Search Results (178)

Microplastic pollution is a problem of global concern, but its effects on forest soils are largely overlooked. This study is based on a laboratory experiment where the effects of soil-added polyethylene microplastic particles (MP-) of two sizes (60 μm and 140 μm) (Cospheric LLC, USA) were measured to examine their effects on three types of temperate forest: dry pine forest, beech-dominated forest, and ash-dominated riparian forest that differ greatly in several physicochemical and biological soil properties. The addition of MP- did not significantly alter the respiration rate of any of the forest soils studied (p = 0.6303), as shown by ANOVA. Soil microbial biomass, as measured by the phospholipid fatty acid (PLFA) method, decreased under 60 µm MP treatment but not under 140 µm MP treatment (p = 0.0094). MP- did affect microbial community structure, especially increasing the proportion of bacteria in the community under 60 µm MP treatment (p = 0.0023). MP- affected the PLFA pattern, as shown by PERMANOVA analysis along with NMDS ordination; the effect was similar in the three studied forest types. As shown by SIMPER analysis, there was a relative decrease in fatty acid 16:1ω7 and a simultaneous increase in 16:0 and 18:0 under both MP treatments. This may potentially serve as an indication of MP pollution in temperate forest soils. Our results suggest that forest soil bacteria, as a group, may benefit from MPs at the expense of fungi, which provides a new perspective on how soil microorganisms interact under globally common MP pollution. Full article

Grassland restoration through grazing exclusion is a key strategy for enhancing soil organic carbon (SOC) sequestration, yet the dynamic contributions of plant- versus microbial-derived carbon (C) remain incompletely understood. We hypothesized that with increasing restoration duration, microbial-derived C would become a major contributor to SOC relative to plant-derived C, and that the relative proportion of bacterial necromass would increase compared to fungal necromass. To explore this, we investigated a 25-year restoration chronosequence (3, 10, 19, 25 years) of a degraded typical steppe on Kastanozem soil in Inner Mongolia, China. While acknowledging the inherent limitations of a space-for-time substitution approach, such as potential unquantified variations in initial pre-enclosure soil conditions and plant species composition, we used lignin phenols, amino sugars, and PLFA analysis to estimate the dynamics of plant- and microbial-derived C. Grassland restoration was associated with significant increases in total PLFAs (15.4–58.8%), bacterial PLFAs (14.5–82.4%), lignin phenols (16.9–91.8%), and estimated microbial-derived C (5.0–8.8 g kg⁻¹). Based on these specific biomarker estimates, which track only a subset of total C and do not equal 100% of the SOC pool, microbial-derived C accounted for 52.8–63.3% of SOC, compared to 10.1–15.5% for plant-derived C. Within the estimated microbial-derived C, the bacterial fraction increased over the restoration chronosequence, while the fungal fraction declined. Correlational analyses, including structural equation modeling, indicated that soil pH, bulk density, SOC, and microbial biomass were key factors closely associated with both C sources. Our findings suggest that microbial-necromass C, particularly from bacteria, is a major contributor to SOC accumulation during long-term grassland restoration in this semi-arid typical steppe, and that grazing exclusion can enhance SOC sequestration under the studied conditions and biomarker-based estimations. Full article

Vegetation mosaics characterize mountainous agroforestry ecosystems, yet how their spatial configuration shapes soil microbial assembly and functions remains unresolved. This study investigated how mosaic elements (monocultures, shrublands, and ecotones) drive microbial communities and enzyme activities across a forest–shrubland–farmland mosaic in western Hunan, China. Nutrient stoichiometry, microbial biomass (PLFA), and six enzyme activities were analyzed via variance partitioning, partial least squares regression, and ordination analysis. Fungal biomass dominated, peaking in ecotones and showing the lowest values in monocultures and shrublands. Microbial assembly was regulated by soil nutrients (31%) rather than soil texture (15%). Fungi (variable importance in projection, VIP = 1.287) and bacteria (VIP = 1.003) were key drivers, indicating distinct functional compartmentalization: fungi drove oxidative enzymes, whereas bacteria mediated nutrient cycling. Actinomycetes and total PLFA acted as secondary drivers, with VIP values of 0.932 and 0.939, respectively. Soil organic matter, dissolved organic carbon, silt content, and available nitrogen were key abiotic predictors. Collectively, vegetation configuration regulates soil functioning via nutrient-mediated microbial assembly and functional differentiation across mosaic elements. These findings underscore the role of landscape heterogeneity in sustaining soil fertility, suggesting that protecting ecotones and maintaining mosaic complexity should be prioritized in mountainous agroforestry management to enhance soil ecological functioning under global land-use change. Full article

Microbial necromass carbon (MNC) is recognized as an important and relatively stable component of soil organic carbon (SOC); however, it is often overlooked and poorly understood in soil management practices, particularly in the context of Loess Plateau farmlands. Here, a 13-year field experiment was carried out to examine the differences in MNC distribution, the role of MNC in SOC storage, and the impact of environmental factors under long-term mulching practices. The experiment used four treatments: (1) no mulching (NT), (2) straw mulching (NSM), (3) plastic mulching (NPM), and (4) ridge mulching (NRM). Compared to NT, all mulching methods increased SOC levels, phospholipid fatty acids (PLFAs), and amino sugar (AS) content. Straw mulching enhanced microbial biomass carbon (MBC), reduced the gap in AS content between rhizosphere and non-rhizosphere soils, and significantly increased MNC. Conversely, NPM and NRM primarily increased MBC and MNC within the rhizosphere soil. Generally, the rhizosphere soil had higher AS content than non-rhizosphere soil. However, regarding the proportion of MNC contributing to SOC, non-rhizosphere soil showed a significantly greater contribution than rhizosphere soil (p < 0.05). The contribution of MNC to SOC ranged from 10.70% to 26.38% under different treatments. Fungal-derived MNC generally contributed more to SOC (7.96–19.73%) than bacterial-derived MNC (2.62–6.65%). Soil temperature, the C/N ratio, pH, and total phosphorus influence microbial community structure and MBC, which in turn affect MNC and regulate SOC. These results enhance our understanding of how agricultural management practices on the Loess Plateau affect carbon sequestration. Full article

Litter decomposition regulates the quantity and quality of plant-derived carbon (C) and nitrogen (N) inputs to soil and is closely associated with microbial community structure. However, how elevated ozone (O₃) and nitrogen (N) addition interactively affect residual litter inputs and their associations with soil microbial communities remains poorly understood, especially in agroforestry systems. Here, we conducted a 12-month in situ litter decomposition experiment using two poplar clones (107 and 546) under ambient or elevated O₃ with or without N addition (60 kg N ha⁻¹ yr⁻¹) at an O₃-FACE platform in northern China. Litter mass and chemical traits were measured during decomposition, and endpoint soil microbial community structure was characterized using phospholipid fatty acid (PLFA) profiling. Treatment effects and litter–microbe associations were evaluated using linear mixed-effects models, correlation analysis, and redundancy analysis (RDA). Endpoint litter mass remaining was significantly affected by O₃, clone identity, and their interactions with N addition, while endpoint litter chemical traits showed trait-specific responses. PLFA-derived microbial community indices also showed treatment- and clone-dependent responses, particularly in bacterial groups, AM fungi, and the fungal-to-bacterial ratio. Endpoint litter mass remaining showed the strongest statistical association with PLFA-derived microbial community structure, whereas individual nutrient concentrations showed weaker independent effects. These findings suggest that O₃- and N-induced changes in residual litter quantity and quality are associated with shifts in PLFA-derived microbial community structure. Because PLFA characterizes microbial community structure rather than process rates, these findings should be interpreted as evidence of structural microbial reorganization associated with altered residual litter inputs, rather than direct evidence of changes in C or N cycling rates. Full article

In high-resolution remote sensing imagery, farmland areas commonly exhibit blurred boundaries, discontinuous internal structures, and high similarity to non-farmland objects such as roads, bare soil, and low vegetation. Meanwhile, because pixel-level annotation is costly and training samples are difficult to obtain, only limited training data are often available in practical applications, making methods that rely on large-scale samples and complex model structures difficult to generalize effectively. To address these two issues, this paper proposes A3UNet, a multi-level attention-enhanced lightweight segmentation network for farmland identification from high-resolution remote sensing imagery. Based on a three-level encoder–decoder structure, the network introduces Point-Local Fusion Attention (PLFA), Medium-Range Attention (MRA), and Tri-Global Attention (TGA) into the skip connections, bottleneck layer, and intermediate decoder layer, respectively, thereby enhancing farmland feature representation from three levels: local boundaries, medium-range connected structures, and global semantic constraints. Few-sample experiments on two public datasets, GID and LoveDA, show that A3UNet achieves IoU values of 83.22% and 75.87%, respectively, with only 2.51 MB of parameters and 2.92 G FLOPs. Compared with the second-best methods on the corresponding datasets, the IoU is improved by 4.78 and 5.68 percentage points, respectively. These results indicate that the proposed method can achieve favorable identification accuracy and result stability while maintaining low model complexity, providing a lightweight solution with stronger practical application potential for farmland identification from high-resolution remote sensing imagery. Full article

The application of organic residues in agriculture helps to replenish soil organic carbon (OC), improve soil fertility and biodiversity, reinforce aggregate stability, and favour water infiltration. Moreover, its application as a soil amendment alters the fate of herbicides applied to the soil. The objective here was (i) to evaluate soil quality by determining the physicochemical and biological parameters of an agricultural soil (Soil) amended with green compost (Soil + GC) over an arable pea–wheat crop rotation in a short-term experiment; and (ii) to study the dissipation and persistence of iodosulfuron-methyl-sodium applied in field plots sown with winter wheat under real field conditions. The experimental field design consisted of 24 plots (10 m²) involving 12 with control and 12 with GC-amended soils. The plots were sown with pea after GC application (~11 t ha⁻¹) in February 2023, and with winter wheat in October 2023. Iodosulfuron-methyl-sodium (Hussar^® Plus, Bayer CropScience S.L., Barcelona, Spain) was applied in post-emergence at the agronomic dose (D1 = 176 mL ha⁻¹) and double dose (D2 = 352 mL ha⁻¹). Soil samples were taken from the plots to assess the soil physicochemical and biological parameters at six sampling times after GC application, with extraction and determination of residual herbicide and metabolite (metsulfuron-methyl) concentrations. In addition, the yield and characteristics of the pea and wheat grain crops were determined. The application of GC to the soil significantly increased pH (0.5 units by July 2024) and electrical conductivity (up to 5.2 times) compared to control soil, which remained constant throughout the experiment. The OC in Soil + GC increased by 40% in July 2024 compared to control soil. Total nitrogen content increased up to 2.0 and 1.3 times during the pea–wheat growing seasons in Soil + GC compared to unamended soil. Soil dehydrogenase activity, respiration, and biomass increased by up to 1.4, 2.2 and 1.4 times, respectively, in Soil + GC compared to unamended soil over the growing seasons. The soil microbial structure, determined by phospholipid fatty acid (PLFA) analysis, recorded no significant differences between the microbial groups in both soil treatments. A non-significant increase in pea and wheat yield was observed in Soil + GC compared to unamended soil. The results revealed an increase in the residual amounts of herbicide and metabolite, being slightly more persistent, with DT₅₀ and DT₉₀ values up to 1.6 times higher, in the Soil + GC plots over time. Much higher amounts of metabolite (DT₅₀ = 24.8–29.7 days) than iodosulfuron-methyl (DT₅₀ = 5.2–8.8 days) were found in all the treatments. This may be due to wheat plants intercepting the herbicide initially at the time of application in post-emergence, the rapid dissipation of the herbicide reaching the soil, and/or the higher persistence of the metabolite compared to that of the herbicide. Overall, the soil’s physicochemical and biological properties were improved in GC-amended soil, and organic amendment increased slightly the persistence of iodosulfuron-methyl-sodium and its metabolite in the soil. Full article

Background and Objectives: Polyethylene (PE) mulching enhances crop productivity through microclimate optimization but introduces synthetic polymer-derived compounds into agricultural soils. Despite widespread use, biochemical and microbial impacts of PE mulch emissions remain poorly understood. This study investigated the impact of PE mulch emissions on soil metabolomes and microbial communities during field pea (Pisum sativum L.) cultivation. Methods: A 75-day field experiment compared PE-mulched and non-mulched soils across five temporal sampling points (T0–T4). Headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry was used to identify PE-derived organic compounds in mulched soils. Microbial community structure was assessed through the phospholipids derived fatty acids (PLFA) approach, whereas mass spectrometric untargeted metabolomics was used to characterize the soil biochemical profiles. Results: Analysis identified 18 PE-derived organic compounds (n-alkanes, phthalates, and additives) in the mulched soils. PE mulching significantly increased bacterial abundance (anaerobic bacteria, actinomycetes, and aerobic bacteria) but suppressed all functional fungal guilds, particularly saprotrophic fungi (30% reduction) and arbuscular mycorrhizal symbionts. PE-derived organic compounds were associated primarily with the first RDA axis (RDA1), which alone explained 44.6% of the metabolome variance. These compounds presented strong positive correlations with organic nitrogen compounds and lipids and negative correlations with benzenoids and nucleotides. Pathway analysis revealed perturbations in energy metabolism, lipid metabolism, and xenobiotic degradation pathways. Conclusions: PE mulch emissions differentially shift soil microbial communities and metabolic networks, with bacterial proliferation contrasting with fungal suppression. These findings highlight the complex trade-offs between agronomic benefits and soil biological impacts, emphasizing the need for sustainable mulching alternatives. Full article

Future global warming is expected to increase carbon (C) losses from terrestrial ecosystems to the atmosphere through soil respiration (SR). However, the underlying mechanisms involving microbial communities and enzymatic responses remain unclear. A long-term field experiment was started in October 2009 to assess intensively cultivated soil in the North China Plain with an infrared-heated warming system. Soil physic–chemical and microbial properties and absolute and specific activities of enzymes were measured in 2019 (the ninth year). Compared to the control, nine years of warming increased the annual average soil temperature at a 5 cm depth by approximately 1.5 °C, with soil water contents decreasing by about 3%. Long-term warming decreased the total contents of phospholipid fatty acid (PLFA) biomarkers by up to 40%. Microbial communities utilizing recalcitrant C were more sensitive to long-term warming compared to those targeting labile C, as indicated by the increased ratio of Gram-positive to Gram-negative bacteria in May and the increased ratio of fungi to bacteria in August. Long-term warming caused similar absolute activity of oxidase but higher absolute and specific activities of C-, nitrogen-, and phosphorus-acquiring hydrolase, reflecting high microbial nitrogen, phosphorus, and energy demands. We conclude that a nine-year warming period relatively enriched the oligotrophic communities and raised the nitrogen, phosphorus and energy requirements. Co-limitation of multiple nutrients and water inhibits the biomass of microbial communities, which may finally promote microbial acclimation to long-term warming. Full article

Reductive soil disinfestation (RSD) is a promising strategy for mitigating soil degradation and enhancing soil health. While soil organic carbon (SOC) is crucial for soil fertility and climate regulation, the mechanisms underlying its stabilization via plant lignin and microbial humus in the RSD process remain elusive. Using a microcosm experiment, we investigated SOC dynamics by quantifying plant-derived (lignin phenols) and microbial-derived (amino sugars) C during RSD at key stages: initial (2 h), anaerobic (14 and 28 days), and aerobic (35 days). Concurrently, soil properties, microbial PLFA, and enzymatic activity were analyzed to elucidate underlying mechanisms. Over the initial 14 days, plant-derived C increased sharply by 61% before declining, yet still showed a 22% increase by the end of the RSD (35 days), a trend mirrored by bacterial-derived C. In contrast, fungal-derived C initially accumulated rapidly with a significant increase of 43%, then stabilized, and its proportion (21.63%) surpassed that of bacterial-derived C (5.56%). Over time, plant- (25.01% to 19.76%) and bacterial-derived C (7.81% to 5.56%) contributions to decreases in SOC, while fungal-derived C (about 21%) remained stable after day 14. This pattern is likely attributable to the initial anaerobic conditions, which caused a massive die-off of fungi and aerobic bacteria that utilize lignin and necromass, resulting in significant accumulation of both plant- and microbial-derived C. Subsequently, the proliferation of anaerobic bacteria consumed these plant- and bacterial-derived C sources in the soil, leading to their eventual decline. Key drivers of plant-derived C included soil pH, living fungi/bacteria, and β-1,4-glucosidase activity, whereas microbial-derived C depended on total nitrogen and living fungi. Our findings demonstrate that early SOC accumulation under RSD is driven by combined plant lignin and microbial necromass inputs, while fungal necromass becomes pivotal for long-term SOC stabilization, shaped by both abiotic and biotic factors. Full article

Rapid urbanization threatens soil biodiversity and ecosystem functions, but the structural and physiological adaptations of soil microorganisms to urbanization remain unclear. We examined variations in soil microbial biomass, community structure and membrane lipid composition along an urban–suburban–exurban gradient in Guangzhou, China, using phospholipid fatty acid analysis. Samples were collected from four to five quadrats per site at three depths during dry and wet seasons. PERMANOVA revealed that both the urbanization gradient and the soil depth significantly shaped microbial communities. Depth was the strongest driver, explaining 45.5% of the variance in total microbial biomass, while site explained 27.2%. Microbial biomass decreased from exurban to urban sites and from surface to deep soils. Concurrently, the ratios of fungi/bacteria and Gram-positive/Gram-negative bacteria increased in urban areas and deeper soils. Physiologically, the membrane lipids shifted toward more saturated fatty acids in urban and surface soils, while unsaturated fatty acids predominated in exurban and deeper layers. These shifts in microbial community structure and membrane lipid composition were strongly correlated with key soil properties, including soil organic carbon, total nitrogen, and bulk density. The findings demonstrate urbanization diminishes microbial biomass and triggers adaptive microbial responses, providing a scientific basis for the sustainable management of urban forests. Full article

To ensure the preservation and sustainable use of Lavandula dentata L., we examined the impact of various growth conditions on the composition of essential oils extracted from the leaves of both cultivated and wild L. dentata. Additionally, we assessed the biological activities of these essential oils, along with the biomass of the root and soil microorganisms. Gas chromatography analysis revealed 21 and 23 components in the EO of the wild and cultivated plants, accounting for over 98% of the total composition in both cases. The major compounds of wild EO were borneol (49.47%), eucalyptol (23.01%), β-pinene (3.95%), β-eudesmol (3.79%), and myrtenol (3.61%). In contrast, the EO extracted from cultivated plants was characterized by a high content of borneol (32.83%), isobornyl acetate (24.45%), eucalyptol (14.71%), and α-pinene (5.83%). Unique compounds were found in wild and cultivated EO, such as linalool, cis-verbenol, carveol, α-selinene, and terpinyl acetate or tricyclene, d-limonene, camphene hydrate, and isobornyl acetate, respectively. PLFA analysis revealed a higher microbial biomass in both soil (10.393 µg/g) and the roots (68.04 µg/g) of the wild plants compared to the cultivated ones (3.91 µg/g in soil and 62.04 µg/g in roots), driven especially by Gram-negative bacteria in soil, and by saprotrophic fungi in the roots. The biological activities of the essential oils showed some variations with growth conditions, with the wild EO generally exhibiting slightly higher antibacterial, antifungal, antioxidant, and nematicidal activities in certain assays. Overall, our findings indicate that the essential oils from wild and cultivated L. dentata exhibit comparable biological value, although some differences were observed. In particular, the wild EO tended to show significantly higher biological activities in certain assays, which may be associated with its distinct chemical composition and growth environment. However, these differences were moderate and not consistently significant across all tests. Therefore, properly managed cultivation can be a dependable alternative for producing L. dentata essential oil, helping to reduce pressure on natural populations. Full article

To investigate the effects of long-term elevated atmospheric CO₂ (eCO₂) on the distribution and stability of soil aggregates and microbial characteristics in wetland soils and to reveal the mechanisms by which eCO₂ influences soil organic carbon (SOC) sequestration, a multi-temporal-scale eCO₂ control experiment was conducted in the Sanjiang Plain wetland with treatments at ambient CO₂ concentration (AC), 550 ppm, and 700 ppm CO₂. Soil aggregate fractionation, phospholipid fatty acid (PLFA) analysis, and redundancy analysis (RDA) were used to analyze changes in aggregate size distribution, stability indices (MWD, GMD), microbial biomass, and community structure. The results showed that eCO₂ significantly affected aggregate size distribution. Both short- and long-term exposure to low-concentration eCO₂ reduced the proportion of large aggregates. Over time, the proportion of silt and clay particles increased, while microaggregates decreased. Although CO₂ concentration did not directly affect MWD and GMD, long-term eCO₂ significantly reduced soil aggregate stability. Microbial biomass and diversity were not sensitive to CO₂ concentration but decreased significantly with prolonged exposure. In contrast, microbial community structure was significantly affected by both CO₂ level and exposure duration. RDA indicated that, under short-term eCO₂, aggregate fractions were positively correlated with microbial biomass, whereas, under medium- and long-term treatments, they were positively correlated with soil physicochemical properties. Macroaggregates were positively correlated with aggregate stability, while microaggregates and silt–clay fractions were negatively correlated—a relationship that strengthened with longer eCO₂ exposure. Thus, long-term eCO₂ altered soil aggregate structure and microbial communities, ultimately influencing SOC stability. These findings provide data and theoretical support for predicting soil carbon stability and ecosystem functioning in wetlands under climate change. Full article

Understory vegetation is a critical component of forest ecosystems. Its removal can substantially alter litter decomposition processes, with cascading effects on carbon (C) and nutrient cycling in terrestrial ecosystems. However, the global response patterns of litter decomposition to understory removal and underlying controlling factors remain unclear. We conducted a meta-analysis of 330 observations from 29 peer-reviewed field litterbag studies to assess the effects of understory removal on litter decomposition. We evaluated the changes in decomposition rate, mass loss, and nutrient dynamics to quantify the impacts of understory removal on litter decomposition. We assessed the associated shifts in soil microbial communities, measured using phospholipid fatty acids (PLFAs), to examine how microbial responses mediate decomposition during understory removal. We examined whether canopy type moderated these responses and explored the key predictors of decomposition for understory removal. Understory removal significantly reduced litter decomposition rate and mass loss by an average of 29.6% and 14.8%, respectively, while increasing lignin remaining by 30.1%. Soil microbial biomass also declined, with total, fungal, and actinomycete PLFAs decreasing by 12.0%, 30.8%, and 27.5%, respectively. Across canopy types, understory removal decreased litter mass loss in both broadleaved and coniferous forests. However, the remaining N and P increased significantly in broadleaved forests but changed only marginally in coniferous forests. Random forest analysis showed that initial litter quality and variations in fungal biomass were the primary predictors of decomposition responses. Understory vegetation removal significantly suppresses litter decomposition by reducing fungal biomass, and interacting with litter quality constraints and canopy type strongly moderates these effects. This highlights the essential role of understory vegetation in sustaining nutrient cycling and microbial functioning in forest ecosystems and underscores its critical role in guiding sustainable forest management. Full article

With continuous increases in nitrogen (N) deposition in the future, its impacts on terrestrial ecosystems are attracting growing concern. Arbuscular mycorrhiza (AM) fungi play a crucial role in shaping both soil microbial and plant communities. AM fungi play a crucial role in shaping the soil microbial and plant communities, yet their patterns of influence under increased N deposition scenarios remain unclear, particularly in desert ecosystems. Therefore, we conducted a field experiment simulating increased N deposition and AM fungal suppression to assess the effects of increased N deposition and AM fungi on soil microbial communities, employing phospholipid fatty acid (PLFA) biomarker technology in the Gurbantunggut Desert of Xinjiang. We found that increased N deposition promoted soil microbial biomass, including AM fungi, fungi, Actinomycetes (Act), Gram-positive bacteria (G⁺), Gram-negative bacteria (G⁻), and Dark Septate Endophyte (DSE). AM fungal suppression significantly increased the content of soil Act and G⁺. There were clearly and significantly interactive effects of increased N deposition and AM fungi on soil microbial contents. Both increased N deposition and AM fungi caused significant changes in soil microbial community structure. Random forest analysis revealed that soil nitrate N (NO₃⁻-N), Soil Organic Carbon (SOC), and pH were main factors influencing soil microorganisms; soil AM fungi, G⁺, and Act significantly affected plant Shannon diversity; soil G⁻, Act, and fungi posed significant effects on plant community biomass. Finally, the structure equation model results indicated that soil fungi, especially AM fungi, were the main soil microorganisms altering the plant community diversity and biomass under increased N deposition. This study reveals the crucial role of AM fungi in regulating soil microbial responses to increased N deposition, providing experimental evidence for understanding how N deposition affects plant communities through soil microorganisms. Full article