Phosphorus Availability Research Articles

Biodegradation of phenol-contaminated soil and plant growth promotion by Myroides xuanwuensis H13.

Physicochemical methods for remediating phenol-contaminated soils are costly and inefficient, making biodegradation an environmentally friendly alternative approach. This study aims to screen for potential phenol-degrading bacteria and to verify the removal capacities of a selected strain in a bioaugmentation experiment at the greenhouse level using Brassica chinensis L. (Chinese cabbage) as the model plant and phenol-contaminated soil. In parallel, pot experiments were conducted using a collaborative approach based on this model system. We found that Myroides xuanwuensis strain H13 showed a high degradation capability, with a 97.67% efficiency in degrading 100 mg/L phenol. Under shaking flask conditions, H13 facilitated the solubilization of tricalcium phosphate and potassium feldspar powder. Pot experiments suggested a phenol removal percentage of 89.22% and enhanced availability of soil phosphorus and potassium for plants with H13 inoculation. In this case, the abundance of soil microbes and the activity of soil enzymes significantly increased as well. Furthermore, both photosynthesis and the antioxidant system in Chinese cabbage were enhanced following H13 inoculation, resulting in its increased yield and quality. Partial least squares path modeling revealed that H13 can primarily affect plant root growth, with a secondary impact on photosynthesis. These findings highlight the potential of biodegradation from phenol-degrading bacteria as a promising strategy for efficient phenol removal from soil while promoting plant growth and health.IMPORTANCEThis study is significant for environmental remediation and agriculture by its exploration of a more environmentally friendly and cost-effective bio-strategy in treating phenol-contaminated soil. These findings have essential implications for environmental remediation efforts and sustainable agriculture. By utilizing the biodegradation capabilities of Myroides xuanwuensis strain H13, it is possible to remove phenol contaminants from the soil efficiently, reducing their negative effects. Furthermore, the enhanced growth and health of the Chinese cabbage plants indicate the potential of this approach to promote sustainable crop production.

Effects of thinning and understory removal on soil phosphorus fractions in subtropical pine plantations.

Forest management changes the physical environments and nutrient dynamics and then regulates the forest productivity. Soil phosphorus (P) availability is critical for productivity in tropical and subtropical forests. However, it was still poorly understood how soil P content and fraction respond to various forest management practices in these regions. Here, we measured the soil total P, available P, and Hedley's P fractions, including inorganic and organic P (Pi and Po), in subtropical pine plantations treated with understory removal (UR), non-dominant species thinning (NDST) and dominant species thinning (DST) after nine years. Compared to plantations without management (CK), treatments such as UR, NDST, and DST decreased soil total P at 0-10 cm and soil available P at 0-10 cm and 10-20 cm. Increases in resin-Pi, NaOH-Pi, and C.HCl-Pi resulted in a higher total Pi in 0-10 cm (p < 0.05) in treated plots (UR, NDST, and DST) than in CK plots. UR, NDST, and DST treatments increased NaHCO3-Po and NaOH-Po (p < 0.05) but decreased C.HCl-Po at a depth of 0-10 cm. Regardless of management treatments, soil total P, available P, and P fractions in 0-10 cm showed higher contents than those in 10-20 cm. There were positive relationships between total P and total Po (p < 0.01) and between available P and total Pi. There were also positive relationships between total P, available P, NaHCO3-Pi, and NaOH-Pi (p < 0.05). In conclusion, forest management such as UR, NDST, and DST decreased soil total P and available P, and transforming soil P fractions to available P will meet the P demand following management in the pine plantations of subtropical China.

Different ectomycorrhizal fungal species impact poplar growth but not phosphorus utilization under low P supply.

Tree growth is often limited by phosphorus (P) availability. The trade-off between P homeostasis and growth is unknown. Ectomycorrhizal fungi (EMF) facilitate P availability but this trait varies among different fungal species and isolates. Here, we tested the hypotheses that (i) colonization with EMF boosts plant growth under P-limited conditions and that (ii) the poplars show P homeostasis because increased P uptake is used for growth and not for P accumulation in the tissues. We used two P treatments (high phosphate [HP]: 64μM Pi, low phosphate [LP]: 0.64μM Pi in the nutrient solution) and four fungal treatments (Paxillus involutus MAJ, Paxillus involutus NAU, Laccaria bicolor dikaryon LBD, Laccaria bicolor monokaryon LBM) in addition to non-inoculated poplar plants (NI) to measure growth, biomass, gas exchange and P contents. High phosphate (HP) stimulated growth compared with LP conditions. Poplars colonized with MAJ, NAU and NI showed higher growth and biomass production than those with LBD or LBM. Photosynthesis rates of poplars with lower biomass production were similar to or higher than those of plants with higher growth rates. The tissue concentrations of P were higher under HP than LP conditions and rarely affected by ectomycorrhizal colonization. Under LP, the plants produced 44% greater biomass per unit of P than under HP. At a given P supply, the tissue concentration was stable irrespective of the growth rate indicating P homeostasis. Laccaria bicolor caused growth inhibition, irrespective of P availability. These results suggest that in young poplars distinct species-specific ectomycorrhizal traits overshadowed potential growth benefits.

Enhancing Fruit Crop Performance: The Role of Phosphate-Solubilizing Bacteria in Growth, Yield and Quality Improvement

Phosphorus is a crucial macronutrient in plant development, playing a vital role in metabolic activities and growth. Due to its poor availability in soil, phosphorus (P) is essential for healthy plant growth, particularly in tropical regions. P is present in nucleic acids, catalysts, coenzymes, nucleotides, and phospholipids. Optimal phosphorus availability is essential for plant reproductive structure formation during early development. Soil phosphorus content is around 0.05%, but due to insoluble phosphates, soluble forms are not readily available for plants. Chemical P fertilizers are used to increase available P levels, but these are costly and have negative environmental impacts. The limited P-source and high-quality rock P deposits may be exhausted within the next century, leading to the search for environmentally friendly alternatives. Biofertilizers with P-solubilizing properties are an environmentally friendly alternative to chemical-based Phosphorus fertilizers. PSB, beneficial microorganisms, hydrolyse insoluble phosphorus compounds into soluble P, facilitating plant uptake. This eco-friendly and economically sound approach overcomes P scarcity. Throughout the review, these PSBs are discussed in terms of how they have been applied and used to improve fruit crop growth, yield, and quality, providing promising evidence that these PSBs can be used as a viable alternative to inorganic phosphate fertilizers in the future for sustainable agriculture.

High-rate pig manure substitution enhances comammox Nitrospira abundance and diversity in the Cinnamomum camphora coppice planting soils

Comammox Nitrospira represents a groundbreaking discovery in nitrogen cycle research, showcasing its remarking ability for complete ammonia oxidation, which challenges prior conceptions of nitrification. In this study, we examined the response of comammox Nitrospira gene abundance, diversity, and community structure to different rates of pig manure substitution (0 %, 25 %, 50 %, 75 %, and 100 %) in subtropical agroforestry soils. The abundance of ammonia-oxidizing microorganisms was assessed by qPCR, whereas the diversity and structure of comammox Nitrospira were determined by high-throughput sequencing. Our findings revealed that pig manure substitution led to an increase in soil pH, available phosphorus (AP), comammox Nitrospira abundance, and diversity within soils under Cinnamomum camphora coppice planting. Soil pH and AP were the primary factors influencing the diversity and community structure of comammox Nitrospira. Moreover, pig manure substitution significantly influenced the composition of comammox Nitrospira, notably by increasing the relative abundance of clade A.2.1 while reducing that of clade A.2.2. However, pig manure substitution did not exert a significant impact on net nitrification rates, suggesting bacterial relative abundances were more sensitive to manure substitution compared to the underlying biogeochemical processes. Overall, our results offer new insights into the response of comammox Nitrospira to different rates of pig manure substitution in Cinnamomum camphora coppice planting soils, highlighting the pivotal role of soil AP and pH as the key determinants shaping comammox Nitrospira diversity and community structure.

Species interactions and bacterial inoculation enhance plant growth and shape rhizosphere bacterial community structure in faba bean – wheat intercropping under water and P limitations

Grain legumes / cereals intercropping systems with microbial inoculants, hold promise for improving crop productivity under stressful conditions. However, the tripartite interaction involving intercropping system, associated microbiota and stress combining water deficit and low phosphorus (P) availability remains understudied. This study evaluated the impact of three bacterial consortia (C4, C6, and Cref containing Rhizobium and PSB strains) including single Rhizobium (Rhizobium laguerreae) on the agro-physiological performance of wheat (Triticum durum) and faba bean (Vicia faba) grown as intercrops or sole-crops under P and water deficient conditions. Inoculation, especially with C6, significantly improved shoot and root biomasses of both wheat (up to 66 and 81 %) and faba bean (up to 54 and 266 %) intercrops compared to single Rhizobium inoculation and control treatments. Intercropping generally outperformed sole-cropping in above-ground physiology, root morphological traits, shoot and root P content, with a notable effect in response to C6 exhibiting low microbial biomass P. Changes in bacterial community structure were primarily driven by cropping pattern and water regime rather than bacterial inoculation. Intercropping maintained bacterial diversity but shifted community structure, favoring Proteobacteria. Overall, inoculating intercropped wheat and faba bean with Rhizobium-containing consortia induced beneficial below-ground interspecies interactions under water and P-limiting conditions.

The Soil Ecological Stoichiometry Characteristics of the Highest Latitude Areas in the Main Tea-Producing Regions of China

To investigate the contents of carbon, nitrogen, and phosphorus in tea plantation soils and their ecological stoichiometric characteristics, as well as their response to environmental factors in high-latitude regions of China, soil samples from 0 to 20 cm depth were collected from tea plantations at different altitudes and cultivation years in the main tea-producing areas of Shaanxi Province. These samples were used to determine the soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) contents and to calculate their stoichiometric ratios. The findings revealed the following: the average soil SOC and TN content in tea gardens were 13.15 and 1.30 g·kg−1, respectively, exceeding the national soil average. These values met the Class I tea garden fertility standards. However, the average soil TP content, at 0.45 g·kg−1, fell below the national soil average, meeting the Class II tea garden fertility standards. In tea gardens, the average ratios of carbon to nitrogen (C:N), carbon to phosphorus (C:P), and nitrogen to phosphorus (N:P) in the soil were 10.42, 30.98, and 3.32, respectively. These ratios were all lower than the national soil average, indicating relatively high phosphorus availability but nitrogen deficiency in tea garden soils. As altitude increased, there was a decline in soil SOC content, C N, and C P ratios, followed by a subsequent increase. No significant changes were seen in TN, TP, and N P ratio in the soil, but there was an increase in SOC content, TN content, and C P ratio during cultivation. The N-to-P ratio initially increased before decreasing, while the C-to-N ratio decreased before increasing. Soil TP content did not change significantly. The study recommends careful nitrogen fertilizer application in tea garden management to balance nitrogen and phosphorus.

Effect of Soil Texture on Soil Nutrient Status and Rice Nutrient Absorption in Paddy Soils

Soil texture affects rice nutrient uptake and yield formation by influencing soil structure, microbial activity, and soil nutrient supply capacity. Analyzing the relationship between soil texture, nutrient content, and rice agronomic traits is of great significance for precise and efficient fertilizer application. The tillage layer (0–20 cm) of 31 paddy fields in China’s main rice-producing areas was collected to perform rice pot experiments, and soil texture characteristics, physicochemical properties, microbial-related indicators, and rice agronomic traits were measured and analyzed. The results showed that these soils could be classified into four types of soil texture: loamy sandy soil, sandy loam soil, silty loam soil, and silty soil. Analysis of variance showed that the available nitrogen (AN), available potassium (AK), and available phosphorus (AP) contents were the highest in silty loam, silty, and sandy loam soils, respectively, and silt loamy soil had the highest CEC. Principal component analysis (PCA) also showed that soil physicochemical properties can be distinguished to a certain extent according to soil texture types. For the relationship of soil texture parameters and soil physicochemical properties, soil organic matter (OM), total nitrogen (TN), AN, ammonium nitrogen (NH4+-N), and microbial carbon (MBC) contents were positively correlated with soil clay content, AK was positively correlated with silt content, and soil phosphorus status was significantly related to pH. Mantel’s test revealed significant correlations between rice N, P, and K nutrient status, dry matter accumulation, and yield, and soil available nutrient content, MBC, pH, and soil texture parameters. Structural equation modeling (SEM) indicated that sand affected soil available nutrients by regulating pH, while clay can positively influence soil available nutrients by affecting soil organic matter mineralization and microbial activity, thus influencing nutrient absorption and yield formation in rice. Overall, in rice production, the silty and silty loam paddy soil with fine texture and higher clay content facilitates the mineralization of soil organic matter and the activity of soil microbes, resulting in more available soil nutrients, which benefits the rice absorption and accumulation of nutrients. Furthermore, a higher content of clay also promotes the distribution of dry matter to the panicle, thereby promoting rice yield formation.

Organophosphorus mineralizing-Streptomyces species underpins uranate immobilization and phosphorus availability in uranium tailings

Phosphate-solubilizing bacteria (PSB) are important but often overlooked regulators of uranium (U) cycling in soil. However, the impact of PSB on uranate fixation coupled with the decomposition of recalcitrant phosphorus (P) in mining land remains poorly understood. Here, we combined gene amplicon sequencing, metagenome and metatranscriptome sequencing analysis and strain isolation to explore the effects of PSB on the stabilization of uranate and P availability in U mining areas. We found that the content of available phosphorus (AP), carbonate-U and Fe-Mn-U oxides in tailings was significantly (P < 0.05) higher than their adjacent soils. Also, organic phosphate mineralizing (PhoD) bacteria (e.g., Streptomyces) and inorganic phosphate solubilizing (gcd) bacteria (e.g., Rhodococcus) were enriched in tailings and soils, but only organic phosphate mineralizing-bacteria substantially contributed to the AP. Notably, most genes involved in organophosphorus mineralization and uranate resistance were widely present in tailings rather than soil. Comparative genomics analyses supported that organophosphorus mineralizing-Streptomyces species could increase soil AP content and immobilize U(VI) through organophosphorus mineralization (e.g., PhoD, ugpBAEC) and U resistance related genes (e.g., petA). We further demonstrated that the isolated Streptomyces sp. PSBY1 could enhance the U(VI) immobilization mediated by the NADH-dependent ubiquinol-cytochrome c reductase (petA) through decomposing organophosphorous compounds. This study advances our understanding of the roles of PSB in regulating the fixation of uranate and P availability in U tailings.

Effects of organic acid application and ectomycorrhizal symbiosis on growth and morphological parameters of &lt;em&gt;Pinus pseudostrobus&lt;/em&gt;

Background: Many landscapes, both natural and anthropogenic, are dominated by degraded soils that have low phosphorus availability due to low overall phosphorus concentration or to phosphorus sequestration by iron-rich minerals. Questions and / or Hypotheses: Does the application of low molecular weight organic acids improve phosphorus availability and plant growth in phosphorus-poor soils, and is this effect modulated by ectomycorrhizal fungi? Studied species / data description /Mathematical model: Pinus pseudostrobus and its ectomycorrhiza Pisolithus arhizus, in addition to six sodium salts of organic acids. Study site and dates: The experiment was carried out in a shade house (35 % shade) in Morelia, Michoacán in 2015. Methods: We conducted experiments with Pinus pseudostrobus and its ectomycorrhiza Pisolithus arhizus in addition to six sodium salts of organic acids. Sodium salts of citrate, oxalate, acetate, tartrate, succinate and malate were added to the soil at 0, 4, 8, 16, 32 and 64 micromolar concentrations. Results: The salts of the organic acids—particularly tartrate and malate-solubilized phosphorus and improved plant growth after 12 months in the absence of P. arhizus. When plants were inoculated with P. arhizus, the effect of most organic acids was either detrimental or non-significant. However, citrate, tartrate and succinate improved biomass and morphological parameters. Conclusions: These results suggest that adding appropriate organic acids to heavily degraded soils can aid P. pseudostrobus establishment and its benefits are higher than the association with mycorrhiza for young plants during the initial stages of fungal colonization.

The Spatiotemporal Variability of Soil Available Phosphorus and Potassium in Karst Region: The Crucial Role of Socio-Geographical Factors

The contents of soil available phosphorus (AVP) and potassium (AVK) in karstic mountainous agricultural areas have changed rapidly in recent decades. This temporal variation displays strong spatial heterogeneity due to these areas’ complex topography and anthropogenic activities. Socio-geographical factors can reflect the changes in the natural environment caused by human beings, and our objective is to enhance understanding of their role in explaining the changes of AVP and AVK. In a typical karst region (611.5 km2) with uniform soil parent material and low climatic variability, 255 topsoil samples (138 in 2012 and 117 in 2021) were collected to quantify the temporal AVP and AVK changes. Random forest (RF) and partial dependence plot analyses were conducted to investigate the responses of these changes to socio-geographical factors (distance from the nearest town center [DFT] and village density [VD]), topography, biology, and landscape pattern indexes. The mean values of AVP (48.25 mg kg−1) and AVK (357.67 mg kg−1) in 2021 were significantly (p &lt; 0.01) higher than those in 2012 (28.84 mg kg−1 and 131.67 mg kg−1, respectively). Semi-variance analysis showed strong spatial autocorrelation for AVP and AVK, ranging from 7.29% to 10.95% and 13.31% to 10.33% from 2012 to 2021, respectively. Adding socio-geographical factors can greatly improve the explanatory power of RF modeling for AVP and AVK changes by 19% and 27%, respectively. DFT and VD emerged as the two most important variables affecting these changes, followed by elevation. These three variables all demonstrated clear nonlinear threshold effects on AVP and AVK changes. A strong accumulation of AVP and AVK was observed at DFT &lt; 5 km and VD &gt; 20. The AVP changes increased dramatically when the elevation ranged between 1298 m and 1390 m, while the AVK changes decreased rapidly when the elevation ranged between 1350 m and 1466 m. The interaction effects of DFT and VD with elevation on these changes were also demonstrated. Overall, this study examined the important role of socio-geographical factors and their nonlinear threshold and interaction effects on AVP and AVK changes. The findings help unravel the complex causes of these changes and thus contribute to the design of optimal soil phosphorus and potassium management strategies.

Performance of Cowpea as a function of residues of organomineral fertilizers applied in corn crop

Organomineral fertilizers can be an excellent alternative through exploitation of the residues left by application in previous crops. Therefore, the objective of this study was to evaluate the agronomic characteristics of cowpea fertilized with residual organomineral fertilizers from the first corn crop in southern Maranhense. The experimental design was randomized blocks, arranged in a split-plot design, with three replications. Two cowpea cultivars (BRS Tucumaque and BRS Nova era) were sown in the plots. The residues of three phosphate fertilizers were sown in the subplot (two of which were organomineral fertilizers and one phosphate fertilizer (single superphosphate). At cowpea harvest, five plants were collected per plot for the following variables: number of nodes on the main stem at maturity, number of legumes per plant, number of grains per legume and weight of one thousand grains, and yield in kg ha-1. The cowpea cultivars are influenced by the cropping system (with and without U. ruziensis and organomineral sources). However, in soils with high phosphorus contents, the absence of U. ruziensis and fertilization or the use of organomineral or super simple fertilization promoted higher grain yields. The cultivar BRS Tucumaque had the highest grain yield. Organomineral and mineral fertilizer residues showed effective alternatives for increasing phosphorus availability in areas with Urochloa ruziziensis.

Unveiling soil bacterial diversity in the Andes-Amazon transition zone: Impacts of forest conversion to pasture

Soil microorganisms play a crucial role in the functioning of ecosystems by performing several essential functions. However, their resilience is tested by disturbances, primarily driven by land use changes. The Andes-Amazon transition zone, renowned for its ecological importance, is experiencing a growing pressure of removing native forests to establish pastures. In the last decades, efforts to characterize biodiversity in this region have been increasing; however, our comprehension of soil microbial communities and their responses to land use changes remains limited. Here, we used a shotgun DNA metagenomic sequencing approach to investigate the composition, diversity, and functions of soil bacterial communities in the litter and topsoil (0–10 cm) of a forest localized in an Andes-Amazon transition zone in Colombia and evaluate how they are affected by pasture establishments. Our findings unveiled the forest litter as a distinct microbial ecosystem, characterized by the highest bacterial richness and diversity. This layer was positively associated with increased availability of carbon (C), nitrogen (N), and phosphorus (P), and enzymatic activity linked to the mineralization of these elements. The transition from forest to pasture altered the microbial community structure, which was accompanied by a reduction of soil acidity. We observed that Proteobacteria, Acidobacteria, and Actinobacteria were the most abundant phyla in all environments, with a predominance of Proteobacteria and Bacteroidetes in forest litter, while forest-pasture conversion increased the abundance of Verrucomicrobia and Firmicutes in the soil. Functional profiles were over-represented in the litter, followed by pasture and forest soils. These results provide a foundational framework for comprehending the microbiome in the Andes-Amazon transition zone and its role in ecosystem functioning. Furthermore, this study sheds light on the far-reaching consequences of land use changes on microbial communities.

L-Arginine enhances stress resilience against P deficiency of Chinese fir in root system: Physiological and proteomics analysis

The diminishing availability of phosphorus (P) in soils poses a significant constraint, impacting over 30 % of global agricultural and forestry production. Root exudates play a crucial role in, helping plants cope with environmental stress and facilitating communication between plants. Conducting physiological and proteomic analyses under low P and L-arginine treatments, this study delved into the internal regulatory mechanisms of L-arginine in Chinese fir under low P conditions. Adding L-arginine not only expanded the root length and surface area but also substantially improved the P accumulate capacity of Chinese fir. Physiological examinations revealed a notable increase in peroxidase (POD) activity by 81.10 % and superoxide dismutase (SOD) activity by 31.39 % with the addition of L-arginine under low P conditions. Proteomics analysis further demonstrated that L-arginine significantly downregulated the expression of phosphate transporters (PHTs) while concurrently upregulating POD expression. The regulation extended beyond POD activity, involving the expression of anthocyanidin synthase, showcasing L-arginine's comprehensive impact on stress tolerance in Chinese fir under low P conditions. It established that the exogenous addition of L-arginine regulated the root development and enhanced P absorption and uptake. This strategic supplementation strengthens the stress resistance of Chinese fir to low P, offering valuable insights into root secretion mechanisms in response to adaptive strategies in a low P environment.

Fine root production and turnover rate responses to long-term warming and nitrogen addition in a semi-arid grassland

Soil carbon pool is closely linked to fine root production and turnover rate. Lack of knowledge about the effects of nitrogen addition and warming on fine root production and turnover rate limits our ability to accurately predict soil carbon stocks. We studied the responses of fine root production and turnover rate with an 8-year soil warming (ambient +1 °C) and nitrogen addition (ambient + 4.42 g N m−2 yr−1) experiment in a semi-arid grassland on the Loess Plateau of China. Warming significantly decreased fine root production but increased fine root turnover rate due to warming-induced reduction in soil water content. Conversely, nitrogen addition significantly increased fine root production due to decreased soil phosphorus availability. Combined warming and nitrogen addition had no significant effect on fine root production, but decreased fine root turnover rate due to low phosphorus availability caused by nitrogen addition and low soil moisture induced by warming. Our findings have important implications for more accurately predicting the belowground responses of dryland to global changes.

Phosphorus Availability and Adsorption Kinetics of Novel DAP Encapsulated Nano Clay Polymer Composites (NCPCs)

Phosphorus Availability and Adsorption Kinetics of Novel DAP Encapsulated Nano Clay Polymer Composites (NCPCs)

Integrated use of phosphorus sources, phosphate solubilizing bacteria, and rhizobium enhanced growth, nitrogen, and phosphorus uptake in chickpea

Expensive phosphatic fertilizers and limited phosphorus (P) availability hamper chickpea production in calcareous soils. Using cheaper P sources could reduce production costs. A field experiment assessed the combined effect of single superphosphate (SSP) and rock phosphate (RP) ratios (RP: SSP; 0:100, 25:75, 50:50, 75:25, and 100:0), phosphate solubilizing bacteria (PSB; with and without), and rhizobium (with and without) on chickpea growth and N and P uptake. RP:SSP ratios of 0:100 and 25:75 yielded higher plant height, growth rate, branch number, N concentration in straw and seeds, crude protein content, and P concentration and uptake in both straw and seeds compared to the 100:0 ratio. PSB application significantly improved chickpea growth, seed and straw N concentration, seed crude protein, and P uptake. Rhizobium-inoculated seeds also enhanced growth, N and P concentration in straw and seed, and P uptake. PSB enhanced rhizobium efficiency by promoting chickpea growth and increasing N and P concentration and uptake through solubilizing low-availability P from RP and SSP. Using RP:SSP (25:75) with PSB and rhizobium is recommended for enhanced chickpea growth and nutrient uptake in calcareous soils.

Effect of Coal Mining Subsidence on Soil Enzyme Activity in Mining Areas with High Underground Water Levels

In order to investigate the changes in soil enzyme activity and their influencing factors in coal mining subsidence areas with high underground water levels, in this study, we collected soil samples at different depths (SL: 0–20 cm; ML: 20–40 cm; DL: 40–60 cm) in a deep coal seam subsidence area (T1), a shallow coal seam subsidence area (T2), and control non-subsidence areas (W1 and W2) in eastern China. Soil physicochemical properties and enzyme activities were determined, and the mechanism of the latter’s response to coal mining subsidence was investigated based on correlation analysis, redundancy analysis, and structural equation modeling. The results show the following: (1) In the coal mining subsidence areas, the soil pH value (pH), soil available nitrogen (AN), available phosphorus (AP), available potassium (AK), and soil organic matter (SOM) contents were lower than those in the non-subsidence areas, while the soil water content (SWC) and bulk density (BD) were higher than those in the non-subsidence areas and increased with depth. (2) The activities of soil urease (URE), sucrase (SUC), alkaline phosphatase (ALP), and catalase (CAT) gradually decreased with depth and were all lower than those in the non-subsidence areas; the largest decreases with respect to the latter were 24.33%, 18.73%, 38.89%, and 5.88%, respectively. (3) The soil nutrient environment had a highly significant and direct positive effect on enzyme activity, with AN, AP, and SOM contents having the greatest impact. (4) Soil BD had a highly significant and direct negative effect and an indirect negative effect (by affecting nutrients) on enzyme activity. The results of this study on the effects of soil physicochemical properties on enzyme activity provide a basis for the ecological restoration of mines.

The Effects of Exogenous Benzoic Acid on the Physicochemical Properties, Enzyme Activities and Microbial Community Structures of Perilla frutescens Inter-Root Soil.

This study analyzed the effects of benzoic acid (BA) on the physicochemical properties and microbial community structure of perilla rhizosphere soil. The analysis was based on high-throughput sequencing technology and physiological and biochemical detection. The results showed that with the increase in BA concentration, soil pH significantly decreased, while the contents of total nitrogen (TN), alkaline nitrogen (AN), available phosphorus (AP), and available potassium (AK) significantly increased. The activities of soil conversion enzymes urease and phosphatase significantly increased, but the activities of catalase and peroxidase significantly decreased. This indicates that BA can increase soil enzyme activity and improve nutrient conversion; the addition of BA significantly altered the composition and diversity of soil bacterial and fungal communities. The relative abundance of beneficial bacteria such as Gemmatimonas, Pseudolabrys, and Bradyrhizobium decreased significantly, while the relative abundance of harmful fungi such as Pseudogymnoascus, Pseudoeurotium, and Talaromyces increased significantly. Correlation analysis shows that AP, AN, and TN are the main physicochemical factors affecting the structure of soil microbial communities. This study elucidates the effects of BA on the physicochemical properties and microbial community structure of perilla soil, and preliminarily reveals the mechanism of its allelopathic effect on the growth of perilla.

Inhibition of phosphorus removal performance in activated sludge by Fe(III) exposure: transitions in dominant metabolic pathways.

Simultaneous chemical phosphorus removal process using iron salts (Fe(III)) has been widely utilized in wastewater treatment to meet increasingly stringent discharge standards. However, the inhibitory effect of Fe(III) on the biological phosphorus removal system remains a topic of debate, with its precise mechanism yet to be fully understood. Batch and long-term exposure experiments were conducted in six sequencing batch reactors (SBRs) operating for 155 days. Synthetic wastewater containing various Fe/P ratios (i.e., Fe/P = 1, 1.2, 1.5, 1.8, and 2) was slowly poured into the SBRs during the experimental period to assess the effects of acute and chronic Fe(III) exposure on polyphosphate-accumulating organism (PAO) growth and phosphorus metabolism. Experimental results revealed that prolonged Fe(III) exposure induced a transition in the dominant phosphorus removal mechanism within activated sludge, resulting in a diminished availability of phosphorus for bio-metabolism. In Fe(III)-treated groups, intracellular phosphorus storage ranged from 3.11 to 7.67 mg/g VSS, representing only 26.01 to 64.13% of the control. Although the abundance of widely reported PAOs (Candidatus Accumulibacter) was 30.15% in the experimental group, phosphorus release and uptake were strongly inhibited by high dosage of Fe(III). Furthermore, the abundance of functional genes associated with key enzymes in the glycogen metabolism pathway increased while those related to the polyphosphate metabolism pathway decreased under chronic Fe(III) stress. These findings collectively suggest that the energy generated from polyhydroxyalkanoates oxidation in PAOs primarily facilitated glycogen metabolism rather than promoting phosphorus uptake. Consequently, the dominant metabolic pathway of communities shifted from polyphosphate-accumulating metabolism to glycogen-accumulating metabolism as the major contributor to the decreased biological phosphorus removal performance.