Bioavailable Phosphorus Research Articles

Chloride and phosphorus retention and release in soils surrounding a salt-contaminated lake in West Michigan

Salinization in freshwater ecosystems has become an increasingly prevalent issue. Past studies indicate that increased salinity levels in lakes can impact biota, stimulate internal nutrient loading, and prevent seasonal turnover, potentially resulting in impairment to the lake ecosystem. Salt retention in soils and groundwater causes elevated salt concentrations in fresh water long after road salt was applied. We examined salt retention and release in soils collected near the tributaries flowing into and out of a salt-impacted urban lake. We distributed each soil sample into plastic trays and exposed them to three treatments, conducted in series: (1) non salt-contaminated water as a conditioning rinse; (2) salt-contaminated water to mimic salt de-icer runoff; and (3) non salt-contaminated water to determine salt release. We measured retention of chloride from each soil sample based on how much chloride was measured in water draining the soil (effluent). We observed considerable variability among sites presumably because of soil heterogeneity, although overall the soils in our study area retained a modest amount of chloride (mean of ∼29 mg/L) from simulated salt runoff events, even at short exposure times (<30 min). In addition, some soils released chloride following a relatively salt-free rinsing event. There was an overall positive relationship between percent soil organic matter and Cl- retention. We also measured the impact of chloride on bioavailable phosphorus concentration in the effluent, which was relatively modest and variable. Soil total phosphorus had a strong positive correlation with %SOM. Our results suggest that in addition to direct runoff of salt de-icers from roads to lakes, soil retention can also serve as a chloride source that can be released over time, resulting in a delayed impact to aquatic ecosystems.

Bioavailability of Macroelements from Synbiotic Sheep's Milk Ice Cream.

To determine the potential bioavailability of macroelements (Ca, Mg, P, K), probiotic ice cream samples (Lactaseibacillus paracasei L-26, Lactobacillus casei 431, Lactobacillus acidophilus LA-5, Lactaseibacillus rhamnosus and Bifidobacterium animalis ssp. lactis BB-12) from sheep's milk with inulin, apple fiber and inulin, or apple fiber and control samples were submitted to in vitro digestion in the mouth, stomach and small intestine. The bioavailability of calcium in the ice cream samples ranged from 40.63% to 54.40%, whereas that of magnesium was 55.64% to 44.42%. The highest bioavailability of calcium and magnesium was shown for the control samples. However, adding 4% inulin reduced the bioavailability of calcium by about 3-5% and magnesium only by about 5-6%. Adding 4% apple fiber reduced the bioavailability of calcium by as much as 6-12% and magnesium by 7-8%. The highest bioavailability of calcium was determined in ice cream with L. paracasei, and the highest bioavailability of magnesium was determined in ice cream with L. casei. The bioavailability of phosphorus in ice cream ranged from 47.82% to 50.94%. The highest bioavailability of phosphorus (>50%) was in sheep ice cream fermented by B. animalis. In the control ice cream, the bioavailability of potassium was about 60%. In ice cream with inulin, the bioavailability of potassium was lower by 3-4%, and in ice cream with apple fiber, the bioavailability of potassium was lower by up to 6-9%. The bioavailability of potassium was significantly influenced only by the addition of dietary fiber. The results of the study confirmed the beneficial effect of bacteria on the bioavailability of Ca, Mg and P.

Integrated Effect of Heavy Metal-Tolerant Rhizobacteria and Phosphorus on Maize Growth and Phosphorus Bioavailability in Contaminated Soil

Toxic metals significantly influence agricultural crop yields and adversely affect animals and humans. Hence, in the current study impact of different strains of phosphorus-solubilizing bacteria (PSB) and levels of phosphorus on the solubility of phosphorus and the stabilization of heavy metals in contaminated soil were studied in a greenhouse pot experiment in 2022. The PSB strains included Bacillus CUM6, Bacillus DUM7, and Bacillus PIS7. Phosphorus was applied at rates of 40, 60, and 80 kg P2O5 ha-1 using single superphosphate, with a basal dose of 120 kg N and 60 kg K2O ha-1. The experiment followed a randomized, two-factorial design. Maize plants (variety "Azam") were inoculated with the PSB strains. Consequently, combining Bacillus PIS7 with 80 kg P2O5 ha-1 significantly increased both fresh and dry maize biomass (35.33 and 24.56 g pot-1) compared to the control (unspiked soil). Phosphorus bioavailability (7.07 and 5.14 mg kg-1) significantly improved with 80 kg ha-1 phosphorus and Bacillus PIS7. Heavy metal concentrations in soil (Cd, Pb, Cr, and Ni) decreased significantly at 80 kg ha-1 phosphorus and Bacillus PIS7, and Cd concentrations in plants decreased to 3.31 mg kg-1 with Bacillus DUM7 and to 2.96, 0.42, and 1.33 mg kg-1 with Bacillus PIS7. The application of PSB strains and phosphorus fertilizer reduced heavy metal concentrations. Notably, 80 kg P2O5 ha-1 with Bacillus PIS7 showed the best performance. Phosphorus uptake increased significantly (0.106 mg pot-1), while heavy metal uptake (Cd, Pb, and Cr) decreased linearly with increasing phosphorus levels and PSB strains. Bacillus PIS7 with 80 kg P2O5 ha-1 had the lowest heavy metal translocation, doing better than the control and other PSB strains (Bacillus CUM6 and Bacillus DUM7). Soil characteristics indicated increased organic matter content (0.73%) and decreased pH (7.61) and electrical conductivity (0.17 dSm-1) with applied phosphorus and PSB strains, suggesting enhanced phosphorus bioavailability and reduced heavy metal concentrations. In conclusion, adding 80 kg P2O5 ha-1 with Bacillus PIS7 helps plants grow better when they are stressed by heavy metals and keeps Cd, Pb, Cr, and Ni stabilized in the soil.

Archean phosphorus recycling facilitated by ultraviolet radiation

Of the six elements incorporated into the major polymers of life, phosphorus is the least abundant on a global scale [E. Anders, M. Ebihara, Geochim. Cosmochim. Acta 46, 2363-2380 (1982)] and has been described as the "ultimate limiting nutrient" [T. Tyrrell, Nature 400, 525-531 (1999)]. In the modern ocean, the supply of dissolved phosphorus is predominantly sustained by the oxidative remineralization/recycling of organic phosphorus in seawater. However, in the Archean Eon (4 to 2.5 Ga), surface waters were anoxic and reducing. Here, we conducted photochemical experiments to test whether photodegradation of ubiquitous dissolved organic phosphorus could facilitate phosphorus recycling under the simulated Archean conditions. Our results strongly suggest that organic phosphorus compounds, which were produced by marine biota (e.g., adenosine monophosphate and phosphatidylserine) or delivered by meteorites (e.g., methyl phosphonate) can undergo rapid photodegradation and release inorganic phosphate into solution under anoxic conditions. Our experimental results and theoretical calculations indicate that photodegradation of organic phosphorus could have been a significant source of bioavailable phosphorus in the early ocean and would have fueled primary production during the Archean eon.

Simultaneous immobilization of lead and arsenic and improved phosphorus availability in contaminated soil using biochar composite modified with hydroxyapatite and oxidation: Findings from a pot experiment

Multi-metals/metalloids contaminated soil has received extensive attention because of their adverse health effects on the safety of the food chain and environmental health. In order to provide additional insight and aid in mitigating environmental risks, a pot experiment was directed to assess the impacts of biochars derived from rice straw (BC), and modified biochars i-e., hydroxyapatite modified (HAP-BC) and oxidized biochars (Ox-BC) on the redistribution, phytoavailability and bioavailability of phosphorus (P), lead (Pb), and Arsenic (As), as well as their effects on the growth of maize (Zea mays L.) in a Lead (Pb)/Arsenic (As) contaminated soil. The results showed that HAP-BC increased the soil total and available P, compared with raw biochar and control treatment. HAP-BC improved soil properties by elevating soil pH and electric conductivity (EC). The Hedley fractionation scheme revealed that HAP-BC enhanced the labile and moderately labile P species in soil. Both HAP-BC and Ox-BC assisted in the P build-up in plant roots and shoots. The BCR (European Community Bureau of Reference) sequential extraction data for Pb and As in soil showed the pronounced effects of HAP-BC towards the transformation of labile Pb and As forms into more stable species. Compared with control, HAP-BC significantly (P ≤ 0.05) decreased the DTPA-extractable Pb and As by 55% and 28%, respectively, subsequently, resulting in reduced Pb and As plant uptakes. HAP-BC application increased the plant fresh and dry root/shoot biomass by 239%, 72%, 222% and 190%, respectively. The Pb/As immobilization by HAP-BC was mainly driven by precipitation, ion exchange and surface complexation mechanisms in soil. In general, HAP-BC application indicated a great capability to be employed as an effective alternative soil amendment for improving P acquisition in soil, simultaneously immobilizing Pb and As in the soil-plant systems.

Fractionation, bioavailability and risk evaluation of phosphorus in lagoons surface sediments, Red Sea, Saudi Arabia

ABSTRACT In this study, eighteen surficial sediments were collected from two shallow lagoons of the Red Sea, King Saudi Arabia (Al-Shaibah and Al-Budhia lagoons), and analyzed for their grain size, CaCO3, and organic matter (O.M.) contents. The concentration of total phosphorus (TP), Organic-P (OP), and Inorganic-P (IP) were determined. In addition, Phosphorus bioavailability was also investigated by a sequential extraction procedure. The results of the current study showed variation in the levels of total phosphorus and the organic and inorganic form (TP, IP, OP). Al-Shaibah lagoon showed higher TP contents (274.78–389.24 and 265.91 ± 29.03 µgg-1) more than Al-Budhia lagoon (227.25–318.55 and 265.91 ± 29.03 µgg-1). The distribution of phosphorus bioavailability concentrations in the studied fractions in Al-Shaibah lagoon sediments was increased in the following order: hot H2O-P (0.10–0.25µgg−1) < NaHCO3-P (1.85–3.11 µgg−1) < exchangeable fraction (NH4Cl-P; 2.64–10.64 µgg−1) < Fe and Al-associated phosphorus (NaOH-P; 29.67–7.32 µgg−1). A similar order was observed in the Al-Budhia lagoon with slight differences in its content. The different fractions of the contribution of phosphorous bioavailability from the Total-P concentration were recorded as: NaOH-P (14.63–18.62%) >> NH4Cl-P (2.11–1.99%) > NaHCO3-P (0.75–1.04%) >H2O-P (0.05–0.09%). The phosphorus concentrations in the HCl-P fraction (calcium-associated phosphate/apatite) represent 32.67–59.60% of the total phosphorus in lagoon sediments.

Characteristic of phosphorus rich compounds in the incinerated sewage sludge ashes: a case for sustainable waste management

Growing concern over mineral resources supply forces us to search for alternative sources of Phosphorus. The possibility to recover phosphorus from incinerated sewage sludge ashes appears to be an important aspect in anthropogenic phosphorus cycle and sustainable economy. To make phosphorus recovery efficient it is important to learn the chemical and mineral composition of ash and phosphorus speciation. The phosphorus content in the ash was over 7%, what corresponds to medium rich phosphorus ores. The main phosphorus rich mineral phases were phosphate minerals. The most widespread was tri-calcium phosphate Whitlockite with various Fe, Mg and Ca proportions. In minority Fe–PO4 and Mg–PO4 were detected. Whitlockite commonly overgrown with hematite, influences negatively mineral solubility and thus recovery potential and indicates low bioavailability of phosphorus. Considerable amount of phosphorus was found in the low crystalline matrix where phosphorus content was around 10 wt% however low crystallinity and dispersed phosphorus also does not strengthen the potential to recover this element.

NEW FEED ENZYME PREPARATIONS FOR THE DESTRUCTION OF NON-STARCH POLYSACCHARIDES AND PHYTATES

New recombinant strains of Penicillium verruculosum have been created with a high level of expression of homologous endo-β-1,4-glucanase II and heterologous phytase A A. niger, as well as heterologous endo-1,4-β-xylanase E P. canescens and phytase A A. niger, allowing to obtain highly active feed enzyme preparations (AF) capable of simultaneously signi cantly reducing viscosity non-starch polysaccharides, as well as increase the bioavailability of phosphorus and minerals of grain-based feed and, thus, increase the digestibility of nutrients of agricultural animal and poultry feed. Speci c AF activities for speci c substrates (xylanau, β-glucan, phytate) were studied, the qualitative and quantitative component composition of new AF was determined. On the basis of a new enzyme preparation containing homologous endo-β-1,4-glucanase II and heterologous phytase A A. niger, a recipient strain ∆nia D - was obtained, into which heterologous endo-1,4-β-xylanase E P. canescens was successfully cloned and, thus, a promising producer of three target enzymes was obtained simultaneously.

Quantification of Nutrient Fluxes from Sediments of Lake Hulun, China: Implications for Plateau Lake Management

Dramatic changes in lake water conditions may induce sensitive feedback in sediments, such as the release of phosphate and ammonia. There is a lack of the understanding of sediment nutrient release fluxes and their responses to various environmental factors in plateau lakes. In this study, nutrient contents in the water and sediment, sediment nutrient release rates, and their responses to various influential factors in a steppe shallow plateau lake, Lake Hulun, China, were investigated. Sediment is a large store of nutrients, with bioavailable phosphorus of 555 mg kg−1 in surface lake sediments. If water became anoxic, sediments will release appreciable amounts of phosphate (2.1 mg P m−2 d−1) and ammonia (40.0 mg N m−2 d−1), three times greater than those in oxic conditions. Raised temperatures greatly increased sediment phosphate release rates, while the highest temperature (23 °C) slightly decreased ammonia release rates due to strong nitrification. Assuming a whole year of internal loading, ammonia and dissolved reactive phosphorus concentrations in water column would increase by an estimated 0.22 mg N L−1 and 0.01 mg P L−1, respectively, which is equal to 2 and 0.5 times of their ambient concentrations. A pH increase from 8.4 to 9.4 significantly decreased internal nitrogen and phosphorus release rates by around three times. Overall, dissolved oxygen (DO) and pH had a greater impact on sediment nutrient release from lake sediments compared to temperature, and further increased the eutrophic status in the overlying water when these three parameters varied within the normal seasonal range (temperature: 1.9–23.1 °C, DO: oxic and anoxic; pH: 7.5–9.4). With the periodic low DO and frequency of drought in the future, lake management strategies that mitigate water eutrophication, such as water diversion, may need to be considered.

Utilizing CaCl2 to promote the enrichment and bioavailability of phosphorus in incinerated sludge ash.

Recovering phosphorus from incineration sludge sewage ash (ISSA) is a well-established technology, with a greater recovery potential than that of supernatant or sludge. ISSA can be utilized as a secondary raw material in the fertilizer industry, or as a fertilizer if heavy metal concentrations do not exceed permissible limits, thus reducing the cost of phosphorus recovery. Increasing the temperature to produce ISSA with higher solubility and plant availability of phosphorus is advantageous for both pathways. But a decrease in the extraction of phosphorus is also observed at high temperatures, thereby diminishing the overall economic benefits. In this study, CaCl2 was utilized to mitigate the decrease in the extraction rate and also to promote the bioavailability of phosphorus. The addition of CaCl2 (80 g/kg of dry sludge) effectively promoted the conversion of non-apatite inorganic phosphorus to apatite inorganic phosphorus at a rate of 87.73% at 750 °C. Furthermore, the decrease in the extraction rate of phosphorus at 1,050 °C was comparatively smaller in the presence of CaCl2. If iron flocculants are used to capture P in wastewater management, it may be necessary to pay special attention to the amount of addition and incineration temperature to maximize the economic potential of recycling.

Unique physical processes of canyon reservoirs regulate the timing and size of algal blooms - based on a study in Three Gorges Reservoir

The management and remediation of algal blooms on a global scale are primarily focused on controlling nutrient inputs, with an emphasis on limiting phosphorus inputs from point and non-point sources. It is well known, however, that physical factors such as water temperature, water column stability and advective flow also play critical roles in the timing and size of algal blooms. For nutrient control programs to be effective, it is essential to understand the relative importance of hydrological processes associated with nutrient dynamics and bioavailability. This study examines the relative importance of physical processes in hyper-eutrophic canyon reservoirs in regulating the development of algal blooms. We hypothesized that water column stability determines when algal blooms develop as well as the potential size of the bloom. To test the hypothesis, the study was implemented in Gaoyang Lake located in the middle of the Pengxi River, a 1st- order tributary in the Three Gorges Reservoir. The CE-QUAL-W2 model was applied to verify the lacustrine nature of Gaoyang Lake. We sampled the lake for 33 consecutive days from April 15th to May 17th in 2019. Algal composition and abundance, chlorophyll-a concentration, and different forms of P from the surface, middle and bottom of the water column, respectively, and available phosphorus in sediment were sampled and measured daily. Water temperature, dissolved oxygen, chlorophyll-a and water velocity were measured in situ daily. We demonstrate that:1. During the initial stratification period, a surface density layer (SDL) was formed as a result of a lack of turbulent wind mixing. The formation of the SDL initiated the development of algal blooms as a result of surface optimum temperatures being achieved early in the year. Although the SDL maintained the algal community within the euphotic zone, it also limited nutrient influx to the surface waters resulting in a decline of bioavailable phosphorus.2. Surface cooling events, however, weakened the SDL resulting in enhanced nutrient flux into the upper water column. The nutrient supply resulted in the formation of subsequent and more severe algal blooms when the SDL was re-established.Our results demonstrate that physical processes such as the formation and stability of the SDL can be used to predict the occurrence and size of algal blooms in canyon reservoirs. To control algal blooms, we suggest conducting further research to regulate the development and stability of SDL through interventions such as artificial mixing or flow modification during critical time periods. These approaches may provide rapid remediation options for managing harmful algal blooms.

Inoculations of phosphate-solubilizing bacteria alter soil microbial community and improve phosphorus bioavailability for moso bamboo (Phyllostachys edulis) growth

Moso bamboo plantations suffer from phosphorus (P) limitations. A better understanding of soil P cycling contributes to the sustainable management and development of the bamboo forests. In this study, different phosphate-solubilizing bacteria (PSB) were applied to soils to stimulate bamboo growth, and the metagenomics method was employed to investigate the changes in soil microbial communities and relative abundances of functional genes. Meanwhile, soil properties and bamboo biomass and physiological indices were also quantitatively analyzed. The PSB inoculations changed soil P fractions and significantly elevated available P (AP) content by stimulating phosphatase activity and functional genes involved in P-transformation. The PSB inoculations significantly stimulated soil acid phosphatase activities and enhanced the relative abundances of functional genes associated with inorganic P-solubilization and organic P-mineralization. Moreover, increased soil available nutrients were beneficial to the moso bamboo growth, and the bamboo biomass in the different treatments increased by from 32.43 % to 69.04 % compared with the control treatment. Significant increases in root activity, carotenoid, chlorophyll a and total chlorophyll contents after the PSB inoculations also contributed to moso bamboo growth. The PSB strain inoculations shaped soil microbial communities and increased microbial connections. Besides adjusting soil P supplies and functional genes, the PSB also promoted the moso bamboo growth by increasing soil mineral N, AK and bamboo chlorophyll contents and stimulating functional microorganisms. Our study could provide a theoretical basis to improve soil nutrient utilization for moso bamboo with the PSB inoculations.

Distribution and Release Potential of Soil Phosphorus Fractions in Water-level Fluctuation Zone of the Tributary Bay, Three Gorges Reservoir

After repeated wetting-drying cycles, the migration and transformation of phosphorus in the water-level fluctuation zone (WLFZ) are accelerated, and the eutrophication of tributary bays in the reservoir becomes increasingly serious. Soils in the WLFZ of a typical tributary of the Three Gorges Reservoir were collected, and then phosphorus forms and the degree of phosphorus saturation (DPS) were determined to analyze the phosphorus release potential. The results showed that, ① the average contents of total phosphorus (TP), inorganic phosphorus (IP), and organic phosphorus (OP) of soils in the WLFZ were 771.80, 485.33, and 166.30 mg·kg-1, respectively. The non-labile IP and OP were the dominate speciation of IP and OP, respectively. ② The distribution of P forms of soils in the WLFZ was affected by wetting-drying cycle. The contents of Ex-P and NaHCO3-Po of soils in the WLFZ were significantly higher than those in the contrasted soils, whereas the contents of Fe-P, HCl-Po, and Fulvic-Po decreased significantly along the elevation (P<0.05). The alternative wetting-drying cycle promoted the generation of labile P and the release and accumulation of moderately labile P of soils in the WLFZ. ③The content and proportion of bioavailable phosphorus (Bio-P) of soils in the WLFZ were in the range of 49.19-148.78 mg·kg-1 and 7.17%-24.78%, and the degree of phosphorus sorption (DPS) was in the range of 5.85%-22.00%. At present, the phosphorus release risk of soils in the WLFZ was low. The soil at 170 m elevation requires further attention. Fe-P, HCl-Po, and Fulvic-Po contributed significantly to phosphorus release. The increase in pH promoted the release of Fe-P. Alkaline phosphomonoesterase (ALP) was an important participant in the transformation of OP. Additionally, organic matter (OM) was the main source of OP.

Determination of TMEn, standardized amino acid digestibility, phosphorus digestibility, and phosphorus bioavailability in conventional and reduced phosphorus distillers dried grains with solubles

The TMEn, amino acid (AA) digestibility, and P availability in 2 conventional corn distillers dried grains with solubles (C-DDGS1 and 2; 0.86 to 1.14% P, DM basis) and reduced phosphorus DDGS (RP-DDGS; 0.39% P) were evaluated. The TMEn of C-DDGS1 and 2 and RP-DDGS were determined in Experiment 1 using conventional adult Leghorn roosters, while standardized AA digestibility was determined in Experiment 2 using cecectomized roosters. Apparent ileal digestibility (AID) of P at different Ca levels was determined using precision-fed (crop intubation) broiler chickens in Experiments 3 and 4. The AID and total tract retention of P in C-DDGS2 were evaluated in Experiment 5 using ad libitum-fed broilers. Phosphorus bioavailability in C-DDGS2 relative to KH2PO4 based on bone ash was determined in Experiment 6. Experiments contained 4 to 5 replicates per treatment. In Experiment 1, the TMEn of C-DDGS1 and RP-DDGS was 3,428 and 2,840 kcal/kg, respectively (DM basis). In Experiment 2, there were no differences (P > 0.05) in rooster AA digestibility values between C-DDGS1 and RP-DDGS. In Experiment 3 with precision-fed chicks, AID of P in C-DDGS1 and RP-DDGS was 81 and 59%, respectively; there was no effect (P > 0.05) of increasing dietary Ca level from 0.04 to 1.0% for C-DDGS1 or reducing Ca from 1.5 to 1.0% for RP-DDGS. The AID of P in precision-fed chicks for C-DDGS2 in Experiment 4 was 48 and 80% at 1.3 and 0.3 Ca:total P ratios, respectively (P < 0.05). In Experiment 5, AID of P in C-DDGS2 at Ca:total P ratios of 1.3 and 2.5 was 63 and 42%, respectively, in precision-fed chicks. Regression of bone ash content (mg/tibia) on supplemental P intake in Experiment 6 yielded a P bioavailability of 61% relative to KH2PO4 for C-DDGS2. In conclusion, total and digestible P content in RP-DDGS was greatly reduced compared with C-DDGS, and the digestibility and bioavailability of the P in C-DDGS was affected by type of experimental assay and dietary Ca level.

Seed phytic acid concentration affects rice seedling vigor irrespective of soil phosphorus bioavailability.

Rice with a black-colored pericarp (hereafter, black rice) is well-known as an antioxidant-rich food, but a high grain phytic acid (PA) concentration affects its nutritional quality. However, phytic acid helps improve seedling vigor, which is crucial for enhancing subsequent plant growth. This study investigated the effect of seed phytic acid concentration in black rice on seedling vigor compared to the effects on white rice. In the first experiment, three phytic acid concentrations in the seeds of black rice, low (LPA, 15.5 mg g-1 per seed), medium (MPA, 24.7 mg g-1 per seed), and high (HPA, 35.4 mg g-1 per seed) were tested for seedling vigor in phosphorus-deficient soils. The HPA seedlings showed substantially increased seedling vigor and shoot P uptake due to early root development and enhanced physiological processes. LPA grown seedlings showed increased ethylene production in response to P stress, which is the main physiological mechanism modulating seedling growth under P stress conditions. In the second experiment, the three phytic acid concentrations in black and white rice seeds were tested under low and high soil P conditions. Again, LPA seedlings showed significantly reduced seedling vigor in both rice varieties in P-deficient soils. Interestingly, seed phytic acid and external P application had an additive effect on seedling vigor, suggesting that the combined effect further improved seedling growth. Our results reveal that black rice seeds with a HPA concentration can be used as a seed source for planting in P-deficient ecosystems for rice plants as they can increase seedling vigor and subsequent growth, thus reducing dependence on finite P resources.

Talaromyces purpurogenus Isolated from Rhizosphere Soil of Maize Has Efficient Organic Phosphate-Mineralizing and Plant Growth-Promoting Abilities

The scarcity of phosphorus (P) makes improving phosphorus use efficiency a critical issue in crop production. Plant rhizosphere microorganisms play a vital role in increasing phosphorus bioavailability and promoting the level of plant-absorbable P in agroecosystems. In this study, Talaromyces purpurogenus SW-10 strain with efficient organic phosphate-mineralizing ability was isolated from maize rhizosphere soil. SW-10 showed efficient phytate utilization with corresponding soluble P levels of 525.43 mg/L and produced phytase in the liquid medium. The response surface methodology (RSM) analysis showed that glucose as the carbon source and (NH4)2SO4 as the nitrogen source at 28 °C and pH 7.0 promoted higher mineralization of insoluble organic phosphate. When cocultivated with different genotypes of maize seedlings, SW-10 significantly increased the shoot’s dry weight by 37.93%, root’s dry weight by 31.25%, and the plant height by 13.03% for low-P sensitive inbred line 31778, while no significant change was observed in the low-P tolerance inbred line CCM454. In addition, SW-10 strain significantly increased total P-concentration in the shoots (22.4%~32.9%) and roots (3.10%~9.77%) for both inbred lines. In conclusion, the isolated T. purpurogenus SW-10 strain possesses an efficient organic phosphate-mineralizing ability and maize plant growth-promoting effect, especially for the low-P sensitive genotype that could be exploited for enhancing P availability in agriculture.

Growth Promoting Role of Phytase Producing Bacteria Isolated from Bambusa tulda Roxb. Rhizosphere in Maize Seedlings Under Pot Conditions

Phytase enzymes have focused on their role in agriculture to generate bioavailable phosphorus (P) requires for plant nutrition. Herein, the feasibility of phytase-producing microbes as biofertilizers was studied. Bacteria with greater potential for hydrolysing calcium phytate based on the halo-to-colony ratio from Bambusa tulda Roxb. rhizosphere was isolated. Phytase activity by incorporating wheat bran, phytase screening and Luria Bertani (LB) medium after acetone precipitation was measured. Bacterial genomes were screened for the presence of β-propeller phytase gene corresponding to the Bacillus spp. using polymerase chain reaction (PCR). Finally, the effect of the isolates on the growth of maize seedlings under pot conditions in P-deficient loamy soil was evaluated. Ten distinct bacterial isolates collected from B. tulda rhizosphere were capable of mineralizing phytate and the maximum effect was observed for designated SRBR-04. Most isolates solubilized Ca3(PO4)2 as a sole P source in Pikovskaya’s agar. Five isolates selected for the study synthesized auxin in the LB broth supplemented with 1 mg mL-1 L-Tryptophan (1.63 to 4.5 μg mL-1). Phytase production was highest in wheat bran with isolate SRBR-04 producing a maximum of 0.34 U mg-1. Two isolates (SRBR-01, SRBR-04) screened positive for the presence of Bacillus phytase gene. Pot assay in P-deficient soil showed significant (p &lt; 0.05) biomass promotion for the isolate SRBR-07 in shoot height (57%), dry shoot weight (178%), dry root weight (104%) and leaf area (113%) over the untreated control. Amendment of P-deficient agricultural soils with phytase-producing bacteria would provide a sustainable approach for P nutrition management in Zea mays.

Cadmium-resistant phosphate-solubilizing bacteria immobilized on phosphoric acid-ball milling modified biochar enhances soil cadmium passivation and phosphorus bioavailability

Cadmium (Cd) can accumulate in agriculture soil from the regular application of phosphorus (P) fertilizer. Microbiological method is considered as a potentially effective strategy that can not only remediate the Cd-contaminated soil but also provide the phosphorus needed for crop growth. However, the toxicity of Cd may affect the activity of microorganisms. To solve this problem, Klebsiella variicola with excellent phosphate solubilization ability (155.30 mg L−1 at 48 h) and Cd adsorption rate (90.84 % with 10 mg L−1 Cd initial concentration) was firstly isolated and identified in this study. Then, a phosphoric acid and ball milling co-modified biochar (PBC) was selected as the carrier to promote the activities of K. variicola under Cd pollution. Surface characterization revealed that the promotion of K. variicola by PBC was mainly attributed to the large specific surface area and diverse functional groups. Compared to contaminated soil, microbial PBC (MPBC) significantly increased the pakchoi biomass and phosphorus (P) content, while the Cd content in leave and root of pakchoi (Brassica chinensis L.) decreased by 25.90–43.46 % (P < 0.05). The combined application also favored the transformation of the resistant P fractions to bioavailable P, and facilitated the immobilization of 20.12 % exchangeable Cd to reducible, oxidizable, and residual Cd in the treated soil. High-throughput sequencing revealed that the response of the soil microbial community to the MPBC was more beneficial than K. variicola or PBC alone. Therefore, the application of MPBC has the potential to act as an efficient, stable, and environmentally friendly sustainable product for Cd remediation and enhanced P bioavailability in agricultural production.

Isolation of Phosphate-Solubilizing Microorganisms and the Formulation of Biofertilizer for Sustainable Processing of Phosphate Rock.

As phosphorus (P) bioavailability is limited in arable lands, chemical fertilizers are being used by farmers to increase crop production. Phosphate-solubilizing microorganisms (PSMs) increase the bioavailability of sparingly soluble inorganic and organic soil phosphorus. Therefore, the current study was an effort to evaluate the phosphate-solubilizing efficiency of PSMs using tricalcium phosphate (TCP) and Eppawala rock phosphate (ERP). The efficiency of phosphate solubilization by a series of identified isolates was compared using TCP (5 g L-1) and ERP (5 g L-1) as a P source in Pikovskava's broth. Twelve microbial isolates that showed a higher efficiency in phosphate solubilization were selected for the production of the biofertilizer. The isolate F10 in ERP broth was characterized by the highest significant level of available phosphorus (896.98 ± 10.41) mg L-1, followed by F5 (Aspergillus sp.) in TCP broth 991.43 ± 1.37 mg L-1. A pot trial was carried out by using Capsicum annuum L. as the test plant in two soil conditions: sterilized soil and non-sterilized soil with six treatments and four replicates. The significantly highest plant height, leaf length, and width were shown by chili plants treated with the formulated biofertilizer. Therefore, the application of native PSMs appeared to be an efficient method of solubilizing sparingly soluble P compounds into plant-available forms.

Influence of organic fertilization on clay mineral transformation and soil phosphorous retention: Evidence from an 8-year fertilization experiment

Organic fertilizer can improve phosphorus (P) bioavailability, while the mechanism of microbial-driven clay mineral transformation on P retention and utilization with organic fertilization is still unclear. An 8-year organic fertilization experiment was carried out in saline alkaline paddy soil with five treatments: (1) CK, no fertilization; (2) NK, mineral N and K fertilization; (3) NPK, NK with mineral P fertilization; (4) NPKC1, NPK with 450 kg C ha−1 year−1; (5) NPKC2, NPK with 900 kg C ha−1 year−1. The results showed that, compared with NPK treatment, the percentage of illite with more P adsorption sites was increased by 26.8% and 20.7% in NPKC1 and NPKC2 treatments, respectively. Meanwhile, transmission electron microscopy-energy dispersive X-ray spectroscopy analysis further confirmed that there was more P adsorption on silicate clay minerals. Compared with NK treatment, the content of total P and available P was significantly increased with organic fertilization. Besides, the diversity of bacterial community was also increased by organic fertilizer addition, redundancy analysis showed that soil organic carbon was the main factor in the diversity of bacterial community. The relative abundance of Firmicutes and Gemmatimonadetes was promoted, which drove the transformation of clay minerals and improved P availability, respectively. Compared with NPK treatment, P use efficiency in NPKC1 and NPKC2 treatments was increased by 47.2% and 58.2%, respectively, while no significant difference was found between the two treatments. Therefore, appropriate organic fertilization was a better fertilization practice to improve P retention and utilization through bacteria-driven clay mineral transformation in saline-alkaline paddy soil.