Search Results (124)

Desert reclamation into oases promotes soil organic carbon (SOC) accumulation across soil profiles, with nitrogen (N) fertilization being a key driver. However, the possible role of soil microorganisms in coupled C–N processes remains poorly understood in desert regions. We conducted a soil incubation experiment to evaluate the effects of N addition to varied soil layers on soil properties, CO₂ efflux, and microbial communities. The fertilized treatments (N, NP, and NPK) were compared with the unfertilized control (CK). All treatments were derived from the original desert soil. After incubation, SOC content decreased by 8–28% below the topsoil (20–100 cm) in the CK treatment, while it increased by 6–32% throughout the soil profile (0–100 cm) in all fertilizer treatments. Compared to the CK, all fertilizer treatments reduced daily and cumulative CO₂ emissions throughout the soil profile, with NP and NPK treatments showing greater reductions (3–19%). Fertilizer addition consistently enriched the phylum Firmicutes—notably the genera Virgibacillus and Bacillus—while lowering the relative abundance of other major phyla. After incubation, all treatments reduced microbial diversity and richness, with the most pronounced declines observed under fertilization. These community shifts were closely linked to changes in SOC and total N below the topsoil. These findings demonstrate that N-based fertilization promotes SOC accumulation in desert regions through microbial community restructuring. This study highlights the important role of exogenous nutrients, particularly N, in regulating C–N cycling and organic C sequestration in deep soil during desert oasis transformation. Full article

Forest soils serve as critical terrestrial carbon sinks. While broad hydrothermal controls on soil respiration (R_s) are established, uncertainties persist regarding high-frequency temporal dynamics and moisture-dependent variations in temperature sensitivity (Q₁₀). Specifically, conventional reliance on discrete, clear-day sampling obscures how precipitation disrupts diurnal patterns. To address this, we continuously monitored R_s and environmental factors in two Northeast Chinese mixed forests (Korean pine, Pinus koraiensis (KP), and Dahurian larch, Larix gmelinii (DL)) to quantify weather-driven daily dynamics and carbon fluxes. Precipitation primarily drove daily variability, but more importantly, it reshaped day–night asymmetry. Under clear-day conditions, R_s exhibited a consistent daytime-dominant pattern, with daytime fluxes being significantly higher than nighttime fluxes (p < 0.05). However, precipitation events fundamentally neutralized this asymmetry, resulting in no significant day–night differences across most phenological stages. Annual R_s effluxes (759 and 965 g C m⁻² yr⁻¹ for KP and DL, respectively) lacked significant inter-stand or temporal variations. Seasonal emissions peaked unimodally in July, with the non-growing season contributing merely 5%–8%. Notably, spring freeze–thaw R_s in the KP stand surged interannually by 143%. While R_s correlated positively with temperature (p < 0.001), Q₁₀ was co-regulated by forest stand and moisture. Under moderate moisture, the KP stand’s Q₁₀ (2.72) was significantly lower than the DL stand’s (3.81); however, this divergence neutralized under low moisture. Consequently, soil moisture acts as both a direct R_s driver and a fundamental regulator of its temperature sensitivity. These empirical findings provide critical data to calibrate forest carbon models, improving predictions of soil carbon feedbacks under future climate scenarios. Full article

Background/Objectives: Soil microbiomes in agroecosystems are natural reservoirs of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs), creating conditions for horizontal gene transfer (HGT) to clinically relevant bacteria. Southern West Siberia—a globally significant grain-producing region—lacks metagenomic characterization of its soil resistome. This study aimed to establish the first baseline profile of resistome and mobilome composition for West Siberian agricultural soils. Methods: Twelve composite soil samples were collected from agroecosystems under seven crop types across diverse soil types in southern West Siberia (September 2022). Shotgun metagenomics was performed on an Illumina NovaSeq 6000 platform. Taxonomic profiling used Kraken2/Bracken; ARG annotation used Prokka/DeepARG (identity ≥ 70%, probability score ≥ 0.8); while MGE characterization used Platon, HMMER v3.3.2, and Prokka-based integrase annotation. Resistome load was normalized to the single-copy housekeeping gene rpoB; ARG–MGE associations were defined as co-localization within 10 kb on the same contig. Results: Microbial communities were dominated by Pseudomonadota and Bacillota, with a stable core of Streptomycetaceae, Nitrobacteraceae, and Sphingomonadaceae. Normalized resistome load (N/rpoB 2.30–5.37) indicated moderate anthropogenic pressure. Dominant ARGs included efflux pumps (emrA, drrA, tetA, bcr, fsr), target modification (lnrL), and lipid A modification (arnA) genes. Class 1 integron integrase (intI1/rpoB 0.64–1.59) was detected in all 12 samples, exceeding unity in 9 of 12. ARG–MGE co-localizations were found in 11 of 12 samples. In sample Mg_155, genes emrA–emrB and bcr (NODE_16) and arnA and lnrL (NODE_6) were each independently associated with distinct prophage IntA integrase copies within Pseudomonas contigs, documenting multiple parallel horizontal transfer events encompassing resistance to five antibiotic classes. Conclusions: This work establishes the first metagenomic baseline of resistome and mobilome for West Siberian agroecosystems. The obtained data indicate moderate anthropogenic pressure on soil microbiomes, consistent with temperate agricultural systems with limited organic fertilizer input. The detected ARG–MGE co-localizations and evidence of prophage-mediated transfer of resistance determinants beyond their natural hosts suggest that mobilization potential in the region warrants consideration in future AMR monitoring programs. Full article

Understanding how soil acidification and moisture jointly regulate carbon mineralization is particularly important in karst grasslands, where high carbonate content can interfere with CO₂-based measurements. In this study, a controlled incubation experiment was conducted using soils collected from a typical karst grassland in Guizhou Province, China. Two pH levels (4.5 and 6.5) and three moisture levels (30%, 40%, and 60% of field water-holding capacity, WHC) were applied in a full-factorial design following a pre-incubation step to minimize carbonate-derived CO₂ interference. Soil CO₂ efflux, emission rate, and cumulative mineralization were monitored over a 60-day incubation period. Both soil moisture and pH significantly affected carbon mineralization, with a clear interaction between the two factors (p < 0.05). CO₂ efflux peaked during the early incubation stage and declined thereafter, indicating rapid depletion of labile carbon substrates. Across both pH levels, increasing moisture consistently enhanced CO₂ efflux and cumulative mineralization. Under comparable moisture conditions, near-neutral soils (pH 6.5) exhibited higher mineralization rates than acidic soils (pH 4.5). The highest carbon mineralization was observed at 60% WHC under pH 6.5, whereas the lowest occurred at 30% WHC under pH 4.5. These results suggest that moisture availability regulates substrate diffusion and microbial activity, while soil acidification constrains microbial metabolism and enzyme function. Notably, the effect of pH became less pronounced under low moisture conditions, indicating that water limitation can override pH regulation. This study offers a methodological framework for quantifying carbon mineralization in carbonate-rich soils and underscores the necessity of accounting for both physical and chemical limiting factors, as well as the confounding influence of inherent carbonates. Nevertheless, given the exclusive use of a single soil type and controlled laboratory conditions, the findings constitute preliminary evidence and require validation under field conditions and across diverse soil types before broader generalization. Full article

Wildfires are key drivers of Mediterranean forest dynamics, yet post-fire recovery and carbon cycling in coastal dune systems remain poorly understood, particularly under invasive species pressure. This study quantified how microtopography and dominant woody species shape vegetation recovery, carbon stocks, and soil CO₂ efflux in a Pinus pinaster plantation burned in 2017 in coastal Portugal, during the fifth post-fire hydrological year (2021–2022). Vegetation composition, aboveground biomass, litter, soil organic matter and total organic carbon were measured across dune crests and slacks, and soil respiration was repeatedly assessed under native—Halimium halimifolium—and exotic invasive—Acacia longifolia—woody species using a closed-chamber system. Woody cover was higher on crests, whereas slacks supported greater herbaceous cover and stronger increases in soil organic matter, with litter dominating biomass and carbon pools in all microsites. A. longifolia showed marked demographic expansion and higher soil respiration than the native shrub, while mixed-effects models revealed non-linear, interacting effects of soil moisture and temperature on CO₂ efflux. Overall, post-fire recovery and carbon dynamics were spatially heterogeneous and increasingly controlled by invasion, underscoring the need for microsite-specific restoration and early invasive control to safeguard carbon sequestration and native forest resilience in Mediterranean coastal dunes. Full article

With the rapid progression of global industrialization and urbanization, heavy metal contamination has emerged as a major global threat, especially cadmium pollution. Consequently, optimizing remediation measures has become a pivotal means to solve cadmium contamination. Compared to traditional physical and chemical remediation methods, microbial remediation has great potential in addressing cadmium pollution. In this study, a novel bacterial strain, Chryseobacterium sp. HGX-24, exhibiting high cadmium resistance was successfully isolated and screened from cadmium-contaminated environments. A preliminary discussion of the response mechanisms of this strain under cadmium stress is provided. Additionally, preliminarily explored the synergistic remediation of microbial-plant in cadmium-contaminated soil. Under conditions of high cadmium concentration, cadmium ions were effectively adsorbed by strain HGX-24 through extracellular polymers and functional groups on the cell wall surface, including −COOH, −CONH−, −NH, −OH, and >C=O. Extracellular proteins and polysaccharides were secreted by strain HGX-24 to regulate the adverse effects of heavy-metal cadmium ions on bacterial growth. Furthermore, the expression of genes such as antioxidant defense and ROS scavenging (katG, fabG, ybjT), Fe-S cluster assembly (sufB, sufD), sulfur metabolism (cysAU), amino acid metabolism (hisA, cysD, aspC), phenylacetic acid catabolism (paaC), and ribosomal proteins (rplC, rpsC, rpsL, rplA, rplY, rpmC) was regulated, affecting the synthesis and metabolism of membrane transporters (ABC transporters and efflux RND transporters), antioxidant enzymes (SOD, COT, POD), Fe-S clusters, thioredoxin family proteins, and ribosomal proteins, thereby enhancing resistance to cadmium toxicity. Moreover, strain HGX-24 was found to regulate the activities of redox enzymes in Zea mays L., thereby alleviating oxidative stress and reducing the negative feedback effects of reactive oxygen species in Z. mays. Full article

This study aimed to characterize the spatiotemporal dynamics of soil respiration (CO₂ efflux), soil moisture, and soil temperature across different land-use systems in a semi-arid environment through in situ monthly monitoring and to evaluate the potential of UAV-based imagery combined with Random Forest modeling to spatialize these variables within the agroforestry system. The variables were monitored monthly using an Infrared Gas Analyzer (IRGA) over 9 months, and UAV imagery was acquired at two distinct time points. The 11-month experimental campaign enabled evaluation of seasonal and spatial variability and of soil physical and hydraulic properties. Soil CO₂ efflux ranged from 1.0 to 6.7 μmol m⁻² s⁻¹, with higher values observed during the rainy period, closely following soil moisture dynamics. Soil moisture and temperature exhibited clear seasonal patterns driven by rainfall variability. The pasture system showed higher CO₂ efflux in most months, while AFS2 presented more stable fluxes over time. In contrast, AFS1 exhibited lower CO₂ efflux, likely associated with its soil characteristics. Despite these patterns, no significant differences were observed among land-use systems for most soil physical properties. UAV-derived data combined with machine learning techniques proved effective for modeling soil CO₂ efflux, soil temperature, and soil moisture, demonstrating their potential for monitoring soil processes in semi-arid environments. Overall, agroforestry systems did not significantly differ from other land uses in terms of CO₂ efflux, likely due to their early stage of development. These findings indicate that the effects of agroforestry systems on soil processes occur gradually and highlight the importance of long-term monitoring to fully capture system dynamics. Full article

Understanding spatiotemporal variation in soil CO₂ flux (FCO₂) along elevational gradients is essential for predicting carbon–climate feedback in alpine ecosystems. However, how temperature- and moisture-related factors jointly regulate daily-scale FCO₂ and how their contributions vary with elevation remain unclear, particularly in the Sejila Mountains (Southeastern Tibetan Plateau). We conducted continuous in situ measurements of daily-scale FCO₂, air temperature (Ta), relative humidity (RH), soil temperature (ST, 0–10 cm), and volumetric soil water content (SW) across five elevational bands (3000–4200 m) in 2024–2025. Across both years, FCO₂ showed a unimodal seasonal cycle and a robust nonmonotonic spatial pattern, with the highest efflux at 3000 and 4200 m and peak rates exceeding 5.0 µmol CO₂ m⁻² s⁻¹. Cumulative carbon loss at 4200 m (909.90 g C m⁻²) exceeded that at mid-elevation sites. Linear mixed-effects models identified Ta as the most consistent positive predictor; the ST × SW interaction was not significant, indicating that temperature and moisture effects are largely additive at the daily scale. Piecewise regression revealed nonlinear SW thresholds (θ) in the FCO₂ response, with θ varying nonmonotonically with elevation. Multiple linear regression further showed that thermal predictors (Ta, ST) explained substantially more variance than moisture predictors (RH, SW), and the relative importance of thermal drivers increased with elevation. These results challenge the common expectation of a monotonic decline in soil respiration with elevation and suggest that, when SW remains above critical thresholds, warming may amplify soil carbon losses at high elevations on the Tibetan Plateau. Full article

Trifoliate orange (Poncirus trifoliata L.) is one of the most widely utilized rootstocks in citrus production; however, it exhibits a relatively high sensitivity to salt stress. When cultivated in salinized soil, it frequently develops nutrient uptake disorders, leaf chlorosis, as well as reduced fruit yield and quality. To enhance the salt stress tolerance of citrus plants, this study investigated the effects of Trichoderma harzianum inoculation on the growth and response mechanisms of citrus seedlings under salt stress conditions. The results showed that salt stress significantly inhibited the growth of citrus seedlings, while T. harzianum inoculation effectively alleviated the inhibitory effect. After treatment with T. harzianum, the plant height, stem diameter, leaf number, and biomass of citrus seedlings increased significantly. The net photosynthetic rate, stomatal conductance, intercellular CO₂ concentration, transpiration rate, and chlorophyll content were significantly increased by T. harzianum inoculation. Meanwhile, T. harzianum inoculation increased the content of nitrogen, phosphorus, calcium, magnesium, zinc, and copper, and decreased sodium content in citrus seedlings. In addition, T. harzianum inoculation significantly up-regulated the expression of stress-responsive genes such as SOSs, PIPs, TIP1, TIP4, and TIP9. In conclusion, T. harzianum inoculation improved the salt stress tolerance of citrus seedlings through increasing photosynthetic efficiency, promoting nutrient absorption, sodium efflux, and water utilization via up-regulating the expression of SOSs and aquaporin genes. Full article

This study evaluated the influence of soil health in riparian and ecotone zones on water quality in four high-Andean rivers (Atillo, Ozogoche, Yasepan, and Cebadas) within the Cebadas River sub-basin, Ecuador. Soil and water samples were collected from 20 sites during three field campaigns (2022–2024). Soil properties included organic carbon concentration, soil organic carbon stock (SOC), bulk density, moisture, and potential microbial activity estimated through laboratory CO₂–C efflux. Water quality parameters were integrated into the National Sanitation Foundation Water Quality Index (NSF-WQI), and riparian condition was assessed using the QBR-And index. Multivariate statistical approaches, including Random Forest and Classification and Regression Trees (CART), were used to identify the most influential predictors of ecosystem quality. Results revealed marked spatial contrasts. Riparian SOC stocks ranged from 22.8 to 32.8 Mg C/ha in the more disturbed Cebadas and Yasepan rivers to 91.4–133.6 Mg C/ha in the better-conserved Atillo and Ozogoche systems. Sites with higher SOC and lower bulk density consistently exhibited better water quality, with NSF-WQI values classified as “good”, whereas more degraded sites showed lower riparian quality and “fair” water quality. Riparian forest quality was strongly correlated with water quality (r = 0.81). Random Forest models identified ammoniacal nitrogen, fecal coliforms, and altitude as the most influential predictors of riparian ecosystem condition. These findings demonstrate that soil health and riparian integrity are tightly linked to water quality patterns in high-Andean fluvial systems and support their integration into ecosystem-based watershed management. Full article

This study investigated the remediation effects of iron-modified biochar (FeBC-1 and FeBC-2) on arsenic (As) and cadmium (Cd) co-contaminated paddy soil and elucidated the underlying mechanisms from the perspectives of rhizosphere microbial ecology and plant As and Cd accumulation. A pot experiment with rice was conducted, comprising a control (CK) and iron-modified biochar treatments (FeBC-1 and FeBC-2). Parameters such as As and Cd speciation in rhizosphere soil, bacterial community composition, and the abundance of As-related functional genes were analyzed. The results demonstrated that iron-modified biochar reduced As and Cd accumulation in rice grains by promoting the formation of iron plaques on root surfaces. Meanwhile, the iron-modified biochar significantly enhanced the alpha diversity of bacterial communities and altered their composition. Quantitative analysis of functional genes revealed that the abundance of the As oxidase gene (aioA) increased from 3.54 × 10⁵ in the CK treatment to 7.20 × 10⁵ in FeBC-1 and 7.14 × 10⁵ in FeBC-2, and the abundance of the As efflux gene (arsA) decreased in the biochar-treated groups. These results indicate reduced As bioavailability in the rhizosphere and enhanced transformation of As(III) to As(V). Full article

As a pivotal component of the global carbon cycle, the spatial variation in soil respiration (Rs) is crucial for forecasting climate change trajectories. Despite extensive research on the spatial patterns of total Rs, the distinct drivers of its two components, heterotrophic respiration (Rh) and autotrophic respiration (Ra), are still not well defined. We compiled a global dataset from studies published between 2007 and 2023 to investigate the drivers of spatial variations in Rs, Ra, and Rh. This dataset comprises 308 annual flux measurements from 172 sites. The results showed that Rh contributed 63% and 60% to Rs in forest and grassland ecosystems, respectively. Further analyses using structural equation modelling (SEM) showed that the spatial variation in Rh and Ra exhibited divergent responses to climatic factors and plant community structure (mostly driven by gross primary production, GPP). Rh was more affected by mean annual temperature (MAT) than by mean annual precipitation (MAP), with standardized total effects of 0.17 (forests) and 0.57 (grasslands) for MAT versus 0.10 and 0.07 for MAP, respectively. In contrast, Ra exhibited greater sensitivity to MAP (0.08 and 0.18) than to MAT (−0.01 and 0.04). GPP exerted biome-specific effects: in forests, high GPP enhanced Rh (0.18) more substantially than Ra (0.08), while in grasslands, elevated GPP significantly increased Ra (0.34) but suppressed Rh (−0.30). Moreover, these variables incorporated into the SEMs accounted for a greater proportion of the variation in Rh and Ra in grasslands (R² = 0.73 for Rh, 0.48 for Ra) as compared to forests (R² = 0.21 for Rh, 0.22 for Ra), suggesting the greater complexity in forest soil C dynamics. By using the whole yearly measured soil respiration data around the world, this study highlights the differential environmental regulation of Rh and Ra, providing critical insights into the mechanisms governing Rs variations under climate change. Full article

Tea (Camellia sinensis) cultivation is a major global industry that faces sustainability challenges due to soil degradation and greenhouse gas (GHG) emissions from intensive management. Biochar—charcoal designed and used as a soil amendment—has emerged as a potential tool to improve soil health, enhance carbon sequestration, and mitigate GHG fluxes in agroecosystems. However, field-scale evidence of its effects on GHG dynamics in woody crops like tea remains limited, particularly regarding methane (CH₄). Here, we present, to our knowledge, the first field assessment of biochar impacts on CO₂, CH₄, and H₂O vapour fluxes in a subtropical tea agroforestry system with and without shade trees in northeastern Bangladesh. Using a closed dynamic chamber and real-time gas analysis, we found that biochar application (at 7.5 t·ha⁻¹) significantly enhanced average soil methane (CH₄) uptake by 84%, while soil respiration (CO₂ efflux) rose modestly (+18%) and water-vapour fluxes showed a marginal increase. Canopy conditions modulated these effects: biochar strongly enhanced CH₄ uptake under both shaded and open canopies, whereas biochar effects on water-vapour flux were detectable only when biochar was combined with a shade-tree canopy. Structural equation modelling suggests that CH₄ flux was primarily governed by biochar-induced changes in soil pH, moisture, nutrient status, and temperature, while CO₂ and H₂O fluxes were shaped by organic matter availability, temperature, and phosphorus dynamics. These findings demonstrate that biochar can promote CH₄ uptake and alter soil carbon–water interactions during the dry season in tea plantation systems and support operational biochar use in combination with shade-tree agroforestry. Full article

Understanding rhizosphere microscale processes is essential for evaluating plant–soil interactions under heavy metal stress. In this study, planar optode imaging was used to investigate the spatio-temporal distribution of O₂, pH, and CO₂ in the rhizosphere of Celosia argentea, a Cd hyperaccumulator, grown in Cd-contaminated and uncontaminated soils. The results demonstrated pronounced spatial heterogeneity, with O₂ hotspots concentrated near root surfaces, localized rhizospheric alkalinization at root tips, and elevated CO₂ levels reflecting active root metabolism. Under Cd stress, O₂ levels were initially suppressed, while pH and CO₂ increased, indicating adaptive physiological responses. As plant growth progressed, O₂-enriched zones expanded, pH elevation persisted, and CO₂ efflux continued, suggesting coordinated regulation of the rhizospheric microenvironment. These changes may influence microbial activity and nutrient dynamics in the rhizosphere, potentially supporting root function and plant adaptation under metal stress. This study provides mechanistic insights into root-induced microenvironmental regulation under Cd stress and demonstrates the potential of planar optode imaging for assessing plant-driven remediation processes in contaminated soils. Full article

Understanding soil respiration (Rs) dynamics in Mediterranean olive groves is crucial for quantifying carbon fluxes under climate change. Soil respiration represents the combined CO₂ efflux from root metabolic activity and microbial decomposition of soil organic matter, processes strongly controlled by soil moisture, temperature, and the quantity and quality of organic matter inputs in semi-arid Mediterranean environments. This study quantified the seasonal and spatial variability of Rs in a traditional rainfed olive orchard planted at a spacing of 11 m between rows and 9 m between trees (≈101 trees ha⁻¹). Continuous measurements were conducted in two contrasting zones, under-canopy (UC) and inter-row (IR), using automated soil CO₂ flux chambers. Annual Rs reached 3.68 Mg CO₂ ha⁻¹ y⁻¹ in UC and 2.21 Mg CO₂ ha⁻¹ y⁻¹ in IR, with substantially higher emissions per unit area beneath the canopy. However, due to its larger surface proportion, the IR zone contributed more to the orchard scale CO₂ budget. Soil water content emerged as the dominant environmental driver of Rs, moderating or suppressing the temperature response during dry periods. These findings highlight the importance of explicitly considering microsite heterogeneity when assessing soil CO₂ efflux and designing sustainable carbon-management strategies in Mediterranean olive agroecosystems. Full article