Tracing anthropogenic mercury in soils from Fe-Hg mining/smelting area: Isotopic and speciation insights.

Mercury (Hg) stable isotope ratios supplemented by Hg solid speciation data were determined in soils in a former Fe-Hg mining/smelting area (Jedová hora, Czech Republic, Central Europe). The dominant Hg phase in the studied soils was found to be cinnabar (HgS). A secondary form of soil Hg(II) was represented by Hg weakly and strongly bound to mineral (micro)particles, as revealed by thermo-desorption analysis. These Hg species probably play a key role in local soil Hg processes and biogeochemical cycling. The Hg isotopic data generally showed small differences between HgS (-1.1 to -0.8‰; δ202Hg) and the soil samples (-1.4 to -0.9‰; δ202Hg), as well as limited isotopic variability within the two studied soil profiles. On the other hand, the detected negative δ202Hg shift (∼0.4‰) in organic horizons compared to mineral soils in the highly contaminated profile suggests the presence of secondary post-depositional Hg processes, such as sorption or redox changes. For the less contaminated profile, the observed Hg isotopic variation (∼0.3‰; δ202Hg) in the subsurface mineral soil compared to both overlying and underlying horizons is likely due to cyclic redox reactions associated with Hg isotopic fractionation. We assume that the adsorption of Hg(II) to secondary Fe(III)/Mn(III,IV)-oxides could be of major importance in such cases.

Peroxydisulfate-Driven Reductive Dechlorination as Affected by Soil Constituents: Free Radical Formation and Conversion.

We report a previously unrecognized but efficient reductive degradation pathway in peroxydisulfate (PDS)-driven soil remediation. With supplements of naturally occurring low-molecular-weight organic acids (LMWOAs) in anaerobic biochar-activated PDS systems, degradation rates of 12 γ-hexachlorocyclohexanes (HCH)-spiked soils boosted from 40% without LMWOAs to a maximum of 99% with 1 mM malic acid. Structural analysis revealed that an increase in α-hydroxyl groups and a diminution in pKa1 values of LMWOAs facilitated the formation of reductive carboxyl anion radicals (COO•-) via electrophilic attack by SO4•-/•OH. Furthermore, degradation kinetics were strongly correlated with soil organic matter (SOM) contents than iron minerals. Combining a newly developed in situ fluorescence detector of reductive radicals with quenching experiments, we showed that for soils with high, medium, and low SOM contents, dominant reactive species switched from singlet oxygen/semiquinone radicals to SO4•-/•OH and then to COO•- (contribution increased from 30.8 to 66.7%), yielding superior HCH degradation. Validation experiments using SOM model compounds highlighted critical roles of redox-active moieties, such as phenolic - OH and quinones, in radical formation and conversion. Our study provides insights into environmental behaviors related to radical activation of persulfate in a broader soil horizon and inspiration for more advanced reduction technologies.

Addressing lanthanum toxicity in plants: Sources, uptake, accumulation, and mitigation strategies.

Lanthanum (La), the second most abundant rare earth element (REE) is emerging as an environmental issue, with the potential to impact ecosystems and human health. Major sources of soil contamination by La include agricultural, and industrial activities. Lanthanum is non-essential for plant growth but accumulates in various plant parts. The uptake of La by plants is intricately influenced by various factors such as soil pH, redox potential, cation exchange capacity, presence of organic acids and rhizosphere composition. These factors significantly impact the availability and absorption of La ions. Lanthanum impact on plants depends on soil characteristics, cultivated species, developmental stage, La concentration, treatment period, and growth conditions. Excessive La concentrations affect cell division, DNA structure, nutrient uptake, and photosynthesis and induce toxicity symptoms. Plants employ detoxification mechanisms like vacuolar sequestration, osmolyte synthesis, and antioxidant defense system. However, higher concentrations of La can overwhelm these defense mechanisms, leading to adverse effects on plant growth and development. Further, accumulation of La in plants increases the risk for human exposure. Strategies to mitigate La toxicity are, therefore, vital for ecosystem protection. The application of phytoremediation, supplementation, chelation, amendments, and biosorption techniques contributes to the mitigation of La toxicity. This review provides insights into La sources, uptake, toxicity, and alleviation strategies in plants. Identifying research gaps and discussing advancements aims to foster a holistic understanding and develop effective strategies for protecting plant health and ecosystem resilience against La contamination.

Comprehensive bioremediation effect of phosphorus-mineralized bacterium Enterobacter sp. PMB-5 on cadmium contaminated soil-crop system.

Phosphate-mineralizing bacteria (PMBs) have been widely studied by inducing phosphate heavy metal precipitation, but current researches neglect to study their effects on soil-microbe-crop systems on cadmium (Cd) contaminated. Based on this, a strain PMB, Enterobacter sp. PMB-5, was inoculated into Cd contaminated pots to detect soil characteristics, Cd occurrence forms, soil biological activities, plant physiological and biochemical indicators. The results showed that the inoculation of strain PMB-5 significantly increased the available phosphorus content (85.97%-138.64%), Cd-residual fraction (11.04%-29.73%), soil enzyme activities (31.94%-304.63%), plant biomass (6.10%-59.81%), while decreased the state of Cd-HOAc (11.50%-31.17%) and plant bioconcentration factor (23.76%-44.24%). These findings indicated that strain PMB-5 could perform the function of phosphorus solubilization to realize the immobilization of Cd in the complex soil environment. Moreover, SEM-EDS, FTIR, XPS, and XRD analysis revealed that strain PMB-5 does not significantly alter the soil morphology, structure, elemental distribution, and chemical composition, which suggested that remediation of Cd contamination using strain PMB-5 would not further burden the soil. This research implies that PMB-5 could be a safe and effective bioinoculant for remediating Cd-contaminated soils, contributing to the sustainable management of soil health in contaminated environments.

Commercial compost amendments inhibit the bioavailability and plant uptake of per- and polyfluoroalkyl substances in soil-porewater-lettuce systems.

Compost is widely used in agriculture as fertilizer while providing a practical option for solid municipal waste disposal. However, compost may also contain per- and polyfluoroalkyl substances (PFAS), potentially impacting soils and leading to PFAS entry into food chains and ultimately human exposure risks via dietary intake. This study examined how compost affects the bioavailability and uptake of eight PFAS (two ethers, three fluorotelomer sulfonates, and three perfluorosulfonates) by lettuce (Lactuca sativa) grown in commercial organic compost-amended, PFAS spiked soils. After 50 days of greenhouse experiment, PFAS uptake by lettuce decreased (by up to 90.5 %) with the increasing compost amendment ratios (0-20 %, w/w), consistent with their decreased porewater concentrations (by 30.7-86.3 %) in compost-amended soils. Decreased bioavailability of PFAS was evidenced by the increased in-situ soil-porewater distribution coefficients (Kd) (by factors of 1.5-7.0) with increasing compost additions. Significant negative (or positive) correlations (R2 ≥ 0.55) were observed between plant bioaccumulation (or Kd) and soil organic carbon content, suggesting that compost amendment inhibited plant uptake of PFAS mainly by increasing soil organic carbon and enhancing PFAS sorption. However, short-chain PFAS alternatives (e.g., perfluoro-2-methoxyacetic acid (PFMOAA)) were effectively translocated to shoots with translocation factors > 2.9, increasing their risks of contamination in leafy vegetables. Our findings underscore the necessity for comprehensive risk assessment of compost-borne PFAS when using commercial compost products in agricultural lands.

[Mechanism and application prospects of microbial fertilizers in regulating quality formation of medicinal plants].

With the promotion of chemical fertilizer and pesticide reduction and green production of traditional Chinese medicines, microbial fertilizers have become a hot way to achieve the zero-growth of chemical fertilizers and pesticides, improve the yield and qua-lity of medicinal plants, maintain soil health, and promote the sustainable development of the planting industry of Chinese herbal medicines. Soil conditions and microenvironments are crucial to the growth, development, and quality formation of medicinal plants. Microbial fertilizers, as environmentally friendly fertilizers acting on the soil, can improve soil quality by replenishing organic matter and promoting the metabolism of beneficial microorganisms to improve the yield and quality of medicinal plants. In this regard, understanding the mechanism of microbial fertilizer in regulating the quality formation of medicinal plants is crucial for the development of herbal eco-agriculture. This study introduces the processes of microbial fertilizers in improving soil properties, participating in soil nutrient cycling, enhancing the resistance of medicinal plants, and promoting the accumulation of medicinal components to summarize the mechanisms and roles of bacterial fertilizers in regulating the quality formation of medicinal plants. Furthermore, this paper introduces the application of bacterial fertilizers in medicinal plants and makes an outlook on their development, with a view to providing a scientific basis for using microbial fertilizers to improve the quality of Chinese herbal medicines, improve the soil environment, promote the sustainable development of eco-agriculture of traditional Chinese medicine, and popularize the application of microbial fertilizers.

Unraveling the effect of phenolic extract derived from olive mill solid wastes on agro-physiological and biochemical traits of pomegranate and its associated rhizospheric soil properties.

Agricultural waste management poses a significant challenge in circular economy strategies. Olive mill wastes (OMW) contain valuable biomolecules, especially phenolic compounds, with significant agricultural potential. Our study evaluate the effects of phenolic extract (PE) derived from olive mill solid wastes (OMSW) on pomegranate agro-physiological and biochemical responses, as well as soil-related attributes. Pomegranate plants were treated with PE at doses of 100 ppm and 200 ppm via foliar spray (L100 and L200) and soil application (S100 and S200). Results showed increased biomass with PE treatments, especially with soil application (S100 and S200). Proline and soluble sugar accumulation in leaves suggested plant adaptation to PE with low-level stress. Additionally, PE application reduced malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents. Higher doses of PE (S200) significantly improved net photosynthesis (Pn), transpiration rate (E), water use efficiency (WUEi), and photosynthetic efficiency (fv/fm and PIabs). Furthermore, PE treatments enhanced levels of chlorophylls, carotenoids, polyphenols, flavonoids, and antioxidant activity. Soil application of PE also increased soil enzyme activities and microbial population. Our findings suggest the beneficial impact of PE application on pomegranate agro-physiological responses, laying the groundwork for further research across various plant species and soil types to introduce nutrient-enriched PE as an eco-friendly biostimulant.

Distinct effects of canopy vs understory and organic vs inorganic N deposition on root resource acquisition strategies of subtropical Moso bamboo plants.

Atmospheric nitrogen (N) deposition inevitably alters soil nutrient status, subsequently prompting plants to modify their root morphology (i.e., adopting a do-it-yourself strategy), mycorrhizal symbioses (i.e., outsourcing strategy), and root exudation (i.e., nutrient-mining strategy) linking with resource acquisition. However, how N deposition influences the integrated pattern of these resource-acquisition strategies remains unclear. Furthermore, most studies in forest ecosystems have focused on understory N and inorganic N deposition, neglecting canopy-associated processes (e.g., N interception and assimilation) and the impacts of organic N on root functional traits. In this study, we compared the effects of canopy vs understory, organic vs inorganic N deposition on eight root functional traits of Moso bamboo plants. Our results showed that N deposition significantly decreased arbuscular mycorrhizal fungi (AMF) colonization, altered root exudation rate and root foraging traits (branching intensity, specific root area, and length), but did not influence root tissue density and N concentration. Moreover, the impacts of N deposition on root functional traits varied significantly with deposition approach (canopy vs. understory), form (organic vs. inorganic), and their interaction, showing variations in both intensity and direction (positive/negative). Furthermore, specific root area and length were positively correlated with AMF colonization under canopy N deposition and root exudation rate in understory N deposition. Root trait variation under understory N deposition, but not under canopy N deposition, was classified into the collaboration gradient and the conservation gradient. These findings imply that coordination of nutrient-acquisition strategies dependent on N deposition approach. Overall, this study provides a holistic understanding of the impacts of N deposition on root resource-acquisition strategies. Our results indicate that the evaluation of N deposition on fine roots in forest ecosystems might be biased if N is added understory.

Effect of inorganic arsenic in paddy soil on the migration and transformation of selenium species in rice plants.

Selenium (Se) in paddy rice is one of the significant sources of human Se nutrition. However, the effect of arsenic (As) pollution in soil on the translocation of Se species in rice plants is unclear. In this research, a pot experiment was designed to examine the effect of the addition of 50 mg As/kg soil as arsenite or arsenate on the migration of Se species from soil to indica Minghui 63 and Luyoumingzhan. The results showed that the antagonism between inorganic As and Se was closely related to the rice cultivar and Se oxidation state in soil. Relative to the standalone selenate treatment, arsenite significantly (p < 0.05) decreased the accumulation of selenocystine, selenomethionine and selenate in the roots, stems, sheaths, leaves, brans and kernels of both cultivars by 21.4%-100.0%, 40.0%-100.0%, 41.0%-100%, 5.4%-96.3%, 11.3%-100.0% and 26.2%-39.7% respectively, except for selenocystine in the kernels of indica Minghui 63 and selenomethionine in the leaves of indica Minghui 63 and the stems of indica Luyoumingzhan. Arsenate also decreased (p < 0.05) the accumulation of selenocystine, selenomethionine and selenate in the roots, stems, brans and kernels of both cultivars by 34.9%-100.0%, 30.2%-100.0%, 11.3%-100.0% and 5.6%-39.6% respectively, except for selenate in the stems of indica Minghui 63. However, relative to the standalone selenite treatment, arsenite and arsenate decreased (p < 0.05) the accumulation of selenocystine, selenomethionine and selenite only in the roots of indica Minghui 63 by 45.5%-100.0%. Our results suggested that arsenite and arsenate had better antagonism toward Se species in selenate-added soil than that in selenite-added soil; moreover, arsenite had a higher inhibiting effect on the accumulation of Se species than arsenate.

Short-term responses of soil enzyme activities and stoichiometry to litter input in Castanopsis carlesii and Cunninghamia lanceolata plantations.

Litter input triggers the secretion of soil extracellular enzymes and facilitates the release of carbon (C), nitrogen (N), and phosphorus (P) from decomposing litter. However, how soil extracellular enzyme activities were controlled by litter input with various substrates is not fully understood. We examined the activities and stoichiometry of five enzymes including ß-1,4-glucosidase, ß-D-cellobiosidase, ß-1,4-N-acetyl-glucosaminidase, leucine aminopeptidase and acidic phosphatase (AP) with and without litter input in 10-year-old Castanopsis carlesii and Cunninghamia lanceolata plantations monthly during April to August, in October, and in December 2021 by using an in situ microcosm experiment. The results showed that: 1) There was no significant effect of short-term litter input on soil enzyme activity, stoichiometry, and vector properties in C. carlesii plantation. In contrast, short-term litter input significantly increased the AP activity by 1.7% in May and decreased the enzymatic C/N ratio by 3.8% in August, and decreased enzymatic C/P and N/P ratios by 11.7% and 10.3%, respectively, in October in C. lanceolata plantation. Meanwhile, litter input increased the soil enzymatic vector angle to 53.8° in October in C. lanceolata plantations, suggesting a significant P limitation for soil microorganisms. 2) Results from partial least squares regression analyses showed that soil dissolved organic matter and microbial biomass C and N were the primary factors in explaining the responses of soil enzymatic activity to short-term litter input in both plantations. Overall, input of low-quality (high C/N) litter stimulates the secretion of soil extracellular enzymes and accelerates litter decomposition. There is a P limitation for soil microorganisms in the study area.

Changes of soil nutrients and organic carbon fractions in Caragana korshinskii forests with different restoration years in mountainous areas of southern Ningxia, China.

Vegetation restoration can effectively enhance soil quality and soil organic carbon (SOC) sequestration. In this study, the distribution characteristics of soil nutrients and SOC along soil profile (0-100 cm), and their responses to restoration years (16, 28, 38 years) were studied in Caragana korshinskii plantations in the southern mountainous area of Ningxia, compared with cropland and natural grassland. The results showed that: 1) the contents of SOC, soil total nitrogen (TN), total phosphorus (TP), particulate organic carbon (POC), mineral-associated organic carbon (MAOC) and the proportion of particulate organic carbon to total organic carbon (POC/SOC) all decreased with increasing soil depth. The ratio of mineral-associated organic carbon to total organic carbon (MAOC/SOC) exhibited an opposite trend. 2) The contents of SOC, TN, TP, C:P, N:P, POC and MAOC gra-dually decreased as the restoration years increased. However, the C:N ratio showed no significant change. The POC/SOC ratio initially increased and then decreased, while the MAOC/SOC ratio decreased initially and then increased. 3) In three different types of vegetation, POC, MAOC, and SOC showed a highly significant positive linear correlation, with the increase in SOC mainly depended on the increase in MAOC. The SOC, TN, TP, POC and MAOC contents in natural grassland and C. korshinskii plantations were significantly higher than those in cropland. In conclusion, soil nutrients and POC and MAOC contents of C. korshinskii plantations gradually decreased with the increases in restoration years. However, when compared with cropland, natural grassland and C. korshinskii plantations demonstrated a greater capacity to maintain and enhance soil nutrient and carbon storage.

Soil C:N:P stoichiometry in rhizosphere and non-rhizosphere of Pinus sylvestris var. mongolica forests.

The aim of this study was to reveal the stoichiometric characteristics of carbon, nitrogen and phosphorus in rhizosphere and non-rhizosphere soils of Pinus sylvestris var. mongolica in the Hulunbuir desert. We investigated the contents and stoichiometry of organic carbon, total nitrogen, and total phosphorus contents of rhizosphere and non-rhizosphere soils across different stand ages (28, 37 and 46 a) of P. sylvestris var. mongolica plantations, with P. sylvestris var. mongolica natural forest as the control. We analyzed the correlation between soils properties and soil stoichiometry. The results showed that rhizosphere effect significantly affected soil N:P, and stand age significantly affected soil organic carbon content in P. sylvestris var. mongolica plantation. Soil organic carbon content in plantation was significantly lower than that in natural forest. Soil organic carbon and total nitrogen contents of plantations in both rhizosphere and non-rhizosphere soils firstly decreased and then increased with increasing stand age, while total phosphorus firstly increased and then decreased in rhizosphere soils, and firstly decreased and then increased in non-rhizosphere soils. There was significant positive correlations between C:N and C:P in rhizosphere soils but not in non-rhizosphere soils, suggesting that higher synergistic rhizosphere soil N and P limitation. The mean N:P values of rhizosphere and non-rhizosphere soils were 4.98 and 8.40, respectively, indicating that the growth of P. sylvestris var. mongolica was restricted by soil N and the rhizosphere soils were more N-restricted. The C:N:P stoichiometry of rhizosphere and non-rhizosphere soils were significantly influenced by soil properties, with available phosphorus being the most important driver. The growth of P. sylvestris var. mongolica was limited by N in the Hulunbuir desert, and root system played an obvious role in enriching and maintaining soil nutrients. It was recommended that soil nitrogen should be supplemented appropriately during the growth stage of P. sylvestris var. mongolica plantation, and phosphorus should be supplemented appropriately according to the synergistic nature of nitrogen and phosphorus limitation.

Characteristics of soil nitrogen and phosphorus fractions and microbial traits with increasing stand age in two-layered Cunninghumia lanceolata + Phoebe bournei plantations.

Soil nitrogen and phosphorus are two key elements limiting tree growth in subtropical areas. Understanding the regulation of soil microorganisms on nitrogen and phosphorus nutrition is beneficial to reveal maintenance mechanism of soil fertility in plantations. We analyzed the characteristics of soil nitrogen and phosphorus fractions, soil microbial community composition and function, and their relationship across three stands of two-layered Cunninghumia lanceolata + Phoebe bournei with different ages (4, 7 and 11 a) and the pure C. lanceolata plantation. The results showed that the contents of most soil phosphorus fractions increased with increasing two-layered stand age. The increase in active phosphorus fractions with increasing stand age was dominated by the inorganic phosphorus (9.9%-159.0%), while the stable phosphorus was dominated by the organic phosphorus (7.1%-328.4%). The content of soil inorganic and organic nitrogen also increased with increasing two-layered stand age, with NH4+-N and acid hydrolyzed ammonium N contents showing the strongest enhancement, by 152.9% and 80.2%, respectively. With the increase of stand age, the composition and functional groups of bacterial and fungal communities were significantly different, and the relative abundance of some dominant microbial genera (such as Acidothermus, Saitozyma and Mortierella) increased. The relative abundance of phosphorus solubilization and mineralization function genes, nitrogen nitrification function and aerobic ammonia oxidation function genes tended to increase. The functional taxa of fungi explained 48.9% variation of different phosphorus fractions. The conversion of pure plantations to two-layered mixed plantation affected soil phosphorus fractions transformation via changing the functional groups of saprophytes (litter saprophytes and soil saprophytes). Changes in fungal community composition explained 45.0% variation of different nitrogen fractions. Some key genera (e.g., Saitozyma and Mortierella) play a key role in promoting soil nitrogen transformation and accumulation. Therefore, the conversion of pure C. lanceolata plantation to two-layered C. lanceolata + P. bournei plantation was conducive to improving soil nitrogen and phosphorus availability. Bacteria and fungi played important roles in the transformation process of soil nitrogen and phosphorus forms, with greater contribution of soil fungi.

Effects of returning paddy field to wetland on composition and stability of soil aggregates in the Yellow River Delta.

The composition and stability of soil aggregates are important indicators for measuring soil quality, which would be affected by land use changes. Taking wetlands with different returning years (2 and 15 years) in the Yellow River Delta as the research object, paddy fields and natural wetlands as control, we analyzed the changes in soil physicochemical properties and soil aggregate composition. The results showed that soil water content, total organic carbon, dissolved organic carbon and total phosphorus of the returning soil (0-40 cm) showed an overall increasing trend with returning period, while soil pH and bulk density was in adverse. There was no significant change in clay content, electrical conductivity, and total nitrogen content. The contents of macro-aggregates and micro-aggregates showed overall increasing and decreasing trend with returning period, respectively. The stability of aggregates in the topsoil (0-10 cm) increased with returning years. Geometric mean diameter and mean weight diameter increased by 8.9% and 40.4% in the 15th year of returning, respectively, while the mass proportion of >2.5 mm fraction decreased by 10.5%. There was no effect of returning on aggregates in subsoil (10-40 cm). Our results indicated that returning paddy field to wetland in the Yellow River Delta would play a positive role in improving soil structure and aggregate stability.

Arsenic stress on soil microbial nutrient metabolism interpreted by microbial utilization of dissolved organic carbon.

In a 120-day microcosm incubation experiment, we investigated the impact of arsenic contamination on soil microbial nutrient metabolism, focusing on carbon cycling processes. Our study encompassed soil basal respiration, key enzyme activities (particularly, ß-1,4-N-acetylglucosaminidase and phosphatases), microbial biomass, and community structure. Results revealed a substantial increase (1.21-2.81 times) in ß-1,4-N-acetylglucosaminidase activities under arsenic stress, accompanied by a significant decrease (9.86%-45.20%) in phosphatase activities (sum of acid and alkaline phosphatases). Enzymatic stoichiometry analysis demonstrated the mitigation of microbial C and P requirements in response to arsenic stress. The addition of C-sources alleviated microbial C requirements but exacerbated P requirements, with the interference amplitude increasing with the complexity of the C-source. Network analysis unveiled altered microbial nutrient requirements and an increased resistance process of microbes under arsenic stress. Microbial carbon use efficiency (CUE) and basal respiration significantly increased (1.17-1.59 and 1.18-3.56 times, respectively) under heavy arsenic stress (500 mg kg-1). Arsenic stress influenced the relative abundances of microbial taxa, with Gemmatimonadota increasing (5.5-50.5%) and Bacteroidota/ Nitrospirota decreasing (31.4-47.9% and 31.2-63.7%). Application of C-sources enhanced microbial resistance to arsenic, promoting cohesion among microorganisms. These findings deepen our understanding of microbial nutrient dynamics in arsenic-contaminated areas, which is crucial for developing enzyme-based toxicity assessment systems for soil arsenic contamination.

Mycorrhizal type and tree diversity affect foliar elemental pools and stoichiometry.

Species-specific differences in nutrient acquisition strategies allow for complementary use of resources among plants in mixtures, which may be further shaped by mycorrhizal associations. However, empirical evidence of this potential role of mycorrhizae is scarce, particularly for tree communities. We investigated the impact of tree species richness and mycorrhizal types, arbuscular mycorrhizal fungi (AM) and ectomycorrhizal fungi (EM), on above- and belowground carbon (C), nitrogen (N), and phosphorus (P) dynamics. Soil and soil microbial biomass elemental dynamics showed weak responses to tree species richness and none to mycorrhizal type. However, foliar elemental concentrations, stoichiometry, and pools were significantly affected by both treatments. Tree species richness increased foliar C and P pools but not N pools. Additive partitioning analyses showed that net biodiversity effects of foliar C, N, P pools in EM tree communities were driven by selection effects, but in mixtures of both mycorrhizal types by complementarity effects. Furthermore, increased tree species richness reduced soil nitrate availability, over 2 yr. Our results indicate that positive effects of tree diversity on aboveground nutrient storage are mediated by complementary mycorrhizal strategies and highlight the importance of using mixtures composed of tree species with different types of mycorrhizae to achieve more multifunctional afforestation.

[Effects of Application of Different Organic Materials on Phosphorus Accumulation and Transformation in Vegetable Fields].

Presently, the improvement of soil organic matter is the basis to ensure food security, but the accumulation and transformation characteristics of soil phosphorus (P) as affected by organic matter remain unclear. The accumulation, transformation, and migration characteristics of soil P in different soil layers of vegetable fields were researched under the application of organic materials. Six treatments were set up in the experiment:control (no fertilization), traditional fertilizer application by farmers, biochar, chicken manure, food waste, and straw application. Available phosphorus (Olsen-P), water-soluble phosphorus (CaCl2-P) content, soil phosphorus forms, soil organic matter (SOM), and pH were determined during the pepper harvest period. In the 0-5 cm and 5-10 cm soil layers, the available phosphorus content of traditional fertilization of farmers was higher, and the available phosphorus content of the four organic materials was in the order of straw > biochar > chicken manure > food waste. Compared to that with food waste, the straw and biochar treatments increased soil available phosphorus by 59.6%-67.3% and 29.1%-36.9%, respectively. The straw treatment could easily enhance the soil labile P pool, and soil labile P in the 0-5 cm soil layer increased by 47.3% and 35.1% compared with that under the chicken manure and food waste treatments, respectively. With the increase in soil depth, the proportion of available phosphorus in the chicken manure treatment decreased the least, and available phosphorus of the 20-30 cm soil layer accounted for 55.9% of the topsoil layer but only accounted for 16.0%-34.0% under treatment with the other three materials. Compared with that under the traditional fertilization of farmers, the pH significantly increased by 0.18-0.36 units after the application of organic fertilizer, and the pH of the chicken manure and food waste treatments was significantly higher than that of biochar and straw (P < 0.05). SOM content under the biochar treatment significantly increased by 7.7%-17.6% compared to that under the other three organic materials. Among the four organic materials, the straw treatment boosted the labile P pool the most, which was conducive to the rapid increase in plant-available P. Phosphorus was most likely to migrate downward under the chicken manure treatment. In the field management based on soil fertility enhancement, the application of biochar could not only improve soil pH and SOM but also avoid excessive accumulation of phosphorus in the surface layer, which decreases environmental risks.

[Intensive Citrus Cultivation Suppresses Soil Phosphorus Cycling Microbial Activity].

Soil microbes are key drivers in regulating the phosphorus cycle. Elucidating the microbial mineralization process of soil phosphorus-solubilizing bacteria is of great significance for improving nutrient uptake and yield of crops. This study investigated the mechanism by which citrus cultivation affects the soil microbial acquisition strategy for phosphorus by measuring the abundance of the phoD gene, microbial community diversity and structure, and soil phosphorus fractions in the soils of citrus orchards and adjacent natural forests. The results showed that citrus cultivation could lead to a decrease in soil pH and an accumulation of available phosphorus in the soil, with a content as high as 112 mg·kg-1, which was significantly higher than that of natural forests (3.7 mg·kg-1). Citrus cultivation also affected the soil phosphorus fractions, with citrus soil having higher levels of soluble phosphorus (CaCl2-P), citrate-extractable phosphorus (Citrate-P), and mineral-bound phosphorus (HCl-P). The phosphorus fractions of natural forest soils were significantly lower than those of citrus soils, whereas the phoD gene abundance and alkaline phosphatase activity were significantly higher in natural forest soils than in citrus soils. High-throughput sequencing results showed that the Shannon diversity index of phosphate-solubilizing bacteria in citrus soils was 4.61, which was significantly lower than that of natural forests (5.35). The microbial community structure in natural forests was also different from that of citrus soils. In addition, the microbial community composition of phosphate-solubilizing bacteria in citrus soils was also different from that of natural forests, with the relative abundance of Proteobacteria being lower in natural forest soils than in citrus soils. Therefore, citrus cultivation led to a shift of soil microbial acquisition strategy for phosphorus, with external phosphorus addition being the main strategy in citrus soils, whereas microbial mineralization of organic phosphorus was the main strategy in natural forest soils to meet their growth requirements.

[Effects of organic fertilizer from traditional Chinese medicine residues on growth and soil microbial community of Salvia miltiorrhiza by metagenomic technique].

Soil microbiome is a key evaluation index of soil health. Previous studies have shown that organic fertilizer from traditional Chinese medicine(TCM)residues can improve the yield and quality of cultivated traditional Chinese medicinal materials. However, there are few reports on the effects of organic fertilizer from TCM residues on soil microbiome. Therefore, on the basis of evaluating the effects of organic fertilizer from TCM residues on the yield and quality of cultivated Salvia miltiorrhiza, the metagenomic sequencing technique was used to study the effects of organic fertilizer from TCM residues on rhizosphere microbiome community and function of cultivated S. miltiorrhiza. The results showed that:(1) the application of organic fertilizer from TCM residues promoted the growth of S. miltiorrhiza and the accumulation of active components, and the above-ground and underground dry weight and fresh weight of S. miltiorrhiza increased by 371.4%, 288.3%, 313.4%, and 151.9%. The increases of rosmarinic acid and salvianolic acid B were 887.0% and 183.0%.(2)The application of organic fertilizer from TCM residues significantly changed the rhizosphere bacterial and fungal community structures, and the microbial community composition was significantly different.(3)The relative abundance of soil-beneficial bacteria, such as Nitrosospira multiformis, Bacillus subtilis, Lysobacter enzymogenes, and Trichoderma was significantly increased by the application of organic fertilizer from TCM residues.(4)KEGG function prediction analysis showed that metabolism-related microorganisms were more easily enriched in the soil environment after organic fertilizer application. The abundance of functional genes related to nitrification and denitrification could also be increased after the application of organic fertilizer from TCM residues. The results of this study provide guidance for the future application of organic fertilizer from TCM residues in the cultivation of traditio-nal Chinese medicinal materials and enrich the content of green cultivation technology of traditional Chinese medicinal materials.

Synthesis of struvite-enriched slow-release fertilizer using magnesium-modified biochar: Desorption and leaching mechanisms.

To improve the retention and slow-release abilities of nitrogen (N) and phosphorus (P), an 82 %-purity struvite fertilizer (MAP-BC) was synthesized using magnesium-modified biochar and a solution with a 2:1 concentration ratio of NH4+ to PO43- at a pH of 8. Batch microscopic characterizations and soil column leaching experiments were conducted to study the retention and slow-release mechanisms and desorption kinetics of MAP-BC. The slow-release mechanism revealed that the dissolution rate of high-purity struvite was the dominant factor of NP slow release. The re-adsorption of NH4+ and PO43- by biochar and unconsumed MgO prolonged slow release. Mg2+ ionized by MgO could react with PO43- released from struvite to form Mg3(PO4)2. The internal biochar exhibited electrostatic attraction and pore restriction towards NH4+, while magnesium modification and nutrient loading formed a physical antioxidant barrier that ensured long-term release. The water diffusion experiment showed a higher cumulative release rate for PO43- compared to NH4+, whereas in soil column leaching, the trend was reversed, suggesting that soil's competitive adsorption facilitated the desorption of NH4+ from MAP-BC. During soil leaching, cumulative release rates of NH4+ and PO43- from chemical fertilizers were 3.55-3.62 times faster than those from MAP-BC. The dynamic test data for NH4+ and PO43- in MAP-BC fitted the Ritger-Peppas model best, predicting release periods of 163 days and 166 days, respectively. The leaching performances showed that MAP-BC reduced leaching solution volume by 5.58 % and significantly increased soil large aggregates content larger than 0.25 mm by 24.25 %. The soil nutrients retention and pH regulation by MAP-BC reduced leaching concentrations of NP. Furthermore, MAP-BC significantly enhanced plant growth, and it is more suitable as a NP source for long-term crops. Therefore, MAP-BC is expected to function as a long-term and slow-release fertilizer with the potential to minimize NP nutrient loss and replace part of quick-acting fertilizer.