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Arbuscular mycorrhizal fungi (AMF) are widespread obligate symbionts of plants. This dynamic symbiosis plays a large role in successful plant performance, given that AMF help to ameliorate plant responses to abiotic and biotic stressors. Although the importance of this symbiosis is clear, less is known about what may be driving this symbiosis, the plant's need for nutrients or the excess of plant photosynthate being transferred to the AMF, information critical to assess the functionality of this relationship. Characterizing the AMF community along a natural plant productivity gradient is a first step in understanding how this symbiosis may vary across the landscape. We surveyed the AMF community diversity at 12 sites along a plant productivity gradient driven by soil nitrogen availability. We found that AMF diversity in soil environmental DNA significantly increased along with the growth of the host plants Acer rubrum and A. saccharum., a widespread tree genus. These increases also coincided with a natural soil inorganic N availability gradient. We hypothesize photosynthate from the increased tree growth is being allocated to the belowground AMF community, leading to an increase in diversity. These findings contribute to understanding this complex symbiosis through the lens of AMF turnover and suggest that a more diverse AMF community is associated with increased host-plant performance.

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Land-use change worldwide has been driven by anthropogenic activities, which profoundly regulates terrestrial C and N cycles. However, it remains unclear how the dynamics and decomposition of soil organic C (SOC) and N respond to long-term conversion of rice paddy to wetland. Here, soil samples from five soil depths (0-25 cm, 5 cm/depth) were collected from a continuous rice paddy and an adjacent wetland (a rice paddy abandoned for 12 years) on Shonai Plain in northeastern Japan. A four-week anaerobic incubation experiment was conducted to investigate soil C decomposition and N mineralization. Our results showed that SOC in the wetland and rice paddy decreased with soil depth, from 31.02 to 19.66 g kg-1 and from 30.26 to 18.86 g kg-1, respectively. There was no significant difference in SOC content between wetland and rice paddy at any depth. Soil total nitrogen (TN) content in the wetland (2.61-1.49 g kg-1) and rice paddy (2.91-1.78 g kg-1) showed decreasing trend with depth; TN was significantly greater in the rice paddy than in the wetland at all depths except 20-25 cm. Paddy soil had significantly lower C/N ratios but significantly larger decomposed C (Dec-C, CO2 and CH4 production) and mineralized N (Min-N, net NH4+-N production) than wetland soil across all depths. Moreover, the Dec-C/Min-N ratio was significantly larger in wetland than in rice paddy across all depths. Rice paddy had higher exponential correlation between Dec-C and SOC, Min-N and TN than wetland. Although SOC did not change, TN decreased by 14.1% after the land-use conversion. The Dec-C and Min-N were decreased by 32.7% and 42.2%, respectively, after the12-year abandonment of rice paddy. Conclusively, long-term conversion of rice paddy to wetland did not distinctly alter SOC content but increased C/N ratio, and decreased C decomposition and N mineralization in 0-25 cm soil depth.

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A network of 137 cultivated fields covering the wide diversity of soils, crop rotations and cropping practices throughout the region of Brittany (France) was monitored to collect data on soil organic nitrogen (SON) mineralization and to identify the factors that explain the observed variability. The dataset presented in this article contains all of the information about the soils, which were subjected to pedological description and in-depth analysis of their topsoil properties. The topsoil (0-30 cm) was sampled by mixing 30 samples to obtain one composite per field, which was divided into one sub-sample sieved at 5 mm to analyze soil microbial biomass (SMB) and SON mineralization via anaerobic incubation, and one subsample dried at 40 °C and sieved at 2 mm. The physico-chemical analyses included the particle-size distribution of five fractions; organic matter (OM); organic C; organic N; pH (water); pH KCl; CEC (Metson); CEC (hexamminecobalt); exchangeable Al, Ca, Fe, K, Mg, Mn and Na (hexamminecobalt); Olsen P; Dyer P; and total Al, Ca, Fe, K, Mg, Mn, Na and P. Physical OM fractionation was used to characterize the 200-2000 µm and 50-200 µm fractions of particulate organic matter (POM). Finally, three chemical methods were used to determine extractable organic nitrogen (EON): hot KCl, hot water and phosphate buffer tests. This dataset covers a wide range of pedological situations and cropping systems, and is of great interest to scientists searching for soil properties that can explain SON mineralization. It provides original data on EON indices, SMB and multiple forms of P. This paper supports and supplements information presented in a previous article [1].

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Afforestation is increasingly important in nutrient cycling in riparian ecotones given that ecosystems in riparian zones are susceptible to anthropogenic activities induced by land use change. However, how land use change (e.g., afforestation) with different planting types influences nitrogen (N) dynamics in riparian zones remains unclear. Here, we examined soil N dynamics following afforestation with three types of plantations of pure willow (Salix babylonica), pure mulberry (Morus alba), and the mixed two species paired with adjacent maize croplands in the upper Yangtze River of China. Our results showed afforestation with the two pure species significantly reduced soil total N (TN) concentration. Soil NO3--N concentration was significantly reduced by the willow and mixed-species afforestation, but soil NH4+-N concentration was significantly higher in the willow and mixed woodlands compared to the paired croplands. Soil N concentrations were tightly associated with the potential N transformation rates, which showed a roughly decreasing trend in N mineralization following afforestation. Soil properties, microbial biomass, and extracellular enzymes jointly explained a large proportion of the total variation in soil N concentrations, with soil enzymes largely contributing to N variation in the topsoil and soil properties primarily contributing to N variation in the subsoil. Overall, our results demonstrate that afforestation with different planting types had contrasting effects on soil N content in the riparian zone. These findings provide new insights into the management of afforestation types to retain soil N by mediating soil properties and microbial activities in the riparian zones under future land use change.

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As its use in agriculture grows, the fate of digestate in soil raises concerns on many different levels. In particular, the degradability of its organic matter when spread on soil is still an ongoing topic. In an effort to better understand the processes and dynamics of digestate soil incubation, C and N mineralization kinetics obtained in 358 days long laboratory incubations during decomposition of digestates were simulated using a dynamic model. The model includes twelve compartments related through processes including 18 parameters. The main novelty of this model is the use of accessibility-related variables to describe the fate of exogenous organic matter in soil, thus enabling a detailed understanding of its outcome in soil. Model calibration on cattle manure digestate incubation resulted in the estimation of parameter values. The newly calibrated model was then tested on an energy crop digestate incubation experiment. The model was able to reproduce accurately the experimental behavior of most variables.

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We hypothesized that the nitrogen-fixing tree Acacia mangium could improve the growth and nitrogen nutrition of non-fixing tree species such as Eucalyptus. We measured the N-mineralization and respiration rates of soils sampled from plots covered with Acacia, Eucalyptus or native vegetation at two tropical sites (Itatinga in Brazil and Kissoko in the Congo) in the laboratory. We used a bioassay to assess N bioavailability to eucalypt seedlings grown with and without chemical fertilization for at least 6 months. At each site, Eucalyptus seedling growth and N bioavailability followed the same trends as the N-mineralization rates in soil samples. However, despite lower soil N-mineralization rates under Acacia in the Congo than in Brazil, Eucalyptus seedling growth and N bioavailability were much greater in the Congo, indicating that bioassays in pots are more accurate than N-mineralization rates when predicting the growth of eucalypt seedlings. Hence, in the Congo, planting Acacia mangium could be an attractive option to maintain the growth and N bioavailability of the non-fixing species Eucalyptus while decreasing chemical fertilization. Plant bioassays could help determine if the introduction of N2-fixing trees will improve the growth and mineral nutrition of non-fixing tree species in tropical planted forests.

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Nitrogen (N) was an important indictor in change of soil fertility, which was closely related with N mineralization process. However, there is still need to further study on how rhizosphere soil N mineralization in paddy field response to different fertilizer management. Therefore, the influence of long-term (37-years) fertilizer regime on rhizosphere soil N mineralization, ammonification and nitrification rates, and its relationship under the double-cropping paddy field in southern of China were investigated in this study. The field experiment included following fertilizer regimes: inorganic fertilizer alone (MF), rice straw and inorganic fertilizer (RF), 30% organic manure and 70% inorganic fertilizer (OM), and no application of any fertilizer as a control (CK). The result indicated that rhizosphere soil organic carbon (SOC), total N, NO3 -N, and NH4 -N contents in paddy field with OM and RF treatments were increased. The result showed that rhizosphere soil NO2 - -N and mineral N contents with OM and RF treatments were increased, and the order of soil NO2 - -N and mineral N contents with all fertilizer treatments was showed as OM > RF > MF > CK. This result proved that soil aerobic and anaerobic N mineralization rates in paddy field with OM and RF treatments were higher than that of CK and MF treatments. Compared with MF treatment, soil ammonification rate with RF and OM treatments increased by 45.16% and 67.74%, soil nitrification rate with RF and OM treatments increased by 45.71% and 77.14%, respectively. There had significantly positively correlation between soil net mineralization, nitrification rate and SOC, total N contents. As a result, applied with rice straw and organic manure was a good measure to improve soil N mineralization in the double-cropping rice field.

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Invasion of plant species with functional traits that influences the rhizosphere can have significant effects on soil organic matter (SOM) dynamics if the invasive species stimulates soil microbial communities with, for example, an enhanced supply of labile carbon and oxygen. We evaluated these effects along a Phragmites invasion chronosequence spanning over 40 years. Using a δ13C and δ15N enriched substrate, we separated SOM-derived and substrate-derived carbon (C) and nitrogen (N) mineralization in surface (top 15 cm), shallow (30-45 cm), and deep (65-80 cm) soils collected from established, newly invaded, and native plant communities. We found all soils were susceptible to SOM priming, but priming profiles differed between vegetation communities, being highest at the surface in native assemblage soils, whereas highest at depth under invasive plants. Changes in functional microbial community composition at depth in Phragmites soils, evidenced by an increase in relative fungal laccase abundance, explained the SOM priming in these deep invaded soils. Our results show that invasive Phragmites maintains a microbial community at depth able to degrade SOM faster than that under native vegetation, evidencing that plant species shifts can fundamentally change soil biogeochemistry, altering element cycling and decreasing SOM residence time. Furthermore, our experimental design allowed to quantify real-time SOM-C and SOM-N gross mineralization, resulting in a new model relating C and N mineralization in these wetland soils and providing new insights on how SOM decomposition impacts N availability and cycling across wetland N pools.

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Biochar (BC) has attracted attention for carbon sequestration, a strategy to mitigate climate change and alleviate soil acidification. Most meta-analyses have insufficiently elaborated the effects of BC on soil N transformation so the practical importance of BC could not be assessed. In this study, a 15N tracing study was conducted to investigate the effects of BC amendment on soil gross N transformations in acidic soils with different land-use types. The results show that the BC amendment accelerated the soil gross mineralization rate of labile organic N to NH4+ (MNlab) (3 %-128 %) which was associated with an increase in total nitrogen. BC mitigated NH3 volatilization (VNH3) (52 %-99 %) in upland and forest soils due to NH4+/NH3 adsorption, while it caused higher gaseous N losses (NH3 and N2O) in flooded paddy soils. An important function was the effect of BC addition on NH4+ oxidation (ONH4). While ONH4 increased (4 %-19 %) in upland soils, it was inhibited (34 %-71 %) in paddy soils and did not show a response in forest soils. Overall, the BC amendment reduced the potential risk of N loss (PRL), especially in forest soils (82 %-98 %). This study also shows that the BC effect on soil N cycling is land-use specific. The suitability of practices including BC hinges on the effects on gaseous N losses.

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Cover crops are supposed to decrease the soil mineral N content (Nmin) during winter and increase the N supply to subsequent main crops due to mineralization of N previously prevented from leaching. However, data on N supply from cover crops grown before sugar beet have rarely been reported for Central European conditions. Therefore, our study aimed to provide information for cover crops differing in frost resistance and biomass quantity applicable for N fertilizer dressing in the subsequent main crop. In 2018/19 and 2019/20, field trials were conducted on two Luvisol sites in Germany typical for sugar beet cultivation, comprising a sequence of autumn sown cover crops grown after field pea followed by unfertilized sugar beet main crops sown in next spring. Apparent net N mineralization and the N effect of cover crops on sugar beet were calculated according to a mass balance approach including Nmin and sugar beet N uptake. Winter rye and oil radish revealed the greatest potential for scavenging nitrate from the soil profile while reductions caused by frost-sensitive saia oat and spring vetch were more variable. The amount of N in the cover crop biomass was negatively correlated with Nmin in autumn and also in spring. Thus, for environmentally effective cover cropping in Central Europe, species with a sufficiently high frost tolerance should be chosen. Despite cover crop N uptake up to 170 kg N ha-1 and C:N ratios < 20, a positive N effect on sugar beet was only found between March and July of the beet growing season and was 50 kg N ha-1 at maximum, while between August and September, net immobilization was predominant with up to 100 kg N ha-1. Differences among crop species were not consistent across the site/years investigated. Sugar yield was lowest after rye at 3 sites/years and correlated positively with Nmin in spring. Correlation between yield and cover crop N effect was mostly low and inconsistent and could not be improved by a multiple regression approach. Thus, factors other than in-season N supply from cover crops apparently impacted sugar beet yield formation to a larger extent.

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To examine the perturbation of atmospheric nitrogen (N) deposition on soil N status and the biogeochemical cycle is meaningful for understanding forest function evolution with environmental changes. However, levels of soil bioavailable N and their environmental controls in forests receiving high atmospheric N deposition remain less investigated, which hinders evaluating the effects of enhanced anthropogenic N loading on forest N availability and N losses. This study analyzed concentrations of soil extractable N, microbial biomass N, net rates of N mineralization and nitrification, and their relationships with environmental factors among 26 temperate forests under the N deposition rates between 28.7 and 69.0 kg N ha-1 yr-1 in the Beijing-Tianjin-Hebei (BTH) region of northern China. Compared with other forests globally, forests in the BTH region showed higher levels of soil bioavailable N (NH4+, 27.1 ± 0.8 mg N kg-1; NO3-, 7.0 ± 0.8 mg N kg-1) but lower net rates of N mineralization and nitrification (0.5 ± 0.1 mg N kg-1 d-1 and 0.4 ± 0.1 mg N kg-1 d-1, respectively). Increasing N deposition levels increased soil nitrification and NO3- concentrations but did not increase microbial biomass N and N mineralization among the study forests. Soil moisture and C availability were found as dominant factors influencing microbial N mineralization and bioavailable N. In addition, by budgeting the differences in soil total N densities between the 2000s and 2010s, atmospheric N inputs to the forests were more retained in soils than lost proportionally (84% vs. 16%). We concluded that the high N deposition enriched soil N without stimulating microbial N mineralization among the study forests. These results clarified soil N status and the major controlling factors under high anthropogenic N loading, which is helpful for evaluating the fates and ecological effects of atmospheric N pollution.

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Limited knowledge about how nitrogen (N) dynamics are affected by climate change, weather variability, and crop management is a major barrier to improving the productivity and environmental performance of soybean-based cropping systems. To fill this knowledge gap, we created a systems understanding of agroecosystem N dynamics and quantified the impact of controllable (management) and uncontrollable (weather, climate) factors on N fluxes and soybean yields. We performed a simulation experiment across 10 soybean production environments in the United States using the Agricultural Production Systems sIMulator (APSIM) model and future climate projections from five global circulation models. Climate change (2020-2080) increased N mineralization (24%) and N2O emissions (19%) but decreased N fixation (32%), seed N (20%), and yields (19%). Soil and crop management practices altered N fluxes at a similar magnitude as climate change but in many different directions, revealing opportunities to improve soybean systems' performance. Among many practices explored, we identified two solutions with great potential: improved residue management (short-term) and water management (long-term). Inter-annual weather variability and management practices affected soybean yield less than N fluxes, which creates opportunities to manage N fluxes without compromising yields, especially in regions with adequate to excess soil moisture. This work provides actionable results (tradeoffs, synergies, directions) to inform decision-making for adapting crop management in a changing climate to improve soybean production systems.

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BACKGROUND: The availability of soil nitrogen (N) decreases as the structure of agricultural soils degrades. Traditional methods focus on organic amendments that indirectly affect the porosity and N content of soil. Due to the low efficiency of such amendments, new materials, particularly highly porous materials, are needed to improve the quality of soil, which has opened new directions. RESULTS: The addition of 2 to 7 mm of porous clay ceramic (PLC) significantly increased the fresh weight of Brassica chinensis. The soil aeration porosity (>50 µm) increased by 0.69% on average in response to 1% PLC application. Soil NO3 - -N, NH4 + -N and mineral N increased by 3.3, 1.3 and 4.6 mg kg-1 on average, respectively, following a 1% PLC application rate. The initial N content of the high PLC treatments was the lowest in the incubation experiment. The parameters of soil N mineralization, i.e. potentially mineralizable N (N0 ), the first-order rate constant (k) and the mineralization composite index (N0  × k), increased obviously as the amount of PLC increased. Porosities larger than 1000 µm were significantly more positively correlated with the parameters of soil N mineralization than those <500 µm. The Pearson correlation coefficients suggested that high porosity, mineral N and N0 values had significant positive relationships with the fresh weights in double seasons. CONCLUSION: The application of PLC increased soil aeration and enhanced the availability of soil N, which yielded large vegetable harvests in clayey soils in the short term. © 2022 Society of Chemical Industry.

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The mineralization and immobilization of nitrogen (N) are critical biogeochemical transformations in estuarine and coastal sediments. However, the biotic and abiotic mechanisms that regulate the two processes in different aged mangrove sediments remain poorly understood. Here, we used 15N isotope dilution method to investigate the changes in sediment N mineralization (GNM) and NH4+ immobilization (GAI) of different aged mangrove habitats (including 0, 10, and 20 years Sonneratia apetala, as well as >40 years mature native Kandelia obovata) in Qi'ao Island, Guangdong Province, China. Measured GNM and GAI rates ranged from 2.69 to 17.53 µg N g-1 d-1 and 2.29-21.38 µg N g-1 d-1, respectively, which varied both spatially and seasonally. The ratio of GNM to total N (PAM%, 0.24-0.86%) also varied spatially and seasonally, but the ratio of GAI to GNM (RAI, 0.79-1.54) only varied spatially. Mangrove restoration significantly increased the N mineralization and immobilization rates, but remained lower than those of mature native Kandelia obovata habitat. The sediment bacterial abundance, labile organic matter and temperature are the dominant factors in controlling N mineralization and immobilization. Our findings suggested that exotic mangrove Sonneratia aperale plantation can enhance sediment N mineralization and immobilization rates and improve N stability through accumulated biomass rapidly. Overall, these results provide new insights into sediment N transformation processes and associated influencing mechanisms in such intertidal wetlands profoundly influenced by human activities.

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The impacts of climate change on ecosystem structure and functioning are likely to be strongest at high latitudes due to the adaptation of biota to relatively low temperatures and nutrient levels. Soil warming is widely predicted to alter microbial, invertebrate, and plant communities, with cascading effects on ecosystem functioning, but this has largely been demonstrated over short-term (<10 year) warming studies. Using a natural soil temperature gradient spanning 10-35°C, we examine responses of soil organisms, decomposition, nitrogen cycling, and plant biomass production to long-term warming. We find that decomposer organisms are surprisingly resistant to chronic warming, with no responses of bacteria, fungi, or their grazers to temperature (fungivorous nematodes being an exception). Soil organic matter content instead drives spatial variation in microorganism abundances and mineral N availability. The few temperature effects that appear are more focused: root biomass and abundance of root-feeding nematodes decrease, and nitrification increases with increasing soil temperature. Our results suggest that transient responses of decomposers and soil functioning to warming may stabilize over time following acclimation and/or adaptation, highlighting the need for long-term, ecosystem-scale studies that incorporate evolutionary responses to soil warming.

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Seasonal precipitation regime plays a vital role in regulating nutrient dynamics in seasonally dry tropical forests. Present evidence suggests that not only wet season precipitation is increasing in the tropics of South China, but also that the wet season is occurring later. However, it is unclear how nutrient dynamics will respond to the projected precipitation regime changes. We assessed the impacts of altered seasonal precipitation on soil net N mineralization in a secondary tropical forest. Since 2013, by reducing throughfall and/or irrigating experimental plots, we delayed the wet season by two months from April-September to June-November (DW treatment) or increased annual precipitation by 25% in July and August (WW treatment). We measured soil net N mineralization rates and assessed soil microbial communities in January, April, August and November in 2015 and 2017. We found that a wetter wet season did not significantly affect soil microbes or net N mineralization rates, even in the mid-wet season (August) when soil water content in the WW treatment increased significantly. By contrast, a delayed wet season enhanced soil microbial biomass and altered microbial community structure, resulting in a two-fold increase in net N mineralization rates relative to controls in the early dry season (November). Structural equation modeling showed that the changes in net N mineralization during the early dry season were associated with altered soil microbial communities, dissolved organic N, and litterfall, which were all affected by enhanced soil water content. Our findings suggest that a delayed wet season could have a greater impact on N dynamics than increased precipitation during the wet season. Changes in the seasonal timing of rainfall might therefore influence the functioning of seasonally dry tropical forests.

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Understanding the effects of fire history on soil processes is key to characterise their resistance and resilience under future fire events. Wildfires produce pyrogenic carbonaceous material (PCM) that is incorporated into the soil, playing a critical role in the global carbon (C) cycle, but its interactions with soil processes are poorly understood. We evaluated if the previous occurrence of wildfires modulates the dynamic of soil C and nitrogen (N) and microbial community by soil ester linked fatty acids, after a new simulated low-medium intensity fire. Soils with a different fire history (none, one, two or three fires) were heat-shocked and amended with charcoal and/or ash derived from Pinus pinaster. Soil C and N mineralization rates were measured under controlled conditions, with burned soils showing lower values than unburned (without fire for more than sixty years). In general, no effects of fire recurrence were observed for any of the studied variables. Microbial biomass was lower in burned, with a clear dominance of Gram-positive bacteria in these soils. PCM amendments increased cumulative carbon dioxide (CO2) production only in previously burned soils, especially when ash was added. This contrasted response to PCM between burned and unburned soils in CO2 production could be related to the effect of the previous wildfire history on soil microorganisms. In burned soils some microorganisms might have been adapted to the resulting conditions after a new fire event. Burned soils showed a significant positive priming effect after PCM amendment, mainly ash, probably due to an increased pH and phosphorous availability. Our results reveal the role of different PCMs as drivers of C and N mineralization processes in burned soils when a new fire occurs. This is relevant for improving models that evaluate the net impact of fire in C cycling and to reduce uncertainties under future changing fire regimes scenarios.

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Interactions between soil fungi and soil environmental factors regulate soil nitrogen (N) mineralization rates on the eastern Qinghai-Tibetan Plateau. Some studies have also illuminated differences in soil N mineralization rate based on different mycorrhizal forests, but the associated effect of soil fungal functional guilds and soil environmental factors underlying this process are not well-understood. Three primary forests respectively dominated by Abies fargesii var. faxoniana (ectomycorrhizal, EcM), Cupressus chengiana (arbuscular mycorrhizal, AM) and Rhododendron phaeochrysum (ericoid mycorrhizal, ErM) trees were selected in this area. Meanwhile, soil net N mineralization rate, soil fungal composition and soil enzyme activity among these three mycorrhizal forests were studied. Our results showed that there were significant differences in the seasonal variation of soil net N mineralization rates among three mycorrhizal forests. Soil net N mineralization rate in the AM forest was faster. EcM fungi and saprotroph are the main functional guilds in these three mycorrhizal forests. Meanwhile, the relative abundances of soil fungal functional guilds, soil temperature and soil peroxidase activity could explain 85.0% in the difference of soil net ammonification rate among three mycorrhizal forests. In addition, soil temperature, soil water-filled pore space and soil ammonium content play a central role in controlling the differing soil net nitrification rate among three mycorrhizal forests. Our results suggest differences in soil net mineralization among different mycorrhizal forest types are driven mainly by soil net ammonification. Soil fungal functional guilds and temperature regulate the rate of soil net ammonification by modulating soil peroxidase activity.

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Improving nitrogen use efficiency (NUE) is essential for sustainable agriculture, especially in high-N-demanding crops such as canola (Brassica napus). While advancements in above-ground agronomic practices have improved NUE, research on soil and below-ground processes are limited. Plant NUE-and its components, N uptake efficiency (NUpE), and N utilization efficiency (NUtE)-can be further improved by exploring crop variety and soil N cycling. Canola parental genotypes (NAM-0 and NAM-17) and hybrids (H151857 and H151816) were grown on a dark brown chernozem in Saskatchewan, Canada. Soil and plant samples were collected at the 5-6 leaf stage and flowering, and seeds were collected at harvest maturity. Soil N cycling varied with phenotypic stage, with higher potential ammonium oxidation rates at the 5-6 leaf stage and higher urease activity at flowering. Seed N uptake was higher under higher urea-N rates, while the converse was true for NUE metrics. Hybrids had higher yield, seed N uptake, NUtE, and NUE, with higher NUE potentially owing to higher NUtE at flowering, which led to higher yield and seed N allocation. Soil N cycling and soil N concentrations correlated for improved canola NUE, revealing below-ground breeding targets. Future studies should consider multiple root characteristics, including rhizosphere microbial N cycling, root exudates, and root system architecture, to determine the below-ground dynamics of plant NUE.

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Plant residue inputs play a crucial role in regulating soil carbon (C) stock and nitrogen (N) availability in cropland. However, little is known regarding how plant inputs mediate the relationships between soil C and net N mineralization, causing additional uncertainty in predicting ecosystem C and N dynamics. This study investigated the influences of long-term deprivation of plant inputs, short-term addition of maize straw and experimental warming on soil C and net N mineralization and their relationships. We conducted an 815-day laboratory incubation experiment under 10 and 20 °C using soils from a long-term bare fallow plot (without plant inputs for 23 years) and its adjacent old field plot (with continuous plant inputs). Our results showed that long-term deprivation of plant inputs decreased soil net N mineralization (per unit total N or TN) by 56% on average, but had minor effect on soil C mineralization (per unit soil organic C). Soil C and net N mineralization rates were positively correlated in the old field soil under 20 °C. However, soil C and net N mineralization rates were not correlated in the bare fallow soil, mainly due to the low level of net N mineralization. Moreover, soil C and net N mineralization rates were significantly increased by the addition of maize straw in both land-use types. When net N mineralization was <162 (or 159) µg N g-1 TN d-1, soil C and net N mineralization rates were negatively correlated due to an increase of microbial N demand during plant litter mineralization. When net N mineralization was >162 (or 159) µg N g-1 TN d-1, soil C and net N mineralization rates were positively correlated owing to a greater microbial mining of N from soil organic matter (SOM). Further, elevated temperature increased soil C and net N mineralization rates, and changed the relationships between soil C and net N mineralization. Taken together, this study provides evidence that plant inputs mediate the relationships between soil C and net N mineralization, and is thus critical in controlling ecosystem C and N cycling.

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