities, especially enriched the core microbiomes associated with soil general functions such as organic decomposition and nitrate removal. The SB+BD treatment also strengthened the soil specific functions including disease suppression through the regulation of unique microbiomes. In addition, the microbial richness, diversity, and evenness were significantly higher in the SB+BD-treated soil as compared to the SB- and BD-treated soils. Taken together, RSD incorporated with organic residue combination not only efficiently restore the degraded soils, but also considerably improve soil functions, which may benefit to the health for the future plant generations. Key points: • Organic residue combination effectively declines pathogen density. • Organic residue combination improves soil microbial activity and functional diversity. • The enriched core microbiome is responsible for soil general functions. • The induced unique microbiome is important for soil specific functions. [ABSTRACT FROM AUTHOR]

Purple soils (Eutric Regosols) are widely distributed in humid subtropical Southwest China. They are characterized by high nitrification activities, with risks of severe NO3− leaching. Incorporation of crop residues is considered an effective method to reduce NO3− loss. In the present study, we compared the effects of alfalfa, rice straw, and sugarcane bagasse on gross N transformation turnover in a purple soil (purple soil, pH 7.62) compared with those in an acid soil (acid soil, pH 5.26), at 12 h, 3 months, and 6 months after residue incorporation. The gross N transformation rates were determined by 15N tracing. All tested crop residues stimulated the gross N mineralization rates, but reduced the net mineralization rates in both soils at 12 h after residue incorporation; however, the extent of the effect varied with the crop residue qualities, with rice straw having the strongest effects. Crop residues reduced net nitrification rates by depressing gross autotrophic nitrification rates and stimulating NO3− immobilization rates in the purple soil, particularly after rice straw incorporation (net nitrification rate decreased from 16.72 mg N kg−1 d−1 in the control to − 29.42 mg N kg−1 d−1 at 12 h of residue incorporation); however, crop residues did not affect the gross autotrophic nitrification rates in the acid soil. Crop residue effects subsided almost completely within 6 months, with sugarcane bagasse showing the longest lasting effects. The results indicated that crop residues affected the N transformation rates in a temporal manner, dependent on soil properties and residue qualities. [ABSTRACT FROM AUTHOR]

Nitrification is a key process in the nitrogen cycle, converting the most reduced N compounds to the most oxidized ones. In general, soil NO 3 − is predominantly produced by two pathways: i) oxidation of NH 4 + via nitrite (NO 2 −) to nitrate (NO 3 −) (autotrophic nitrification, An) and ii) oxidation of NH 4 + and organic N to NO 3 − (heterotrophic nitrification, Hn). While, much research has gone into the study of An and much less is known about Hn, although a growing number of studies demonstrate the importance of Hn to N cycling in many terrestrial ecosystems. In this paper, we collected 491 observations from 84 publications (covering cropland, forest and grassland ecosystem) that also considered Hn. Results show that Hn accounts for 24 %, 32 % and 43 % of NO 3 − production in forest, cropland and grassland soils, respectively. The gross rates and the contribution of Hn to total nitrification are significantly and negatively affected by temperature (P < 0.05) rather than moisture. Although soil pH and C:N ratio was reported to affect Hn, only pH has a significant negative effect (P < 0.05). And Hn is reported to occur over a wide pH range (pH 3.6–7.0). Neither the gross rate nor the contribution of Hn is significantly related to the C and N additions (P > 0.05). Thus, the effect of soil C and N substrates needs further investigation. Interestingly, Hn is significantly related to other heterotrophic processes, such as dissimilatory nitrate reduction to ammonia (DNRA), NO 3 − immobilization (I NO3) and organic N mineralization (M org) (P < 0.05). These correlations provide potential insights that the occurrence of Hn probably contributes to the maintenance of inorganic N balance in soils, since the growth of heterotrophs was proposed independent of their nitrification. Conclusively, Hn occurs in cropland, forest and grassland ecosystems, which is much more widespread than previously thought. Its occurrence is significantly related with temperature and soil pH, while its correlation with soil C and N substrates and other N transformation processes needs further investigation. [ABSTRACT FROM AUTHOR]

Denitrification and its products composition were evaluated in four typical Chinese paddy soils with pH (HO) ranging from 4.80 to 8.29 after application of 50 or 100 mg kg soil KNO and subsequent anaerobic incubation. Denitrification rates, which were indicated by nitric oxide (NO), nitrous oxide (NO), and dinitrogen gas (N) production, significantly varied among different paddy soils. The denitrification rates of the neutral and alkaline paddy soils were 2.6 to 16.6 times higher, respectively, than those of acidic paddies. Furthermore, denitrification in paddy soils could produce end products other than N, and the product composition depended on the paddy soil type. The percentage of total N gases (NO + NO + N) present as NO was negatively and linearly correlated with denitrification rate ( P < 0.05). Soil pH and C/N showed positive effects on denitrification rate ( r = 0.800 and r = 0.781, respectively, P < 0.05 for both), but negative effects on the percentage of total N gases present as NO ( r = −0.976, P < 0.01 and r = −0.781, P < 0.05, respectively). Denitrification rate and the percentage of total gases present as NO increased as the nitrate (NO) concentration increased. However, there was no effect of NO concentration on the percentage of total N gases present as NO. Our results indicate that the potential N loss through denitrification may be higher in alkaline paddies than that in neutral and acidic paddies. Moreover, the variation of the NO percentage in denitrification products of different paddy soils should be considered when estimating the denitrification-derived NO emission and when calculating the N budget in paddy soils. [ABSTRACT FROM AUTHOR]

Background and Aims: Great attention has been paid to NO emissions from paddy soils under summer rice-winter wheat double-crop rotation, while less focus was given to the NO emissions. Besides, neither mechanism is completely understood. Therefore, this study aimed at evaluating the relative importance of nitrification and denitrification to NO and NO emissions from the two soils at different soil moisture contents Methods: NO and NO emissions during one winter wheat season were simultaneously measured in situ in two rice-wheat based field plots at two different locations in Jiangsu Province, China. One soil was neutral in pH with silt loam texture (NSL), the other soil alkaline in pH with a clay texture (AC). A N tracer incubation experiment was conducted in the laboratory to evaluate the relative importance of nitrification and denitrification for NO and NO emissions at soil moisture contents of 40 % water holding capacity (WHC), 65 % WHC and 90 % WHC. Results: Higher NO emission rates in the AC soil than in the NSL soil were found both in the field and in the laboratory experiments; however, the differences in NO emissions between AC soil and NSL soil were smaller in the field than in the laboratory. In the latter experiment, nitrification was observed to be the more important source of NO emissions (>70 %) than denitrification, regardless of the soils and moisture treatments, with the only exception of the AC soil at 90 % WHC, at which the contributions of nitrification and denitrification to NO emissions were comparable. The ratios of NO/NO also supported the evidence that the nitrification process was the dominant source of NO and NO both in situ and in the laboratory. The proportion of nitrified N emitted as NO ( P) in NSL soil were around 0.02 % in all three moisture treatments, however, P in the AC soil (0.04 % to 0.10 %) tended to decrease with increasing soil moisture content. Conclusions: Our results suggest that NO emission rates obtained from laboratory incubation experiments are not suitable for the estimation of the true amount of NO fluxes on a field scale. Besides, the variations of P with soil property and soil moisture content should be taken into account in model simulations of NO emission from soils. [ABSTRACT FROM AUTHOR]

The study examined the influence of compost and mineral fertilizer application on the content and stability of soil organic carbon (SOC). Soil samples collected from a long-term field experiment were separated into macroaggregate, microaggregate, and silt + clay fractions by wet-sieving. The experiment involved seven treatments: compost, half-compost N plus half-fertilizer N, fertilizer NPK, fertilizer NP, fertilizer NK, fertilizer PK, and control. The 18-year application of compost increased SOC by 70.7-121.7%, and mineral fertilizer increased by 5.4-25.5%, with no significant difference between control soil and initial soil. The C mineralization rate (rate per unit dry mass) in microaggregates was 1.52-2.87 mg C kg day, significantly lower than in macroaggregate and silt + clay fractions ( P < 0.05). Specific C mineralization rate (rate per unit SOC) in silt + clay fraction amounted to 0.48-0.87 mg C g SOC day and was higher than in macroaggregates and microaggregates. Our data indicate that SOC in microaggregates is more stable than in macroaggregate and silt + clay fractions. Compost and mineral fertilizer application increased C mineralization rate in all aggregates compared with control. However, compost application significantly decreased specific C mineralization rate in microaggregate and silt + clay fractions by 2.6-28.2% and 21.9-25.0%, respectively ( P < 0.05). By contrast, fertilizer NPK application did not affect specific C mineralization rate in microaggregates but significantly increased that in silt + clay fractions. Carbon sequestration in compost-amended soil was therefore due to improving SOC stability in microaggregate and silt + clay fractions. In contrast, fertilizer NPK application enhanced SOC with low stability in macroaggregate and silt + clay fractions. [ABSTRACT FROM AUTHOR]

Although crop residue return increases upland soil emissions of nitrous oxide (N 2 O), a potent greenhouse gas, the mechanisms responsible for the increase remain unclear. Here, we investigate N 2 O emission pathways, gross nitrogen (N)-cycling rates, and associated N-cycling gene abundances in an upland soil following the addition of various organic material under aerobic incubation using a combination of 15N tracing technique, acetylene (C 2 H 2) inhibition, and real-time PCR (qPCR) methods. Increased total N 2 O emissions following organic material amendment was attributed to both increased nitrification-derived N 2 O emissions, following increased ammonia-oxidizing bacteria (AOB)- amoA abundance, and denitrification-derived N 2 O emissions, following increased nirS and decreased nosZ abundance. Increasing plant residue carbon (C)/N ratio decreased total N 2 O emissions by decreasing the contribution of denitrification to N 2 O emissions, potentially due to higher proportions of denitrified N emitted as N 2 O than nitrified N emitted as N 2 O. We further propose a novel conceptual framework for organic material input effects on denitrification-derived N 2 O emissions based on the decomposable characteristics of the added organic material. For slowly decomposing organic materials (e.g., plant residue) with insufficient available C, NO 3 −-N immobilization surpassed denitrification, resulting in gradual decrease in denitrification-derived N 2 O emissions with an increase in mineralization of plant residue C losses. In contrast, available C provided by readily available C sources (e.g., glucose) seemed sufficient to support the co-occurrence of NO 3 −-N immobilization and denitrification. Overall, for the first time, we offer a microbial process perspective of N 2 O emissions following organic material input. The findings could facilitate the improvement of process-orientated models of N 2 O emissions and the formulation of appropriate N 2 O mitigation strategies for crop residue-amended soils. [Display omitted] • We investigate how crop residue stimulate soil N 2 O emissions. • Residue C/N ratio negatively correlated with N 2 O emissions. • Enhanced N 2 O emission was due to both increased nitrification and denitrification. • Increasing residue C/N decreased N 2 O emissions by decreasing denitrification. • Organic material characteristics affected denitrification-derived N 2 O emissions. [ABSTRACT FROM AUTHOR]

The original version of this article, unfortunately, contained errors. Corrections in the Table 1 and “Results and discussion” section are presented in this article. [ABSTRACT FROM AUTHOR]

Sanqi ginseng (Panax notoginseng) is a typical geo-authentic medicinal herb and the accumulation of saponins heavily relies on its growing environment. However, the effects of soil factors on saponin accumulation are still not well characterized. In this study, four different varieties (improved varieties: KZ, HD and PK; common variety: PT) and two typical soils (geo-authentic soil: QB; non-geo-authentic soil: SL) were selected for pot experiments, and the root biomass and saponin content, as well as the soil microbiome were investigated after one-year of cultivation. Results showed that soil, rather than variety, was the determinant of the root development and saponin accumulation of Sanqi ginseng. Sanqi ginseng cultivated in the QB soil had better root morphology (with long and dense fibrous roots) and higher saponin accumulation. Compared to the physicochemical properties, the soil microbiome exhibited a higher explanatory power (24.68 %) for the biomass and saponin of Sanqi ginseng, and its α-diversity and β-diversity were strongly related to biomass, saponin content and saponin accumulation. Random forest regression analysis further revealed that those having high and positive contributions to biomass and saponin accumulation, such as bacterial genera Arthrobacter , Gaiella , Granulicella , Bradyrhizobium , Rhizomicrobium , Rhizobium and Streptomyces , and fungal genera Fusarium , Plenodomus , Setophoma and Trichoderma , were significantly enriched in QB soil. This study revealed that soil is one of the key factors for producing geo-authentic Sanqi ginseng and highlighted the importance of key soil microbial taxa in the saponin accumulation of Sanqi ginseng, thus providing a theoretical basis for quality improvement through microbiome regulation. [Display omitted] • Sanqi ginseng cultivated in geo-authentic soil had a higher saponin accumulation. • Soil microbiome was mainly responsible for the differences in saponin accumulation. • Some key microbial taxa showed positive relationships with saponin accumulation. [ABSTRACT FROM AUTHOR]

Aims: Soil nitrogen (N) mineralization-immobilization turnover (MIT) regulates the inorganic N supply in terrestrial ecosystems. Much research has been done to understand the factors that control the MIT in soils, but how plants-soil-microbe interactions influence the MIT remains to be further explored.A series of 15N tracing experiments, including with and without maize (Zea mays L.) planting, maize shading, and maize root endophytes inoculation, were conducted to investigate the drivers of the change in MIT by the presence of plant.Soil gross N mineralization (M), especially the mineralization of recalcitrant organic-N to NH4+ (MNrec, 0.51 mg N kg−1 d−1) was significantly improved by maize compared with the control treatment (without maize) (0.07 mg N kg−1 d−1). MNrec significantly decreased after removing maize or covering maize with a black box (preventing photosynthesis). Soil dissolved organic carbon (DOC) concentration significantly decreased after preventing photosynthesis, and showed a significant positive relationship with MNrec, confirming that photosynthetic substrate supply was the dominating factor in stimulating MNrec. Simultaneously, the release of absorbed NH4+ on the cation exchange sites increased with decreasing MNrec when photosynthesis was prevented. Microbial N immobilization (I), especially NO3− immobilization rate (INO3), was significantly stimulated in all maize treatments compared to the control. The INO3 of unsterilized soil applied with unsterilized plant endophytes was significantly higher than unsterilized soil applied with sterilized endophytes, indicating a close relationship between endophytes and microorganisms on INO3.MNrec was stimulated by the photosynthetic substrate supply, and the increasing microbial N immobilization induced by plant significantly increased the ratio of I to M in the presence of maize, which was beneficial to soil N retention and reduced N loss. Our results provide new insights of the MIT for better understanding the productivity of agricultural systems and its driving factors.Methods: Soil nitrogen (N) mineralization-immobilization turnover (MIT) regulates the inorganic N supply in terrestrial ecosystems. Much research has been done to understand the factors that control the MIT in soils, but how plants-soil-microbe interactions influence the MIT remains to be further explored.A series of 15N tracing experiments, including with and without maize (Zea mays L.) planting, maize shading, and maize root endophytes inoculation, were conducted to investigate the drivers of the change in MIT by the presence of plant.Soil gross N mineralization (M), especially the mineralization of recalcitrant organic-N to NH4+ (MNrec, 0.51 mg N kg−1 d−1) was significantly improved by maize compared with the control treatment (without maize) (0.07 mg N kg−1 d−1). MNrec significantly decreased after removing maize or covering maize with a black box (preventing photosynthesis). Soil dissolved organic carbon (DOC) concentration significantly decreased after preventing photosynthesis, and showed a significant positive relationship with MNrec, confirming that photosynthetic substrate supply was the dominating factor in stimulating MNrec. Simultaneously, the release of absorbed NH4+ on the cation exchange sites increased with decreasing MNrec when photosynthesis was prevented. Microbial N immobilization (I), especially NO3− immobilization rate (INO3), was significantly stimulated in all maize treatments compared to the control. The INO3 of unsterilized soil applied with unsterilized plant endophytes was significantly higher than unsterilized soil applied with sterilized endophytes, indicating a close relationship between endophytes and microorganisms on INO3.MNrec was stimulated by the photosynthetic substrate supply, and the increasing microbial N immobilization induced by plant significantly increased the ratio of I to M in the presence of maize, which was beneficial to soil N retention and reduced N loss. Our results provide new insights of the MIT for better understanding the productivity of agricultural systems and its driving factors.Results: Soil nitrogen (N) mineralization-immobilization turnover (MIT) regulates the inorganic N supply in terrestrial ecosystems. Much research has been done to understand the factors that control the MIT in soils, but how plants-soil-microbe interactions influence the MIT remains to be further explored.A series of 15N tracing experiments, including with and without maize (Zea mays L.) planting, maize shading, and maize root endophytes inoculation, were conducted to investigate the drivers of the change in MIT by the presence of plant.Soil gross N mineralization (M), especially the mineralization of recalcitrant organic-N to NH4+ (MNrec, 0.51 mg N kg−1 d−1) was significantly improved by maize compared with the control treatment (without maize) (0.07 mg N kg−1 d−1). MNrec significantly decreased after removing maize or covering maize with a black box (preventing photosynthesis). Soil dissolved organic carbon (DOC) concentration significantly decreased after preventing photosynthesis, and showed a significant positive relationship with MNrec, confirming that photosynthetic substrate supply was the dominating factor in stimulating MNrec. Simultaneously, the release of absorbed NH4+ on the cation exchange sites increased with decreasing MNrec when photosynthesis was prevented. Microbial N immobilization (I), especially NO3− immobilization rate (INO3), was significantly stimulated in all maize treatments compared to the control. The INO3 of unsterilized soil applied with unsterilized plant endophytes was significantly higher than unsterilized soil applied with sterilized endophytes, indicating a close relationship between endophytes and microorganisms on INO3.MNrec was stimulated by the photosynthetic substrate supply, and the increasing microbial N immobilization induced by plant significantly increased the ratio of I to M in the presence of maize, which was beneficial to soil N retention and reduced N loss. Our results provide new insights of the MIT for better understanding the productivity of agricultural systems and its driving factors.Conclusions: Soil nitrogen (N) mineralization-immobilization turnover (MIT) regulates the inorganic N supply in terrestrial ecosystems. Much research has been done to understand the factors that control the MIT in soils, but how plants-soil-microbe interactions influence the MIT remains to be further explored.A series of 15N tracing experiments, including with and without maize (Zea mays L.) planting, maize shading, and maize root endophytes inoculation, were conducted to investigate the drivers of the change in MIT by the presence of plant.Soil gross N mineralization (M), especially the mineralization of recalcitrant organic-N to NH4+ (MNrec, 0.51 mg N kg−1 d−1) was significantly improved by maize compared with the control treatment (without maize) (0.07 mg N kg−1 d−1). MNrec significantly decreased after removing maize or covering maize with a black box (preventing photosynthesis). Soil dissolved organic carbon (DOC) concentration significantly decreased after preventing photosynthesis, and showed a significant positive relationship with MNrec, confirming that photosynthetic substrate supply was the dominating factor in stimulating MNrec. Simultaneously, the release of absorbed NH4+ on the cation exchange sites increased with decreasing MNrec when photosynthesis was prevented. Microbial N immobilization (I), especially NO3− immobilization rate (INO3), was significantly stimulated in all maize treatments compared to the control. The INO3 of unsterilized soil applied with unsterilized plant endophytes was significantly higher than unsterilized soil applied with sterilized endophytes, indicating a close relationship between endophytes and microorganisms on INO3.MNrec was stimulated by the photosynthetic substrate supply, and the increasing microbial N immobilization induced by plant significantly increased the ratio of I to M in the presence of maize, which was beneficial to soil N retention and reduced N loss. Our results provide new insights of the MIT for better understanding the productivity of agricultural systems and its driving factors. [ABSTRACT FROM AUTHOR]

Abstract: To understand maize- and N-induced diel variations in CO2 emission, we examined hourly CO2 emissions during the three typical growth stages of maize in sandy loam soil. There was a distinct diel pattern in soil CO2 emissions, with the peak occurring between 14:00 and 18:00 and the trough occurring between 0:00 and 4:00. Maize presence delayed the time of the peak. The absolute amount and diel fluctuation of CO2 emissions tended to diminish with time in the bare soil fertilized with 150kgNha−1 (BS). In contrast, N-fertilized maize (N150) significantly enhanced the total amount of CO2 emissions and the peak-trough differences in CO2 emissions, which reached a maximum at the pollination stage and then decreased. Control soil (CK) containing maize but no N fertilizer had highest overall CO2 emissions but reduced diel fluctuation because rhizosphere respiration was elevated in the nighttime. Soil temperature accounted for 61–71% of diel variation in the BS treatment but for only 44–59% and 38–58% in the N150 and CK treatments, respectively. Photosynthesis rates affected diel variation at the seedling and pollination stages. Both temperature and photosynthesis rates together explained up to 67–84% of diel variation at the seedling and pollination stages in the N150 treatment, but only 61% at the seedling stage in the CK treatment due to more CO2 released in the nighttime. The increased nighttime CO2 release, in turn, decreased the effect of temperature and even reduced the influence of photosynthesis rate on diel variations in CO2 release. Based on the present results, the best time for obtaining a representative daily CO2 measurement was found to be approximately 8:00 at the seedling stage and 9:00–11:00 at the other growth stages. The current findings indicate that N addition reduces soil CO2 emissions and its diel fluctuation. [Copyright &y& Elsevier]

The processes and characteristics of nitrogen mineralization in paddy soils of the Taihu Region of China were studied with 120-day anaerobic incubation at 25 and 35 °C. Results showed that the organic nitrogen mineralized ranged from 4.0% to 9.4% of total N (60–241 mg kg−1) and that the mineral N was only correlated with total N (partial correlation analysis). The pH changed greatly and was related to the mineral nitrogen contents during mineralization. Temperature was one of the main factors influencing the mineralization of nitrogen. Four models, (1) effective cumulated temperature model; (2) a one-component, first-order exponential model (one-pool model); (3) a two-component, first-order exponential model (two-pool model); and (4) a two-component, mixed first- and zero-order exponential model including a constant term (special model), were fitted to the observed mineral N vs. incubation days using a non-linear regression procedure. The exponential models were significantly better than the effective cumulated temperature model, and the two-pool model and the special model gave the best fits among the four models. The special model was the unique one that could appropriately reflect the responses of organic nitrogen mineralization to incubation temperature in all studied paddy soils. All results showed that the special model made a better prediction of nitrogen mineralization under flooded conditions than the other models. [Copyright &y& Elsevier]

Soil microbial immobilization of nitrate (NO 3 −-N, I NO3) and its role in mitigating NO 3 −-N pollution in agricultural ecosystems globally is often neglected because of the tenet that microbes preferentially use ammonium over NO 3 −-N. Soil I NO3 driven by heterotrophic microorganisms is often carbon (C)-limited, and may therefore be stimulated by C sources with high C/nitrogen (N) ratios. Here, using 15NO 3 −-N labelling coupled with acetylene inhibition, quantitative PCR and Illumina high-throughput sequencing approaches, we demonstrated that I NO3 was stimulated from zero to a substantial level by crop residue amendment without any environmental risk; the degree of stimulation depending on residue quality and soil type. The stimulation was predicted well by C mineralization of the added residue. Soil with a lower initial nutrient status had reduced I NO3 efficiency due to stronger C constraint and lower return on energy investment. Fast-growing bacterial r-strategists were identified as the key driver of I NO3. We estimate that, globally, residue amendment could cause a total NO 3 −-N loss reduction of about 33.6 Tg N yr−1 through I NO3 stimulation. We suggest that soil I NO3 driven by addition of exogenous C is an overlooked process that can help curb NO 3 −-N accumulation in soil and its subsequent release to the environment, the "nitrate time bomb". • Organic residue amendments reduce nitrate accumulation by activating soil I NO3. • The intensity of stimulated I NO3 was best predicted by mineralization of residue-derived carbon. • Soil with lower initial nutrient status had lower I NO3 efficiency. • Fast-growing bacterial r-strategists were identified as the key driver of I NO3.. [ABSTRACT FROM AUTHOR]

Reductive soil disinfestation (RSD) and chemical soil disinfestation (CSD) are two common agricultural strategies for the elimination of soil-borne pathogens. However, the differences in soil bacterial microbiome and its associated functional characteristics between CSD and RSD are poorly understood. In this study, five soil treatments, un-treated control (CK), CSD with 0.5 t ha−1 dazomet (DZ), RSD with 10 t ha−1 ethanol (ET), 15 t ha−1 sugarcane bagasse (SB), and 15 t ha−1 bean dregs (BD), were compared. We evaluated their effects on microbial metabolic activity, functional diversity, nitrogen-related genes abundance, and bacterial community structure using Biolog analysis, real-time PCR, and high-throughput sequencing. RSD-related treatments improved soil metabolic activity, functional diversity, and the abundance of denitrifying genes to a greater extent than the DZ treatment. Carbon source utilization preference and bacterial community structure were strikingly altered by CSD and RSD practices. Bacterial richness, diversity, and evenness were notably lowered in the SB- and BD-treated soils compared with the CK and DZ-treated soils. Moreover, compared with the DZ- and ET-treated soils, the SB- and BD-treated soils harbored distinct unique and core microbiomes that were comprised of more abundant and diverse potentially disease-suppressive and organic-decomposable agents. Collectively, these results suggest that RSD practices incorporated with organic residues could considerably restore soil functional activity and diversity, and act as a potential agricultural practice for the development of disease-suppressive soils. • Soil disinfestation practices improve the metabolic activity of the diseased soil. • Organic residues amended RSDs harbor distinct bacterial microbiome compared to CSD. • Organic residues amended RSDs involve lower bacterial richness and diversity. • Organic residues amended RSDs are characterized by higher functional richness and diversity. • RSDs foster unique and core bacterial microbiomes beneficial to plant growth. [ABSTRACT FROM AUTHOR]

In this study, a 15N tracing experiment was conducted to determine gross N transformation rates in soils with 18 years of repeated N fertilizer applications and to quantify the underlying mechanisms to explain the variability of crop yield in a subtropical rain-fed purple soil. Six N fertilizer treatments were evaluated: unfertilized control (CK), mineral N fertilizer (NPK), pig manure (OM), mineral N fertilizer plus pig manure (OM-NPK), crop residue (RSD) and mineral N fertilizer plus crop residue (RSD-NPK). The results showed that the soil organic carbon (SOC) concentration in OM (average 13.79 g kg−1) and RSD-NPK (average 13.15 g kg−1) were significantly higher than the other treatments (varied from 5.91 to 11.23 g kg−1) after 18 years. Higher maize yields were observed in NPK, OM, OM-NPK, and RSD-NPK, and especially in RSD-NPK and OM-NPK after 18 years, compared with the data measured in the 11th years. Soil gross N mineralization rates (M) were significantly higher in all N fertilizer treatments (varied from 13.00 to 31.17 mg N kg−1 soil d−1) compared to CK (average 5.53 mg N kg−1 soil d−1). After 18 years of repeated N fertilizer applications, M were significantly higher than those in the 11th years for the same N fertilizer treatment, indicating that long-term repeated N fertilizer application, whether mineral N or organic fertilizer, continuously enhances M. M was positively correlated with SOC (p < 0.05) and total N (TN) (p < 0.05), suggesting that soil organic substrates are key factors regulating M. Maize yield was positively correlated with M (p < 0.05), suggesting that available N produced through soil N mineralization played the important role in yield formation. All N fertilizer treatments continuously stimulated gross autotrophic nitrification rates (O NH4). O NH4 increased with increasing M (p < 0.01) and ammonia-oxidizing bacteria (AOB) abundance (p < 0.05). However, compared to the 11th year, rates of dissimilatory nitrate reduction to ammonium (DNRA) and immobilization of NH 4 + (except RSD) and NO 3 − (except OM-NPK) decreased significantly in the N fertilizer treatments in the 18th year, indicating that N retention capacity is reduced over time and the risk of N losses increased. Considering the best balance among food security, soil C sequestration, and reduction of N leaching, mineral N in combination with straw return (RSD-NPK) can be recommended for regions with similar soils and climates. • Mineral N combined with straw returning is an efficient management improving SOC. • Mineral N combined with organic matter is the efficient management enhancing yield. • Long-term N fertilization can stimulate N mineralization and nitrification rates. • N retention capacity is reduced with long-term N fertilizer application. • Mineral N combined with straw returning is recommended in the studied region. [ABSTRACT FROM AUTHOR]

Conservation tillage practices, such as no tillage (NT) and ridge tillage (RT), have been widely proposed for use in many countries to increase carbon sequestration. However, understanding of how conservation tillage affects soil gross N transformation is still very limited. In this study, a 15 N-tracing experiment was carried out to investigate the effects of 14 years of RT and NT practices on the gross N transformation rates in black soils of northeast China. Based on the results for soil N transformations, soil organic carbon (SOC) sequestration, and crop yields, we propose suitable conservation tillage practices. The results showed that the NH 4 + immobilization rates were significantly higher under RT than NT. The heterotrophic nitrification rate in RT was significantly higher than in either conventional tillage (CT) or NT, contributing more than 89% of the total nitrate production in RT. NO 3 − immobilization was negligible under NT and CT, but this process was significantly stimulated by RT. Consequently, relative to NT and CT, a long-term RT treatment can stimulate inorganic N retention capacity and thus provides greater capacity to supply available N for uptake by crop plants. In addition, the average concentrations of SOC and total nitrogen (TN) in the 0–15 cm soil layer under RT were significantly higher than those under NT and CT. The average maize yields (2011–2015) under RT were similar to NT, both of which were significantly higher than under CT. Therefore, RT is arguably a more suitable tillage practice than NT and CT for enhancing the N retention, maize yield, and C sequestration for the studied black soils. [ABSTRACT FROM AUTHOR]

Appropriate N management can improve soil fertility and favour crop growth and production. Plant activities (e.g. N uptake and root exudates) also have feedback effects on soil N transformations and influence soil N supply and retention capacity. However, the inherent mechanisms between the feedback effect intensities and soil fertilizer are not fully elucidated. Thus, we carried out 15N tracing studies with arable soils at various long-term N fertilizer applications, including unfertilized control, synthetic N fertilizer, biochar, pig manure with and without synthetic N fertilizer, crop residues with and without synthetic N fertilizer. Soil gross N transformation rates, maize N uptake rates, and rhizosphere priming effects (RPE) on soil gross N transformations were quantified to explore mechanisms of soil N dynamics. Results showed that long-term N fertilizer applications significantly stimulated soil mineral N production rates, i.e. gross rates of N mineralization (M) and autotrophic nitrification (O NH4), and further enhanced maize N uptake and yield. Negative RPE on M were observed following long-term N fertilizer applications, ranging from −6.71 to −17.44 mg N kg−1 d−1. Furthermore, the strongest negative RPE on M were found for the combinations of chemical and organic N fertilizers. RPE on O NH4 (ranging from −3.10 to −31.91 mg N kg−1 d−1) also showed a similar trend to RPE on M in different treatments. Microbial N immobilization rates (I TN) and dissimilatory NO 3 − reduction to NH 4 + (D NO3) were stimulated by the presence of maize, showing an obvious positive RPE on I TN and D NO3. Therefore, N retention capacity in the rhizosphere was enhanced via a strong negative RPE on O NH4 , and a positive RPE on I TN and D NO3 in presence of maize following long-term N fertilizer applications. The stronger capacity of soil N supply in response to appropriate N management leads to higher maize activities and stronger feedbacks between plant and soil N transformation to improve N retention in rhizosphere, suggesting that the "Matthew effect" also applies to nutrient dynamics in the rhizosphere. Our results show that the combined applications of chemical and organic N fertilizers are the best way to enhance yield, NUE and N retention, and reduce the risks of soil N losses in arable soils. • Rhizosphere priming effects on soil N dynamics at various fertility levels were investigated. • Long-term N fertilizer applications improve soil mineral N supply and yield. • Rhizosphere priming effects on soil N dynamics vary following long-term N fertilizer applications. • The 'Matthew effect' exists in plant-soil systems. • Combination of chemical and organic N fertilizer is best N management in the studied region. [ABSTRACT FROM AUTHOR]

Long-term application of high doses of N fertilizer to achieve high yields has led to a significant accumulation of soil N (largely in the form of NO 3 −) in greenhouse vegetable production (GVP). At present, it is not clear how efficiently vegetables can use the NO 3 − accumulated in soil and from which source the N taken up by vegetables in GVP originates. In this study, three greenhouse soils with various degrees of soil NO 3 − accumulation (N1

In this study, a 15 N tracing incubation experiment and an in situ monitoring study were combined to investigate the effects of different N fertilizer regimes on the mechanisms of soil N dynamics from a long-term repeated N application experiment. The field study was initiated in 2003 under a wheat-maize rotation system in the subtropical rain-fed purple soil region of China. The experiment included six fertilization treatments applied on an equivalent N basis (280 kg N ha −1 ), except for the residue only treatment which received 112 kg N ha −1 : (1) UC, unfertilized control; (2) NPK, mineral fertilizer NPK; (3) OM, pig manure; (4) OM-NPK, pig manure (40% of applied N) with mineral NPK (60% of applied N); (5) RSD, crop straw; (6) RSD-NPK, crop straw (40% of applied N) with mineral NPK (60% of applied N). The results showed that long-term repeated applications of mineral or organic N fertilizer significantly stimulated soil gross N mineralization rates, which was associated with enhanced soil C and N contents following the application of N fertilizer. The crop N offtake and yield were positively correlated with gross mineralization. Gross autotrophic nitrification rates were enhanced by approximately 2.5-fold in the NPK, OM, OM-NPK, and RSD-NPK treatments, and to a lesser extent by RSD application, compared to the UC. A significant positive relationship between gross nitrification rates and cumulative N loss via interflow and runoff indicated that the mechanisms responsible for increasing N loss following long-term applications of N fertilizer were governed by the nitrification dynamics. Organic fertilizers stimulated gross ammonium (NH 4 + ) immobilization rates and caused a strong competition with nitrifiers for NH 4 + , thus preventing a build-up of nitrate (NO 3 − ). Overall, in this study, we found that partial or complete substitution of NPK fertilizers with organic fertilizers can reduce N losses and maintain high crop production, except for the treatment involving application of RSD alone. Therefore, based on the N transformation dynamics observed in this study, organic fertilizers in combination with mineral fertilizer applications (i.e. OM, OM-NPK, and RSD-NPK treatments) are recommended for crop production in the subtropical rain-fed purple soils in China. [ABSTRACT FROM AUTHOR]

Our understanding of how plants influence the gross rates of specific soil N transformations in plant-soil systems is still rudimentary, providing the incentive for our current study. A 15N tracing study was carried out with plants known for their NH 4 +-preference to quantify the gross soil N transformation and gross plant N uptake rates. Significant interactions between plants and gross rates of soil N transformations were observed. The rates of NH 4 + uptake by sugarcane (3.74 mg N kg−1 d−1) and tea (3.34 mg N kg−1 d−1) were much higher than microbial NH 4 + immobilization rates (0.01, and 0.27 mg N kg−1 d−1, respectively), suggesting that NH 4 +-preferring plants outcompeted microbial NH 4 + acquisition. The gross rates of NO 3 − immobilization increased with decreasing gross NH 4 + immobilization rates, indicating a switch towards microbial NO 3 − uptake under high plant NH 4 + demand. Moreover, the gross rates of autotrophic nitrification, the classical NO 3 − production pathway, was generally low in the studied acidic soil (average 0.40 mg N kg−1 d−1 in plant treatments), and was insufficient to meet the total NO 3 − demand (average 2.37 mg N kg−1 d−1). Gross rates of heterotrophic nitrification, ranging from 0.31 to 0.57 mg N kg−1 d−1, were stimulated by the presence of plants and were generally responsible for 49–69% of total NO 3 − production in the plant treatments, while this rate was negligible in the absence of plant. Heterotrophic nitrification might provide additional NO 3 − to meet N requirements of plants and microorganisms. This is supported by the positive correlation of gross heterotrophic nitrification coupled with gross NO 3 − immobilization and plant N uptake rates. Interactions between plant N acquisition and soil N transformations exist and plant-soil studies are key to identify feedbacks between plants and soil microbes. • Significant interactions between plants and soil N transformations were observed. • NH 4 +-preferring plants outcompeted microbes for NH 4 +. • Soil microorganisms switched to assimilate NO 3 − in the presence of NH 4 +-preferring plants. • Plants preferring NH 4 + can induce heterotrophic nitrification. [ABSTRACT FROM AUTHOR]