Soil Organic Nitrogen Research Articles

Aridity regulates the impacts of multiple dimensional plant diversity on soil properties in the drylands of northern China

Relationships between plant diversity and soil properties are important for restoring ecosystem function to adapt climate change in drylands. Taxonomic, functional and phylogenetic diversity are widely used for understanding community assembly and the responses of plant communities to environmental change. However, one dimension of diversity index is difficult to reflect the multiple dimensional plant diversity, and their effects on soil properties (i.e., moisture, nutrients, and texture characteristics) along aridity gradient in drylands are limitedly understood. In this study, we proposed a holistic biodiversity (HB) index to integrate all the characteristics of plant diversity, and investigated the relationships between plant diversity and soil properties across 41 sites along aridity gradient (from hyperarid to arid and semiarid levels) in drylands of northern China. The results showed that the taxonomic diversity and phylogenetic diversity increased significantly while most of functional diversity indices did not differ significantly along the aridity gradient. The functional diversity was more important than taxonomic and phylogenetic diversity to plant communities, and the importance of taxonomic and phylogenetic diversity varied greatly and inversely along the aridity gradient. The HB index could much better reflect the positive or negative exponential relationships with soil properties compared to the single diversity index. Further, the aridity weakened the positive effects of plant diversity on several soil properties (including soil water content, soil organic carbon and soil total nitrogen), and indirectly strengthened the accumulation of soil total phosphorus, as well as intensified the soil coarsening by limiting the negative effects of plant diversity on soil sand content. Our findings suggest that the holistic biodiversity index can represent the overall traits of plant diversity in drylands, and guide a further step to understand the role of plant diversity in plant-soil relationships of dryland ecosystems.

Vermicompost Supply Enhances Fragrant-Rice Yield by Improving Soil Fertility and Eukaryotic Microbial Community Composition under Environmental Stress Conditions.

Heavy-metal contamination in agricultural soil, particularly of cadmium (Cd), poses serious threats to soil biodiversity, rice production, and food safety. Soil microbes improve soil fertility by regulating soil organic matter production, plant nutrient accumulation, and pollutant transformation. Addressing the impact of Cd toxicity on soil fungal community composition, soil health, and rice yield is urgently required for sustainable rice production. Vermicompost (VC) is an organic fertilizer that alleviates the toxic effects of Cd on soil microbial biodiversity and functionality and improves crop productivity sustainably. In the present study, we examined the effects of different doses of VC (i.e., 0, 3, and 6 tons ha-1) and levels of Cd stress (i.e., 0 and 25 mg Cd kg-1) on soil biochemical attributes, soil fungal community composition, and fragrant-rice grain yield. The results showed that the Cd toxicity significantly reduced soil fertility, eukaryotic microbial community composition and rice grain yield. However, the VC addition alleviated the Cd toxicity and significantly improved the soil fungal community; additionally, it enhanced the relative abundance of Ascomycota, Chlorophyta, Ciliophora, Basidiomycota, and Glomeromycta in Cd-contaminated soils. Moreover, the VC addition enhanced the soil's chemical attributes, including soil pH, soil organic carbon (SOC), available nitrogen (AN), total nitrogen (TN), and microbial biomass C and N, compared to non-VC treated soil under Cd toxicity conditions. Similarly, the VC application significantly increased rice grain yield and decreased the Cd uptake in rice. One possible explanation for the reduced Cd uptake in plants is that VC amendments influence the soil's biological properties, which ultimately reduces soil Cd bioavailability and subsequently influences the Cd uptake and accumulation in rice plants. RDA analysis determined that the leading fungal species were highly related to soil environmental attributes and microbial biomass C and N production. However, the relative abundance levels of Ascomycota, Basidiomycota, and Glomeromycta were strongly associated with soil environmental variables. Thus, the outcomes of this study reveal that the use of VC in Cd-contaminated soils could be useful for sustainable rice production and safe utilization of Cd-polluted soil.

Soil nitrogen and phosphorus regulate decomposition of organic nitrogen compounds in the rothamsted experiment

The effects of long-term N and P fertilisation on soil organic nitrogen (SON) turnover are unclear. We sampled soils fertilised by N and/or P since 1843 at Rothamsted Research to investigate the effects of long-term N and P fertilisation on high- or low-molecular-weight SON decomposition and gross N mineralisation. Short-term assays with added 14C-labelled proteins, peptides, and amino acids and gross organic N mineralisation were measured, and the microbial communities and functions were also assessed in parallel. Long-term N fertilisation increased the contents of soil extractable organic N and peptides but decreased organic N-hydrolysing enzyme activities (N-acetyl-β-D-glucosaminidase and leucine aminopeptidase). Fertilisation with P and N accelerated and reduced the decomposition of 14C-labelled organic N compounds, respectively. The decomposition of peptides and amino acids, as labile SON components, was mainly regulated by soil P content because microbial biomass and activity were more sensitive to P fertilisation than to N fertilisation. Gross NH4+/NO3− production and consumption were accelerated by 41%–60% under N fertilisation but remained unchanged under P fertilisation compared to the unfertilised treatment. Metagenomic sequencing showed that N fertilisation increased microbial diversity and enriched functional genes associated with organic N decomposition, compared to the unfertilised treatment. P fertilisation had no effect on the abundance of these functional genes. In agricultural practices, it is essential to comprehensively consider the interaction between N and P fertilisation to optimise the cycling and utilisation of SON.

Plateau pika bioturbation leads to lower soil organic nitrogen fractions of bare patches in alpine meadows

The small semi–fossorial herbivore bioturbation has been verified to affect available soil nitrogen in grasslands, but the effects of small semi–fossorial herbivore bioturbation on soil organic nitrogen (SON) fractions that are main compositions of soil total nitrogen and sources of soil available nitrogen remain poorly known. The plateau pika (Ochotona curzoniae) bioturbation creates numerous bare patches, which intersperse within vegetated surfaces in grasslands. In this study, plateau pika was considered as an example animal to examine the differences of SON fractions between bare patches and vegetated surfaces under the small semi–fossorial herbivore bioturbation across six sites. This study demonstrated that acid–hydrolysable nitrogen (AHN) was 27.58% lower in bare patches than in vegetated surfaces. Amino acid nitrogen (AAN), ammonium nitrogen (AN), amino sugar nitrogen (ASN) and unknown nitrogen (UN) in bare patches were 35.23%, 17.07%, 17.70% and 19.87% lower than those in vegetated surfaces, respectively. The contribution of AAN to AHN was 5.3% lower in bare patches than in vegetated surfaces, but the contributions of AN, ASN and UN to AHN were 2.42%, 1.11%, and 1.77% higher, respectively. The response of AAN to plateau pika bioturbation was more sensitive than AN, ASN and UN. These findings verify the plateau pika bioturbation leads to a lower potential capacity of soil nitrogen supply in bare patches than in vegetated surfaces, and present a possible pattern of SON fractions in relation to small semi–fossorial herbivore bioturbation in grasslands.

Comparison of field and imaging spectroscopy to optimize soil organic carbon and nitrogen estimation in field laboratory conditions

Regenerative agriculture (RA) aims to improve soil health, water retention capacity, and resilience through sustainable regeneration and retention of soil organic carbon (SOC) and soil nitrogen (SN). Although laboratory analysis offers a reliable method for measuring SOC and SN, access to such facilities can be limited in remote areas and inconvenient, particularly if a large number of samples need to be analyzed. To address this, we compared two hyperspectral sensors, SVC HR-1024i field spectroradiometer (FS) and Specim IQ imaging spectrometer (IS), to estimate SOC and SN using 157 soil samples collected from agricultural sites in Taita Hills, Kenya. Reference SOC and SN content (%) were analyzed in the laboratory, and spectral measurements and images of the air-dried soil samples were generated using protocols suitable for field laboratories. Finally, we employed partial least squares regression (PLSR), Gaussian process regression (GPR), and least absolute shrinkage and selection operator (LASSO) to estimate SOC and SN from the preprocessed soil spectra over different wavelength ranges. Our best models yielded better accuracy for SOC estimation (R2 = 0.83andRMSE = 0.36 %) and an R2of 0.70with anRMSEof0.07 % for SN using the field spectroradiometer. Both SOC and SN modeling over the full wavelength and shortwave-infrared (SWIR) regions achieved considerably better predictive accuracy than visible to near-infrared regions. These results suggest that FS with the SWIR region is best suited for SOC and SN estimation to support the planning and monitoring needs of RA initiatives.

Soil Carbon and Nitrogen Stocks and Their Influencing Factors in Different-Aged Stands of Sand-Fixing Caragana korshinskii in the Mu Us Desert of Northwest China

Establishing artificial sand-fixing shrubs is a key measure to curb dune flow and drive changes in the soil stocks and cycling of carbon and nitrogen. But our understanding of these dynamics across years of sand-fixing afforestation and the factors influencing them remains inadequate, making it hard to accurately assess its capacity to sequester carbon. To fill that knowledge gap, this study investigated soil organic carbon (SOC) and soil total nitrogen (STN) stocks in Mu Us Desert under artificial sand-fixing shrub stands of different ages (10, 30, 50, and 70 years old) vis-à-vis a mobile sand dune, to determine whether Caragana korshinskii afforestation improved stock characteristics and whether SOC and STN stocks were correlated during the restoration processes. The results showed that the pattern observed is consistent with an increase over time in the stocks of both SOC and STN. At 10, 30, 50, and 70 years, these stocks were found to be 1.8, 2.3, 3.2, and 5.5 times higher for SOC, and 1.3, 1.6, 2.1, and 2.7 times higher for STN, respectively, than those of the control (mobile sand) dune. Stocks of SOC and STN mainly increased significantly in the 0–10 cm soil layer. The SOC stock was correlated positively with the STN stock as well as the C:N ratio. The slope of the regression for the C:N ratio against stand age was positive, increasing slightly faster with afforestation age. Additionally, our findings suggest that during the establishment of artificial stands of shrubs, the size of the STN stock did not expand as fast as the SOC stock, resulting in an asynchronous N supply and demand that likely limits the accumulation of soil organic matter. This research provides important evidence for the sustainable development of desertified ecosystems.

Exploring the Impact of Tea (Camellia sinensis (L.) O. Ktze.)/Trachelospermum jasminoides (Lindl.) Lem. Intercropping on Soil Health and Microbial Communities

Intercropping, a well-established agroecological technique designed to bolster ecological stability, has been shown to have a significant impact on soil health. However, the specific effects of tea/Trachelospermum jasminoides intercropping on the physicochemical properties and functional microbial community structure in practical cultivation have not been thoroughly investigated. In this study, we utilized high-throughput sequencing technology on the 16S/ITS rDNA genes to assess the impact of tea intercropping with T. jasminoides on the composition, diversity, and potential functions of the soil microbial community in tea gardens. The results indicated that the tea/T. jasminoides intercropping system significantly increased pH levels, soil organic matter, available nitrogen, phosphorus, potassium, and enzyme activity, ultimately augmenting soil nutrient levels. Furthermore, an in-depth analysis of the bacterial co-occurrence network and topological structure portrayed a more intricate and interconnected soil bacterial community in tea gardens. Remarkably, the abundance of beneficial genera, including Burkholderia, Mesorhizobium, Penicillium, and Trichoderma, underwent a substantial increase, whereas the relative abundance of pathogenic fungi such as Aspergillus, Fusarium, and Curvularia experienced a marked decline. Functional predictions also indicated a notable enhancement in the abundance of microorganisms associated with nitrogen and carbon cycling processes. In summary, the intercropping of tea and T. jasminoides holds the potential to enrich soil nutrient content, reshape the microbial community structure, bolster the abundance of functional microorganisms, and mitigate the prevalence of pathogenic fungi. Consequently, this intercropping system offers a promising solution for sustainable tea garden management, overcoming the limitations of traditional cultivation methods and providing valuable insights for sustainable agriculture practices.

Effects of Polyethylene Microplastics on Soil Nutrients and Enzyme Activities

The threat of microplastic pollution in soil ecosystems has caused widespread concern. In order to clarify the effect of polyethylene microplastics on soil properties, a 4-month soil incubation experiment was conducted in this study to investigate the effect of different mass fraction (1 %, 2.5 %, and 5 %) and particle sizes (30 mesh and 100 mesh) of polyethylene microplastics on soil chemical properties, nutrient contents, and enzyme activities. The results showed that:① When the particle size was 100 mesh, microplastics at the mass concentrations of the 2.5 % and 5 % treatments significantly reduced soil pH, and the exposure of polyethylene microplastics had no significant effect on soil conductivity. ② Compared to that in CK, the addition of microplastics reduced soil available potassium, available phosphorus, and nitrate nitrogen to varying degrees. The addition of 100 mesh microplastics significantly increased soil organic matter and ammonium nitrogen. ③ When the particle size was 100 mesh, compared to that in CK, treatments of all concentrations significantly increased soil catalase activity and alkaline phosphatase, showing an increasing but not significant trend, and the 5 % concentration treatment significantly decreased soil sucrase activity. ④ Changes in soil properties were influenced by the addition of microplastics of different concentrations and sizes, with higher concentrations and smaller particle sizes having more significant effects. In conclusion, the effects of microplastics on soil properties were not as pronounced as expected, and future research should focus on the mechanisms involved in the different effects.

Deployment strategy of multiple miniaturized near-infrared spectrometers based on spectral transfer for characterizing soil organic matter and nitrogen

Developing timely, convenient, and low-cost methods for high-frequency characterization of soil nutrients is necessary for implementing precise soil nutrient management. With the current availability of numerous calibration models of laboratory benchtop near-infrared (NIR) spectrometers for rapid soil nutrient characterization and the appearance of low-cost, convenient miniaturized NIR spectrometers, this study proposes an efficient deployment strategy to address model failure due to inter-device variation based on spectral transfer. The strategy involves using Direct Standardization (DS) to migrate the spectra from multiple miniaturized NIR spectrometers with a laboratory benchtop NIR spectrometer and then directly applying the existing calibration models of the laboratory benchtop instrument to the transferred spectra for soil nutrient analysis. The results indicated that the DS method successfully transferred the spectra of miniaturized devices to be consistent with the spectra of the laboratory benchtop instrument. The soil organic matter (SOM) predictions using the transferred spectra and the calibration models of the laboratory benchtop instrument were even more accurate than those using the respective models developed for each miniaturized devices, with root mean square error (RMSE) of 0.177 %, 0.177 %, and 0.150 %, respectively, while the performances of total nitrogen (TN) predictions were comparable to those using the respective models, with RMSE of 0.013 %, 0.012 %, and 0.010 %, respectively. Bland-Altman plots demonstrated good consistency between the strategy proposed in this study and the strategy of developing respective models for each miniaturized device, with no difference in predictions for the independent validation set compared to the laboratory benchtop instrument. This study proved the feasibility of deployment strategy of multiple miniaturized NIR spectrometers based on spectral transfer, offering a new solution for high-frequency on-site soil nutrient characterization.

Introducing Native Tree Species Alter the Soil Organic Carbon, Nitrogen, Phosphorus, and Fine Roots in Moso Bamboo Plantations

Bamboo and wood-mixed forests are management models that remarkably enhance the balance and productivity of bamboo ecosystems. However, the effects of this model on soil nutrients and enzyme activities remain largely unknown. This study compared the soil organic carbon, nitrogen, phosphorus, and enzyme activity, along with the characteristics of fine roots in pure Moso bamboo plantations (CK) and those mixed with Liriodendron chinense (ML), Sassafras tzumu (MS), Cunninghamia lanceolata (MC), and Pseudolarix amabilis (MP). The results showed that mixed forests improve carbon pools in 0–40 cm soil layers, increasing the total organic C(TOC), free particulate organic C (fPOC), occluded particulate organic C (oPOC), hot-water-extractable organic C (DOC), and mineral-associated organic C (MOC). They also increase soil total N, total P, available N, available P, NH4+-N, NO3−-N, inorganic P, organic P, and microbial biomass N. Bacterial and fungal abundances, along with enzyme activities (urease, acid phosphatase, polyphenol oxidase, peroxidase, and β-glucosidase), also improved. MP and MS were the most effective. Moreover, MS and MP supported a higher biomass and length of fine root and increased the nitrogen and phosphorus uptake of Moso bamboo. In conclusion, Sassafras tzumu and Pseudolarix amabilis are optimal for mixed planting, offering substantial benefits to soil nutrient dynamics and preventing soil quality decline in Moso bamboo forests, thereby supporting better nutrient cycling and carbon sequestration. This research offers insights into enhancing soil quality through diversified Moso bamboo forestry.

Soil Organic Nitrogen Mineralization and N2O Production Driven by Changes in Coastal Wetlands

AbstractPlant invasion and land reclamation have drastically transformed the landscape of coastal wetlands globally, but their resulting effects on soil organic nitrogen (SON) mineralization and nitrous oxide (N2O) production remain unclear. In this study, we examined 21 coastal wetlands across southern China that have undergone habitat transformation from native mudflats (MFs) to Spartina alterniflora marshes (SAs), and subsequently to earthen aquaculture ponds (APs). We determined the SON net mineralization rate and the presence of pertinent enzyme‐encoding genes, namely chiA, pepA, and pepN. The SON net mineralization rate increased by 46.7% following the conversion of MFs to SAs but decreased by 33.1% in response to the transformation of SAs to APs. Nevertheless, there was no significant difference in the estimated mineralization efficiency of soil microbes among the habitat types. The results of structural equation modeling showed that N‐mineralization gene abundance played a major role in regulating SON mineralization. Although less than 20% of the SON was estimated to be labile/semi‐labile, SON mineralization was important in sustaining soil N2O production, with 5.8% of the mineralized N being fed into N2O production. Overall, our findings showed that the presence of S. alterniflora increased both SON content and mineralization rate, which would in turn promote further proliferation of this exotic plant along the coast. The conversion of S. alterniflora marshes to APs partially mitigated the positive effects of exotic plant invasion on SON turnover.

Effects of Biochar and Straw Amendment on Soil Fertility and Microbial Communities in Paddy Soils.

Straw and biochar, two commonly used soil amendments, have been shown to enhance soil fertility and the composition of microbial communities. To compare the effects of straw and biochar on soil fertility, particularly focusing on soil dissolved organic matter (DOM) components, and the physiochemical properties of soil and microbial communities, a combination of high-throughput sequencing and three-dimensional fluorescence mapping technology was employed. In our study, we set up four treatments, i.e., without biochar and straw (B0S0); biochar only (B1S0); straw returning only (B0S1); and biochar and straw (B1S1). Our results demonstrate that soil organic matter (SOM), available nitrogen (AN), and available potassium (AK) were increased by 34.71%, 22.96%, and 61.68%, respectively, under the B1S1 treatment compared to the B0S0 treatment. In addition, microbial carbon (MBC), dissolved organic carbon (DOC), and particulate organic carbon (POC) were significantly increased with the B1S1 treatment, by 55.13%, 15.59%, and 125.46%, respectively. The results also show an enhancement in microbial diversity, the composition of microbial communities, and the degree of soil humification with the application of biochar and straw. Moreover, by comparing the differences in soil fertility, DOM components, and other indicators under different treatments, the combined treatments of biochar and straw had a more significant positive impact on paddy soil fertility compared to biochar. In conclusion, our study revealed the combination of straw incorporation and biochar application has significant impacts and is considered an effective approach to improving soil fertility.

Identification of Soil Fertility Constraints of Erstwhile Warangal District, Telangana, India, using GIS for their Precise Management for Sustainable Crop Productivity

The present investigation was carried out to identify soil fertility constraints and map the fertility status of erstwhile Warangal District, Telangana, India using geographic information system (GIS) and global positioning system (GPS). 241 geo-referenced surface soil samples (0-20 cm) from the study area were analyzed for their fertility parameters. Soil fertility maps were prepared for each parameter under GIS environment using Arc-GIS v 10.8.2. The soils in study area were slightly acidic to slightly alkaline in reaction (6.16 - 8.34), non saline in nature (0.14 to 1.00 dS m–1) and low to high (0.12 - 1.14%) in organic carbon (OC%) content. The soils were low in available nitrogen (136 to231 kg ha-1), low to high in available phosphorus (14.00 to 166.00 kg P2O5 ha-1) and medium to high in available potassium (199 to 997 kg K2O ha-1). The wide variation from deficient to sufficient was observed in the status of available zinc (0.13 to 2.05 mg kg-1), iron (0.09 to 11.80 mg kg-1), copper (0.14 to 2.14 mg kg-1) and manganese (0.18 to 10.30 mg kg-1). The soil fertility status in study area revealed that soil organic carbon, available nitrogen and zinc are important soil fertility constraints in the erstwhile Warangal District Telangana India. To build up organic matter, zinc content, native nitrogen and maintain nutrient balance in the soil the farmers are advised to adopt farmyard manure (FYM) and ZnSO4 application regularly.

Spectral and molecular insights into the characteristics of dissolved organic matter in nitrate-contaminated groundwater

The characteristics of dissolved organic matter (DOM) serve as indicators of nitrate pollution in groundwater. However, the specific DOM components associated with nitrate in groundwater systems remain unclear. In this study, dual isotopes of nitrate, three-dimensional Excitation emission matrices (EEMs) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were utilized to uncover the sources of nitrate and their associations with DOM characteristics. The predominant nitrate in the targeted aquifer was derived from soil organic nitrogen (mean 46.0%) and manure &sewage (mean 34.3%). The DOM in nitrate-contaminated groundwater (nitrate-nitrogen >20 mg/L) exhibited evident exogenous characteristics, with a bioavailable content 2.58 times greater than that of uncontaminated groundwater. Regarding the molecular characteristics, DOM molecules characterized by CHO + 3N, featuring lower molecular weights and H/C ratios, indicated potential for mineralization, while CHONS formulas indicated the exogenous features, providing the potential for accurate traceability. These findings provided insights at the molecular level into the characterization of DOM in nitrate-contaminated groundwater and offer scientific guidance for decision-making regarding the remediation of groundwater nitrate pollution.

Soil organic carbon, pH, and ammonium nitrogen controlled changes in bacterial community structure and functional groups after forest conversion

IntroductionLand-use changes significantly impact soil properties in forests, which is an area of concern. Therefore, the effects of changing forest types on soil microbial communities and their functions in northern subtropical forest regions need to be further researched.MethodsWe used 16S rDNA sequencing and Functional Annotation of Prokaryotic Taxa (FAPROTAX) to assess the variation of soil bacterial communities and potential functions related to carbon (C) and nitrogen (N) cycling in two soil layers (0–10 and 10–30 cm) after the conversion of the secondary masson pine (Pinus massoniana, PM) forest to plantations of slash pine (Pinus elliottii, PE) and Chinese fir (Cunninghamia lanceolata, CL) located in Jingde County, Anhui Province, China.ResultsThe study found that converting coniferous secondary forests to coniferous plantations resulted in a notable increase in soil pH and a decrease in nitrate nitrogen and organic carbon contents. Additionally, soil microbial diversity increased significantly, and microbial community structure changed, particularly in the topsoil. These changes might affect the C- and N-cycling mediated by soil bacteria. The analysis revealed a significant decrease in the abundance of functional groups associated with C-cycling and a significant increase in the abundance of functional groups associated with N-cycling, particularly those associated with denitrification. Soil organic carbon, pH, and ammonium nitrogen were the most critical variables affecting changes in the soil microbial community.DiscussionThese findings provide valuable information for ecological restoration and future sustainable forest management.

Variability of soil organic carbon and nutrient content across land uses and agriculturally induced land use changes in the forest-savanna transition zone of Cameroon

Data expressing the effects of land use change on soil attributes is still very scarce in Cameroon as in most of Africa. In this regard, this study aimed to assess soil organic carbon (OC), nitrogen (N), phosphorus (P), and potassium (K) content across land uses and agricultural-induced land use changes in the forest-savanna transition zone of Cameroon. Nine land uses were identified in the study area showing five directions of land use changes namely the change from the native forest to cocoa agroforestry, native savannah to cocoa agroforestry, native savannah to cropland, savannah fallow to cropland, and transition zone fallow to cropland. The soil was sampled at 0–10 cm (upper layer) and 10–30 cm (lower layer) depths in three replicates for each land use and analyzed for physicochemical properties. There were significant differences across the land uses for OC (p < 0.02), N (p < 0.01), C/N (p < 0.01), pH (p < 0.02), soil organic carbon stocks (SOCS) (p < 0.01), and soil nitrogen stocks (SNS) (p < 0.01), with a relatively higher magnitude in the upper soil layer. Higher magnitudes of OC (26.1 to 22.5 g kg−1), N (2.5 to 1.6 g kg−1), SOCS (32.1 to 27.8 Mg ha−1), and SNS (2.9 to1.9 Mg ha−1) were observed in native lands and cocoa agroforestry with the highest in the native forest and the forest-based cocoa agroforestry. Meanwhile, the effect of land use change on soil properties was mainly significant in the change from native savannah to croplands at p < 0.05 for OC, N, SOCS, and SNS, and p < 0.02 for P. Therefore, agroforestry is an alternative to enhance the ecological resilience of lands affected by land use changes.

Genomic fingerprints of the world's soil ecosystems.

Despite the explosion of soil metagenomic data, we lack a synthesized understanding of patterns in the distribution and functions of soil microorganisms. These patterns are critical to predictions of soil microbiome responses to climate change and resulting feedbacks that regulate greenhouse gas release from soils. To address this gap, we assay 1,512 manually curated soil metagenomes using complementary annotation databases, read-based taxonomy, and machine learning to extract multidimensional genomic fingerprints of global soil microbiomes. Our objective is to uncover novel biogeographical patterns of soil microbiomes across environmental factors and ecological biomes with high molecular resolution. We reveal shifts in the potential for (i) microbial nutrient acquisition across pH gradients; (ii) stress-, transport-, and redox-based processes across changes in soil bulk density; and (iii) greenhouse gas emissions across biomes. We also use an unsupervised approach to reveal a collection of soils with distinct genomic signatures, characterized by coordinated changes in soil organic carbon, nitrogen, and cation exchange capacity and in bulk density and clay content that may ultimately reflect soil environments with high microbial activity. Genomic fingerprints for these soils highlight the importance of resource scavenging, plant-microbe interactions, fungi, and heterotrophic metabolisms. Across all analyses, we observed phylogenetic coherence in soil microbiomes-more closely related microorganisms tended to move congruently in response to soil factors. Collectively, the genomic fingerprints uncovered here present a basis for global patterns in the microbial mechanisms underlying soil biogeochemistry and help beget tractable microbial reaction networks for incorporation into process-based models of soil carbon and nutrient cycling.IMPORTANCEWe address a critical gap in our understanding of soil microorganisms and their functions, which have a profound impact on our environment. We analyzed 1,512 global soils with advanced analytics to create detailed genetic profiles (fingerprints) of soil microbiomes. Our work reveals novel patterns in how microorganisms are distributed across different soil environments. For instance, we discovered shifts in microbial potential to acquire nutrients in relation to soil acidity, as well as changes in stress responses and potential greenhouse gas emissions linked to soil structure. We also identified soils with putative high activity that had unique genomic characteristics surrounding resource acquisition, plant-microbe interactions, and fungal activity. Finally, we observed that closely related microorganisms tend to respond in similar ways to changes in their surroundings. Our work is a significant step toward comprehending the intricate world of soil microorganisms and its role in the global climate.

Coupled processes involving ammonium inputs, microbial nitrification, and calcite dissolution control riverine nitrate pollution in the piedmont zone (Qingshui River, China)

Rivers in agricultural countries widely suffer from diffuse nitrate (NO3−) pollution. Although pollution sources and fates of riverine NO3− have been reported worldwide, the driving mechanisms of riverine NO3− pollution associated with mineral dissolution in piedmont zones remain unclear. This study combined hydrogeochemical compositions, stable isotopes (δ18O–NO3−, δ15N–NO3−, δ18O–H2O, and δ2H–H2O), and molecular bioinformation to determine the pollution sources, biogeochemical evolution, and natural attenuation of riverine NO3− in a typical piedmont zone (Qingshui River). High NO3− concentration (37.5 ± 9.44 mg/L) was mainly observed in the agricultural reaches of the river, with ~15.38 % of the samples exceeding the acceptable limit for drinking purpose (44 mg/L as NO3−) set by the World Health Organization. Ammonium inputs, microbial nitrification, and HNO3-induced calcite dissolution were the dominant driving factors that control riverine NO3− contamination in the piedmont zone. Approximately 99.4 % of riverine NO3− contents were derived from NH4+-containing pollutants, consisted of manure & domestic sewage (74.0 % ± 13.0 %), NH4+-synthetic fertilizer (16.1 % ± 8.99 %), and soil organic nitrogen (9.35 % ± 4.49 %). These NH4+-containing pollutants were converted to HNO3 (37.2 ± 9.38 mg/L) by nitrifying bacteria, and then the produced HNO3 preferentially participated in the carbonate (mainly calcite) dissolution, which accounted for 40.0 % ± 12.1 % of the total riverine Ca2+ + Mg2+, also resulting in the rapid release of NO3− into the river water. Thus, microbial nitrification could be a new and non-negligible contributor of riverine NO3− pollution, whereas the involvement of HNO3 in calcite dissolution acted as an accelerator of riverine NO3− pollution. However, denitrification had lesser contribution to natural attenuation for high NO3− pollution. The obtained results indicated that the mitigation of riverine NO3− pollution should focus on the management of ammonium discharges, and the HNO3-induced carbonate dissolution needs to be considered in comprehensively understanding riverine NO3− pollution in piedmont zones.

Vermicompost and millicompost as a resource in sustainable agriculture in semiarid: decomposition, nutrient release, and microstructure under the action of nitrogen and organic-mineral fertilizers.

With the expansion of organic agriculture, research is needed to indicate economically and ecologically viable fertilizer options, especially in semiarid regions, with low soil organic matter and nitrogen content. In the Brazilian semiarid region, vermicomposts are widely used by farmers and are scientifically investigated; however, there is no information for millicompost, a new type of organic compound that has shown very promising results in other regions. Thus, this study aimed to analyze the decomposition rate, nutrient release, and microstructure evaluation of vermicomposts from different sources and of millicompost produced from plant residues, with the application of mineral nitrogen-urea and organo-mineral fertilizer in the Brazilian semiarid region. The experimental design was a randomized block in a 4 × 3 factorial scheme, with four replicates; four organic composts (millicompost, commercial vermicompost, vermicompost from bovine manure, vermicompost from goat manure); and three types of fertilization (without fertilizer, with mineral-urea and organo-mineral fertilizer). The organic composts were decomposed using litterbags at the soil surface. The variable's decomposition rate and the nutrient release were evaluated at six-time intervals (0, 30, 60, 90, 120, and 150days), and microstructure was evaluated at the beginning and the end of the experiment, with scanning electron microscopy (SEM). The highest decomposition was verified for commercial vermicompost rich in macro and micronutrients and with lower P contents. The lignin:N ratio and the initial P content were more important in the permanence of the organic compost in the field than the C:N ratio. Regardless of the organic composts, the use of urea as a mineral fertilizer stimulated decomposition more than the organo-mineral fertilizer. The initial composition of the nutrients was decisive in the dynamics of nutrient release, mass loss, and decomposition of C. There was no pattern in the release order of macronutrients. However, for the micronutrients, the release order was Cu > Fe > Mn, in all treatments. Microstructure analysis is a visual analysis where differences are detected through microphotographs and the biggest difference occurred with millicompost, which showed elongated fibers and fiber bundles, forming a relatively open structure characteristic of the presence of fulvic acid. However, the addition of organo-mineral fertilizer formed agglomerates in compacted micro-portions, helping the mineralization of C and N.

A strategy to enhance soil quality and soil organic carbon stock in abandoned lands: Pasture regeneration through shrub clearing

AbstractFarmland abandonment in Mediterranean mid‐mountain areas can lead to the degradation or recovery of soil properties. Typically, after abandonment, fields are covered with shrubs, which hinders livestock grazing and constitutes high wildfire risk. To avoid these negative effects, shrubs are cleared in selected areas. The main objective of this study is to evaluate whether shrub clearing can improve soil quality and enhance carbon sequestration. A case study was conducted in the Leza Valley (La Rioja, Spain), examining five different land uses/management practices in both acid and alkaline soil environments. These included shrubland (control), three shrub clearing sites (managed &lt;5, 15, and 25 years ago), and control pasture (reference). Soil replicates at different depths (0–40 cm) were collected, and physico‐chemical properties were analysed. A theoretical map of potential shrub clearing areas was created, and the potential to accumulate carbon was evaluated. Results showed that shrub clearing increases soil organic carbon and nitrogen, specially in 25‐year clearings. The increases were greater and significant on alkaline environments. The cartographical analysis reveals that 3388 ha can be still cleared in the Leza Valley, which could increase soil organic carbon accumulation by up to 31.6% in 25‐year period. We propose shrub‐clearing as a strategy for enhancing carbon sequestration in Mediterranean mountain areas.