Search Results (266)

Soil extracellular enzyme activity reflects microbial resource acquisition and metabolic efficiency. However, applying enzyme stoichiometry to explore microbial metabolic limitations and carbon use efficiency (CUE) in rhizosphere and bulk soils under saline conditions remains limited. In this study, rhizosphere and bulk soils of Tamarix austromongolica were sampled along a salinity gradient in the Yellow River Delta to assess microbial metabolic limitation and CUE. Results showed that increasing salinity intensified microbial metabolic limitations and markedly reduced CUE, identifying salinity as the dominant factor constraining microbial efficiency. Rhizosphere soils consistently exhibited phosphorus limitation, whereas bulk soils shifted from balanced N–P limitation to pronounced N limitation with increasing salinity. Despite stronger microbial C limitation, CUE remained significantly higher in the rhizosphere than in the bulk soils, suggesting that continuous carbon inputs and enhanced enzyme activity partially mitigated salinity-induced stress. These findings highlight the complex interplay between salinity stress and rhizosphere effects in regulating microbial nutrient acquisition and carbon metabolism. Overall, this study demonstrates the utility of enzyme stoichiometry for evaluating microbial functional adaptation in saline habitats and provides insights that may contribute to the theoretical basis for vegetation restoration in saline-alkali ecosystems. Full article

The valorization of nutrient-rich institutional effluents represents a promising route for sustainable algal biotechnology. This study investigates the potential of canteen wastewater (CW) as an alternative culture medium for Spirulina platensis, integrating wastewater treatment with high-value carotenoid and lipid production. Growth performance, biochemical composition, and nutrient removal efficiencies were systematically evaluated in 2 L photobioreactors under optimized conditions. Spirulina cultured in 75% CW under 180 μmol photons m⁻² s⁻¹ achieved a biomass productivity of 0.071 g L⁻¹ day⁻¹, nearly three-fold higher than the synthetic BG-11 control (0.023 g L⁻¹ day⁻¹). Nutrient remediation was highly efficient, with 92.12% nitrate and 90.05% phosphate removal, effectively reducing effluent concentrations below discharge limits. Biochemical profiling revealed that wastewater-grown biomass contained 54.3% protein and 7.85% lipids, with a remarkable carotenoid yield of 21.81 mg g⁻¹ DW—significantly higher than the control (6.85 mg g⁻¹ DW). Mechanistic analysis suggests that the balanced nutrient stoichiometry (C:N:P ≈ 30:4:1) and mixotrophic conditions enhanced biomass quality while mitigating ammonia toxicity. This study demonstrates the first integrated application of canteen wastewater for dual-purpose bioremediation and pigment-rich biomass production, establishing a scalable circular bioeconomy framework for institutional waste management. Full article

Ecological stoichiometry provides a useful lens for linking nutrient status to ecosystem functioning, but cross-compartment (green leaves, surface litter, and topsoil) evidence for subtropical secondary forests is still limited. In particular, it remains unclear how forest type regulates coupled carbon (C), nitrogen (N), and phosphorus (P) patterns in leaves, litter, and soils on P-retentive Acrisols and how these patterns can be used to infer nutrient limitations. We measured C, N, and P concentrations and stoichiometric ratios in leaves, surface litter, and topsoil (0–10 cm) from 38 plots representing four dominant forest types (shrub, coniferous, mixed coniferous–broadleaf, and broadleaf) in subtropical public welfare forests of eastern China. We compared elemental concentrations and ratios among forest types and compartments and examined cross-compartment associations. Forest-type differences in stoichiometric patterns were most pronounced for leaf and soil concentrations/ratios, whereas litter metrics were comparatively conservative. Coniferous stands had the highest leaf C concentration and the highest litter C:N and C:P ratios, together with relatively low soil N and P concentrations. Broadleaf stands had the highest soil C and N concentrations and the highest litter and soil N:P, suggesting a tendency toward P limitation under comparatively N-rich conditions. Shrub and mixed forests were intermediate, with shrubs exhibiting the lowest litter N:P. Leaf N:P averaged 7.5 in coniferous stands and 12.5–14.9 in mixed and broadleaf stands. Coherent correlations of C:P from leaves to litter and soils and a negative relationship between leaf N:P and soil C:N suggested coordinated stoichiometric linkages along the leaf–litter–soil continuum. Overall, the results show that forest type organizes plot-scale C:N:P coupling on Acrisols and that leaf–litter–soil stoichiometry can be used as a practical framework for identifying whether N- versus P-related constraints are more likely to dominate different subtropical forest types and for informing nutrient-aware restoration and management. Full article

Understanding how straw incorporation affects soil stoichiometry and biochemical processes is essential for improving soil fertility in dryland wheat systems on the Loess Plateau. We quantified effects of four wheat straw return rates [0 (W0), 3500 (W1), 7000 (W2), and 14,000 kg ha⁻¹ (W3)] on C-N-P stoichiometry, microbial biomass, active carbon fractions, and enzyme activities in a randomized block experiment in Dingxi, Gansu. Composite soil samples from 0–10, 10–20, and 20–30 cm were analyzed for soil organic carbon (SOC); total nitrogen (TN); total phosphorus (TP); microbial biomass C, N, and P; dissolved, particulate, and readily oxidizable organic C; and sucrase, urease, alkaline phosphatase, and catalase activities. Increasing straw input significantly increased SOC, TN, and TP across all depths, with W3 increasing them by up to 42, 33, and 24% relative to W0, respectively. Under W3, microbial biomass C and N more than doubled, and labile C fractions and enzyme activities increased by 35–80% compared with W0. Straw return also modified soil and microbial C:N:P stoichiometry, decreasing microbial C:N and C:N:P and increasing N:P, suggesting alleviated N limitation. Overall, moderate-to-high straw incorporation improved soil fertility and functioning, supporting straw return as a sustainable management practice for Loess Plateau drylands. Full article

The effect of nitrogen (N) deposition on soil organic carbon (SOC) and the underlying mechanisms in grassland ecosystems remain a topic of debate. Moreover, previous research has primarily concentrated on interaction between carbon (C) and N cycles in response to N deposition, with less attention paid to how N-induced phosphorus (P) deficits impact SOC sequestration. To further investigate whether soil microbial stoichiometry influences SOC sequestration under N enrichment, we conducted a field experiment involving N and P additions. The soil properties, nutrients within plant leaves and microbial biomass, and the potential activity of eco-enzymes related to microbial nutrient acquisition were measured. Results showed that SOC did not significantly change with N addition, and SOC significantly increased with addition of N and P together, which suggested that the SOC was depleted with N addition. Soil available phosphorus and microbial biomass phosphorus (MBP) did not significantly decrease alongside N addition, which suggested that microbes alleviated P limitation. Microbial metabolic limitation analysis showed microbial P limitation was enhanced by N10 treatment. At the same time, microbial P limitation enhanced microbial C limitation. Consequently, microbes also required more C as an energy resource to invest in enzyme production. Microbial P and C limitations were both significantly negatively correlated with SOC. Results from SEM analysis also showed that the MBC:MBP ratio was significantly negatively correlated with SOC. These results support the idea that consumer-driven nutrient recycling shapes the dynamics of SOC. Therefore, nitrogen deposition-induced MBC:MBP imbalance may regulate SOC in alpine grassland ecosystems. Full article

Ecological stoichiometry offers a powerful framework for linking the elemental composition of ecosystems to their biogeochemical functions. However, whether soil stoichiometry directly controls greenhouse gas (GHG) emission ratios remains largely unexplored. This study provides a case study investigating the link between the soil carbon-to-nitrogen (C:N) mass ratio and the gaseous C:N molar emission ratio in three distinct temperate island-like forests (Larix gmelinii forest, LGF; Betula platyphylla forest, BPF; and a Populus-Betula mixed forest, PBMF) in the Qixing River Wetland. Using the static chamber–gas chromatography method, we measured soil fluxes of CO₂, CH₄, and N₂O throughout the growing season. Our results revealed a strong, significant positive linear relationship (R² = 0.99, p < 0.001) between the soil C:N ratio and the gaseous C:N emission ratio across all forest types. The LGF, possessing the highest soil C:N ratio, exhibited the highest gaseous C:N emission ratio, driven by substantial CO₂ emissions (mean flux of 512.45 mg·m⁻²·h⁻¹). Furthermore, the Larix gmelinii forest (LGF) exhibited the highest total Global Warming Potential (GWP), primarily driven by its significant CO₂ emissions. In contrast, the PBMF was the strongest CH₄ sink (−25.82 μg·m⁻²·h⁻¹) and a N₂O emission hotspot (15.24 μg·m⁻²·h⁻¹), corresponding to its low soil C:N ratio. These findings provide strong evidence that soil elemental stoichiometry is a key driver regulating the functional signature of GHG emissions. This case study highlights the potential of using stoichiometric theory to develop predictive tools for assessing ecosystem sustainability and informing sustainable forest management strategies under climate change. Full article

Ecological stoichiometry offers critical insights into nutrient dynamics and soil–plant interactions in agroecosystems. To explore the effects of long-term fertilization on soil–cotton C, N, P stoichiometry and stoichiometric homeostasis in arid gray desert soils, this study was conducted at a national gray desert soil monitoring station in Xinjiang (87°28′27″ E, 43°56′32″ N, elevation: 595 m a.s.l.)—an arid and semi-arid region with an annual mean temperature of 5–8 °C and annual precipitation of 100–200 mm. Established in 1989, the 31-year experiment adopted a wheat–maize–cotton annual rotation system with six treatments: CK (control, no fertilizer), N (nitrogen fertilizer alone), NK (nitrogen + potassium fertilizer), NP (nitrogen + phosphorus fertilizer), PK (phosphorus + potassium fertilizer), and NPK (nitrogen + phosphorus + potassium fertilizer). Key results showed that balanced NPK fertilization significantly increased soil organic carbon (SOC) by 22.7% and soil total phosphorus (STP) by 48.6% compared to CK, while the N-only treatment elevated soil N:P to 3.2 (a 68.4% increase vs. CK), indicating severe phosphorus limitation. For cotton, NPK increased seed phosphorus content by 68.2% (vs. N treatment) but reduced straw carbon content by 10.2% (vs. PK treatment), reflecting a carbon allocation trade-off from vegetative to reproductive organs under nutrient sufficiency. Stoichiometric homeostasis differed between organs: seeds maintained stricter carbon regulation (1/H = −0.40) than straw (1/H = −0.64), while straw exhibited more plastic N:P ratios (1/H = 1.95), highlighting organ-specific adaptive strategies to nutrient supply. Redundancy analysis confirmed that soil available phosphorus (AP) was the primary driver of cotton P uptake and yield formation. The seed cotton yield of NPK (5796.9 kg ha⁻¹) was 111.7% higher than CK, with NP (N-P co-application) achieving a 94.7% yield increase vs. CK—only 7.9% lower than NPK, whereas single N application showed the lowest straw yield (5995.0 kg ha⁻¹) and limited yield improvement. These findings demonstrate that long-term balanced NPK fertilization optimizes soil C-N-P stoichiometric balance by enhancing SOC sequestration and phosphorus retention, regulating cotton organ-specific stoichiometric homeostasis, and promoting efficient nutrient uptake and assimilate translocation. The study confirms that phosphorus is the key limiting factor in arid gray desert soil cotton systems, and balanced NPK supply is essential to mitigate stoichiometric imbalances and sustain soil fertility and productivity. This provides targeted practical guidance for rational fertilization management in arid agroecosystems, emphasizing the need to prioritize phosphorus supply and avoid single-nutrient application to maximize resource use efficiency. Full article

The sustainability of wheat-maize rotation systems in the North China Plain is challenged by the over-reliance on chemical fertilizers, which leads to the decline of soil organic matter and structural degradation, particularly in the unique Shajiang black soil (Vertisol). While straw return is widely recommended to mitigate these issues, the synergistic mechanisms of its long-term combination with chemical fertilizers on soil nutrient stoichiometry and aggregate stability remain inadequately quantified. A long-term field experiment was conducted with the five fertilization treatments including: (1) no fertilizer or straw (CK), (2) chemical fertilizer alone (NPK), (3) straw return chemical fertilizer (NPKS), (4) straw return with 10% straw-decomposing microbial inoculant combined with chemical fertilizer (10%NPKS), and (5) straw return with 20% straw-decomposing microbial inoculant combined with chemical fertilizer (20%NPKS) in the Shajiang black soil (Vertisol) region to investigate the effects of straw return combined with chemical fertilizers on soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP) stoichiometry, aggregate stability, and crop yield in winter wheat-summer maize rotation systems of North China Plain. Our study demonstrated that the co-application of straw with a straw-decomposing microbial inoculant is a highly effective strategy for enhancing soil health and crop productivity, with its efficacy being critically dose-dependent. Our results identified the 10%NPKS treatment as the optimal practice. It most effectively improved soil physical structure by significantly increasing the content of large macroaggregates (>0.5 mm) and key stability indices (MWD, GMD, WA), while concurrently enhancing nutrient cycling, as evidenced by elevated SOC, TN, and shifted C/P and N/P stoichiometry. Multivariate analyses confirmed strong positive correlations among these soil properties, indicating a synergistic improvement in soil quality. Crucially, these enhancements translated into significant yield gains, with a notable crop-specific response: maize yield was maximized under the 10%NPKS treatment, whereas wheat yield benefited sufficiently from NPKS treatment. A key mechanistic insight was that 20%NPKS treatment, despite leading to the highest SOC and TN, induced a relative phosphorus limitation and likely caused transient nutrient immobilization, thereby attenuating its benefits for soil structure and yield. We conclude that co-applying straw with a 10% microbial inoculant combined with chemical fertilizer represents the superior strategy, offering a sustainable pathway to synergistically improve soil structure, nutrient availability, and crop productivity, particularly in maize-dominated systems. Full article

The intensity of wildfires is projected to increase with the rising frequency of droughts due to climate change. Management practices following forest fires must include restoring the appropriate species composition. This study was performed within the wider context of the regeneration of soil properties, including the stock and soil organic matter (SOM) content, at the largest forest fire site in Poland (more than 9000 ha) in the Rudziniec Forest District, Upper Silesia. Research plots were established on sandy soils (Podzols and Arenosols) in pure stands of Scots pine (Pinus sylvestris L.), common birch (Betula pendula Roth), and black alder (Alnus glutinosa (L.) Gaertn.). The organic and mineral soil horizons were sampled from each research plot and control plots unaffected by the fire. The trees’ foliage was also sampled to determine the nutrient supply. Basic soil properties were determined, including the texture, pH, bulk density, organic carbon (C), macronutrient contents, soil microbial biomass, and labile C and nitrogen (N) fractions. We found that, 30 years after the fire, the post-fire soils had similar SOC stocks (34.80 Mg ha⁻¹) to the control plots (31.72 Mg ha⁻¹); however, they differed in their stocks of labile C and N fractions. The post-fire soils had a less stable C pool due to a higher stock of the fraction associated with particulate organic matter. In contrast, the N pool was more stable in the post-fire soils than in the control soils due to a lower contribution of the most labile fractions. The soils under Scots pine had the least stable SOM, which may have influenced the intensification of the podzolization process, whereas the highest biomass of soil microorganisms was observed under common birch. The soils under black alder had the highest acidity and lowest phosphorus (P) content. The C:N:P ratios in the post-fire soils and tree foliage indicated that P may have been the limiting factor in alder growth, and N for pine and birch. Our findings indicate that tree species composition is an important factor in the recovery of post-fire soil properties. However, the introduction of pure black alder stands to post-fire soils with low moisture and P availability showed little effectiveness in restoring the SOM content and N pool. Full article

The deposition of atmospheric nitrogen (N) includes organic N (ON) and inorganic N (IN). The effect of varying ON:IN ratios on the elemental composition in the root zone of T. grandis remains poorly understood. In this study, N deposition with different ON:IN ratios was simulated to analyze its effects on soil organic carbon (C), total N (TN), total and available phosphorus (P), available potassium (K), exchangeable calcium, exchangeable magnesium, and C:N, C:P, and N:P ratios. The results showed that N deposition increased soil organic C and total N content when compared with the control group. Different N sources had varied effects on soil P, with high inorganic N inputs potentially exacerbating P depletion. Nitrogen addition significantly reduced available K and exchangeable calcium and magnesium. Nitrogen addition treatment at an ON:IN ratio of 9:1 resulted in elevated C:N and C:P ratios, while nitrogen addition at an ON:IN ratio of 7:3 resulted in a notably increased N:P ratio. In conclusion, N deposition in different forms significantly affects soil elemental contents and ecological stoichiometry in T. grandis by altering C-N accumulation and soil acidification. Monitoring the loss of calcium, magnesium, and K is essential, and soil nutrient management should be enhanced to sustain forest health amid increasing N deposition. Full article

Fire is a crucial ecological factor, however, the organ-level effects of wildfire on plant non-structural carbohydrates (NSC) and stoichiometric characteristics are poorly understood. We studied the effects of fire on sugar, starch, carbon (C), nitrogen (N), and phosphorus (P) content in the needles, branches, stems, and fine roots of fire-damaged Pinus yunnanensis trees (F-trees). Starch, sugar, and NSC content were higher in the roots and needles of F-trees than in that of undamaged individuals (H-trees). C, N, and P content and stoichiometry characteristics of F-trees also differed significantly from H-trees. The N/P content of both F-tree and H-tree needles were <14 prior to forest fire disturbance and increased thereafter, indicating that the N limitation increased after fire disturbance. In addition, F-tree physiology did not return to control levels nine months after fire disturbance, indicating that more time is needed to recover. These findings suggest that forest management practices that increase soil N content will likely accelerate post-fire recovery. Because fire frequency and intensity will continue to increase in response to climate change, our results are of great value in improving our understanding of post-fire ecosystem dynamics. Full article

Soil microbial nutrient limitation is of great significance for the maintenance of soil fertility, the sustainability of plant growth, and the stability of the alpine meadow ecosystems, which are particularly sensitive to global climate change. This study aimed to explore the effects of soil extracellular enzyme activities on soil microbial nutrient limitation across three altitudinal gradients—low altitude (LA: 2900–3200 m above sea level (masl)), middle altitude (MA: 3200–3500 masl), and high altitude (HA: 3500–3800 masl)—in alpine meadows in the northeastern Qinghai–Tibet Plateau, using the method of ecological stoichiometry. The research results showed that soil nutrients mostly accumulate in the surface layer: with increasing altitude, soil organic carbon (SOC) and total nitrogen (TN) contents gradually increase (p < 0.05), and their contents at high altitude in the 0–20 cm soil layer are twice those at low altitude. The activities of β-1,4-glucosidase (BG) and β-1,4-N-acetylglucosaminidase (NAG) at high altitude are significantly 26.77% and 30.88% higher than those at low altitude, respectively. Linear regression analysis shows a significant positive correlation between soil nutrients and C/N/P-related enzymes after logarithmic transformation along the altitudinal gradient. Enzyme vector analysis revealed that in the alpine meadows at altitudes ranging from 2900 to 3800 masl, relative nitrogen limitation was widespread, while relative carbon limitation was more significant in both high-altitude and low-altitude regions (p < 0.05). Notably, this study did not account for the granulometric composition of the soil at the sampling sites. Nevertheless, it partially reveals the nutrient acquisition strategies of microorganisms across different altitudinal gradients, providing a theoretical basis for understanding nutrient cycling in alpine meadow ecosystems and addressing global change. Full article

Tea plantations are one of the most intensive land-use systems in subtropical China, but the long-term effects on soil microbial functioning remain insufficiently understood. This study combined extracellular enzyme activity, ecoenzymatic stoichiometry, and partial least squares path modeling (PLS-PM) to assess the impacts of forest-to-tea conversion and plantation age on microbial nutrient acquisition and metabolic limitations. The results showed that tea plantations had significantly higher activities of carbon (C)-, nitrogen (N)-, and phosphorus (P)-acquiring hydrolases compared to adjacent pine forests, and oxidase activity increased significantly with plantation age, reaching a fivefold higher level in the oldest plantation. Soil acidification, decreased soil organic carbon, and shifts in microbial composition (decline in bacteria and actinomycetes, increase in fungi) were the main drivers of these changes. The study indicates that tea planting intensifies microbial limitations on carbon and phosphorus and shifts microbial metabolism toward oxidative pathways, which may destabilize soil carbon pools and reduce long-term fertility. These findings highlight the importance of balanced nutrient management in tea plantation practices. However, the study is limited by the short duration of field sampling. Future research should focus on long-term monitoring to better understand the sustained impacts of tea cultivation on soil microbial functions and explore the role of different management practices in mitigating these effects. Full article

Excessive nitrogen addition in farmland on the Loess Plateau reduces soil quality and endangers the atmospheric environment. We designed an experiment to investigate the effects of different nitrogen application rates on the soil physicochemical properties and microbial diversity of spring wheat fields on the Loess Plateau, aiming to identify the optimal nitrogen application rate and avoid the detrimental effects of excessive nitrogen addition. A field experiment was conducted from 2022 to 2023 with four nitrogen (N) application rates (0, 55, 110, and 220 kg·N·ha⁻¹·y⁻¹). This study aimed to assess the changes in soil properties, nutrient contents, enzyme activities, and bacterial community structure. The results showed that increasing N application generally enhanced soil bulk density, nitrate nitrogen (NO₃⁻-N), ammonium nitrogen (NH₄⁺-N), and microbial biomass nitrogen (MBN) (p < 0.05). In contrast, soil water content initially increased and then decreased. Soil organic carbon and total nitrogen rose markedly with higher N inputs, particularly in the 0–20 cm layer, whereas total phosphorus was less affected. Nitrogen addition stimulated soil enzyme activities (protease, urease, nitrate reductase, and nitrite reductase), though excessive input (220 kg·N·ha⁻¹·y⁻¹) produced inhibitory effects. Actinobacteria (relative abundance: 29–35%) and Proteobacteria (relative abundance: 14–22%) were the dominant phyla in all treatments. Alpha diversity peaked at low nitrogen input (55 kg·N·ha⁻¹·y⁻¹), while high N level reduced evenness and species richness (p < 0.05). Principle Coordinate Analysis (PCoA) revealed that both N application and soil depth shaped microbial community assembly, with deeper layers (20–40 cm) being more sensitive to N input. Correlation analysis indicated that soil moisture, bulk density, and C:N:P stoichiometry were key drivers of bacterial community variation. Overall, moderate nitrogen input (110 kg·N·ha⁻¹·y⁻¹) improved soil fertility and supported microbial functionality, whereas excessive application degraded soil structure and reduced biodiversity. These findings highlight the need for balanced N management strategies in rain-fed agriculture of the Loess Plateau to sustain both productivity and ecological stability. Full article

Most traits of assimilative branches (ABs) present large spatial and interspecific differences; however, it is still unclear how small-scale soil heterogeneity influences nutrient traits in ABs under the same climatic conditions. The AB samples of Ephedra przewalskii (EP; small-sized), Calligonum mongolicum (CM; medium-sized), and Haloxylon persicum (HP; large-sized), as well as soil samples, were collected at three sites (north, middle, and south; within 65 km) in the southeastern Gurbantunggut Desert, China. The interspecific and inter-site differences in C:N:P:K stoichiometry and the relationships with soil properties were discussed. From north to south, soil nutrients and biocrust development improved, whereas coarse sand proportion decreased. Species and site markedly influenced ABs’ stoichiometry, with a significant interaction. At the species level, each stoichiometric trait differed among species. CM exhibited the lowest C:P and N:P, whereas HP had the highest N:P. At the site level, N:P and C:P of EP and CM increased from north to south, whereas HP changed unclearly. CM and HP had higher N–P scaling exponents, EP and CM exhibited a higher K allocation rate, resulting in the co-limitation of N and P for all species. The overall stoichiometric homeostasis ranked as follows: HP > CM > EP. The three shrubs were dispersed among each other in an ordination diagram based on nutrient metrics, with different distribution patterns. The nutrient traits in the ABs of EP and CM, rather than HP, were markedly correlated with most soil factors. Local-scale soil variation indeed influenced the nutrient strategies of desert shrubs; plant size might be another important factor. Full article