Microbial Nitrogen Research Articles

Nitrogen availability and its related enzyme activities affect microbial residue nitrogen accumulation during Chinese fir plantation development

Microbial growth, metabolism, and reproductive activities have a significant role in the generation, transformation, and storage of soil nitrogen (N). However, the time-integrated effect of microorganisms on long-term N sequestration in plantation forests remains poorly understood. We investigated the microbial residue N (MRN) and its contribution to soil total N (TN) among the young (8-year), middle (16-year), near-mature (24-year), mature (34-year), and over-mature (106-year) stands of Chinese fir plantation (CFP) in subtropical China. The soil TN content showed a general pattern of increasing with stand age, ranging from 2.61 to 3.42 g kg−1, and was higher in the over-mature and mature stands than in the other three stands (p < 0.001). In addition, soil carbon (C), N, phosphorus (P), and hydrolase stoichiometric ratios indicated that P limitation was widespread during all stages of CFP development. The average ratio of soil fungal residue N (FRN) to bacterial residue N (BRN) was 3.64:1. The MRN content and its contribution to soil TN exhibited a falling and then rising pattern from young to over-mature stands, ranging from 1.24 to 1.70 g kg−1 and 38.8 % to 57.5 %, respectively. Soil N fraction contents and hydrolase activities were higher in the 0–5 cm soil layer than in the 5–30 cm soil layer (p < 0.05). Regression analysis showed that soil MRN content increased with soil N fraction contents, C-N-P stoichiometric ratios, and hydrolase activities (p < 0.001). Redundancy analysis and partial least squares path modeling revealed that soil available N (AN) and N hydrolase were the main factors affecting MRN accumulation. These parameters may partially indicate the dynamics of MRN accumulation. Our study discovered that the long-term development of CFP promotes soil N sequestration, with microbial residues playing a significant role in contributing to N pools.

Conversion of monocropping to intercropping promotes rhizosphere microbiome functionality and soil nitrogen cycling

Intercropping can increase soil nutrient availability and provide greater crop yields for intensive agroecosystems. Despite its multiple benefits, how intercropping influences rhizosphere microbiome assemblages, functionality, and complex soil nitrogen cycling is not fully understood. Here, a three-year field experiment was carried out on different cropping system with five fertilization treatments at the main soybean production regions. We found that soybean yields in intercropped systems were on average 17 % greater than in monocropping system, regardless of fertilization treatments. We also found that intercropping systems significant increased network modularity (by 46 %) and functional diversity (by 11 %) than monocropping systems. Metagenomics analyses further indicated intercropping promotes microbiome functional adaptation, particularly enriching core functions related to nitrogen metabolism. Cropping patterns had a stronger influence on the functional genes associated with soil nitrogen cycling (R2 = 0.499). Monocropping systems increased the abundance of functional genes related to organic nitrogen ammonification, nitrogen fixation, and denitrification, while functional guilds of nitrate assimilation (by 28 %), nitrification (by 31 %), and dissimilatory nitrate reduction (by 10.1 %) genes were enriched in intercropping systems. Furthermore, we found that abiotic factors (i.e. AP, pH, and Moisture) are important drivers in shaping soil microbial community assemblage and nitrogen cycling. The functional genes include hzsB, and nrfA, and nxrA that affected by these biotic and abiotic variables were strongly related to crop yield (R2 = 0.076 ~ R2 = 0.249), suggesting a key role for maintaining crop production. We demonstrated that land use conversion from maize monocropping to maize-soybean intercropping diversify rhizosphere microbiome and functionality signatures, and intercropping increased key gene abundance related to soil nitrogen cycling to maintain the advantage of crop yield. The results of this study significantly facilitate our understanding of the complex soil nitrogen cycling processes and lay the foundation for manipulating desired specific functional taxa for improved crop productivity under sustainable intensification.

ОЦЕНКА ДИФФЕРЕНЦИАЦИИ АЗОТА МИКРОБНОЙ БИОМАССЫ В СЛОЯХ АГРОЧЕРНОЗЕМА В ПРОЦЕССЕ ПЕРЕХОДА НА БЕСПЛУЖНЫЕ СПОСОБЫ ОБРАБОТКИ

The objective of the study is to evaluate the heterogeneity of the compared soil layers in terms of the content of microbial biomass nitrogen under conditions of nonplow techniques of processing agrochernozems. The studies were conducted in the Krasnoyarsk Natural District based on a production experiment conducted on the land plots of the Shilinskoye agricultural production cooperative in the Sukhobuzimo District (56°37' N, 93°12' E). The soil of the experimental plot was leached high-humus medium-deep light clayey chernozem on red-brown clay. The experimental design included the following options (processing methods): 1. Zero. 2. Minimum. 3. Moldboard (st). The content of microbial biomass nitrogen (Nm.b.) was determined by the rehydration-extraction method. Differentiation of the studied soil layers by the value of nitrogen immobilization by microbial biomass was statistically significant in 67 % of cases and was more often observed in the first half of the vegetation seasons. It was found that hydrothermal conditions have a significant effect on the process of nitrogen fixation by microbial plasma. When using nonplow techniques of cultivation, the "temperature" factor was the most significant. In the 0–5 cm layer, when using surface disking, an increase in temperature was accompanied by remineralization of microbial nitrogen (r = –0.81...–0.97), and under no-till conditions – by its immobilization (r = 0.91...–0.96). Despite the relative homogeneity of the 0–20 cm layer during moldboard plowing, significant differentiation was found, which also indicated a significant role of abiotic factors in the assimilation of nitrogen by microorganisms. In general, the values of assimilated nitrogen by the microbial biomass of the studied agrochernozem indicate its significant reserves, which play an important agronomic role in the nutrition of agricultural crops.

Organic substitution regime with optimized irrigation improves potato water and nitrogen use efficiency by regulating soil chemical properties rather than microflora structure

Context or problemImproving water and fertilizer use efficiency is an inevitable choice for sustainable potato production in North China. However, the regulation mechanism of potato water and nitrogen use efficiency under water-nitrogen coupling (W-N) regime is still unknown. Objective or research questionThe objectives from a 3-year field experiment were (1) to assess the impact of W-N regimes on potato yield and water and nitrogen use efficiency, (2) to elucidate the soil microflora structure under W-N regimes, and (3) to determine the relationship between soil chemical properties, microflora structure, and potato water and nitrogen use efficiency. MethodsA three-year two-factor split-zone potato field experiment was conducted in arid and semi-arid regions of the Inner Mongolian Plateau, with irrigation [(rainfed (W0), optimized (soil-based) irrigation (W1), conventional irrigation (W2)] as the primary treatment and N fertilizer [no N (N0), chemical N (N1), 25 % manure substitution (N2)] as the secondary treatment. ResultsPotato yield and water productivity followed N2 > N1 > N0, and partial nitrogen productivity and nitrogen agronomic efficiency followed N2 > N1 at the same irrigation level. Potato yield, nitrogen internal efficiency, partial nitrogen productivity and nitrogen agronomic efficiency first increased and then decreased, whereas water productivity gradually decreased with increasing irrigation levels under the same fertilization regime. Moreover, potato yield, soil total nitrogen, organic carbon, and microbial biomass carbon and nitrogen content peaked with the W1N2 regime. W-N regimes significantly influenced soil microbial community structure. Soil microbial α-diversity was less variable under W1 and N2 conditions. Soil bacterial network complexity and robustness were higher in W1 and W2 than in W0 regimes, whereas the opposite was true for fungi. The complexity and robustness of the soil bacterial and fungal network demonstrated for three fertilization regimes were higher in N1 and N2 than in N0 regimes. Neutral community model showed that soil microflora in W-N regime was mainly influenced by stochastic processes. PLSPM showed that organic substitution regime with optimized irrigation improves potato water and nitrogen use efficiency by regulating soil chemical properties rather than microflora structure. ConclusionsW1N2 regime synergizes well to improve potato water and N use efficiency and soil microflora stability, and organic substitution regime with optimized irrigation improves potato water and nitrogen use efficiency by regulating soil chemical properties. Implications or significanceOur findings initially clarified the regulatory mechanisms of potato water and nitrogen use efficiency in North China, offering theoretical guidance for further optimizing irrigation and fertilization management.

Distinct microbial nitrogen cycling processes in the deepest part of the ocean.

The metabolic features and adaptation strategies of the nitrogen cycling microorganisms in the deepest part of the ocean are largely unknown. This study revealed that anammox bacteria might perform aerobic respiration in response to nutrient limitation or O2 fluctuations in the Mariana Trench sediments. Meanwhile, an abundant alkane-oxidizing Ketobacter species could fix N2 in hadal seawater. This study provides new insights into the roles of hadal microorganisms in global nitrogen biogeochemical cycles. It substantially expands our understanding of the microbial life in the largely unexplored deepest part of the ocean.

Exploring the distribution and co-occurrence of rpf-like genes and nitrogen-cycling genes in water reservoir sediments.

Water reservoir sediments represent a distinct habitat that harbors diverse microbial resources crucial for nitrogen cycling processes. The discovery of resuscitation promoting factor (Rpf) has been recognized as a crucial development in understanding the potential of microbial populations. However, our understanding of the relationship between microorganisms containing rpf-like genes and nitrogen-cycling functional populations remains limited. The present study explored the distribution patterns of rpf-like genes and nitrogen-cycling genes in various water reservoir sediments, along with their correlation with environmental factors. Additionally, the co-occurrence of rpf-like genes with genes associated with the nitrogen cycle and viable but non-culturable (VBNC) formation was investigated. The findings indicated the ubiquitous occurrence of Rpf-like domains and their related genes in the examined reservoir sediments. Notably, rpf-like genes were predominantly associated with Bradyrhizobium, Nitrospira, and Anaeromyxobacter, with pH emerging as the primary influencing factor for their distribution. Genera such as Nitrospira, Bradyrhizobium, Anaeromyxobacter, and Dechloromonas harbor the majority of nitrogen-cycling functional genes, particularly denitrification genes. The distribution of nitrogen-cycling microbial communities in the reservoir sediments was mainly influenced by pH and NH4 +. Notably, correlation network analysis revealed close connections between microorganisms containing rpf-like genes and nitrogen-cycling functional populations, as well as VBNC bacteria. These findings offer new insights into the prevalence of rpf-like genes in the water reservoir sediments and their correlation with nitrogen-cycling microbial communities, enhancing our understanding of the significant potential of microbial nitrogen cycling.

Enhanced degradation of polylactic acid microplastics in acidic soils: Does the application of biochar matter?

Biodegradable plastics, as an alternative to petroleum plastics, are fiercely increasing, but their incomplete degradation under natural conditions may lead to the breakdown into microplastics (MPs). Here, we explored the impacts of chicken manure-derived (MBC) and wood waste-derived biochar (WBC) on the degradation of polylactic acid microplastics (PLA-MPs) during soil incubation for one year. Both biochars induced more pronounced degradation characteristics in PLA-MPs, including enhanced surface roughness, the proportion of MPs < 100 µm by 12.89 %−25.67 %, oxygen loading and O/C ratio to 71.74 %−75.87 % and 1.70–1.76, as well as accelerated carbon loss and the cleavage of ester group and C-C bond. Also, biochar increased soil pH, depleted inorganic nitrogen and available phosphorus, and changed enzymic activity in PLA-MP-polluted soils. We proposed that both biochars accelerated the PLA-MP degradation by inducing alkaline, aminolysis/ammonolysis, oxidative, and microbial degradation. Among these, MBC induced aminolysis/ammonolysis by NH4+ via Fe2+-driven NO3-/NO2- reduction and microbial nitrogen fixation, and oxidative degradation by radicals generated through Fenton/Fenton-like reaction. WBC caused aminolysis/ammonolysis and oxidative degradation mainly through dissimilatory nitrate reduction to ammonium and surface free radicals on biochar. These findings indicate that biochar has the potential to accelerate PLA-MP degradation, and its regulatory mechanism depends on the type of biochar.

Biodegradable Microplastic-Driven Change in Soil pH Affects Soybean Rhizosphere Microbial N Transformation Processes.

The potential impacts of biodegradable and nonbiodegradable microplastics (MPs) on rhizosphere microbial nitrogen (N) transformation processes remain ambiguous. Here, we systematically investigated how biodegradable (polybutylene succinate, PBS) MPs and nonbiodegradable (polyethylene, PE) MPs affect microbial N processes by determining rhizosphere soil indicators of typical Glycine max (soybean)-soil (i.e., red and brown soils) systems. Our results show that MPs altered soil pH and dissolved organic carbon in MP/soil type-dependent manners. Notably, soybean growth displayed greater sensitivity to 1% (w/w) PBS MP exposure in red soil than that in brown soil since 1% PBS acidified the red soil and impeded nutrient uptake by plants. In the rhizosphere, 1% PBS negatively impacted microbial community composition and diversity, weakened microbial N processes (mainly denitrification and ammonification), and disrupted rhizosphere metabolism. Overall, it is suggested that biodegradable MPs, compared to nonbiodegradable MPs, can more significantly influence the ecological function of the plant-soil system.

Microbial nitrogen immobilization reduces competitive advantage of nitrophilous plants with soybean

Microbial nitrogen immobilization reduces competitive advantage of nitrophilous plants with soybean

How does intercropping contribute to soil organic carbon accumulation? A global synthesis

Soil organic carbon (SOC) is the largest terrestrial carbon pool that can provide nutrients to plants. Intercropping is a sustainable agriculture method with appreciable potential to improve crop productivity and enhance SOC pools and mitigate soil degradation. However, the inconsistent findings generated by on-site experiments necessitate a comprehensive assessment of how intercropping affects SOC. To address this gap, we conducted a meta-analysis to assess the effect of intercropping on SOC. The data was collected through Web of Science, Scopus, and China National Knowledge Infrastructure (CNKI). The results showed that the SOC content of intercropping was 17.75 % higher than that of monocropping. The crop composition and depth of the soil layer were identified as the main factors affecting the accumulation of SOC. Further, the presence of legume crops is not necessary to promote SOC accumulation, and intercropping contributes to SOC accumulation in the 0–20 cm soil layer. Soil total nitrogen (TN), soil microbial carbon (MBC), soil microbial nitrogen (MBN), and the soil carbon/nitrogen (C/N) ratio are positively correlated with SOC accumulation, while soil microbial diversity and enzyme activity are negatively correlated with SOC accumulation. The advantage of SOC accumulation in intercropping is lost when the soil C/N ratio is higher than 10.79 compared to monocropping, and intercropping has a higher potential for SOC accumulation when the MBC is higher than 182.92 mg·kg–1. The SOC accumulation potential of intercropping is greater than that of monocropping when soil bacterial diversity is greater than 6.55. Thus, SOC accumulation in intercropping is affected by crop composition and depth of soil layer, and regulated by soil C/N ratio and microorganisms, especially in soil with low N or low C/N ratio.

Effects of exogenous copper on microbial metabolic function and carbon use efficiency of Panax notoginseng planting soil.

Soil copper (Cu) pollution is a serious environmental risk in the Panax notoginseng planting area. However, the effect of Cu on soil microbial metabolism and nutrient cycling in this area remains unknown. Therefore, Biolog ECO-plate and enzyme stoichiometry methods were utilized in this study to investigate the impact of exogenous Cu (control: 0 mg·kg-1; Cu100: 100 mg·kg-1; Cu400: 400 mg·kg-1; and Cu600: 600 mg·kg-1) on the metabolic function of soil microbial and nutrient limitation in the P. notoginseng soil. The results indicated that Cu100 significantly increased soil organic carbon (SOC), total phosphorus (TP), soil C:N, microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN) 9.89%, 15.65%, 17.91%, 61.87%, and 90.56% higher than the control, respectively. Moreover, the carbon source utilization ratio of carbohydrates, amino acids, and amphiphilic compounds of Cu100 also increased by 7.16%, 25.47%, and 84.68%, respectively, compared with the control. The activities of β-1,4-glucosidase, cellobiohyrolase, leucine amino peptidase, β-1,4-N-acetylglucosaminidase, and phosphatase significantly decreased with increasing Cu concentration. Soil enzyme stoichiometry showed that all treatments were limited by nitrogen (vector angle < 45°; 19.045-22.081). Cu600 led to the lowest carbon limitation (1.798) and highest carbon use efficiency (CUE:0.267). The PLS-SEM model also showed that MBC, MBN, MBP, and microbial diversity positively affected carbon and nitrogen limitation (0.654 and 0.424). Soil carbon, nitrogen, phosphorus, stoichiometric ratio, MBC, MBN, and MBP positively affected CUE (0.527 and 0.589). The microbial diversity index significantly negatively affected CUE (-1.490). Multiple linear stepwise regression analyses showed that CUE was mainly influenced by MBC, AP, C:P, and LAP. Thus, P. notoginseng soil can benefit soil microbial carbon and nitrogen limitations at low Cu concentrations. Clarifying the metabolic activity and nutritional status of microorganisms under Cu stress can provide some theoretical basis for realizing China's comprehensive and effective management and control policies for environmental risks from metals by 2035.

Study on Soil Fertility Characteristics of Walnut Orchards with Different Parent Materials and Soil Types in Gyaca County, Tibet

Walnut trees on the Tibetan Plateau have sustainable and nutritious characteristics. They grow naturally without the use of any chemical fertilizers and pesticides. Therefore, the soil fertility of walnut orchards is a key factor influencing walnut yield and quality. This experiment measured and analyzed the basic soil nutrient content, microbial biomass carbon (MBC), nitrogen (MBN), phosphorus (MBP), and leaf nutrient indicators in five types of representative walnut orchard soil parent materials in Gyaca County to clarify the fertility characteristics of different soil types and their correlations with walnut nutrients, providing a basis for the sustainable development of the plateau walnut industry. The results showed that there were significant differences in soil organic matter (SOM), total nitrogen (TN), available nutrient contents, and microbial activity among soil types with different parent materials. The comprehensive representation of available nutrient levels in the soils is as follows: gray-cinnamon soil and calcareous alluvial soil &gt; mountain meadow soil &gt; plateau prairie soil and brush prairie soil. The average MBC, MBN, and MBP contents in the five soils were 368.8 mg/kg, 28.4 mg/kg, and 23.6 mg/kg, respectively, and the content in the topsoil (0–20 cm) was higher than that of the subsoil (20–40 cm). The total nitrogen (PN), total phosphorus (PP), and total potassium (PK) contents in walnut leaves were found to be closely related to the soil physicochemical properties and microbial activity, among which five indicators, including soil TN, available nitrogen (AN), SOM, MBC, and slowly available potassium (SAK), had the greatest impact on leaf nutrient levels. These findings are valuable for the future management and development of walnut orchards. Therefore, for different soil parent materials and soil types, improving the soil fertility and actively applying nitrogen-rich organic fertilizers should be prioritized to improve the yield and quality of Tibetan Plateau walnuts.

The microbial community structure and nitrogen cycle of high-altitude pristine saline lakes on the Qinghai-Tibetan plateau.

The nitrogen (N) cycle is the foundation of the biogeochemistry on Earth and plays a crucial role in global climate stability. It is one of the most important nutrient cycles in high-altitude lakes. The biogeochemistry of nitrogen is almost entirely dependent on redox reactions mediated by microorganisms. However, the nitrogen cycling of microbial communities in the high-altitude saline lakes of the Qinghai-Tibet Plateau (QTP), the world's "third pole" has not been investigated extensively. In this study, we used a metagenomic approach to investigate the microbial communities in four high-altitude pristine saline lakes in the Altun mountain on the QTP. We observed that Proteobacteria, Bacteroidota, and Actinobacteriota were dominant in these lakes. We reconstructed 1,593 bacterial MAGs and 8 archaeal MAGs, 1,060 of which were found to contain nitrogen cycle related genes. Our analysis revealed that nitrite reduction, nitrogen fixation, and assimilatory nitrate reduction processes might be active in the lakes. Denitrification might be a major mechanism driving the potential nitrogen loss, while nitrification might be inactive. A wide variety of microorganisms in the lake, dominated by Proteobacteria, participate together in the nitrogen cycle. The prevalence of the dominant taxon Yoonia in these lakes may be attributed to its well-established nitrogen functions and the coupled proton dynamics. This study is the first to systematically investigate the structure and nitrogen function of the microbial community in the high-altitude pristine saline lakes in the Altun mountain on the QTP. As such, it contributes to a better comprehension of biogeochemistry of high-altitude saline lakes.

Effects of biochanin A on lactational performance, nitrogen metabolism, and blood metabolites in dairy cows

Optimizing nitrogen utilization efficiency and mitigating nitrogen losses in cows plays a pivotal role in fostering economic sustainability within contemporary agricultural systems. Biochanin A (BCA), a natural component in red clover, has the potential to improve nitrogen metabolism in dairy cows. The primary objective of this study was to probe the impact of biochanin A supplementation on lactational performance, nitrogen metabolism, and blood metabolites in dairy cows. A complete randomized block design experiment was conducted over 28 d, involving 36 multiparous Holstein cows (comparable milk yield = 37.1 ± 2.90 kg, BW = 642 ± 70.0 kg, days in milk = 92 ± 8.0 d, and parity = 2.4 ± 0.50), which were allocated to three treatment groups: the Control group (with 0 g/d BCA), the Low group (with 10 g/d per cow BCA), and the High group (with 40 g/d per cow BCA). Biochanin A supplementation improved the lactational performance of cows by increasing milk yield by 6.3% (P = 0.007) and feed efficiency by 12.7% (P = 0.009). Total intestinal apparent digestibility was unaffected by BCA supplementation (P > 0.05), but microbial nitrogen was increased by 30.0% (P = 0.002) for promoting nitrogen utilization efficiency by 20.7% (P = 0.004). Milk competent yields (protein, lactose, and non-fat milk solid) were increased with increasing BCA supplementation (P < 0.05). Urea nitrogen levels in plasma and milk were both decreased by BCA supplementation (P < 0.05). Blood routine parameters and plasma biochemical parameters both received no effect by BCA supplementation (P > 0.05). BCA did not affect body health of dairy cows. Additionally, none of the plasma endocrine hormones were affected (P > 0.05). A total of 95 significantly different metabolites were screened from the plasma metabolites of cows in the BCA-added and non-added groups. After performing an enrichment analysis of the metabolic pathways associated with the different metabolites, six specific pathways were identified: bile acid biosynthesis, aspartate metabolism, pyrimidine metabolism, arginine and proline metabolism, the urea cycle, and ammonia recycling. The inclusion of BCA is suggested to enhance milk yield and modulate nitrogen metabolism by influencing relevant metabolites within the metabolic pathways.

Stockpiling turf alters microbial carbon and nitrogen use efficiency on the Tibetan Plateau

Microbial carbon use efficiency (CUE) and nitrogen use efficiency (NUE) are crucial parameters reflecting soil C and N sequestration. Concerns about how artificial activities disturb alpine meadow ecosystem are increasing, but the knowledge of variances in microbial CUE and NUE in response to turf storage remains scarce. Here, we conducted a turf storage experiment on the Tibetan Plateau with two common storage methods, laying turfs method (LT) and stacking turfs method (ST). Plant litter, aboveground and belowground biomass declined considerably in the LT and ST than those in natural meadow. Soil pH and available phosphorus were significantly lower, but soil organic carbon, total nitrogen, dissolved organic carbon, and available nitrogen were substantially higher in stored turfs (both ST and LT) than in natural meadow. These results led to a differentiation in nutrient status among treatments. Vetor model indicated a stronger C limitation (vector length > 0.61) in ST than that in the LT and a shift from N to P limitation (vector angle >55°) in all stored turfs. Microbial CUE was prominently higher in the LT than those in the ST, signifying that microbes allocated more exogenous C to self-growth in the LT. Microbial NUE declined considerably in stored turfs, indicating a great proportion of N used for catabolic process instead of anabolic process. Microbial CUE and NUE were tightly linked to nutrient content and availability, enzymatic stoichiometry, microbial traits and plant biomass. Our results suggest that variations in microbial CUE and NUE were indirectly regulated by soil physicochemical properties via mediating nutrient imbalance and enzymatic stoichiometry in stored turfs.

Simulated Lunar Soil: Can It Be Organically Modified through Compost Cultivation?

This study aimed to explore the possibility of improving the fertility of lunar soil through the reuse of resources by composting household waste and collecting composting fermentation broth. The fermentation broth was used to culture a simulated lunar soil at different concentration gradients for 30 days under aerobic and anaerobic conditions. Microbial biomass carbon and nitrogen content, typical mineral elements, and the microbial community were tested to determine whether the fertility of the lunar soil had improved. Results showed that the microorganisms in the simulated lunar soil samples successfully adhered and grew under both aerobic and anaerobic experimental conditions. The simulated lunar soil samples cultured in the anaerobic environment outperformed those in the aerobic environment regarding microbial biomass growth and water-soluble mineral elements. The study results create opportunities for the future reuse of domestic garbage on the lunar base, providing a technical basis for the in situ reuse of lunar soil resources for plant cultivation.

Edaphic factors mediate the responses of forest soil respiration and its components to nitrogen deposition along an urban-rural gradient

Exploring the influences of nitrogen deposition on soil carbon (C) flux is necessary for predicting C cycling processes; however, few studies have investigated the effects of nitrogen deposition on soil respiration (Rs), autotrophic respiration (Ra) and heterotrophic respiration (Rh) across urban-rural forests. In this study, a 4-year simulated nitrogen deposition experiment was conducted by treating the experimental plots with 0, 50, or 100 kg·ha−1·year−1 of nitrogen to check out the mechanisms of nitrogen deposition on Rs, Ra, and Rh in urban-rural forests. Our finding indicated a positive association between soil temperature and Rs. Soil temperature sensitivity was significantly suppressed in the experimental plots treated with 100 kg·ha−1·year−1 of nitrogen only in terms of the urban forest Rs and Ra and the rural forest Ra. Nitrogen treatment did not significantly increase Rs and had different influencing mechanisms. In urban forests, nitrogen addition contributed to Rh by increasing soil microbial biomass nitrogen and inhibited Ra by increasing soil ammonium‑nitrogen concentration. In suburban forests, the lack of response of Rh under nitrogen addition was due to the combined effects of soil ammonium‑nitrogen and microbial biomass nitrogen; the indirect effects from nitrate‑nitrogen also contributed to a divergent effect on Ra. In rural forests, the soil pH, dissolved organic C, fine root biomass, and microbial biomass C concentration were the main factors mediating Rs and its components. In summary, the current rate of nitrogen deposition is unlikely to result in significant increases in soil C release in urban-rural forests, high nitrogen deposition is beneficial for reducing the temperature sensitivity of Rs in urban forests. The findings grant a groundwork for predicting responses of forest soil C cycling to global change in the context of urban expansion.

PBAT microplastics exacerbates N2O emissions from tropical latosols mainly via stimulating denitrification

Biodegradable plastic mulching films are regarded as promising substitutes for their non-degradable counterparts to ameliorate serious plastic pollution in agriculture. Inevitably, biodegradable microplastics (BMs) can be formed and profoundly affect the function of soil ecosystems. However, little is known about the effects of BMs loading on soil nitrogen (N) dynamics and loss in tropical agricultural soils. Hereby, a 120-day soil incubation trial was performed to evaluate the effects of polybutylene adipate co-terephthalate (PBAT) microplastics on nitrous oxide (N2O) emissions, N transformation, and bacterial community structure in latosols. The results showed that PBAT addition raised soil ammonium nitrogen (NH4+–N) and dissolved organic carbon (DOC) contents, but lowered nitrate nitrogen (NO3––N) contents, accompanied with a smaller potential nitrification rate and a greater potential denitrification rate. The microbial biomass nitrogen and nrfA gene abundance were increased by PBAT, suggesting the processes of microbial N immobilization and dissimilatory nitrate reduction to ammonia were largely promoted. Positive correlations existed between N2O emissions and denitrification-related enzymatic activities and functional gene abundances (narG, nirK/S and Fungal nirK). PBAT amendment stimulated N2O emissions by 54.8 − 317.3 %, accompanied with increased values of those denitrification-related parameters, suggesting that stimulated denitrification was responsible for the exacerbated N2O emissions. Moreover, PBAT addition changed bacterial alpha diversity and bacterial community composition, where the relative abundances of Proteobacteria increased while those of Nitrospirae and Acidobacteria decreased. These findings are beneficial to understanding the fate of N in microplastics-polluted soil, which will provide a new insight into the impact of BMs on soil functions and environmental risks.

Straw Retention with Reduced Fertilization Enhances Soil Properties, Crop Yields, and Emergy Sustainability of Wheat-Soybean Rotation.

Cereal + legume rotation is an integrated system that facilitates soil fertility and sustainable agricultural production. However, research on the management compatibility affecting soil physico-chemical properties yields overall agro-ecosystem sustainability, but profitability is lacking, especially under straw retention and potential reductions in fertilizer application. An 11-year field experiment investigated three treatments: no straw retention + traditional mineral fertilization (TNS), straw retention + traditional mineral fertilization (TS), and straw retention + reduced mineral fertilization (DS). Compared with TNS, TS significantly improved soil physico-chemical properties, including macro-aggregates (R > 0.25 mm), porosity, field water capacity (FWC), soil organic carbon (SOC) storage, total nitrogen storage, microbial biomass carbon (MBC), and microbial biomass nitrogen (MBN) by 17.3%, 3.2%, 13.0%, 5.5%, 3.2%, 15.5%, and 13.8%, respectively. TS also significantly increased total (wheat + soybean) yields (TYs), economic profits, and emergy sustainability index (ESI) by 15.8%, 25.0%, 3.7 times that of TNS, respectively. Surprisingly, compared with TS, DS further significantly improved R > 0.25 mm, porosity, FWC, SOC storage, MBC, MBN, TY, economic profits, and ESI by 11.4%, 1.5%, 6.1%, 3.0%, 10.6%, 7.2%, 5.7%, 11.1%, and 36.5%, respectively. Overall, retaining straw with reduced fertilization enhances soil properties, yields, and emergy sustainability in wheat-soybean rotation systems.

Riparian plant-soil-microbial C:N:P stoichiometry: are they conserved at plant functional group level?

As a consequence of the tight linkages between plants, soil, and microorganisms, we hypothesized the variations in plant species would change soil and microbial stoichiometry. Here, we examined the plant leaf carbon (C):nitrogen (N):phosphorus (P) ratios of nine species coming from three plant functional groups (PFGs) in the riparian zones of Hulunbuir steppe during near-peak biomass. The soil C:N:P, microbial biomass carbon (MBC):microbial biomass nitrogen (MBN), and extracellular enzyme's C:N:P were also assessed using the soils from each species. We found that plant tissue, soil nutrient, microbial, and enzyme activity stoichiometry significantly differed among different PFGs. Plant leaf and soil nutrient ratios tended to be similar (p > 0.05) between different species within the same PFGs. The variations in leaf C:N:P significantly correlated with the changes in soil C:N:P and MBC:MBN ratios. The homeostatic coefficients (H) < 1 suggested the relationships between plants and their resources C:N:P ratios might be non-homeostatic in the examined riparian zone. By assessing plant tissue and its soil nutrient stoichiometry, this study provided a perspective to understand the linkages of plant community, soil nutrient, and microbial characteristics.