Search Results (12)

Substituting chemical fertilizers with organic alternatives represents an effective strategy for mitigating soil nitrogen (N) loss and reducing chemical fertilizer use. However, the efficacy of organic substitution in regulating soil N fertility and rice growth requires further investigation, and mechanistic studies elucidating how organic fertilizers affect soil N transformation processes and availability are still deficient. To address this, we conducted a three-year field experiment from 2021 to 2023, comparing three rice fertilization regimes: (1) chemical fertilizer as the control (CK), (2) substitution with organic fertilizer (OF), and (3) substitution with biochar-based organic fertilizer (BF). Both organic substitution treatments were applied as basal fertilizer, and the rice plants received equivalent topdressing applications. The soil N availability, gross and net N transformation rates, and soil microbial activity were analyzed, and the rice growth index and yield were determined. The results showed that organic substitution (OF and BF) significantly increased the soil total carbon content, stimulated microbial biomass growth and enhanced enzymatic activity associated with soil C and N cycling. However, the limited N input from organic substitution significantly decreased the soil gross N mineralization rate by 28.30% (OF) and 58.14% (BF), compared to chemical fertilization (CK). It also reduced the gross N nitrification rate by 38.30% (OF) and 36.17% (BF). These suppressed N transformation processes ultimately led to 11.97% (OF) and 14.72% (BF) lower soil mineral N contents. The soil N deficiency during critical early vegetative growth stages substantially constrained rice development, resulting in significant yield reductions in the OF and BF treatments compared to chemical fertilization (CK). These results indicate that complete organic substitution compromises rice yields due to insufficient N availability; therefore, we recommend integrated organic–mineral fertilization as an optimal strategy to achieve both crop productivity and environmental benefits. Full article

Long-term monoculture of poplar plantations for industrial material production has been widely reported to cause severe soil degradation, while the presence of understory vegetation might enhance soil nitrogen (N) transformation and supply. This study employed a field experiment using a randomized block design with three blocks and four understory treatments, including understory removal, N-fixing species planting, single-species retention, and diverse vegetation retention, in poplar plantations on a mid-latitude alluvial plain in China over 6 years to assess the effects of different species and richness of understory on soil N transformation and related microbial traits via ¹⁵N assays and shotgun metagenomics. The results showed that understory removal significantly reduced soil N transformation rates, bacterial abundance, and gene abundance associated with N transformation. Compared to a single-species understory, retaining a diverse understory with high species richness significantly increased soil gross N transformation rate of mineralization by 149%, nitrification by 221%, and immobilization by 85%; comprehensively enriched dominant bacterial phyla; and elevated gene abundances of gdh_K15371, ureB, hao, and amoA_B associated with N transformation. No significant difference in N transformation rates existed between N-fixing species planting treatment and single-species retention treatment, while N-fixing species planting treatment specifically promoted the soil bacterial phyla Nitrospirae and Chloroflexi, and increased the gene abundances of gdh_K15371 and hao. These findings demonstrate that both introducing N-fixing species and an increase in species richness of the understory effectively promoted soil N transformation but that different underlying mechanisms existed. Planting N-fixing species selectively increased the soil bacterial phyla of Nitrospirae and Chloroflexi, whereas the increase in species richness broadly enriched soil bacterial diversity, thereby inducing the enrichment of the functional genes and enhancing soil N transformation. In conclusion, both planting N-fixing species and retaining diverse understory vegetation were effective strategies for maintaining sustainable management of poplar plantations by increasing soil N availability. Full article

Nitrogen (N) cycling in agroecosystems is a complex process regulated by both biological and agronomic factors, with ammonia-oxidizing archaea (AOA) and bacteria (AOB) playing pivotal roles in nitrification. Despite extensive fertilizer applications to achieve maximum crop yields, nitrogen use efficiency (NUE) remains less than ideal, with substantial losses contributing to environmental degradation. This review synthesizes current knowledge on plant-mediated and fertilization-induced shifts in ammonia-oxidizer communities and their implications on nitrogen cycling. We highlight the differential ecological niches of AOA and AOB, emphasizing their responses to plant community composition, root exudates, and allelopathic compounds. Fertilization regimes of inorganic nitrogen inputs and biological nitrification inhibition (BNI) are examined in the context of microbial adaptation and ammonia tolerance. Our review highlights the need for integrated nitrogen management strategies comprising optimized fertilization timing, nitrification inhibitors, and plant–microbe interactions in order to optimize NUE and mitigate nitrogen losses. Future research directions must involve applications of metagenomic and isotopic tracing techniques to unravel the mechanistic AOA and AOB pathways that are involved in regulating these dynamics. An improved understanding of these microbial interactions will inform the creation of more sustainable agricultural systems that aim to optimize nitrogen retention and reduce environmental footprint. Full article

Plant invasions play a significant role in global environmental change. Traditionally, it was believed that invasive plants absorb and utilize nitrogen (N) more efficiently than native plants by adjusting their preferred N forms in accordance with the dominant N forms present in the soil. More recently, invasive plants are now understood to optimize their N acquisition by directly mediating soil N transformations. This review highlights how exotic species optimize their nitrogen acquisition by influencing soil nitrogen dynamics based on their preferred nitrogen forms, and the various mechanisms, including biological nitrification inhibitor (BNI) release, pH alterations, and changes in nutrient stoichiometry (carbon to nitrogen ratio), that regulate the soil nitrogen dynamics of exotic plants. Generally, invasive plants accelerate soil gross nitrogen transformations to maintain a high supply of NH₄⁺ and NO₃⁻ in nitrogen-rich ecosystems irrespective of their preference. However, they tend to minimize nitrogen losses to enhance nitrogen availability in nitrogen-poor ecosystems, where, in such situations, plants with different nitrogen preferences usually affect different nitrogen transformation processes. Therefore, a comprehensive understanding requires more situ data on the interactions between invasive plant species’ preferential N form uptake and the characteristics of soil N transformations. Understanding the combination of these processes is essential to elucidate how exotic plants optimize nitrogen use efficiency (NUE) and minimize nitrogen losses through denitrification, leaching, or runoff, which are considered critical for the success of invasive plant species. This review also highlights some of the most recent discoveries in the responses of invasive plants to the different forms and amounts of N and how plants affect soil N transformations to optimize their N acquisition, emphasizing the significance of how plant–soil interactions potentially influence soil N dynamics. Full article

This study investigates the properties of Benitaka grape pomace (Vitis vinifera L.), a byproduct of the wine industry, focusing on its potential for applications in the circular economy and biorefinery processes. The analysis covers a range of physical, chemical, and structural characteristics, including the composition of proteins, moisture, lipids, ash, sugars, fiber fractions (such as neutral-detergent fiber, cellulose, lignin, and hemicellulose), pH, acidity, gross energy, as well as bioactive compounds such as total phenolics, flavonoids, anthocyanins, and antioxidant capacity. Advanced characterization techniques, such as nitrogen adsorption/desorption isotherms, Fourier-transform infrared spectroscopy, differential scanning calorimetry, scanning electron microscopy, and high-performance liquid chromatography coupled with mass spectrometry, were employed. The results revealed an acidic pH of 4.05 and a titratable acidity of 1.25 g of tartaric acid per 100 g. The gross energy was 3764 kcal kg⁻¹, indicating high energy capacity, similar to wood chips. The pomace exhibited high hygroscopicity (31 to 50 g of moisture per 100 g), high levels of fiber, cellulose, and lignin, as well as bioactive compounds with significant values of total phenolics (5956.56 mg GAE 100 g⁻¹), flavonoids (1958.33 mg CAT 100 g⁻¹), and anthocyanins (66.92 mg C3G 100 g⁻¹). Antioxidant analysis showed promising results, with DPPH and FRAP values of 20.12 and 16.85 μmol TEAC g⁻¹ of extract, respectively. This study not only validates existing data but also provides new insights into the composition of hemicellulose and lignocellulosic phase transitions, highlighting grape pomace as a promising resource for sustainability in industry and biorefinery processes. Full article

Shrubland is a pivotal terrestrial ecosystem in China. Soil nitrogen transformations play a crucial role in maintaining the productivity of this ecosystem, yet the driving forces underlying it have not been sufficiently addressed, particularly under ongoing climate changes. Herein, by incorporating ¹⁵N isotope pool dilution method in laboratory incubation, the rates of gross N ammonification, nitrification, and inorganic N consumption in soils in response to varying temperature and humidity conditions were determined at different depths (SL10: 0–10 cm, and SL20: 10–20 cm) in a typical shrub ecosystem in the Yanshan mountain and hilly region, North China. The gross rates of ammonification and nitrification of soils in SL10 were higher than those in SL20, which was likely affected by the higher soil organic matter and total N contents at a shallower depth. Both temperature and humidity significantly affected the N transformations. The gross ammonification and nitrification were significantly stimulated as the incubation temperature increased from 5 to 35 °C. The gross ammonification increased exponentially, while the gross nitrification increased differently in different temperature ranges. The increment of soil water contents (from 30% WHC to 60% and 100% WHC) promoted the gross nitrification rate more significantly than the gross ammonification rate. The gross nitrification ceased until soil water content reached 60%WHC, indicating that soil water availability between 60% and 100% WHC was not a limiting factor in the nitrification process for the shrubland soils in this study. The ammonium (NH₄⁺) immobilization was significantly lower than nitrification irrespective of varying environmental conditions, even though the NH₄⁺ consumption rate might be overestimated, uncovering two putative processes: (1) heterotrophic nitrification process; (2) and more competitive nitrifying bacteria than NH₄⁺-immobilizing microorganisms. Our study is indispensable for assessing the stability and sustainability of soil N cycling in the shrub ecosystem under climate changes. Full article

Biological nitrification inhibition (BNI) in the tropical grass Brachiaria humidicola could reduce net nitrification rates and nitrous oxide (N₂O) emissions in soil. To determine the effect on gross nitrogen (N) transformation processes and N₂O emissions, an incubation experiment was carried out using ¹⁵N tracing of soil samples collected following 2 years of cultivation with high-BNI Brachiaria and native non-BNI grass Eremochloa ophiuroide. Brachiaria enhanced the soil ammonium (NH₄⁺) supply by increasing gross mineralization of recalcitrant organic N and the net release of soil-adsorbed NH₄⁺, while reducing the NH₄⁺ immobilization rate. Compared with Eremochloa, Brachiaria decreased soil gross nitrification by 37.5% and N₂O production via autotrophic nitrification by 14.7%. In contrast, Brachiaria cultivation significantly increased soil N₂O emissions from 90.42 μg N₂O-N kg⁻¹ under Eremochloa cultivation to 144.31 μg N₂O-N kg⁻¹ during the 16-day incubation (p < 0.05). This was primarily due to a 59.6% increase in N₂O production during denitrification via enhanced soil organic C, notably labile organic C, which exceeded the mitigated N₂O production rate during nitrification. The contribution of denitrification to emitted N₂O also increased from 9.7% under Eremochloa cultivation to 47.1% in the Brachiaria soil. These findings confirmed that Brachiaria reduces soil gross nitrification and N₂O production via autotrophic nitrification while efficiently stimulating denitrification, thereby increasing soil N₂O emissions. Full article

External organic nitrogen (N) inputs can contrastingly affect the transformation and availability of N in forest soils, which is an important potential N resource and is possibly vulnerable to soil properties. Little is known about the transformation and availability of external small molecule organic N in forest soils and the underlying microbial mechanisms. Soil samples from Changbai Mountain at different altitudes (from 750 m to 2200 m) that ranged widely in soil properties were incubated with ¹³C, ¹⁵N-labeled glycine. The fate of ¹⁵N-glycine and the incorporation of ¹³C into different phospholipid fatty acids (PLFAs) were measured at the same time. The addition of glycine promoted gross N mineralization and microbial N immobilization significantly. Mineralization of glycine N accounted for 6.2–22.5% of the added glycine and can be explicable in the light of a readily mineralizable substrate by soil microorganisms. Assimilation of glycine N into microbial biomass by the mineralization-immobilization-turnover (MIT) route accounted for 24.7–52.1% of the added label and was most mightily affected by the soil C/N ratio. We also found that the direct utilization of glycine is important to fulfill microorganism growth under the lack of available carbon (C) at upper elevations. The labeled glycine was rapidly incorporated into the PLFAs and was primarily assimilated by bacteria, indicating that different groups of the microbial community were answerable to external organic N. G+ bacteria were the main competitors for the exogenous glycine. Increased intact incorporation of glycine into microbial biomass and the concentration of PLFAs in general, particularly in G+ bacteria, suggest a diversified arrangement to response changes in substrate availability. Full article

The effect of displacement amplitude on fretting wear behavior and damage mechanisms of alloy 690 in air and nitrogen atmospheres was investigated in detail. The results showed that in air, the friction coefficient gradually increased with the increase in displacement amplitude which conformed to the universal law. In nitrogen, however, it had the highest point at the displacement amplitude of 60 μm due to very strong adhesion. Whether in air or nitrogen, the wear volume gradually increased with the increase in displacement amplitude. The wear volume in air was larger than that in nitrogen except at 30 μm. At 30 μm, the wear volume in air was slightly smaller. With an increase in displacement amplitude, a transformation of fretting running status between partial slip, mixed stick-slip, and final gross slip occurred along with the change of Ft-D curves from linear, to elliptic, to, finally, parallelogrammical. Correspondingly, the fretting regime changed from a partial slip regime to a mixed regime to a gross slip regime. With the increase in displacement amplitude, the transition from partial slip to gross slip in nitrogen was delayed as compared with in air due to the strong adhesion actuated by low oxygen content in a reducing environment. Whether in air or nitrogen, the competitive relation between fretting-induced fatigue and fretting-induced wear was prominent. The cracking velocity was more rapid than the wear. Fretting-induced fatigue dominated at 30 μm in air but at 30–60 μm in nitrogen. Fretting-induced wear won the competition at 45–90 μm in air but at 75–90 μm in nitrogen. Full article

Soil temperature change caused by global warming could affect microbial-mediated soil nitrogen (N) transformations. Gross N transformation rates can provide process-based information about abiotic–biotic relationships, but most previous studies have focused on net rates. This study aimed to investigate the responses of gross rates of soil N transformation to temperature change in a subtropical acidic coniferous forest soil. A ¹⁵N tracing experiment with a temperature gradient was carried out. The results showed that gross mineralization rate of the labile organic N pool significantly increased with increasing temperature from 5 °C to 45 °C, yet the mineralization rate of the recalcitrant organic N pool showed a smaller response. An exponential response function described well the relationship between the gross rates of total N mineralization and temperature. Compared with N mineralization, the functional relationship between gross NH₄⁺ immobilization and temperature was not so distinct, resulting in an overall significant increase in net N mineralization at higher temperatures. Heterotrophic nitrification rates increased from 5 °C to 25 °C but declined at higher temperatures. By contrast, the rate of autotrophic nitrification was very low, responding only slightly to the range of temperature change in the most temperature treatments, except for that at 35 °C to 45 °C, when autotrophic nitrification rates were found to be significantly increased. Higher rates of NO₃⁻ immobilization than gross nitrification rates resulted in negative net nitrification rates that decreased with increasing temperature. Our results suggested that, with higher temperature, the availability of soil N produced from N mineralization would significantly increase, potentially promoting plant growth and stimulating microbial activity, and that the increased NO₃⁻ retention capacity may reduce the risk of leaching and denitrification losses in this studied subtropical acidic forest. Full article

The soil microbial community and nitrogen (N) dynamics change seasonally due to several factors. The microbial community structure (MCS) can regulate N dynamics. However, there is insufficient information on seasonal changes in MCS and the relationship between MCS and N dynamics. We investigated MCS and N dynamics in forest soils with two different fertilities throughout a year. MCS, measured with phospholipid fatty acid (PLFA) analysis, showed a consistent seasonal trend, regardless of the fertility. Microbial indices (particularly the Saturated-/monounsaturated-PLFA ratio; Sat/mono) indicated a major PLFA shift among seasons, with temperature likely the most important factor. The fungal-/bacterial-PLFA ratio in the dormant season (December–April) was approximately 1.3 times greater than in the growing season (June–November). The trend in N dynamics showed that in summer (June–August), the gross N mineralization potential was greater than immobilization, whereas in winter (December–April), immobilization was dominant. The net mineralization potential in the growing season was approximately 1.6 times higher than in the dormant season. Moreover, a relationship was found between Sat/mono and N transformation potentials. We highlight the microbial sensitivity to seasonal dynamics which can be associated with temperature, as well as carbon and N dynamics. Full article

Manure produced by livestock activity is a dangerous product capable of causing serious environmental pollution. Agronomic management practices on the use of manure may transform the target from a waste to a resource product. Experiments performed on comparison of manure with standard chemical fertilizers (CF) were studied under a double cropping per year regime (alfalfa, model I; Italian ryegrass-corn, model II; barley-seed sorghum, model III; and horse-bean-silage sorghum, model IV). The total amount of manure applied in the annual forage crops of the model II, III and IV was 158, 140 and 80 m³ ha⁻¹, respectively. The manure applied to soil by broadcast and injection procedure provides an amount of nitrogen equal to that supplied by CF. The effect of manure applications on animal feeding production and biochemical soil characteristics was related to the models. The weather condition and manures and CF showed small interaction among treatments. The number of MFU ha⁻¹ of biomass crop gross product produced in autumn and spring sowing models under manure applications was 11,769, 20,525, 11,342, 21,397 in models I through IV, respectively. The reduction of MFU ha⁻¹ under CF ranges from 10.7% to 13.2% those of the manure models. The effect of manure on organic carbon and total nitrogen of topsoil, compared to model I, stressed the parameters as CF whose amount was higher in models II and III than model IV. In term of percentage the organic carbon and total nitrogen of model I and treatment with manure was reduced by about 18.5 and 21.9% in model II and model III and 8.8 and 6.3% in model IV, respectively. Manure management may substitute CF without reducing gross production and sustainability of cropping systems, thus allowing the opportunity to recycle the waste product for animal forage feeding. Full article