Organic Phosphorus Content Research Articles

Impact of Interaction between Biochar and Soil Microorganisms on Growth of Chinese Cabbage by Increasing Soil Fertility

We investigated the improvement of cabbage growth through the interaction of biochar, which can promote microbial activity, with the microbes in the soil. An increase in cabbage growth could be detected in soil with biochar or soil microbes, but the fresh weight of cabbage in soil supplemented with both biochar and microbes was 8.8% and 5% higher, respectively, than that with either microbes or biochar alone. The phosphorus content in Chinese cabbage was also increased by 36.3% when compared with the control without the addition of biochar and microbes. Such an improvement on cabbage growth is closely related to the soil amelioration. The application of biochar in soil significantly stimulated the growth of soil microbes and further altered the microbial community structure in soil. When 2% biochar and microbes were simultaneously applied in soil, the content of the organic matter and available phosphorus content in soil was 36.7% and 45.5% higher, respectively, than that in soil with or without biochar. The maximal increment in the available potassium content was observed in the soil supplemented with both 5% biochar and soil microbes, which was 46.4% higher than that in soil without the addition of biochar and microbes. Both phosphatase and urease activity in soil were also increased by 61.2% and 49.4%, respectively, by applying 2% biochar in soil together with microbes, as the interaction of biochar with the microbes could promote the activity of soil microbes and enzymes which resulted in an improvement in soil fertility. The interaction of biochar with microbes in soil could promote the plant growth of Chinese cabbage by increasing the soil fertility.

Effect of bacterial community succession on environmental factors during litter decomposition of the seaweed Gracilaria lemaneiformis

In large-scale seaweed farming, an understanding of the decomposition process plays a pivotal role in optimizing cultivation practices by considering the influence of the bacterial community. Therefore, we assessed the bacterial community structure and its influence on environmental factors during Gracilaria lemaneiformis decomposition, utilizing both microcosms and in-situ simulations. The decomposition rates in the microcosms and in situ simulations reached 79 % within 180 days and 81 % within 50 days, respectively In the microcosms, the dissolved oxygen content decreased from 5.3 to 0.4 mg/L, while the concentrations of total organic carbon, nitrogen, and phosphorus in the water increased by 165 %, 1636 %, and 2360 %, respectively. The common dominant bacteria included Proteobacteria, Planctomycetes, Firmicutes, Bacteroidetes, and Spirochaetae. Planctomycetes and Firmicutes were positively correlated with the total organic carbon, nitrogen, and phosphorus concentrations. Planctomycetes species played significant roles during the decomposition process. The overall findings of this study could inform more sustainable seaweed cultivation practices.

Influence of Integrated Nutrient Management on Physico-Chemical Properties of Soil, Growth, Flowering and Yield of Guava Grown as a Component Crop in Coconut-Based Cropping System

An experiment on integrated nutrient management in guava grown as a component crop in a coconut-based cropping system was conducted under the coastal condition of Odisha. Adoption of integrated nutrient management like the application of organic manures with or without NPK fertilizers resulted in improvement in the physico-chemical properties of soil, which was reflected in terms of pH, organic carbon content, available nitrogen, phosphorus and potash content. Among the different combination of integrated nutrient management applied in guava, the plant height, canopy spread, flushing intensity, yield and yield attributing parameters. The maximum available soil nitrogen, available phosphorus and available potassium contents were estimated to be maximum in the treatment applied with 50% RDF +50% N through vermicompost + FYM +bio fertilizer, while the soil pH was highest owing to application of 75% RDF + 25% N through vermicompost + FYM which was at par with results obtained with application of 75% RDF + 25% N through vermicompost and 75% RDF +25% N through vermicompost + FYM +bio fertilizer.

Metal mobility in an anaerobic-digestate-amended soil: the role of two bioenergy crop plants and their metal phytoremediation potential

Panicum virgatum and Pennisetum alopecuroides, two non-food bioenergy crops, were evaluated for their capacity to phyto-manage trace metals (Pb, Zn, Ni, Fe, Mn, Co, Cr, and Cu) from municipal solid waste digestate after its application to a marginal soil. For that, 90-day vertical soil column mesocosm (columns with 0.6 × 0.2 m) experiments were carried out to assess 1) the impact of digestate application on the health of marginal soil, 2) plant effect on digestate-borne trace metals’ mobility along the soil profile (measuring total metal levels and fractionation in different soil layers by atomic absorption spectroscopy, and 3) plant growth performance and trace metal (Pb, Zn, and Cu) uptake capacity. The results showed that trace metals were mostly confined in the 0–0.2 m soil horizon over the course of the experimental period, migrating from the digestate-amended soil layer (0–0.1 m) to the layer underneath (0.1–0.2 m) within the first 21 days and remaining stable afterward. No evidence of the trace metals’ mobility to deeper soil layers was detected. Migration of trace metals was reduced in the presence of P. virgatum and P. alopecuroides, suggesting a phytoremediation (phytostabilization) effect. For both plant species, no trace metal accumulation in the roots was observed (bioconcentration factor <1), although both plants showed a potential for Zn translocation for aboveground tissues (translocation factor >1). The growth of both plants was positively affected by municipal solid waste digestate application, which also improved soil quality (increased concentration of total organic carbon and available phosphorus, as well as cation exchange capacity and water holding capacity).

Soil Enzyme Activity Differs among Native Species and Continuously Planted Eucalyptus Plantations

In recent years, monoculture and multi-rotation successional Eucalyptus plantations have given rise to several environmental issues, including the degradation of soil quality and nutrient imbalance, and the conversion of logging sites to multi-rotation Eucalyptus plantations has attracted considerable attention from the scientists involved. However, the effects of different management strategies on soil extracellular enzyme activities (EEAs) and enzyme stoichiometry (ES) in degraded Eucalyptus plantations are not clear. In this study, we investigated the responses and mechanisms of soil physicochemical properties, microbial biomass, carbon, and nitrogen- and phosphorus-acquiring enzyme activities, as well as the microbial resource requirements of Eucalyptus plantations, under different management strategies. The findings revealed that second-rotation (TWE) and third-rotation (THE) continuous plantings of pure Eucalyptus plantations resulted in significant decreases in soil organic carbon (SOC), total nitrogen (TN) and effective available phosphorus (AP) contents, while soil nutrient contents increased after the introduction of Manglietia glauca to form mixed forests (EM) with Eucalyptus or pure Manglietia glauca (M). Meanwhile, phosphorus-acquiring enzymes significantly increased with successive rotations of Eucalyptus (TWE and THE), while EEAC:P and EEAN:P gradually decreased and phosphorus limitation gradually increased compared to that of a native-species-mixed plantation (CK). After the introduction of Manglietia glauca (EM and M), phosphorus-acquiring enzyme activities showed lower levels and there were significant increases in EEAC:P and EEAN:P compared to those of continuous plantings of pure Eucalyptus plantations, which reduced microbial phosphorus demand. Moreover, soil nutrients played a more significant role in altering the EEAs and ES than did microbial biomass (0–10 cm: 72.7% > 53.3%, 10–20 cm: 54.5% > 32.6%). The results showed that EM and M improved soil fertility quality conditions and alleviated soil nutrient phosphorus limitations for soil microorganisms. Therefore, the introduction of Manglietia glauca, either to form mixed forests with Eucalyptus or in rotation with Eucalyptus, can be used as technical means for the conversion of multi-rotation successive Eucalyptus plantations.

Soil phosphorus fractions dynamics along a 22-ka chronosequence of landslides, western Sichuan, China

Landslides significant influence on bedrock weathering, pedogenesis, and ecological succession, thereby playing a pivotal role in driving biogeochemical cycles. Landslide chronosequences have traditionally served as invaluable study systems for investigating vegetation succession and exploring soil development and nutrient dynamics. In this study, we analyzed soil phosphorus fractions across a 22,000-year landslide chronosequence. Our investigation examined the impact of environmental factors on these fractions and elucidated the supply of bioavailable phosphorus. Our findings revealed a decline in the concentration of all phosphorus fractions with soil age. Notably, even at an age exceeding 22,000 years, primary mineral phosphorus constituted 23 % of the total phosphorus pool at the later stages of soil development, while organic phosphorus accounted for a mere 7 %. This discrepancy can be attributed to frequent landslides replenishing phosphorus stocks. These findings indicate that the Walker and Syers model may not adequately anticipate alterations in soil phosphorus fractions under geologically unstable landscapes. Environmental factors had limited impact on primary mineral phosphorus concentrations. Yet, they significantly influenced occluded and nonoccluded phosphorus. Changes in organic phosphorus concentrations cannot be fully explained by the examined environmental factors, as organic phosphorus in the soil primarily originates from plant litter decomposition. The sources of bioavailable phosphorus in the investigated region were elucidated using structural equation modeling. The bioavailable phosphorus in the study area is mainly derived from nonoccluded phosphorus rather than organic phosphorus. This observation can be attributed to the distinct landform conditions, which sustain elevated levels of primary mineral phosphorus during soil development. Consequently, the continuous availability of nonoccluded phosphorus ensures a reliable supply of bioavailable phosphorus. In conclusion, the landslide chronosequence serves as a vital example of long-term ecosystem development under unstable landforms. Its refinement of the Walker and Syers model under unstable landscapes.

Evaluation of Phytoremediation, Physicochemical and Heavy Metal Assessment of Crude Oil Polluted Soil Using Pseudomonas and Bacillus spp, Rivers State, Nigeria

Crude oil exploration has been beneficial to our economy but detrimental to our environment with the artisanal `refineries further compounding the challenge. This research was aimed at investigating the phytoremediation, physicochemical and heavy metal assessment of crude oil polluted soil using Peudomonas spp. and Bacillus spp. as augmenting microorganism, in Rivers state, Nigeria. This study was carried out in in south-south Nigeria (B-dere in Gokana Local government of `Rivers State). Contaminated Soil were collected and subjected to standard microbiological methods. Contaminated Soil samples were collected from two different area of Rivers state with sterilized soil auger at two depths of 0-15cm and 15-30cm. The contaminated soil sampled were analyzed for heavy metal (Cadium Chromium, Lead and Zinc) using Atomic Absorption spectrophotometric method. Microbiological analysis was carried out on the soil samples. Ten (10) treatments consisiting of contaminated soil (CS), uncontaminated soil (US), uncontaminated soil(US), Panicum subalbidum and Schoenoplectus senegalensis were setup for a period of 28 days. Physicochemical parameters were analyzed for uncontaminated soil and contaminated soil. The physicochemical parameters analyzed were pH, Temperature, Nitrogen, Phosphorus, Potassium and Total Hydrocarbon Content. The physiochemical parameters of the uncontaminated soil were pH (5.43), temperature (27oC), Electrical conductivity (9uS/cm), Moisture content (7.80%), Total organic carbon (0.93%), Soil organic matter (1.60%), total Nitrogen (56.695mg/kg), available phosphorus (0.621mg/kg), potassium (7.125mg/kg) and total hydrocarbon content (700mg/kg). Results revealed that the amount of hydrocarbon remediated and percentage (%) bioremediation in the soil after 28 days of monitoring from the initial THC value of (4050 mg/kg), is higher in set up with CS+PSE+SCH (3454mg/kg; 85.28%) and lowest in set up with US+SCH (434mg/kg: 62%) and the amount uptake of phytoremediation in the root after 28 days of monitoring to be higher in set up with CS+BAC+SCH (632Mg/kg; 15.6%) and lowest in set up with US+SCH (12.2mg/kg; 1.74%). The heavy metals assessed were cadium (Cd), chromium (Cr), lead (Pb) and zinc (Zn). This research revealed and recommend that Schoenoplectus senegalensis as a suitable plant species for phytoremediation of crude oil contaminated soil. Hydrocarbon utilizing bacteria identified in this study were; Pseudomonas and Bacilus spp.

EFFICIENCY OF UTILIZATION OF ORGANIC SUBSTANCES PRODUCED FROM ORGANIC WASTE ON ORDINARY CHERNOZEM

The authors presented in the article the results of studying the effect of solid and liquid organic fertilisers obtained at their installation and when composting from agricultural waste on spring wheat yield and quality in a laboratory experiment on ordinary chernozems of the Orenburg region. The effectiveness of using the obtained substances as liquid and solid organic fertilisers was assessed. The authors substantiated that according to all options for studying the norms and types of organic fertilisers in the soil, the content of organic matter, ammonium nitrogen, mobile phosphorus and potassium increased. The data on the green mass of spring wheat for all research options in the laboratory experiment are given. It has been established that when liquid organic fertilisers are applied to the soil, ammonium nitrogen is highly mobile and available to plants, so plants become taller at the initial vegetation stage. The authors determined the lower efficiency of applying solid organic fertilisers in short-term laboratory studies. As a result, it has been established that 4 t/ ha for solid organic fertilisers and 8 t/ha for liquid organic fertilisers is the most effective. With such a rate of application of liquid organic fertilisers, the germination of spring wheat reaches 98.7%, and the yield of green mass of plants increases by three times compared to the control. In addition, the trend of the highest efficiency of applying liquid organic fertilisers compared to solid ones was noted.

Application of Soil Organic Reconstruction Technology in Sandy Land Improvement

Improving sandy soil by soil organic reconstruction technology can effectively reduce soil permeability and increase soil nutrient content. The results show that the artificial plough bottom layer of 1.7 g·cm-3and 5 cm thick and the tillage layer of 1.2 g·cm-3 and 25 cm thick can be constructed on sandy soil with loess as raw material, and the water infiltration rate is reduced to 12 cm·d-1, which is 89% lower than that of sandy soil. After reconstruction, the contents of organic matter, total nitrogen, available phosphorus and available potassium were all abundant, which increased by 1.06 times, 2.07 times, 8.54 times and 1.23 times compared with sandy soil, respectively.

Arbuscular Mycorrhizal Fungi Restored the Saline-Alkali Soil and Promoted the Growth of Peanut Roots.

Peanut (Arachis hypogaea L.) is an important oil and cash crop. An efficient utilization of saline-alkali soil resources, the development of peanut planting in saline-alkali soil, and obtaining high and stable yield have become urgent needs to ensure peanut production. Arbuscular mycorrhizal fungi (AMF) have been reported to develop the potential productivity of host plants and improve their salt resistance and tolerance. However, there is still limited research on promoting the growth and morphology of peanut roots. Therefore, in this study, seeds of salt-tolerant peanut variety "HY 25" were coated with commercial AMF inoculant before being planted in saline-alkali and normal soils to investigate the effects of AMF on peanut root growth and rhizosphere soil. The results showed that root morphological characteristics were significantly increased by the use of AMF at the podding stage in saline-alkali soil and from the flowering and pegging stage to the maturity stage in normal soil. Of note, the total root volume of peanut inoculated with AMF significantly increased by 31.57% during the podding stage in saline-alkali soil. Meanwhile, AMF significantly increased the phosphatase and invertase activities in the peanut rhizosphere of saline-alkali soil from the flowering stage to maturity stage and soil CAT activity at the maturity stage (41.16~48.82%). In normal soil, soil phosphatase and urease activities were enhanced by AMF at the flowering stage and the podding stage, respectively. AMF also increased the contents of soil organic matter, available phosphorus, and hydrolysable nitrogen, but decreased soil EC in saline-alkali soil. In addition to the significant increase in soil available phosphorus content, AMF had no significant effect on the physical and chemical properties of the soil and other soil nutrients in normal soil. AMF significantly increased pod biomass and yield in saline-alkali soil and normal soil, and improved their agronomic characteristics. In conclusion, peanut seeds coated with AMF improved the root morphological characteristics of peanuts and improved the physical and chemical properties in peanut rhizosphere, especially in saline-alkali soil. The process of rhizosphere soil nutrient transformation was also enhanced. Finally, AMF improved plant agronomic traits to increase the pod yield (16.5~21.9%). This study provides the theoretical basis and technical support for the application of AMF in peanut production in saline-alkali soil.

Preparation of environmental remediation material based on manganese-slag and sewage sludge as a strategy for remediation of cadmium pollution

Both manganese-slag and sewage sludge are typical solid wastes, but their utilization is limited. Based on the soil properties, the abovementioned pollutants were combined with Broussonetia papyrifera to treat soil cadmium (Cd) pollution. Three materials (sewage sludge-derived biochar (SSB), Mn-SSB, and Mn-slag (Slag)) were prepared using oxygen-limited pyrolysis technology with Slag and sewage sludge, and the effects of the three materials on the phytoremediation of Cd-polluted soil were investigated. All three materials had distinct morphological characteristics, good functional group structure, specific surface area, and porosity. The adsorption and leaching experiments in the solution indicated that the three materials could not only directly absorb Cd2+ but also release nutrients, such as nitrogen and phosphorus. The soil pH increased significantly (p < 0.05) with the addition of the above environmental remediation materials. Furthermore, the contents of soil organic carbon, available nitrogen, and available phosphorus in soil increased significantly, whereas the electrical conductivity of the soil decreased significantly (p < 0.05). During remediation of Cd-polluted soil by integrating the above materials with B. papyrifera, Slag significantly increased the B. papyrifera biomass, but the effects of SSB and Mn-SSB were not significant. SSB, Mn-SSB, and Slag significantly increased the protein content of B. papyrifera leaves, with Mn-SSB having the most significant effect (p < 0.05). The applications of SSB, Mn-SSB, and Slag reduced the malondialdehyde content and increased the activities of superoxide dismutase and peroxidase, reducing the damage to B. papyrifera. Mn-SSB significantly reduced the Cd content in the roots, stems, and leaves of B. papyrifera, and SSB and Slag promoted Cd enrichment in B. papyrifera. This study realized the comprehensive utilization of Mn-slag and sewage sludge and established a recycling system from solid waste to the treatment of waste soil.

Effects of pruning on tea tree growth, tea quality, and rhizosphere soil microbial community.

Pruning is an important agronomic measure in tea plantation management. This study analyzed the effects of pruning on tea tree growth, tea quality, rhizosphere soil physicochemical indexes, microbial communities, and metabolic pathways. The results showed that pruning was beneficial for promoting tea tree growth and increasing tea yield, but not for the synthesis and accumulation of quality-related compounds in tea leaves. After pruning, organic matter, available phosphorus content and catalase, acid phosphatase, and sucrase activities in rhizosphere soil were significantly higher than those in unpruned tea trees, while total phosphorus, total potassium, and available nitrogen content were significantly lower than those in unpruned tea trees. The results of microbial community analysis of tea rhizosphere soil showed that the key changed characteristic microorganisms after pruning were Haliangium, Acidicaldus, Reyranella, Acidobacterium, Aquicella, and Granulicella, and the key changed characteristic microbial metabolic pathways were ko00072, ko00473, ko00750, ko01055, ko00521, and ko02040. Furthermore, the results found that pruning promoted Haliangium, Acidicaldus, and Reyranella abundances, ko00072, ko00473, and ko00750, respectively, microbial metabolic pathways in tea trees rhizosphere soil, and reduced Acidobacterium, Granulicella, and Aquicella abundance, ko01055, ko00521, and ko02040, respectively, microbial metabolic pathways, thereby increasing the activities of soil catalase, acid phosphatase, and sucrase, improving soil organic matter decomposition efficiency and available phosphorus content, and promoting tea yield, but not synthesis and accumulation of quality-related compounds in tea leaves. This study provides an important theoretical reference for the management of agronomic measures in tea plantations. IMPORTANCE Pruning is an important agronomic measure in tea cultivation and management. We found that pruning was beneficial to increase tea yield, but it would reduce tea quality, especially the content of polyphenols, theanine, flavonoids, and free amino acids in tea leaves was reduced. The reason for this phenomenon was that pruning promotes the enrichment of special functional microorganisms and the enhancement of special metabolic pathways in the soil, leading to changes in the nutrient cycle in the soil.

Inoculation of cold-adapted microbial consortium screened from alpine meadows promotes the growth of mixed grasses by changing soil properties and enzyme activity

The objective of this study was to investigate the effect of co-inoculation of three PGPR strains and inoculation ratio on the growth characteristics and soil properties of mixed grasses. In this study, we used 3 strains of PGPR for the material, which were Acinetobacter calcoaceticus called HMAJ1, Pseudomonas piscium called HMAJ5, and Pseudarthrobacter psychrotolerans called NCZ1, with nitrogen fixation and phosphorus solubilization ability. By mixing the bacteria in a different ratio, the effect of inoculating with a microbial consortium on the plant and soil properties of mixed grasses (Elymus nutans Griseb, Festuca sinensis, and Poa pratensis L.) was evaluated and the best microbial inoculants ratio was selected. The results showed that inoculating with a microbial consortium increased the soil organic carbon , available phosphorus, ammonium and nitrate nitrogen content, and the activities of soil alkaline phosphatase, sucrase, peroxidase, and urease, which promoted the plant height and biomass of mixed grasses. Pearson correlation analysis showed that plant characteristics were differently correlated with soil properties. Grey correlation analysis of plant biomass, soil properties, and soil enzyme activity revealed that T7 (HMAJ1:NCZ1 = 3:7) was the most effective in improving mixed-grasses biomass and soil quality. Our results indicated that the positive interaction of nitrogen-fixing bacteria with phosphorus-solubilizing strains may become a novel and effective bio-inoculant to achieve sustainable pulse productivity.

Microbiome Reveals the Effects of Biogas Fertilizer on Soil Microbial Community Structure and Diversity in Perennial Apple Orchards

Fruit trees are perennial crops that grow in one place for their whole lives, which leads to the deterioration of the soil as well as a decline in fruit quality and yield. Microbial diversity and community structure are important soil factors affecting stress resistance and the quality of fruit trees. Additionally, biogas fertilizer also plays an important role in improving fruit quality. Whether biogas fertilizer can improve continuous cropping barriers by affecting microbial diversity and community structure remains to be further investigated. Therefore, 7-year-old Fuji apples were used as material, and biogas fertilizer was applied continuously for three years. The results show that the contents of soil organic matter (SOM), available nitrogen (AN), available phosphorus (AP), and soil porosity (SP) increased by 0.712, 0.217, 1.089, and 0.401 after applying biogas fertilizer, respectively. The concentrations of vitamin C, titratable acid, and soluble solids also significantly increased. We also found that the relative abundance of dominant soil flora significantly increased, such as Sphingomonas (g_Sphingomonas), Chlamydomonas (g_Chlamydomonas), and Stachybotry (g_Stachybotry), while the relative abundance of inferior flora significantly decreased, such as Cryptococcus (g_Cryptococcus) and Alternaria (g_Alternaria). In summary, biogas fertilizer can improve the physicochemical properties of the soil as well as the structure and diversity of the microbial communities in rainfed orchards, resulting in higher fruit quality.

Identification of mutations related to phytate accumulation in barley kernels

Aim. To conduct DNA marker testing on a sample of Ukrainian selection barley samples for identify various lpa-mutations that affect to the qualitative composition of phosphorus in barley grains. Мethods. Isolation of DNA (CTAB method), polymerase chain reaction (PCR) and electrophoretic determination of DNA amplification products in agarose gel for the identification of lpa mutations in barley grains. Results. The conducted molecular genetic studies of 20 breeding lines of hulless barley made possible to identify samples that have lpa-1 and lpa-2 mutations. The presence of such mutant genes determines a low content of organic (unavailable inorganic) phosphorus and an increased content of mineral (available) phosphorus that can be absorbed by the human body. Conclusions. The applied methods of identification of lpa-1 and lpa-2 mutations that affecting to the phytate content in whole grain barley allow for effective analysis of selection lines and mutant samples that can be used in future crossing schemes.

Diversity of Endomycorrhizal Fungi in Argan Forest Stands: Implications for the Success of Reforestation Programs

Over the last few decades, argan trees (Argania spinosa L.) skeels have faced harsh ecological conditions and anthropogenic pressure, leading to a dramatic decline in surface and density of cultivation. Nowadays, most techniques used to regenerate argan trees have failed. Arbuscular mycorrhizal fungi (AMF) are root symbionts that increase plant resistance to biotic and abiotic stresses during transplantation. The exploration of these symbiotic fungi from different soils of argan stands is the starting point for the selection and production of high-performance organisms adapted to the reforestation sites. The objective of this study is to investigate the composition of the AMF community associated with the argan tree rhizosphere. Forty adult argan trees were sampled in eight forest sites representative of the distribution and genetic diversity of argan forest stands. Five sub-samples of rhizospheric soil were taken around each tree. Our results revealed the presence of different AMF structures (i.e., hyphae, vesicles/and arbuscules) in root samples. Based on morphological characterization, six genera of AMF spores were identified with a dominance of the genera Septoglomus (34%). In addition, soil organic matter and phosphorus concentrations showed a highly significant correlation with AMF spore density. The chi-square test showed a highly significant dependence of the distribution of genera on the site conditions of forest stands. These AMF could be tested and used during the inoculation of argan seedlings in forest nurseries for the success of restoration and reforestation programs, as well as for the development and sustainable improvement of this agroforestry system.

Response of soil microbial community diversity to continuous cucumber cropping in facilities along the Yellow River irrigation area.

Cucumber is an important cash crop; however, continuous cropping obstacles readily occur within the intensive production processes of facility horticulture. This study aimed to determine the effects of continuous cropping on soil quality and the microbial community in the rhizosphere soil of cucumbers. Rhizosphere soil of cucumber planted continuously for 4, 8, and 12 years was investigated, and soil that was not continuously planted was used as the control. Soil physicochemical properties, enzyme activity, microbial diversity, and richness were determined. The results showed that with the increase in continuous cropping years (0, 4, 8, and 12 years), soil total salt content continuously increased, while the pH value significantly decreased. Compared with the control, soil organic matter, alkali-hydrolyzed nitrogen, available phosphorus, available potassium, and nitrate nitrogen contents increased significantly after 4 and 8 years of continuous cropping. Spearman correlation analysis showed that pH was negatively correlated with sucrase or sucrose and available phosphorus was positively correlated with alkaline phosphatase. Compared with the control, the diversity and abundance of bacterial and fungal communities in cucumber rhizosphere soil decreased after 4 and 12 years of continuous cropping. Continuous cropping led to a significant increase in the richness of the dominant phylum of cucumber rhizosphere soil. Principal coordinates analysis showed that, compared with the control, the soil microbial community structure was significantly separated after 4, 8, and 12 years of continuous cropping, and the microbial community structure was most similar after 4 and 8 years of continuous cropping. In addition, redundancy analysis showed that pH was the main driver of soil microbial dominance. In conclusion, continuous cropping of cucumber along the Yellow River irrigation area has led to the deterioration of soil nutrients and microbial communities in that region. This experiment provides a theoretical foundation for addressing the challenges associated with continuous cropping in cucumber cultivation.

Effect of depositional evolution on phosphorus enrichment in aquifer sediments of alluvial-lacustrine plain

Groundwater with high geogenic phosphorus (P) is increasingly concerned as a potential risk to surface water eutrophication. Although hydrogeochemical processes responsible for P mobilization in groundwater systems have been studied, the burial characteristics of P and the effect of depositional evolution on P enrichment in aquifer sediments remain unclear. In this study, aquifer sediments were collected from the Dongting Lake Plain (DTP) within the central Yangtze River Basin, a high P groundwater area, and the effect of depositional evolution on P enrichment was elucidated by comprehensively analyzing the lithology, grain size, geochronology, and geochemistry of the sediments, coupled with groundwater chemistry and sediment incubation experiments. The results showed that the contents of total organic carbon (TOC), iron (Fe), and P (the relative content of bioavailable phosphorus (BAP)) were higher in lacustrine sediments deposited under a warm-wet climate, but lower in fluvial sediments deposited under a cold-dry climate. During depositional evolution, the sedimentary facies mainly controlled the content of organic phosphorus (OP), while the paleo-climate controlled the content of both OP and Fe-bound inorganic P (FeP), which jointly affected total P content in aquifer sediments. Under the interaction of groundwater and sediment, the reductive dissolution of P-rich Fe (oxyhydr)oxides and the mineralization of OP in sediment continuously release P into groundwater. Notably, the rapid accumulation of alluvial sediments after the Last Glacial Maximum in the DTP and rapid evolution of Dongting Lake during the Holocene led to a large amount of organic matter (OM) and P buried in sediments, providing materials for P release in aquifers, which seriously threatens groundwater quality. This exploration can provide a new understanding of the enrichment of geogenic P in groundwater from the perspective of depositional evolution.

The soft rock can promote the improvement of aeolian sandy soil in Mu Us Sandy Land, China

This study focuses on the significance of improving the land degradation of Mu Us Sandy Land to increase cultivated land area and promote ecological green development. The research objects were four kinds of mixed soils, and rhizosphere soils were collected during the crop harvesting period. The volume ratio of soft rock to sand was 0:1 (control check, CK), 1:5 (composite soil one, PS1), 1:2 (composite soil two, PS2), and 1:1 (composite soil three, PS3). The results showed that the large aggregates were primarily mechanically stable aggregates, while the small aggregates were mainly water-stable aggregates. The soft rock promoted the increase of clay and silt content in sandy soil, and the soil texture changed from sand to loam. The contents of organic matter, available phosphorus, and available potassium increased significantly under PS2 and PS3 treatments, but there was no significant difference between them. Total nitrogen had no significant difference among treatments. Actinobaciota, Proteobateria, and Chloroflexi were the dominant bacteria in rhizosphere soil, accounting for about 75% of all microorganisms. At the Genus level, the soft rock contributes to richer species composition. The diversity index, evenness index, and richness index was higher in PS1, and the available phosphorus and available potassium content promoted the increase of diversity. Therefore, when the proportion of soft rock and sand compound soil is between 1: 5 and 1: 2, it can be used as an important basis and technical parameter for Mu Us Sandy Land improvement.

Abundance of colloidal organic phosphorus in the Taiwan Strait

The Taiwan Strait is a coastal sea with dynamic hydrologic condition and dissolved organic matter (DOM) cycling. To better understand its phosphorus (P) transformation, phosphate and bulk dissolved organic phosphorus (DOP) concentrations were determined in the surface water of the Taiwan Strait during 2010 and 2011 summers. The bulk DOP was further fractionated into the low molecular weight (LMW) DOP and colloidal organic phosphorus (COP) with the application of the cross-flow ultrafiltration technique at a size cut-off of 10 kDa. The surface water in the Taiwan Strait generally showed higher bulk DOP concentration than phosphate excluding estuarine stations. This is similar to the surface waters in the subtropical gyres, implying a P-deficient condition in the Taiwan Strait. The LMW-DOP followed a constant permeation behavior in the ultrafiltration experiments, allowing the quantification of LMW-DOP and COP concentrations with the ultrafiltration permeation model. The average COP concentration was 0.044 ± 0.022 μmol/L and 0.042 ± 0.027 μmol/L during 2010 and 2011 summers, respectively. Accordingly, COP accounted for 35 ± 13% and 34 ± 16% of bulk DOP during 2010 and 2011 summers, respectively, suggesting a substantial occurrence of organic phosphorus in the colloidal fraction. The C/P ratio decreased from LMW-DOM to bulk DOM and to colloidal organic matter (COM), supporting the degradation pathway of bulk DOM from colloidal to LMW fractions and the lability of COP in the Taiwan Strait. The fractionation of C/P ratio between bulk DOM and COM in the Taiwan Strait, denoted by the fractionation factor (FC/D), was comparable to the open oceans, but significantly stronger than rivers and estuaries. It might indicate an autochthonous input and rapid turnover of bulk DOP pool in the Taiwan Strait in the context of low phosphate concentration. The FC/D also showed a spatial variability in the Taiwan Strait, high in the South China Sea Warm Current and upwelling occupied stations and low in inshore areas influenced by terrestrial input. This further supports the FC/D as an indicator of bulk DOM sources besides its application to decipher the diagenetic status of bulk DOM and biogeochemical cycles of bulk DOP in the coastal oceans.