Search Results (198)

As the unique edible nut species in China, Chinese hickory (Carya cathayensis Sarg.) is vulnerable to anthropogenic disturbances that reduce vegetation residue inputs and soil organic matter accumulation. To investigate the effects of net-harvesting-associated understory management on the soil carbon pool management index (CPMI), soil samples were collected from C. cathayensis plantations subjected to net harvesting for 2, 3, 6, and 7 years, with traditional beating as the control. Long-term net harvesting significantly increased particulate and dissolved organic carbon, microbial biomass carbon, and labile organic carbon (p < 0.05). It also altered soil enzyme activities, microbial community composition, and microbial co-occurrence network complexity. Soil physical and chemical properties and carbon pools were key drivers of enzyme activities and microbial complexity. Partial least squares path modeling (PLS-PM) revealed that understory vegetation positively influenced the CPMI (total effect = 0.57), while soil biological processes also contributed to CPMI variation. Overall, net harvesting reduced anthropogenic disturbance, enhanced litter-derived carbon inputs, and promoted soil biological functions, thereby improving the CPMI. These findings provide insights into sustainable soil management and carbon sequestration in C. cathayensis plantations. Full article

Organic amendments can alter soil structure, root development, and carbon cycling, yet their coordinated effects remain unclear. Based on a long-term field microplot experiment established in 2009, four amendment systems with equivalent annual N, P, and K inputs but differing in amendment properties and nominal annual organic-material C inputs were compared: maize straw with NPK (CS), pig manure compost with NPK (PMC), biochar with NPK (BIO), and biochar-based fertilizer (BF). After 15 years, dry-sieved aggregate distribution, CT-resolved air-filled pores (>30 μm), peanut root morphology, and easily oxidizable organic carbon (EOC), microbial biomass carbon (MBC), and dissolved organic carbon (DOC) were determined. PMC had the highest CT-resolved total and connected porosities (19.01% and 10.86%), a greater proportion of small macroaggregates, and the largest root surface area. CS produced a greater proportion and mean size of large dry-sieved aggregates and the highest bulk-soil MBC content. BIO and BF showed lower CT-resolved total porosity but greater isolated porosity, anisotropy, mean pore diameter, and pore fractal dimension (collectively termed CT-resolved macropore heterogeneity); these treatments were also associated with greater root volume or length and increased EOC and DOC contents in small macroaggregate- and microaggregate-sized fractions. Root length correlated more strongly with macropore heterogeneity than with total porosity. Because measurements were obtained once from 12 microplots, these relationships and SEM results represent exploratory associations rather than causal pathways. Overall, traditional amendments were associated with aggregation or macropore connectivity, whereas carbonized amendments were associated with greater macropore heterogeneity. BF had the highest percentage of EOC in TOC (52.45%), indicating a greater relative contribution of labile carbon, not increased stable carbon stock. Full article

The coupled mechanisms governing carbon–nitrogen turnover across soil particle-size fractions remain unclear. This study investigated soil organic carbon (SOC) and total nitrogen (TN) dynamics across five particle-size fractions in Cambisols under conventional and organic orchard management. Results showed that particle size dominated δ¹³C variation (Partial η² = 0.36) while management practice regulated δ¹⁵N variation (Partial η² = 0.38), revealing a fundamental decoupling of C and N cycling within the particle-size matrix. The progressive linear increase in δ¹³C with declining particle size signaled a transition of SOC from net accumulation to net decomposition, accompanied by directional carbon translocation from coarse sand to clay fractions. A universal critical soil pH threshold ~5.3 was identified, where inter-particle-size carbon flow reached its maximum while microbial decomposition was minimized. Organic management reduced the intensity of plant-derived carbon translocation between particle-size fractions, yet substantially enhanced microbial anabolism, leading to drastically elevated stocks of microbial necromass carbon (MNC) in both particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) pools. Notably, the relative proportional distribution of POC and MAOC remained unchanged across the two management practices, which was intrinsically constrained by the inherent textural properties of the studied Cambisols. Counterintuitively, progressive soil acidification concurrently increased SOC lability and overall carbon stabilization, a paradox that directly demonstrated decoupling between chemical oxidizability and physical protection during particle-size carbon translocation. These findings confirmed incomplete carbon–nitrogen coupling within soil particle-size fractions, and demonstrated that SOC stabilization was co-regulated by organo-mineral interactions and microbial processing, whereas nitrogen dynamics were primarily modulated by exogenous management-derived inputs. This work provided novel insights for optimizing agricultural management strategies to synergistically enhance soil fertility and long-term carbon sequestration. Full article

Mercury (Hg) mobility in contaminated soils may be altered by solarization-induced thermal disturbance and organic amendments. This study evaluated whether a cover-induced prior solarization pretreatment of a mining-impacted soil–compost system modifies the operationally defined labile Hg fraction (F1 + F2, considered potentially bioavailable), rice productivity, grain Hg accumulation, and screening-level health risk. Mining soils from San Jorge River basin were amended with compost at a 1:9 ratio and solarized for one month before crop establishment, generating temperatures of 32, 40, 44, and 50 °C under different cover conditions. After pretreatment, covers were removed and rice was cultivated for four months under uniform flooded conditions. Total Hg in soils and grains was determined by EPA Method 7473, and the potentially bioavailable fraction by modified Bloom extraction. Prior thermal exposure increased this fraction, especially at 50 °C, whereas compost reduced total Hg and partially buffered this increase. Productivity depended on the compost × temperature interaction: compost improved yield at 40 and 44 °C, while no grain production occurred in substrates previously exposed to 50 °C. Compost-amended treatments showed lower grain Hg than unamended soils, although all values exceeded the 20 μg kg⁻¹ reference limit. Hazard quotients remained below 1, with the highest value in unamended soil previously exposed to 44 °C. Full article

The basins of former mill ponds are a common element of the cultural landscape, while soil science studies focusing on mill pond sediments remain relatively rare. One of the key properties relevant to the sustainable management of these sites is the content and stocks of organic carbon in the soils developed from the mill pond sediments. Therefore, the study aimed to analyze the total organic carbon (TOC) and total nitrogen content, as well as its stocks in the studied soils, the share of the labile fractions of these compounds in relation to the environmental factors influencing these properties and finally their potential changes over time (stability). The obtained results confirmed that the studied soils (mostly classified as Gleyic Fluvisols and Fluvic Phaeozems) are characterized by a high amount of TOC. This manifests in the large TOC stocks in the upper 50 cm (mean = 18.1; min = 8.35; max = 35.5 kg m⁻²) and in the whole soil profiles (mean = 43.7; min = 10.6; max = 93.6 in kg m⁻²). The dissolved organic carbon share in TOC content was slightly over 1% on average (mean = 1.06; min = 0.19; max = 4.75) and the specific UV absorbance averaged about 2.40 L mg C⁻¹ m⁻¹, indicating the relatively large proportion of recalcitrant organic fractions and low potential for further degradation. Full article

Long-term continuous cropping is common in greenhouse tomato production and can cause soil degradation, nutrient imbalance, and yield decline; however, its effects on soil phosphorus (P) fractionation and P-cycling microbial communities remain unclear. This study aimed to determine how continuous cropping duration affects soil P fractions, phosphatase activities, phoD- and pqqC-harboring microbial communities, and tomato yield. Soils representing eight continuous cropping cycles (1, 2, 6, 8, 10, 16, 26, and 32 cycles; two cropping cycles per year) were used in a greenhouse pot experiment. Soil chemical attributes, Hedley P fractions, acid and alkaline phosphatase activities, the diversity and composition of phoD- and pqqC-harboring microbial communities, and tomato yield were evaluated. With increasing continuous cropping cycles, total P, available P, and soil organic matter increased by 171.2%, 210.9%, and 59.3%, respectively. Labile P increased during the early and intermediate cropping cycles but declined after 16 cycles, whereas moderately labile and non-labile P fractions accumulated progressively. Acid phosphatase activity increased, alkaline phosphatase activity decreased, and the richness and diversity of phoD- and pqqC-harboring microbial communities generally declined. Tomato yield peaked after six cropping cycles but subsequently decreased, with a 20.25% reduction after 32 cycles compared with that after one cycle. These findings demonstrate that prolonged continuous cropping promotes soil P accumulation but shifts P toward less readily available fractions and reduces the diversity of P-cycling microbial communities, which is associated with decreased tomato productivity. Full article

Soil mulching influences soil organic carbon (SOC) dynamics and microbial communities, yet the functional potential linking these factors remains unclear. This two-year field study compared biodegradable liquid film (BLF, C:N = 26:1, 161 kg C·ha⁻¹) and grapevine branch mulch (GBM, C:N = 51:1, 2790 kg C·ha⁻¹) applied in-row in a vineyard, with clean tillage as control. The Vitis vinifera cv. Meili was used as the test material, SOC fractions were determined and metagenomic sequencing was performed. The results showed that GBM had the highest SOC content and significantly increased the levels of total organic carbon, all five labile fractions, and the three recalcitrant fractions. BLF significantly increased the levels of recalcitrant fractions, while its effect on labile fractions varied by year. Metagenomic analysis revealed that the two mulching treatments significantly influenced the abundances of Acidobacteria, Verrucomicrobia, and Bacteroidetes. Redundancy analysis identified soil moisture, pH, SOC, and total nitrogen as key drivers of community structure. Mulching downregulated carbon fixation and methane metabolism genes but upregulated carbohydrate metabolism pathways, including O-glycan biosynthesis, which correlated positively with SOC. Glycosyl transferases were the dominant carbohydrate-active enzymes across all treatments. These results demonstrate that GBM and BLF differentially affect SOC fractions and microbial functional traits, providing empirical evidence for mulch selection in vineyard carbon management. Full article

Under full straw return, changes in cropland management may be reflected first in the vertical distribution of soil organic carbon (SOC) rather than in total SOC stock. However, how tillage practices and nitrogen application are related to SOC profile distribution and associated biological processes remains unclear. Based on a five-year field experiment in the brown soil region of Northeast China, this study compared no-tillage/deep tillage rotation (NPT), continuous deep tillage (PT), and continuous rotary tillage (RT) under two nitrogen rates: 150 kg N ha⁻¹ (LN) and 240 kg N ha⁻¹ (HN). SOC, total nitrogen (TN), labile C and N fractions, microbial biomass, and enzyme activities were measured in the 0–5, 5–15, and 15–30 cm soil layers. After five years of treatment application, total SOC stock in the 0–30 cm profile did not differ significantly among treatments (p > 0.05), whereas SOC and TN stocks showed distinct vertical distribution patterns. PT and RT were associated with higher SOC, TN, and labile C and N levels mainly in the 0–15 cm layer, whereas NPT showed an advantage for SOC and TN retention in the 15–30 cm layer. The highest SOC stock in the 15–30 cm layer occurred under NPT-LN, reaching 25.91 Mg ha⁻¹ and exceeding other treatments by 12.5–44.1%. High nitrogen application increased dissolved inorganic nitrogen (DIN) and TN stock, but did not further increase the total SOC stock. Biological indicators showed clear depth-dependent responses, and RDA combined with exploratory SEM suggested that SOC-associated pathways shifted from management and inorganic N-related associations in the surface layer to stronger coupling among input position, labile C–N status, microbial processing, and retention conditions in the 15–30 cm layer. Overall, under five years of full straw return, tillage and nitrogen treatments were associated with SOC distribution patterns within the plough layer rather than a significant increase in total SOC stock. NPT combined with low nitrogen application may represent a favorable management option for enhancing SOC retention in the 15–30 cm lower plough layer. Full article

Nitrogen (N) fertilization is a fundamental agronomic practice that governs crop productivity, yet its effects on the molecular composition and chemical stability of soil organic carbon (SOC) remain poorly understood, especially in cereal–legume intercropping systems. Traditional studies have focused on total SOC stocks rather than molecular-level changes, and the mechanistic pathway linking N addition to SOC functional group transformation remains unclear. This study addressed these critical gaps by investigating how graded N addition (0, 180, 270, and 360 kg N ha⁻¹) reshapes SOC chemistry in a subtropical soybean–maize intercropping system. Soil physicochemical properties, inorganic N pools, N-transformation enzyme activities (urease, nitrate reductase, and glutaminase), microbial biomass indices, labile organic carbon fractions (particulate, mineral-associated, and dissolved organic carbon), and SOC functional groups characterized by Fourier transform infrared (FTIR) spectroscopy were quantified across a two-year field experiment (2024–2025). Results showed that increasing N rates significantly elevated nitrate nitrogen (NO₃⁻-N) accumulation while depressing soil pH. Nitrogen-transformation enzymes, especially nitrate reductase and glutaminase, responded strongly and positively to the N gradient. Microbial biomass carbon (MBC) and nitrogen (MBN) increased with moderate N input but exhibited saturation or decline at 360 kg N ha⁻¹, accompanied by reduced microbial carbon use efficiency (CUE) and a lower MBC/MBN ratio. Among labile carbon fractions, dissolved organic carbon (DOC) was the most responsive pool, increasing markedly with N addition and correlating strongly with NO₃⁻-N. FTIR analysis revealed that N addition shifted SOC functional group composition toward chemically recalcitrant structures: the relative abundances of aromatic C=C and carbonyl C=O groups increased significantly, whereas labile C–O groups declined. Random forest modelling identified C=C, NO₃⁻-N, and DOC as the three most influential predictors of SOC chemical composition. Structural equation modelling (SEM) demonstrated a sequential mechanistic pathway: N fertilization increased NO₃⁻-N, which stimulated glutaminase activity and enhanced DOC, ultimately promoting C=C/C=O stabilization and explaining 91.3% of the variance in SOC aromaticity. These findings reveal that N addition does not merely augment SOC quantity but fundamentally transforms its molecular architecture toward greater chemical stability through a nitrate-mediated, enzyme–labile carbon coupling mechanism. This study provides a novel spectroscopic–mechanistic framework for understanding carbon–nitrogen interactions in intercropping agroecosystems and informs precision N management strategies aimed at simultaneous crop production and long-term soil carbon sequestration. Full article

Orchard soils have distinct stratification heterogeneity, while the responses of soil organic carbon mineralization (essentially microbial-mediated decomposition of organic matter, mainly producing CO₂) and bacterial communities to exogenous carbon addition in different soil layers are still unclear. In this study, a laboratory incubation experiment was conducted to investigate the differences in soil organic carbon mineralization characteristics and bacterial communities between glucose addition and no-glucose addition treatments in three soil layers (N1: 0–20 cm, N2: 20–40 cm, N3: 40–60 cm) of hilly orchards. The results demonstrated that soil organic carbon mineralization rates in all layers generally declined with increasing incubation duration. At D3, compared with the CK group, glucose addition increased the soil organic carbon mineralization rate by 3.28-fold, 9.30-fold, and 15.03-fold in the N1, N2 and N3 soil layers, respectively. Cumulative organic carbon mineralization followed the order N1 > N2 > N3. Compared with the CK treatment, glucose addition increased C₀ by 65.62% and 203.97% in the N2 and N3 soil layers, respectively. Two-way ANOVA was applied to quantitatively separate and compare the contributions of carbon addition treatment, incubation time and soil layer, and Beta diversity analysis revealed that soil layer was the primary driving factor. Under glucose addition, the key microorganisms related to organic carbon mineralization varied across soil layers: Gemmatimonadota and Acidobacteriota may exert a negative effect on soil organic carbon mineralization in orchard soils, whereas copiotrophic taxa, including Sphingomonas and Bacteroidota, contributed more strongly to carbon mineralization. Our results highlight the pronounced impact of labile carbon input on soil organic carbon mineralization within different soil layers, and reveal associations between soil bacterial communities and organic carbon mineralization in orchard ecosystems. Full article

Parent material is a fundamental determinant of soil pedogenesis, yet its specific role in regulating the molecular composition and vertical evolution of dissolved organic matter (DOM) in paddy soils remains poorly understood. The primary objective of this study was to elucidate how distinct parent materials and soil depths interact to shape DOM chemodiversity. This study investigated 14 paddy soil samples from the plow horizon (Ap, 0–20 cm) and subsoil horizon (Br, 20–50 cm) paddy soils derived from seven parent materials (plate shale: PS, quaternary red clay: QRC, granite: GR, Alluvial Sediment: AS, limestone: LS, sandy gravel: SG, and purple soil: PR). For each composite sample, DOM extraction and subsequent optical characterizations were performed in triplicate (n = 3 analytical replicates). The analysis of soil physicochemical properties was integrated with ultraviolet-visible (UV-Vis) absorption and excitation-emission matrix spectroscopy combined with parallel factor analysis (EEMs-PARAFAC). Our results revealed that parent material significantly dictated the soil chemical microenvironments, with LS, SG, and PR maintaining alkaline profiles, whereas others exhibited distinct surface acidity. Consequently, this microenvironmental heterogeneity profoundly influenced DOM characteristics. While DOM generally shifted towards higher molecular weight and increased aromaticity with depth, its evolutionary trajectory was highly dependent on the parent material. For instance, SG soils preserved a strong autochthonous signature in Ap, whereas GR soils exhibited the highest humification degree. Furthermore, PARAFAC analysis identified a dominant refractory humic-like component (C1 and C2) alongside a highly variable labile protein-like component (C3, 15–40%). Correlation and principal component analyses (PCA) further demonstrated that soil depth and parent material jointly drive DOM evolution, wherein soil organic matter (SOM) abundance showed strong positive associations with total nitrogen (TN), total phosphorus (TP), and available arsenic. These findings underscore that parent material properties are critical variables for understanding soil carbon cycling and managing heavy metal risks in paddy ecosystems. Full article

Wildfires are increasing in frequency and severity across Mediterranean ecosystems. However, the immediate soil biogeochemical responses that determine shortly post-fire resilience remain poorly understood. This study assessed how contrasting fire severity levels influence soil physicochemical, nutrient, and biochemical properties in ecologically relevant vegetation microsites—beneath Quercus ilex L. canopy, Stipa tenacissima L. tussock, and open interspaces—in a Mediterranean holm oak woodland in central Spain. Soils were sampled early after a wildfire and analyzed for organic matter, nutrient pools, water repellency, microbial respiration, nitrogen mineralization, and enzyme activities. Fire severity was the dominant driver of immediate post-fire soil responses. High-severity fire reduced soil organic matter, cation exchange capacity, total C and N, nitrate, microbial respiration, and all measured enzyme activities, with the most pronounced losses occurring beneath Q. ilex canopy. In contrast, ammonium, labile phosphorus, pH and soil water repellency increased under high severity, mainly in this microsite. Low-severity fire generally preserved biological functioning, with values comparable to unburned soils. Microsite identity modulated the magnitude of fire effects, with soils beneath Q. ilex cover microsite showing the greatest sensitivity, and open interspaces the least. The microsite × severity interaction detected for key nutrients and biochemical variables suggests that high-severity fire might destroy the microsite-specific fertility islands that constitute the functional core of Mediterranean woodland soils. These findings should be considered in management strategies prioritizing their monitoring and protection. Full article

This study investigated the effects of different straw return practices—no-tillage with straw mulching (SM), shallow tillage with straw incorporation (SS), and deep tillage with straw incorporation (DS)—on the content and structural characteristics of soil water-soluble organic carbon (WSOC) under a maize–soybean rotation in the black soil region in the Northeast of China. Compared with SM, SS and DS increased WSOC content by 39.0% and 28.8% in the 0~20 cm layer (p < 0.05), and by 28.4% and 8.5% in the 20–40 cm layer, respectively. Deep tillage combined with straw return reduced the WSOC/SOC ratio. The DS treatment exhibited the highest levels under maize straw incorporation, while SM treatment showed the highest levels under soybean straw incorporation. Spectral indices in both maize and soybean seasons—including the fluorescence index (FI, ranging from 1.53 to 1.57 in the maize season and from 1.53 to 1.67 in the soybean season), biological index (BIX, ranging from 0.84 to 1.79 in the maize season and from 0.61 to 0.74 in the soybean season), and humification index (HIX, ranging from 0.51 to 0.79 in the maize season and from 0.84 to 0.97 in the soybean season)—collectively indicated that WSOC predominantly consisted of microbially processed organic matter with a low degree of humification. PARAFAC modeling resolved two fluorescent components in maize season: C1 (humic acid-like substances, accounting for 34.8–54.9%) and C2 (Tryptophan-like substance, accounting for 45.1–65.2%), and two components in the soybean season: C1 (humic-like substances, 51.0–53.7%), and C2 (Fulvic acid-like substance 46.3–49.0%). Overall, deep straw return promotes soil humification but increases the structural complexity of WSOC. This systematic investigation provides mechanistic insights into how straw return practices regulate the quantity and quality of labile carbon pools in agricultural ecosystems over time. Full article

Conservation tillage has an influence on the cultivation and sustainable utilization of farmland. However, the microbial mechanism driving soil nutrient cycling in conservation tillage and its regulation pathway remain unclear. Based on a positioning experiment in black soil areas, this study systematically compared the effects of no-tillage (NT) and moldboard tillage (MT) combined with different straw returning amounts (straw non-returning, NS; straw half-returning, HS; straw full-returning, TS) on the composition of soil carbon (C), nitrogen (N) and phosphorus (P) and focused on the role of microbial community structure succession and functional changes in soil nutrient cycling. Microbial community remodeling driven by tillage measures was mainly regulated by C and N components. Bacterial modules 2 and 4 and fungal modules 1 and 2 were key for regulating the C, N and P cycle, of which 87 bacteria and 45 fungi taxa represented the core driving microorganisms. The total amount of no-tillage straw return reduced the formation and accumulation of labile organic carbon fractions by enriching yeast-like fungi and inhibiting the expression of complex organic matter decomposition genes. Tillage mainly promoted the accumulation of labile organic carbon fractions and nutrient release by regulating the bacterial community, while no-tillage straw returning promoted the accumulation of total organic carbon and organic nitrogen fixation by promoting the fungal community. This study revealed the biological pathway of conservation tillage that drives soil nutrient cycling by regulating key microbial communities. It also provides a microbiological basis for sustainable soil management in black soil areas. Full article

Hydrochar has emerged as a promising carbonaceous amendment to enhance soil quality, yet its short-term effects on soil carbon (C) and nitrogen (N) dynamics and microbial functioning remain poorly understood. Here, a 77-day greenhouse pot experiment was conducted using a Cambisol cultivated with sunflower (Helianthus annuus L.) under two irrigation regimes simulating well-irrigated (WI) and water-deficit (WD) scenarios. Two doses of chicken-manure-derived hydrochar (3.25 and 6.5 t ha⁻¹, corresponding to 2.35 and 4.69 g kg⁻¹ of dry soil, respectively) and mineral fertilizer (MF) treatments providing equivalent N inputs were evaluated. Hydrochar promoted microbial growth and enhanced enzymatic and respiratory activities despite its low apparent C and nutrient input. After 77 days under WI, the addition of 6.5 t ha⁻¹ hydrochar enhanced the activity of phenol oxidase (POA) and acid phosphomonesterase (AcPA). Concomitantly, the availability of soluble C and N increased, whereas total organic C (TOC) and N decreased relative to the initial values. These responses may suggest enhanced mineralization potentially related to early-stage priming processes. The increase in POA relative to β-glucosidase is in line with a functional shift from a predominant degradation of labile compounds towards an increased oxidation of more complex structures. This interpretation is supported by solid-state ¹³C NMR data, revealing a higher degradation index of the soil organic matter. Under WD, the overall effects of hydrochar were attenuated or suppressed, particularly those related to C and N dynamics, emphasizing the interactive influence of moisture and amendment dose. Overall, our results show that hydrochar can modulate short-term soil biochemical processes, partly through enhanced microbial responses. Full article