Soil Inorganic Nitrogen Research Articles

Nitrogen addition alleviates the negative effects of reduction in precipitation on soil multifunctionality in a typical steppe

The increasing frequency of drought events and nitrogen deposition have fundamentally changed soil microbial functions in terrestrial ecosystems. However, most studies have mainly concentrated on the impact of a single environmental factor on ecosystem functions; how drought and nitrogen enrichment interactively affect soil multifunctionality remains largely unknown. In this study, the effects of different drought scenarios [intense drought (ID), chronic drought (CD), and reduced rainfall frequency (RF)] and nitrogen addition on soil microbial biomass, and soil multifunctionality (determined using soil enzyme activity) were examined in the fourth year of a field manipulative experiment conducted in a typical steppe in northern China. The results demonstrated that both ID and CD significantly reduced soil multifunctionality, microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN). The CD treatment also decreased the ratio of MBC to MBN, while RF had less impacts on soil multifunctionality and the biomass of soil microbes. In contrast, nitrogen addition enhanced soil multifunctionality, MBC and MBN. Structural equation modeling analysis demonstrated that drought decreased soil multifunctionality directly and indirectly by reducing MBN and soil water content, whereas nitrogen addition increased soil multifunctionality mainly by increasing MBN and soil inorganic nitrogen. This study provides the first experimental evidence of the opposing impacts of reduction in precipitation and nitrogen enrichment on soil microbial biomass and soil multifunctionality in a semiarid typical steppe, and suggests that nitrogen fertilization could be an effective measure to alleviate the negative effects of climate drought on soil functions in nitrogen- and water-limited grassland ecosystems.

A mycoheterotrophic orchid uses very limited soil inorganic nitrogen in its natural habitat

Mycoheterotrophic plants acquire nitrogen (N) directly from the soil and through their symbiotic fungi. The fungi-derived N has received considerable attention, but the contribution of soil-derived N has been largely overlooked. We investigated how the leafless, rootless, and almost mycoheterotrophic orchid Cymbidium macrorhizon obtains soil N by applying 15N-labeled ammonium nitrate in its natural habitat, and tracking metabolite accumulation and mycorrhizal fungal association after N application. The decline of N in the rhizome from flowering to fruiting indicated a transfer of N from the rhizome to fruits. At current dose of N application (0.6 g NH4NO3 each plant), only 1.5% of the plant's N was derived from fertilizer, resulting in a low nitrogen use efficiency of 0.27%. The majority of those newly absorbed N (88.89%) was found sank in the rhizome. Amino acids (or their derivatives) and alkaloids were predominant differentially accumulated nitrogenous metabolites after N application, with amino acids occurring in both fruits and the rhizome, and alkaloids primarily in the fruits. The addition of N did not alter the richness of mycorrhizal fungi, but did affect their relative abundance. Our findings suggest that Cymbidium macrorhizon uses very limited soil inorganic nitrogen in its natural habitat, and the root-like rhizome primarily stores N rather than absorbs its inorganic forms, offering new insights into how mycoheterotrophic plants utilize soil N, and the influence of nutrient availability on the orchid-fungi association.

Soil profile distribution of organic, inorganic, and labile carbon and nitrogen fractions vary in semi‐arid drylands under long‐term conservation tillage systems

AbstractChanges in soil carbon (C) and nutrients considerably influence soil health and agricultural sustainability. However, how agricultural management affects C and N allocation among various soil organic matter pools and their linkages with soil health are not clear for arid and semi‐arid regions. This study aimed to evaluate the soil profile distribution of selected C and N fractions and associated soil health properties in conventional tillage (CT), no‐tillage (NT), and strip tillage (ST) fields and quantify the relationship of labile and inorganic C and N fractions to soil organic carbon (SOC) sequestration in semi‐arid dryland cropping systems. Crop rotation was a 4‐year cycle of corn (Zea mays L.)—sorghum (Sorghum bicolor L. Moench)—winter wheat (Triticum aestivum L.)—fallow across all tillage systems. Soil samples were collected from 0–20, 20–40, and 40–60 cm depths of each plot in July 2022, after 9 years of plot establishment, and analysed for potentially mineralizable carbon (PMC), microbial biomass carbon (MBC), SOC, soil inorganic (SIC), soil total carbon (STC), soil inorganic nitrogen (SIN), total labile nitrogen (TLN), total organic nitrogen (SON), and labile organic nitrogen (LON) and other soil health indicators. The results indicate that PMC was 31% more and LON was 23% more in NT than in CT, whilst ST resulted in lower pH and had only 10%, 9%, and 24% more SON, STN, and LON, respectively, than CT in 0–60 cm profile. The SIC stock was negatively correlated with MBC, PMC, SON, STN, LON, TLN, and SIN, whilst positively correlated with depth, STC, and pH. After 9 years of conservation tillage, whilst depth‐wise distribution varied among tillage systems, soil C sequestration rate was negative in the 0–60 cm profile under both NT and ST compared with CT, mainly owing to more SIC accumulation in deeper depth of conventional system. These results show the complexity of soil C and N allocation under different tillage systems, with NT and ST supporting greater C and N storage in the surface soil and CT supporting more C and N storage in the deeper depth. Soil biological activity indicators appear to drive surface SOC accumulation, whilst soil pH and N availability influenced SIC accumulation in lower depths.

Cover crop quality and quantity influences organic corn performance more than soil context

AbstractCover cropping is a common practice among organic growers, well-known for its potential to supply nitrogen (N) to subsequent cash crops. Uncertainties and challenges exist in understanding how cover crops interact with soil properties and management practices across organic farms to supply N, and if such N supply is synchronous with subsequent cash crop N demand. An on-farm study examined cereal rye (Secale cereale) versus crimson clover (Trifolium incarnatum) planted before corn (Zea mays L.) in five organic farms in Michigan with a range of soil properties and management practices. High quality crimson clover residue [Carbon (C):N ratio 15:1] was associated with higher soil inorganic nitrogen, corn chlorophyll content, tissue N content, and grain yields relative to low quality cereal rye residue (C:N ratio 25:1). There were several lines of evidence that low quality cereal rye residue coupled with substantial biomass and a dry season limited N release during peak corn N demand. Nitrogen uptake efficiency (NUE, ratio of total N removed by corn to total N input) was above 1 for corn farms with low soil organic matter (SOM), active N and C pools, and lower than 1 for farms with high SOM and active N and C pools. Overall, cover crop biomass and cover crop quality was a more important driver of corn performance than background SOM content in organic corn farms. Our research highlights the challenges of ensuring sufficient N supply in organic field production, and the importance of planting a legume cover crop before corn.

Water addition but not reduction alters plant biomass-diversity relationship.

The relationship between plant aboveground biomass and diversity typically follows a unimodal pattern, showing a positive correlation in resource-poor habitats and a negative correlation in resource-rich environments. Precipitation is a crucial resource for both plant biomass and diversity in terrestrial ecosystems. However, the impact of precipitation changes on the relationship between plant biomass and diversity remains unclear. We conduct a water addition field experiment in a semiarid grassland and identify a unimodal relationship between plant biomass and species richness under ambient conditions. Water addition delays the declining phase of this unimodal curve and shift it upward compared to ambient conditions. Our meta-analysis of water addition experiments conducted across major biomes worldwide (grassland, shrubland, desert, and forest) supports this finding, while water reduction does not alter the biomass-diversity relationship. Water addition increases biomass in all climate but only increases species richness in arid and semiarid climate. Similarly, water reduction decreases biomass in all climate but only reduces species richness in arid and semiarid climate. Species richness in dry subhumid and humid climate does not change significantly. Furthermore, our field experiment shows that water addition increases plant diversity while decreasing soil inorganic nitrogen levels. The increase in one resource, such as water, leads to the scarcity of another, such as nutrient, thus postponing the declining phase of the plant biomass-diversity relationship typically observed in resource-rich habitats. Our research contributes to predicting the plant biomass-diversity relationship under changing precipitation conditions and highlights the complex interplay between water availability, nutrient level, and plant diversity.

Effects of poly‐γ‐glutamic acid addition on the transformation and distribution of soil nitrogen under different water conditions

AbstractThe impact of external poly‐γ‐glutamic acid (γ‐PGA) on soil nitrogen (N) transformation and distribution remains unclear, despite its contrasting effects on N use efficiency. Therefore, soil culture and soil column experiments were conducted using three different γ‐PGA addition rates (0%, 4% and 8% of dry soil weight, w/w) under different soil water contents (40%, 60% and 80% of field water capacity) and dry–wet cycles (0, 2, 4 and 8 times cycles; a single dry–wet cycle involved reducing soil water content from 80% to 40% of field water capacity) in sandy loam soil. The results of soil culture experiment showed that the γ‐PGA significantly increased soil –N and –N contents, as well as nitrification and transformation rates. However, these effects were observed to be influenced by both the culture time and soil water content. In addition, the results of soil column experiment showed that γ‐PGA not only significantly enhanced the soil inorganic nitrogen content within the 0–20 cm soil layer, but also improved water retention capacity. However, the differences between the γ‐PGA treatments gradually diminished with an increase in dry–wet cycle times. These results indicate that γ‐PGA addition enhanced soil inorganic N content and soil water retention by influencing soil N transformation and water distribution. However, the impact of γ‐PGA addition on soil improvement was regulated by soil water content, which should be taken into full consideration in agricultural practices.

Cross-talk between antioxidant production and secondary metabolite biosynthesis under combined effects of ozone stress and nitrogen amendments: A case study of lemongrass

The present experiment was done to study the interactive effects of soil nitrogen (N) amendments and elevated ozone (O3) (N–O3) on a medicinal plant, lemongrass [Cymbopogon flexuosus (Steud.) (Wats.)]. The experiment used two doses of inorganic soil nitrogen (N1, recommended and N2, 1.5-times recommended dose) in open-top chambers under ambient and elevated (ambient + 15 ppb and ambient + 30 ppb) O3 conditions. To analyze various characteristics, samples were collected at 45 and 90 days after transplantation (DAT). Additionally, at 110 days after transplantation (DAT), the metabolite contents of the leaves and essential oils were analyzed. The present study aims to investigate the mechanistic approach involving the crosstalk between antioxidant production and secondary metabolite biosynthesis in lemongrass upon N–O3 interactions. The present experiment showed that N amendments can be an efficient measure to manage O3 injury in plants, along with ensuring a balance between primary and secondary metabolic pathways, thus sustaining the plant defense and production of bioactive compounds, simultaneously. Under N–O3, not only the Halliwell asada pathway was stimulated resulting in the increased activities and concentrations of antioxidant pools; the shikimate, phenylpropanoid and mevalonic acid pathways were also invigorated, producing more number and contents of secondary metabolites (SMs), compared with plants that were not treated with N doses. This study suggests that soil nitrogen amendments will improve the therapeutic qualities of lemongrass, along with the strengthening of its antioxidant machinery, upon exposure to O3 stress.

Quantitative importance of subsoil nitrogen cycling processes in Andosols and Cambisols under temperate forests

Nitrogen availability often limits plant growth in forest ecosystems. Plants, including trees, utilize soil inorganic nitrogen transformed via nitrogen cycling processes, including mineralization and nitrification. While most plant fine roots are distributed in surface soil layers, plants take up nitrogen even from subsurface soil layers in addition to the surface soil layers, especially under high nutrient competition. However, there is still limited knowledge about nitrogen cycles within deeper soil layers. In this study, we investigated the vertical profiles (0–60 cm) of the net nitrogen mineralization and nitrification rates at four Japanese forest sites with two different soil types (Andosols and Cambisols). The partial least square path modeling (PLS-PM) was used to determine factors affecting nitrogen cycling processes. The net nitrogen mineralization and nitrification rates per unit soil weight were considerably higher in the surface soil layer than in the deeper soil layers in Andosols but not in Cambisols. PLS-PM analysis showed that microbial biomass and soil organic matter quantities were the important factors influencing the net nitrogen mineralization and nitrification rates, indicating that a similar mechanism, which drives the spatial variations of nitrogen cycling processes in the surface soil layer, predominantly regulates the vertical variations of the processes. Moreover, it was estimated that the net nitrogen mineralization rate could be comparable at all soil types and depths when the rate was expressed per unit soil volume. Therefore, subsoil layers could be a quantitatively important source of plant-available nitrogen in Andosols and Cambisols.

Response of soil inorganic nitrogen dynamics to planting age and vegetation type in artificial sand‐fixing land

AbstractVegetation restoration in dryland regions may be a powerful way to control desertification and promote local habitat recovery. In these artificial revegetation systems, ecosystem processes and functioning are strongly determined by nitrogen (N) availability, while soil inorganic N (SIN) is the major available N form and is absorbed as a main N source for plants. However, SIN dynamics, their influencing factors, and their relative importance to the ecosystem of these N‐limited systems are not well understood. A field investigation was conducted to examine the monthly variations in SIN and its response to planting age and vegetation type in a typical artificial sand‐fixing system in northwestern China. The SIN content in topsoil (0–20 cm) during the growing season ranged from 7.10 to 95.65 mg kg−1, with a mean value of 27.14 mg kg−1. Soil nitrate N had a dominant role in determining SIN monthly dynamics, which showed a fluctuating trend with two peak values in early July and late August. SIN showed a significant increasing trend with the planting age of sand‐fixing vegetation, and it was highest for Nitraria sphaerocarpa (55.66 ± 5.76 mg kg−1), followed by Haloxylon ammodendron (29.81 ± 3.47 mg kg−1) and interspace (11.39 ± 1.13 mg kg−1). SIN displayed a hump‐shaped relationship with air temperature (R2 = 0.96, p < 0.01) and had a maximum at 19.88°C. The change rate of SIN was positively correlated with accumulated precipitation (R2 = 0.99, p < 0.05). SIN was correlated significantly with soil organic carbon (SOC), total nitrogen (TN), and soil clay content. Our results revealed that climatic (air temperature and precipitation), abiotic (soil texture), plant (planting age and vegetation type), and nutrient‐related (SOC and TN) factors regulate SIN dynamics in artificial sand‐fixing vegetation systems. Climate was the predominant factor affecting soil ammonium N, and soil nutrients (SOC and TN) were the predominant factor affecting soil nitrate N. Therefore, these factors should be integrated into optimizing regional vegetation establishment and improving ecosystem management practices in sand‐fixing lands.

Increase in precipitation will facilitate the ecological stability of desert steppe in the future

Community stability plays a vital role in ensuring the consistent provision of ecosystem services despite climatic changes. It is presumed that future changes to annual precipitation will impact the ecological stability of many systems, particularly the ‘fragile’ desert steppe. However, most studies of ecological stability are inferred from short-term field precipitation manipulation experiments. There is still extensively to learn regarding how the desert steppe reacts to long-term changes in precipitation. We conducted a 7-year experimental study monitoring the aboveground biomass of major plant functional groups (perennial grasses, perennial forbs, annual herbs, and semi-shrubs) under four experimentally manipulated precipitation gradients [reducing natural precipitation by 50% (-50%), natural precipitation (CK), increasing natural precipitation by 50% (+50%), and increasing natural precipitation by 100% (+100%)] to evaluate how changes in precipitation affect the biomass stability of plant communities. We did observe higher levels of species asynchrony, resistance, resilience, and temporal stability of community and functional groups in experimental plots receiving more precipitation. Interestingly, the contribution of species richness to community stability was not observed in our experiment. The increase in soil water content in the 20–30 cm soil layer caused by increased precipitation promoted the resilience of perennial grasses but inhibited the resistance of perennial forbs. At the same time, the decrease in soil inorganic nitrogen caused by increased rainfall inhibited the resilience of perennial grasses. Notably, community resilience predominantly hinged on the resilience of perennial grasses, while community resistance was primarily dictated by the resistance of perennial forbs. Moreover, species asynchrony emerged as the primary regulator of community temporal stability. Our long-term experimental evidence underscores the transformative potential of precipitation in reshaping grassland stability across both functional and structural dimensions. Importantly, sustaining the high stability of perennial herbs emerges as a strategic avenue for enhancing the ecological stability of the desert steppe in the face of evolving precipitation patterns.

Adapting service crop termination strategy in viticulture to increase soil ecosystem functions and limit competition with grapevine

Soil management and particularly service crops are a promising solution for addressing current challenges in viticulture as they limit the use of herbicides while increasing potential ecosystem services. Scientific literature barely considers the importance of service crop management to reach trade-offs between ecosystem services and disservices. This study evaluates during a three-year experiment, 6 service crop termination strategies for winter service crops, combining two service crops termination periods (early termination in February vs. termination at grapevine budburst) and three termination methods (mower (M), mower + tillage (T), roller-crimper (R)). Service crop (biomass, C:N ratio, weeds, and mulch following termination), soil ( soil organic matter, microbial biomass, and water and nitrogen stocks), and grapevines (predawn leaf water potential, yield components, δ13C, yeast assimilable nitrogen in juice, and pruning weight) were monitored from 2019 to 2022. Allowing service crops to develop until the budburst of the vine resulted in a two to three-fold increase in biomass compared to early destruction. Termination involving soil tillage was the most effective method, as treatments destroyed early with soil tillage exhibited almost no regrowth. Soil tillage termination led to the lowest biomass of weeds at the grapevine flowering two years out of three, and prevented the regrowth of certain sown plants, especially Poaceae. The roller was less effective in destroying service crop species but was the best method for maintaining plant residues on the soil surface. A higher soil microbial biomass was observed with termination at budburst, combined with no-till termination methods. Termination involving soil tillage was notably more effective in stopping service crop transpiration, increasing soil water stocks and improving grapevine water status. In 2020 and 2022, soil inorganic nitrogen stocks were almost 4 times higher in the T treatments compared to the other two termination methods, achieving a level of approximately 61 kg ha−1 that closely corresponds to the annual nitrogen requirements of grapevines. The yeast-assimilable nitrogen (YAN) content in grape juice mirrored this trend. Pruning weight varied significantly between different termination methods, with T treatments exhibiting a higher pruning weight per vine in comparison to R and M treatments. In general terms, the T treatment had a significantly higher number of bunches, the M treatment had the lowest, and the R treatment exhibited intermediate values. Overall, the average grapevine yield ranged from 7.25 to 13.7 t ha−1, corresponding to 52–98 hL ha−1 (with 4000 vines ha−1, 140 kg hL−1). This level of production may be accepted for Protected Designations of Origin that limit grapevine yield to 40 or 60 hL ha−1, but it could be a limitation for Protected Geographical Indications, which permit 90 hL ha−1, or unlabeled productions without yield limitations. Given the Mediterranean climate context, with rising frequencies of dry winters due to climate change, termination involving soil tillage appears to be the least risky strategy to preserve grapevine vigor and production while improving soil-based ecosystem functions. However, this might be contingent on the targeted yield and wine valuation.

Characteristics of soil nitrogen and phosphorus fractions and microbial traits with increasing stand age in two-layered Cunninghumia lanceolata + Phoebe bournei plantations.

Soil nitrogen and phosphorus are two key elements limiting tree growth in subtropical areas. Understanding the regulation of soil microorganisms on nitrogen and phosphorus nutrition is beneficial to reveal maintenance mechanism of soil fertility in plantations. We analyzed the characteristics of soil nitrogen and phosphorus fractions, soil microbial community composition and function, and their relationship across three stands of two-layered Cunninghumia lanceolata + Phoebe bournei with different ages (4, 7 and 11 a) and the pure C. lanceolata plantation. The results showed that the contents of most soil phosphorus fractions increased with increasing two-layered stand age. The increase in active phosphorus fractions with increasing stand age was dominated by the inorganic phosphorus (9.9%-159.0%), while the stable phosphorus was dominated by the organic phosphorus (7.1%-328.4%). The content of soil inorganic and organic nitrogen also increased with increasing two-layered stand age, with NH4+-N and acid hydrolyzed ammonium N contents showing the strongest enhancement, by 152.9% and 80.2%, respectively. With the increase of stand age, the composition and functional groups of bacterial and fungal communities were significantly different, and the relative abundance of some dominant microbial genera (such as Acidothermus, Saitozyma and Mortierella) increased. The relative abundance of phosphorus solubilization and mineralization function genes, nitrogen nitrification function and aerobic ammonia oxidation function genes tended to increase. The functional taxa of fungi explained 48.9% variation of different phosphorus fractions. The conversion of pure plantations to two-layered mixed plantation affected soil phosphorus fractions transformation via changing the functional groups of saprophytes (litter saprophytes and soil saprophytes). Changes in fungal community composition explained 45.0% variation of different nitrogen fractions. Some key genera (e.g., Saitozyma and Mortierella) play a key role in promoting soil nitrogen transformation and accumulation. Therefore, the conversion of pure C. lanceolata plantation to two-layered C. lanceolata + P. bournei plantation was conducive to improving soil nitrogen and phosphorus availability. Bacteria and fungi played important roles in the transformation process of soil nitrogen and phosphorus forms, with greater contribution of soil fungi.

Biochar application regulating soil inorganic nitrogen and organic carbon content in cropland in the Central Europe: a seven-year field study

Biochar incorporation into soil has shown potential, in enhancing nitrogen fertilizer (N-fertilizer) efficacy and soil organic carbon content (SOC). This study addresses a critical gap in the literature by investigating the effects of biochar addition over a seven-year period (2014–2020) on inorganic N, SOC, and pH in Haplic Luvisol. The research involved a rain-fed field experiment, with a crop rotation comprising spring barley, maize, spring wheat, and pea. Biochar, applied at the rates of 0, 10, and 20 t ha−1 in 2014, was reapplied to specific plots in 2018. Biochar was also combined with N-fertilizer at three level (N0, N1, and N2). Results showed a significant interactive influence of biochar and N-fertilizer combination on NO3− and NH4+ contents. Intriguingly, the addition of 10 t biochar ha−1 consistently decreased soil inorganic N levels across most of the examined months. Increasing biochar application rates led to a significant rise in pH, establishing a clear, negative correlation between soil pH and inorganic N content. Biochar significantly increased SOC compared to the control, particularly after the reapplication in 2018. However, this effect showed a diminishing trend over time. The study suggests that incorporating biochar treatments may enhance N-fertilizer effectiveness. However, the long-term implications of biochar application with N-fertilizer on N mineralization are specific to individual soil and biochar combinations. Except the application of 20 t ha−1 biochar at N2 in 2019, biochar did not affect the crop yields. Studied soil properties, including those influenced by biochar had nuanced impact on different aspects of crop yield.Graphical

Improved Method for Extracting Nitrites in Soil

Soil nitrite (NO2−) is an important reactive intermediate in many nitrogen transformation processes, but it is unstable under acidic conditions and may be lost as gaseous N. The canonical extraction method of soil NO2− using a potassium chloride (KCl) solution greatly underestimates its concentration. To reflect the concentration more accurately, we optimized the extraction method of soil NO2− for three agricultural soils differing in soil texture and pH, an alkalic fluvo-aquic soil and acidic Mollisol and Ultisol soils, respectively. Both extractable soil ammonium (NH4+) and nitrate (NO3−) were systematically investigated to optimize the simultaneous extraction of soil inorganic nitrogen. The effects of different extractants (deionized water (DIW), un-buffered 2 mol L−1 KCl, and pH-buffered 2 mol L−1 KCl), shaking time (10 and 30 min), and storage duration of the extracts (stored at −20 °C for 1 day, and at 4 °C for 1, 3, and 6 days) on the determination of soil inorganic nitrogen were investigated. The results showed that the un-buffered KCl extractant significantly underestimated soil NO2− concentration compared to DIW. The highest recovery of NO2− was obtained by extracting with DIW at 10 min of shaking for all three soils. Compared with DIW, the concentration of NH4+ and NO3− in soil extracted from the KCl solution increased significantly. Furthermore, the soil inorganic nitrogen content of extracts stored at 4 °C for one day was closer to the direct measurements of fresh samples than with the other storage methods. Overall, the recommended analysis method for soil NO2− was extraction by DIW, shaking for 10 min, and filtering with a 0.45 µm filter, while soil NH4+ and NO3− were extracted with a KCl solution and shaken for 30 min. The extract should be stored at 4 °C and analyzed within 24 h. Our study provides an efficient extraction method for soil NO2− and supports studies on the biogeochemical nitrogen cycle, e.g., in the investigation of soil nitrous acid (HONO) and nitric oxide (NO) emissions.

Long term response and adaptation of farmland water, carbon and nitrogen balances to climate change in arid to semi-arid regions

Climate change poses a challenge for resource utilization and environmental pollution issues caused by agricultural production, especially in arid to semi-arid regions. Farmland water, carbon and nitrogen balances are closely related to these resource and environmental issues. Thus, the Agro-Hydrological & chemical and Crop systems simulator was used to assess the response of water, carbon and nitrogen balances to climate change in a spring wheat farmland of arid to semi-arid Northwest China and to propose adaptation strategies. Five Global Climate Models from the Coupled Model Intercomparison Project 6 and two Shared Socioeconomic Pathways (SSP1–2.6 and SSP5–8.5) were used to establish scenarios with the Agro-Hydrological & chemical and Crop systems simulator to simulate farmland water, carbon and nitrogen balances for the 2025–2100 period. Various irrigation amounts and nitrogen fertilization rates were tested as compensation strategies. Results indicated that climate change could negatively affect farmland water, carbon and nitrogen balances, especially under the SSP5–8.5 scenario. Precipitation showed an increasing trend, thus percolation increased and soil water consumption decreased from 2025 to 2100. However, for the carbon budget, although the soil carbon dioxide emissions tend to decrease, the net primary production was also significantly reduced, which resulted in declining the net ecosystem carbon budget under future climatic conditions. In addition, higher temperature and increased precipitation enhanced soil inorganic nitrogen leaching and nitrous oxide emissions but reduced ammonia volatilization from 2025 to 2100. Overall, the soil total nitrogen loss was increased over time, whereas crop nitrogen uptake was significantly reduced. In relation to the SSP1–2.6 scenario, the SSP5–8.5 scenario accelerated the increase rates of soil water percolation and total nitrogen loss over time, as well as the decrease rates of crop nitrogen uptake and net primary production over time. The negative effects caused by climate change can be mitigated by reducing irrigation and increasing nitrogen fertilization. For the SSP1–2.6 scenario, 30% irrigation reduction and 30% nitrogen fertilization increase can effectively decrease soil water percolation and the related nitrogen losses while crop nitrogen uptake, net primary production and net ecosystem carbon budget increase in relation to the current management (irrigation = 240 mm and nitrogen fertilization = 200 kg ha–1). For SSP5–8.5 the strategy with 45% irrigation reduction and 45% nitrogen fertilization increase can also decrease nitrogen losses and increase crop nitrogen uptake, net primary production and net ecosystem carbon budget.

Impacts of one-time large amounts of leafy vegetable waste incorporated into dryland fields on soil fertility and forage maize production

A large amount of vegetable waste is often dumped into the environment, causing serious pollution in major market distribution areas. This paper explores the feasibility and optimization of incorporating vegetable waste into dryland fields to improve soil fertility and crop productivity. The experimental design included three quantities of fresh leafy vegetable waste (QVW) buried into the soil: 800, 1600, and 2400 t·ha−1 and three covering soil thicknesses (CST): 10, 20, and 30 cm. Zero QVW was the control NW. By planting forage maize for two consecutive years, the variations of soil parameters and aboveground dry biomass (ABM) of maize plants were observed. Compared with the NW, the incorporation led to a distinct decline in soil bulk density (BD) by 2.00–17.41%, an increase in soil moisture (SM), organic carbon (SOC), total nitrogen (TN), and microbial carbon (MBC) by 5.84% −29.72%, 5.93% −50.17%, 16.98% −245.71% and 19.66% −304.08%, respectively. Topsoil conductivity (EC) and soil inorganic nitrogen (IN) were 3.81–9.43 fold and 19.02–88.29 fold that of NW. BD was significantly negatively correlated with the QVW and CST. SM, SOC, TN, and IN increased significantly with the increase of QVW and CST. The topsoil EC was significantly positively correlated with QVW, and negatively correlated with CST. The sequestration rates of SOC and nitrogen were significantly positively correlated with CST. The ABM in the incorporating vegetable waste treatment was 1.59–2.74 fold that of NW. The ABM showed a parabolic relationship with QVW (R2 = 0.97 **), and a linear relationship with CST (R2 = 0.91 **). Conclusively, the optimal QVW was 1346 t·ha−1, and the corresponding CST was 30 cm. Excessive QVW can cause topsoil salinization and constrain crop growth. Increasing CST contributes to sequestrating more water and nutrients and mitigating secondary salinization of the soil.

Impact of soil inorganic nitrogen on bacterial phylogeny in estuarine intertidal zones: a study of nitrogen metabolism.

Here we investigated the potential impacts of soil inorganic nitrogen (SIN) content on the phylogenetic characteristics and ecological functions of soil bacterial communities in estuarine intertidal zones in China, aiming to comprehend the response mechanism of soil microorganisms to variations in SIN content within estuarine wetlands. Our results show that SIN in estuarine areas has a significant spatiotemporal variation on spatial and seasonal scales, in this study and is significantly associated with the phylogenetic diversity and phylogenetic turnover of soil bacterial communities. In addition, the results of the metagenomic analysis showed that the relative abundance of nitrogen-cycling functional genes in bacterial communities did not differ significantly in sampling sites and seasons, and weakly correlated with SIN content. Further, the results based on structural equation modeling (SEM) analysis showed that SIN directly and significantly regulated the phylogenetic characteristics of bacterial communities, thereby indirectly affecting the potential of bacterial nitrogen metabolism. This study emphasizes the key influence of SIN variations on the phylogenetic dissimilarity in soil bacterial communities. Moreover, although there was a weak direct relationship between the functional characteristics of the bacterial nitrogen metabolism and SIN content, the spatiotemporal variation of bacterial nitrogen metabolic potential may be indirectly regulated by SIN content by influencing the phylogenetic diversity in bacterial communities. Our study unravels the pivotal mechanisms through which SIN content influences bacterial communities, thereby offering novel insights into the microbial intricacies governing nitrogen metabolism within estuaries.

Shifts in Soil Bacterial Communities under Three-Year Fertilization Management and Multiple Cropping Systems

The current study was undertaken to investigate how organic and inorganic fertilizers shape soil bacterial communities and soil nitrogen and carbon status and to find their relationships with plant production. Soils were collected from fields under a three-year application of green manures (vetch (GMV), field bean (GMB), and wheat (GMW)), livestock manure (MF), inorganic mineral fertilizer (IF), and control (no nitrogen fertilization). The plants cultivated during the three years were tomato, watermelon, and pepper, respectively. The findings showed an increase in crop yields under both organic and inorganic fertilizers, in which the effects of leguminous green manures (GMV and GMB) were more pronounced, equal to +65–81% in tomato, +32–40% in watermelon, and +51–57% in pepper. An extensive modification in the bacterial communities was observed under organic fertilization. These changes were associated with a higher ratio of Proteobacteria (a copiotrophic phylum) to Acidobacteria (an oligotrophic phylum) in GMV and GMB, due to higher soil N content compared to IF and control treatments. Therefore, the data indicated an increase in soil N and organic C levels, as well as higher plant production by replacing IF with GMV, GMB, and MF, suggesting a promising movement to preserve the soil ecosystem. Such changes were more pronounced in MF-treated soils, where bacterial diversity improved and the heterogeneity of bacterial communities was preserved.

Influencing mechanism of stand age to the accumulation of microbial residue carbon in the Pinus masso-niana plantations

Clarifying the accumulation pattern of soil microbial residue carbon and its contribution to soil organic carbon (SOC) across stand age is helpful to understand the mechanism underlying soil carbon cycling. In this study, we analyzed the differences of amino sugar content, physicochemical properties and microbial composition in surface soil (0-10 cm) in young (6 a), middle-aged (13 a), near-mature (29 a), mature (38 a) and over-mature (57 a) Pinus massoniana plantations of subtropical China, quantified the microbial residue carbon content and its contribution to SOC, and discussed the mechanism. The results showed that SOC, total nitrogen, amorphous iron oxide and leucine aminopeptidase contents in the middle-aged plantation were significantly lower than those in the mature plantation. Soil pH and fungal/bacteria in young plantation were significantly higher than those in other age groups. Across the stand age gradient, the ranges of microbial, fungal and bacterial residue carbon were 7.52-14.63, 4.03-8.00 and 3.48-6.63 g·kg-1, respectively. The contents of all the residue carbon were significantly higher in the mature plantation than that of the middle-aged plantation, which were positively affected by soil total nitrogen content. The contribution of microbial, fungal, and bacterial residue carbon to SOC was 59.7%-72.3%, 33.4%-45.6%, and 24.3%-30.8%, respectively. The contribution of fungal residue carbon to SOC in young plantation was significantly higher than that in other age groups, and the contribution of bacterial residue carbon to SOC in middle-aged plantation was significantly higher than that in young and near-mature plantations, both of which were affected by soil inorganic nitrogen. Fungal residue carbon content was 1.2-1.7 times as that of bacterial residue carbon content, and dominated for the accumulation of microbial residue carbon. Results of the partial least squares model showed that stand age, soil environmental factors (such as leucine aminopeptidase, amorphous iron oxide, pH, and total nitrogen), bacterial residue carbon, fungal residue carbon and the contribution of bacterial residue carbon to SOC had total effects on the contribution of fungal residue carbon to SOC (-0.37, -1.16, 0.90, 1.09, and 0.83, respectively). In conclusion, stand age promoted the accumulation of microbial residue carbon but did not increase its contribution to SOC.

Efficiency and driving factors for the retention of exogenous inorganic nitrogen in different forest soils

Forest soils play a vital role in purifying exogenous nitrogen ions and mitigating eutrophication in downstream water bodies. However, the heterogeneity of nitrogen ion removal efficiency in different forest soils and the underlying driving mechanisms remain not fully known. In our research, we selected soils from four typical forest stands, namely, Pinus massoniana-Quercus variabilis mixed forest (MF), Quercus variabilis forest (QF), Pinus massoniana forest (PF), and Citrus reticulata forest (CF), surrounding China’s second largest reservoir in the Yangtze River Basin. Using laboratory simulation experiments, we observed variations in concentration of ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3−-N) in soil leachate after addition of exogenous NH4+-N and NO3−-N solutions, along with the corresponding physical, chemical, and microbial factors. The results showed that on Day 21, all soils exhibited comparable removal rates of approximately 93% for NH4+-N and 70% for NO3−-N. On Day 4, 6–15, PF and QF demonstrated significantly higher removal efficiencies for NH4+-N and NO3−-N, respectively. Combining direct with indirect effects from Partial Least Squares Path Modeling (PLS-PM), NH4+-N removal efficiency was promoted by total organic carbon (TOC), soil NO3−-N and NO2−-N, while it was inhibited by soil water content (SWC), urease activity, soil NH4+-N, and ammonia-oxidizing archaea (AOA). NO3−-N removal efficiency was facilitated by SWC, TOC, and urease, while it was restrained by soil NO3−-N and ammonia-oxidizing bacteria (AOB). Notably, TOC was the only factor that had a comprehensive promoting effect on both NH4+-N and NO3−-N removal efficiency. Our study indicates that soil in coniferous forest excels in NH4+-N removal while broadleaf forest in NO3−-N, and the spatial layout of water source forests should consider water replenishment time, the form of nitrogen ion pollutants, and the nitrogen purification features of different forest types when the prime objective is to purity the water. Additionally, enhancing soil organic carbon could be an effective forest management approach to improve soil nitrogen ion purification and mitigate agricultural and nitrogen deposition pollution.