Total Po Research Articles

An assessment of the autotrophic/heterotrophic synergism in microalgae under mixotrophic mode and its contribution in high-rate phosphate recovery from wastewater

Dual carbon metabolisms and the synergism contribute to improving nutrient recovery under mixotrophy. However, how synergism influences nutrient recovery has yet to be understood, which is revealed in the current study. Due to dual carbon metabolisms and synergism,the PO4−-P recovery rate under mixotrophy reached 0.34 mg L−1 h−1. Due to the internal cycling of respiratory CO2, the mutualistic index (MI) in terms of synergism helped Scenedesmus accumulate 27.49 % more biomass under mixotrophy than sum of the two controls. In contrast, MI contributed 0.26 g L−1 d−1 to the total modeled mixotrophic productivity of 1.15 g L−1 d−1. To total modeled PO4−-P recovery, mixotrophic-auto, and mixotrophic-hetero shares were 42 % and 58 %. The synergism under mixotrophy contributed 20 % in total PO4−-P recovery. The PO4−-P recovery rate under mixotrophywas comparable to other biological P removal methods. These findings emphasize the potential of synergism in improving productivityand promoting resource recovery for sustainable wastewater treatment.

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

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

Phosphorous Fractions in Soils of Natural Shrub-Grass Communities and Leucaena leucocephala Plantations in a Dry-Hot Valley

Afforestation is an effective approach for restoring degraded ecological functions in the dry-hot valleys of southwest China. Afforestation can affect soil carbon and nitrogen storage; however, how it affects soil P fractions, and their driving factors. is poorly understood in this region. To address these questions, we conducted a field study of Leucaena leucocephala plantations at three different stand age sites (3, 10, and 20 years) and an adjacent natural shrub-grass community control site to investigate changes in soil total phosphorus (Pt), Pi (inorganic phosphorus), Po (organic phosphorus), and phosphorus (P) fractions and their driving factors. Soil Pt, Po, labile P, and moderately labile P significantly increased in the Leucaena leucocephala plantation compared with the natural shrub grass site, and the Leucaena leucocephala plantation increased soil Pt content by significantly increasing soil Po. Soil Pt, Po, Pi, labile P, moderately labile P and non-labile P were not significantly different among the different stages of the Leucaena leucocephala plantation, and soil Pt and its fractions were all significantly higher in the middle-age forest stage of the Leucaena leucocephala plantation. These results indicate that Leucaena leucocephala plantations increased the soil P transformation ability, and soil Po played a critical role in sustaining soil P availability. The middle-age forest stage of Leucaena leucocephala plantations had the best conditions for P stocks and P conversion capacity. The abundance of actinomycetes and fungi showed significant positive relationships with soil Pi fractions (NaHCO3-Pi, NaOH-Pi, and NaOHu.s.-Pi); soil Pt and moderately labile P were significantly and directly influenced by fungal abundance. Soil organic carbon (SOC), NH4+-N, and NO3−-N showed significant and positive relationships with the soil Pi fractions (NaHCO3-Pi, NaHCO3-Po, and HCl-Po). SOC and NO3−-N were the key drivers of soil Pt, labile P, moderately labile P and non-labile fractions. These results indicate that abiotic and biotic factors differently affected the soil P fractions and Pt in Leucaena leucocephala plantations in the dry-hot valley.

Purification process and mechanism analysis of low-concentration phosphorus wastewater with novel electrodeposition - biochar filter bed

Phosphate‑phosphorus (PO43−-P) is a non-renewable resource. Rapid agricultural activities and inefficient use of phosphate fertilizers contribute to the contamination of natural water resources due to PO43−-P accumulation. PO43−-P recovery in natural water with a low PO43−-P concentration, is conducive to the sustainable utilization of phosphate. Electrodeposition using Ca2+ to recover PO43−-P in natural water has great potential. However, the limitations of low-concentration PO43−-P recovery need to be addressed. This study designed a novel electrodeposition-biochar filter bed (E-BFB) to investigate the removal and recovery ability of PO43−-P at low concentrations. Efficient removal and recovery of PO43−-P was achieved through electrodeposition, biochar adsorption, and accumulation by microorganisms. Effects of different parameters on the performance of E-BFB for PO43−-P removal were studied, including influent PO43−-P concentration, voltage, and electrode spacing. Results showed that 69.4 % PO43−-P was removed when the influent PO43−-P concentration was 0.8 mg/L by E-BFB, as the average removal rate in the biochar filter bed (BFB) was only 11 %. The PO43−-P recovery rate of cathodic electrodeposition was as high as 37.22 %, accounting for 57 % of the total PO43−-P removal amount. The PO43−-P electrodeposition precipitate mainly was amorphous calcium phosphate (ACP) through analysis. 16S rRNA results demonstrated that electrodeposition altered the microbial communities. At the genus level, such as Acinetobacter (26.6 %), Acidocella (11.7 %), and Pelomonas (7.2 %) were promoted in the biochar substrate of E-BFB. Overall, this novel E-BFB can remove PO43−-P at low concentrations effectively. It has great application prospects in the treatment of surface water by biofilters or constructed wetlands.

Uptake, translocation, and nutrient efficiency of nano-bonechar as a plant growth regulator in hydroponics and soil systems

The use of nanotechnology in terms of nanoparticles, carbon nanotubes, and quantum dots, when exposed to the plants, helps increase their productivity. It is worth the effort to comprehend the fate of these nanoparticles in plants. Bonechar derived from bones is a rich source of C, P, Ca2+, and Mg2+ nutrients, which can significantly contribute to the growth of the plants. This study focused on the uptake of nano-bonechar (NBC) in the Syngonium podophyllum plant, and its effects on plant growth under hydroponics and soil systems. The compound microscopy and SEM-EDX results confirmed the presence of NBC in the leaves and roots of the plants in hydroponics and soil systems. The FTIR spectra reflected the presence of functional groups of the NBC in the leaves of the Syngonium podophyllum plant. The plant's growth parameters showed an increase in fresh weight, dry weight, shoot length, chlorophyll content, leaf count, total Ca2+, total PO43−, and total organic carbon of plants in both systems. The NBC not just improved plant physiochemical parameters but also built up the soil quality in terms of bioavailable Ca2+, PO43−, water holding capacity, and soil organic matter. It is concluded that the production of carbon-based NBC not only helps manage bone waste but also their efficient uptake in plants significantly improving plant productivity.

Investigating the potential of nanobonechar toward climate-smart agriculture.

Extreme climates and the unpredictability of the weather are significant obstacles to agricultural productivity. This study is the first attempt to explore the capacity of nanobonechar (NBC) for promoting climate-smart agriculture. A pot experiment was performed on maize (Zea mays L.) under a deficit irrigation system (40, 70, and 100% irrigation rates) using different soil application rates of the NBC (0, 0.5, 1, and 2% wt/wt). Additionally, the CO2-C efflux rate and cumulative CO2-C were measured in an incubation experiment. The results indicated the best performance of the 1% NBC treatment under a 70% irrigation rate in terms of the fresh and dry weights of maize plants. Total PO43- and Ca2+ were significantly higher in the plants grown in the NBC-amended soil as compared to the control, showing a gradual increase with an increase in the NBC application rate. The improved productivity of maize plants under a deficit irrigation system was associated with enhanced water-holding capacity, organic matter, and bioavailability of cations (Ca2+, K+, and Na+) and anions (PO43- and NO3-) in the soils amended with NBC. The CO2-C efflux rate and cumulative CO2-C emissions remain higher in the NBC-amended soil than in the un-amended soil, pertaining to the high contents of soil organic matter emanating from the NBC. We conclude that NBC could potentially be used as a soil amendment for promoting maize growth under a water stress condition.

Crops use inorganic and labile organic phosphorus from both high‐ and low‐availability layers in no‐till compost‐amended soils

AbstractOrganic fertilization in no‐till soils increases soil organic matter and nutrient pools primarily in surface soils. However, little is known about how microbial activity affects crop access to phosphorus (P) forms at the surface, where the organic fertilizer is applied, and the subsurface, the main rooting zone. We aimed to study the changes in organic and inorganic P (Po; Pi) forms and compounds in no‐till compost amended surface (0–5 cm) and subsurface (5–15 cm) soils growing a crop rotation for 2 years in pots. Crops were grown in pots with compost amended to the soil surface, while unamended and compost‐amended pots without crops were used as controls. We measured changes in microbial C (carbon), soluble C, total Po and Pi forms, the moderately accessible EDTA‐NaOH‐Pi (‐Po), and labile NaHCO3‐Pi (‐Po). P compounds in the EDTA‐NaOH extract were measured by 31P‐NMR. Compost addition increased the levels of total Pi and although it had no effect on total Po, increases of inositol, other phosphate monoesters and orthophosphate diesters could be observed. After the application of compost, the amount of total organic C, soluble carbon and all P forms increased in surface soil, while in the subsurface soil, there was a reduction in organic C and an increase in soluble C, total Pi, EDTA‐NaOH‐Pi and NaHCO3‐Pi and the EDTA‐NaOH‐Po and labile NaHCO3‐Po. Growing crops reduced all measured Pi forms and labile NaHCO3‐Po, increased EDTA‐NaOH‐Po in surface soils and had no observable impact on total Po in either organic C‐enriched surface or organic C‐reduced subsurface soils. Crops mostly used Pi from the low P availability C‐reduced subsurface layer, where NaHCO3‐Po pools also decreased. Large reductions in NaHCO3‐Po and increased levels of IHP and other‐monoesters in crop‐growing organic C‐enriched surface layers may suggest microbial formation of monoesters Po and crop use of labile Po pools. In summary, Po formation in C‐enriched surface layers and the mobilization of all Pi forms throughout the soil profile are particularly important findings for the understanding of P dynamics in compost‐amended no‐till systems.

Formation and transformation of Fe(III)- and Ca-precipitates in aqueous solutions and effects on phosphate retention over time

Exfiltration of anoxic phosphate-rich groundwater into surface water leads to the oxidation of dissolved Fe(II) and the formation of Fe(III)-precipitates that can retain phosphate (PO4) and thereby attenuate eutrophication. Fresh Fe(III)-precipitates transform into more stable phases over time, and retained PO4 may be released again. In parallel, CO2 outgassing can promote the formation of Ca-phosphates or -carbonates that also sequester PO4. In laboratory experiments, we studied the effects of Mg, Ca, silicate (SiO4) and PO4 on these processes. Fresh Fe(III)-precipitates were formed in bicarbonate-buffered aqueous solutions at pH ∼ 7.0 via the oxidation of 0.5 mM Fe(II) in the presence of 0.15 or 0.025 mM PO4, at Mg or Ca concentrations of 0, 0.4, 1.2 or 4 mM and in the absence or presence of 0.5 mM SiO4. After CO2 outgassing, the suspensions were allowed to age for 100 d at pH ∼ 8. Changes in the composition and structure of Fe(III)- and Ca-precipitates over time were probed with spectroscopic and microscopic techniques and were linked to variations in the retention of PO4. The oxidation of Fe(II) led to effective PO4 removal via the formation of Fe(III)-precipitates that consisted of amorphous (Ca-)Fe(III)-phosphate ((Ca)FeP), ferrihydrite (Fh) and, in SiO4-free treatments, lepidocrocite (Lp). During aging, FeP and Fh that had formed in the absence of Mg, Ca and SiO4 rapidly and nearly completely transformed into Lp. Via effects on molecular- and nanoscale precipitate structure, Mg slowed down FeP transformation into Fh, stabilized Fh, and decreased the crystallinity of Lp (in SiO4-free suspensions), Ca stabilized CaFeP against transformation into Fh, and SiO4 stabilized Fh and (Ca)FeP. Core/shell CaFeP/Fh particles formed in electrolytes that contained Ca and SiO4 hardly transformed within 100 d. Calcite only formed at low dissolved PO4 concentrations and, by incorporation of PO4, contributed to PO4 retention. Higher levels of dissolved PO4 inhibited calcite formation but could induce Ca-phosphate precipitation. Differences in precipitate formation and transformation pathways and kinetics were reflected in the extents of PO4 release over the 100-d aging period, ranging from rapid release of 77% of the total PO4 in the treatment without Mg, Ca and SiO4 at 0.15 mM total PO4 to slow release of only 0.1% of the total PO4 at initial concentrations of 4 mM Ca, 0.5 mM SiO4, and 0.025 mM PO4. In summary, this study reveals the conditions and the extents and timescales over which Fe(III)- and Ca-precipitates form and transform and how these processes affect PO4 immobilization in near-neutral natural waters. The detailed new insights into the coupling between Fe(III)- and Ca-precipitate formation and into the interdependent effects of Mg, Ca, SiO4 and PO4 are not only relevant with respect to PO4 but also with respect to the cycling of trace elements in natural and engineered systems.

Time‐dependent effects of ecological rehabilitation on soil phosphorus fractions on cut slopes in the mountains of Southwest China

AbstractWhen a cut slope is excavated, the ecological environment in the footprint is destroyed. Soil spray seeding technique is used for the ecological rehabilitation of cut slopes in the mountain areas of Southwest China. However, there have been few studies of the temporal variation in soil phosphorus (P) fractions during the rehabilitation of the cut slopes. In this study, time‐dependent changes in soil inorganic P (Pi) and organic P (Po) fractions of the cut slopes were assessed at selected post‐rehabilitation ages (i.e., 1 year, 1a; 3 years, 3a; 5 years, 5a; and 11 years, 11a). The results showed that the amounts of Pi and Po fractions in soils on rehabilitated cut slopes varied with time. The reduction in the total Po (TPo) content was mainly caused by the change in high concentration hydrochloric acid‐soluble Po (HHCl‐Po) in the soil. The reason for the highest TP content in 3a was the addition of inorganic fertilizer and straw in the artificial soil. The analyses of Pearson correlation and multiple stepwise linear regression showed that TPo and N:P were the main factors affecting the availability of soil P. With the increase in the post‐rehabilitation age, the limitation of soil P gradually weakened, but nitrogen became one of the limiting factors for plant growth. Overall, soil nutrient monitoring is very important for vegetation restoration of the cut slopes. Applying organic fertilizer after 5 years of ecological rehabilitation is conducive to long‐term supply of nutrients required for plant growth.

Sugarcane green harvest management influencing soil phosphorus fractions

Few researchers have evaluated phosphorus (P) fractions in soils from humid tropical regions in which sugarcane (Saccharum spp) is harvested without prior burning. Aiming to evaluate if that practice may promote substantial changes in the availability of soil P, we analyzed the differences in total P, organic P (Po), and extractable inorganic P (Pi) fractions in soil samples collected from an Oxisol. A long-term (14 years) randomized block design was employed with six replicates and two treatments: green-harvest (GH) and burned-harvest (BH) in a sugarcane plantation. Soil samples, with six replicates, were collected at depths of 0–0.05 m, 0.05–0.1 m, 0.1–0.2 m, 0.2–0.3 m, and 0.3–0.4 m from the planting row, 0.25 m perpendicular to the row, and in the inter-row. The total Po fraction had the greatest variation between the GH and BH systems. Total Po concentration was lower in the 0–0.05 m soil layer of the GH system than that of the BH system. Total Po had also accumulated in the 0.2–0.3 m layer, which is where P fertilizer was applied at planting. These differences were observed in the planting row and 0.25 m from the planting row, but not in the inter-row. There was also no relationship between Pi fractions and row position or sampling depth in the two harvest systems. Long-term GH management rather than conventional BH sugarcane promoted greater cycling of Po in the soil, while concentrations of Pi fractions did not differ between harvest systems.

An assessment of various pools of organic phosphorus distributed in soil aggregates as affected by long‐term P fertilization regimes

AbstractThe phosphorus (P) forms in long‐term fertilization determine the fate and transport of P in soil. However, the fate of various pools of organic P of added P in the long‐term measured with sequential chemical fractionation is not well‐understood. Four soil physical aggregates (&gt;250, 125–250, 63–125 and &lt;63 μm) from 0‐ to 20‐cm depth after 35 years of long‐term fertilization treatments including control (CK), nitrogen and phosphorus fertilizer (NP) and NP combined with farmyard manure (NPM) under continuous winter wheat were separated using settling tube apparatus. Results showed that the application of long‐term P fertilization had no apparent effects on promoting the mass proportion of soil aggregates except for &gt;250 μm, where the NP and NPM treatments significantly increased the mass proportion by 60% and 70% over CK, respectively. Compared with CK, P fertilizer (NP and NPM) treatments significantly increased organic P (Po) contents in each size aggregate. In particular, mean labile Po increased by 35% and 246%, moderately labile Po by 125% and 161%, nonlabile Po by 105% and 170% and total Po (TPo) by 101% and 178%, respectively, under NP and NPM treatments, respectively. There was a significant correlation between soil organic carbon (SOC) and Po fractions. SOC was exponentially positively correlated with labile Po but linearly positively correlated with moderately labile Po, nonlabile Po and TPo fractions among soil aggregates. A reduced C:Po ratio (&lt;100) in soil aggregates among treatment indicates a large amount of available P accumulated in soils, and soil P loss risk in the study site is still high. Our results show that the Po pool measured by sequential chemical fractionation may represent an important, yet often overlooked, source of P in agriculture ecosystems. According to the result, long‐term mineral P fertilizer combined with organic amendments better sustains soil structural stability in large aggregates, contributing more Po availability in the moderately labile P followed by labile P in soil aggregates.

Environmental and energy impacts of battery electric and conventional vehicles: A study in Sweden under recycling scenarios

Electromobility is the future main system for Swedish road transport that encourage sustainable urban transportation. However, emission impacts of applying electric vehicles (EVs) are currently controversial. This study evaluates and compares internal combustion engine vehicles (ICEVs) refer to both petrol and diesel-based engines and BEVs, focusing on environmental and energy impacts. The entire life cycle of vehicles production, fuel production and fuel use are considered and life cycle emissions impacts due to various electricity generation alternatives will be studied. LCA of BEV is also conducted under different recycling scenarios to determine what extent CO2 can be further reduced owing to car and battery recycling. The results show that BEVs charged by natural-gas, and renewable electricity produce less emissions of CO2, SO2, PM, VOCs, NOX and Sb than ICEVs but higher PO4 emissions and need more energy. The largest fraction of CO2 emissions for BEVs charged via renewable electricity is due to vehicle production (61-78% of BEV's life cycle CO2 emissions). CO2 emissions regarding to vehicle production for BEVs is 14.6 ton (60.8 gCO2/km) which is 132% and 123% of that for petrol and diesel ICEVs, respectively. Human toxicity and eutrophication impacts highlight as potentially important categories for transition from ICEVs to BEVs due to high toxicity and PO4 emissions in BEV production. By applying high scenario for car and battery recycling, CO2 emissions in BEVs lifespan charged by renewable electricity can be reduced 50% (83 gCO2/km); total PO4 emissions can be also decreased 56% with production of 79 mgPO4/km.

Response of soil phosphorus fractions to land use change in the subalpine ecosystems of Southeast margin of Qinghai-Tibet Plateau, Southwest China

Land use change has a significant effect on soil nutrient cycling. However, data on soil phosphorus (P) fractions following land use change are scarce, especially in the subalpine ecosystem of China. Here, we investigated the influence of land use change on soil P fractions in the subalpine ecosystem of the Southeast margin of Qinghai-Tibet Plateau, Southwest China. In total, we took 168 soil samples from four land use types, including natural forest (NF), artificial forest (AF), farmland (FL), and shrubland (SL), at a depth of 0–20 and 20–40 cm. Phosphorus fractions were determined using Hedley fractionation procedures. The results showed that land use change and soil depths had a significant impact on the status of P fractions (p≤0.05). Organic P (Po) fraction significantly decreased following land use change but varied among land use types. Farmland soils showed the highest losses of Po fractions ranging from 23 to 54%, due to organic material reduction. Total P also decreased by 9.63% after the conversion of NF to AF (p≤0.05). Conversely, total P and inorganic P (Pi) fractions were significantly higher in FL soil than in other land uses (p≤0.05), likely due to the application of chemical fertilizers. Organic P extracted by NaOH was the dominant total Po fraction in all land uses, accounting for 63.3 to 73.14% of total Po, while Pi extracted by HCl was the dominant Pi fraction in FL soil, accounting for 42.74% of total P. Soil moisture content, pH, soil organic carbon (SOC), total nitrogen (total N), and calcium were key soil properties governing soil P fractions. Organic P fractions were strongly positively correlated with SOC and total N, implying that soil organic matter (SOM) plays a vital role in maintaining the soil P reserves. Generally, our findings shed light on how land use changes significantly affected P fractions. This result may have substantial implications for soil P management to maintain soil P reserves by reducing SOM losses.

Biogeochemical dynamics of particulate organic phosphorus and its potential environmental implication in a typical “algae-type” eutrophic lake

Organic phosphorus (Po) plays a very important role in the process of lake eutrophication, but there is still a lack of knowledge about the internal cycle of Po in suspended particulate matter (SPM) dominated by algal debris. In this study, the characterization of bioavailable Po by sequential extraction and enzymatic hydrolysis showed that 45% of extracted TP was Po in SPM of Lake Dianchi, and 43–98% of total Po in H2O, NaHCO3 and NaOH fractions was enzymatically hydrolyzable Po (EHP, H2O−EHP: 31–53%). Importantly, labile monoester P was the main organic form (68%) of EHP, and its potential bioavailability was higher than that of diester P and phytate-like P. According to the estimation of P pools in SPM of the whole lake, the total load of Pi plus EHP in the H2O extract of SPM was 74.9 t and had great potential risk to enhance eutrophication in the lake water environment. Accordingly, reducing the amount of SPM in the water during the algal blooming period is likely to be a necessary measure that can successfully interfere with or block the continuous stress of unhealthy levels of P on the aquatic ecosystem.

Phosphorus Stock Depletion and Soil C:N:P Stoichiometry Under Annual Crop Rotations and Grassland Management Systems Over 13 Years

Phosphorus (P) nutrition is essential to both plant yield and soil organic matter (SOM) input. However, continuous extraction of P by plants and biomass harvesting can lead to soil P stock depletion, a reduction in crop yields and ultimately a reduction in organic matter input to the soil. In this work, we analysed P, C and N stock trends in the 0-30 cm topsoil layer cultivated with permanent cropland (CC) and mowed permanent grassland (GG) for 13 years. In addition, we characterized the changes in P organic forms by using 31P-NMR. The results showed that the amount of P exported within 13 years was 10% greater in GG than in CC (295 and 268 kg ha-1, respectively). The total P stocks decreased under both the CC and GG management systems (0.30 and 0.25 Mg ha-1, respectively). This depletion was mainly observed in total Pi forms, which recorded reductions of 0.75 and 0.29 Mg ha-1 in GG and CC, respectively. The total Po stock increased by 42.6% in GG; these results were consistent with the increase in C and N stocks in GG (2.6 and 0.19 Mg ha-1, respectively) and their reduction in CC (-4.2 and -0.38 Mg ha-1, respectively). Although P depletion mainly affected the P pool presenting the highest lability (labile P), this depletion did not have a negative effect on plant yield after 13 years due to the buffering capacity of P pools presenting less lability (moderately labile P). Mowing permanent grasslands led to a change in the pool of labile P from inorganic to organic forms and an increase in soil C and N stocks. Based on the 31P-NMR technique, permanent grasslands significantly reduced α-glycerophosphate and increased myo-IHP and adenosine monophosphate more than the permanent cropland. Although there was no significant decrease in productivity, the depletion of available P should be monitored over time, especially in mown permanent grassland crops, to prevent potential nutrient stress.

Microorganisms drive stabilization and accumulation of organic phosphorus: An incubation experiment

At the earliest stage of pedogenesis, microorganisms are the main biological drivers of nutrient transformation and mobilization from rock minerals. However, this driving process is not yet well understood despite its importance for the formation and fertility of soil. The aim of this study was to determine the microbial accumulation of organic phosphorus (Po) and microbial release of bioavailable phosphorus (bio-P) from rock minerals and to analyse which factors control these processes. We hypothesized that microorganisms contribute to stabilization and accumulation of Po. For this purpose, we carried out a series of incubation experiments with model soils (with soil Po removed) and soil extracts of natural soil from the earliest stage of pedogenesis in the newest retreat area of the Hailuogou glacier. A modified Hedley fractionation method was used to characterize the P forms in soils. Microbial synthesis of Po was clearly observed in this study. In view of the fact that carbon (C) and nitrogen (N) are the main energy and material sources of microorganisms and that their stoichiometry plays an important role in microbial metabolism, we hypothesized that the C and N (ratio and level) play a regulatory role in microbial transformation of P. Therefore, the different C/N gradients were constructed in our incubation experiments. Results showed addition of C and N resulted in an accumulation of stable Po and decrease in pH in soils. These results suggest that not all microbial biomass P is easily degraded. Along two C/N ratio gradients (same ratio but keeping C vs N constant), opposite patterns of total Po (TPo) changes was observed. Opposite patterns were also observed for bio-P along the two C/N ratio gradients. Regardless of the C/N ratio, high CN additions always led to lower TPo accumulations, higher bio-P releases and higher phosphatase activity compared to low CN additions. We conclude that microbial synthesis of Po contributed to the P fractions in soil stable residual pools and that microbial release of bioavailable P was driven by two modes (i.e., N-driven mode and C-driven mode). Our study highlights that microorganisms drive the accumulation of soil Po during the earliest stage of pedogenesis in our study area.

Study of the effect of agricultural and domestic pollutants on the water quality of the Diyala River in Iraq

This study was conducted to assess the effects of agriculture and domestic pollutant on the quality of the Diyala River. Water samples and fish samples were taken bimonthly at three stations in Diyala River and18 parameters (air and water temperature, TDS, dissolved oxygen, BOD, pH, EC, No2, NO3, total PO4, heavy metals (Cd, Pb, Al) in water and heavy metals (Cd, Pb, Al) in fish sample) were analyzed. The river has a total length of 574 km and a drainage area of which 25% is in Iran and 75% is in Iraq, Results of the study indicated that the Diayla River is more polluted and this is confirmed by Physico-chemical properties, as well as the carp fish was one of the most local fish sensitive to water pollution, especially heavy metals (HMs). The model gave a good idea to assess the water quality of the Diyala River under the effect of dryness and large quantities of pollutants on it.

Partial substitution of chemical fertilizers with manure alters soil phosphorus fractions and optimizes vegetable production in alkaline soil

ABSTRACT Maintaining phosphorus (P) supply for plants or reducing P mobility is critical to sustainable agricultural production and the environment. However, substituting long-term chemical fertilizer with a fraction of (i.e. partial substitution) manure and its effect on soil P surplus and P fractionation have not been widely studied. An eight-year protected field study with no fertilization (NF), chemical fertilizer substituted with no manure (NS), partial manure (40%, PS), and total manure (100%, TS) combined with multiple P characterization methods were conducted to examine P pools and stability in alkaline soil. NS, PS, and TS have the same input amount of nutrients. It showed that PS treatment lowered the annual P surplus by 6.21% and 11.2% compared with NS and TS, respectively, maintaining optimal P input–output balance and vegetable yields. TS decreased total Po by 31.9% and stable Ca-associated P by 21.1%, while increased labile organic P, compared with NS. The labile P in PS was at a moderate level compared with NS and TS treatments, which not only maintained the soil labile P pools but also reduced P leaching risk. Therefore, partial substitution of chemical fertilizer with manure leads to an optimal level of nutrients for vegetable production.

Application of alginate immobilized microalgae in treating real food industrial wastewater and design of annular photobioreactor: A proof-of-concept study

Microalgae immobilization was widely studied to address the challenge of algal cells harvesting, however, its stability and efficiency in treating real food industrial wastewater has not been well studied. In this study, microalgae were co-immobilized with sludge bacteria in alginate beads for treatment of real meat processing wastewater and an annular photobioreactor was designed to facilitate efficient light transmission at high beads-to-wastewater ratios. Results showed that increasing alginate mixture from 1.25% to 2.00% (w/v) extended beads stability in real wastewater from three to seven days. When beads were suspended in wastewater the overshading effect at beads-to-wastewater ratio of 20% (v/v) was significant and average algal growth (0.17 mg/bead) was lower than 2% (0.46 mg/bead) and 5% (0.36 mg/bead). Nevertheless, the ratio of 20% (v/v) was preferred as the higher beads count may compensate the disadvantage, however, the light transmission efficiency needed to be improved. The effect of environmental temperature indicated that at 37 °C beads started rupturing after three-days treatment due to the excessive growth of immobilized microorganisms. In comparison with suspended photobioreactor, in improved annular photobioreactor algal growth increased from 1412.6 to 3191.0 mg/L and removal of chemical oxygen demand (COD) and total nitrogen (TN) were improved from 78.5 to 82.9% and from 68.5 to 84.4% respectively with 89.4% total phosphate (PO43−) being removed. By the end of treatment, 135.9 mg/L TN and 99.2 mg/L total PO43− were removed and it was speculated that most of nitrogen and phosphorus were removed by algal assimilation rather than the physical adsorption of alginate gel. Findings of this study provided directions for the application of immobilized microalgae in the real world.

Surface reactivity of the natural metal (hydr)oxides in weathered tropical soils

Assessing the surface reactivity of metal (hydr)oxides in soils is essential for quantifying ion adsorption phenomena that control the availability of nutrients and pollutants. Despite the high natural abundance of Fe and Al (hydr)oxides in intensively weathered environments, the surface reactivity of these pedogenic materials has not been consistently characterized for weathered tropical soils. Here, we used a novel probe-ion methodology combined with state-of-the-art surface complexation modelling (SCM) to derive the reactive surface area (RSA) of the soils, as well as the amount of phosphate (PO4) that can be potentially desorbed (R-PO4) from the natural fraction of metal (hydr)oxides and thereby controlling the solid-solution partitioning of PO4. We applied this methodology to a series of weathered topsoils from the sub-Saharan region. The results showed that nanocrystalline ferrihydrite (Fh) is a better proxy than well-crystallized goethite for describing with SCM the reactivity of the natural metal (hydr)oxides, even though well-crystallized materials dominate the mass fraction of metal (hydr)oxides of these weathered tropical soils. Using Fh as a proxy in the SCM, the RSA ranged from ∼2 to 40 m2 g−1 soil. Nanoparticles with a mean diameter of ∼1.5–5.0 nm dominate the reactive fraction of metal (hydr)oxides in these tropical topsoils. Our SCM in conjunction with soil extractions indicates that only a fraction of the total PO4 associated with the metal (hydr)oxides is reversibly adsorbed, whereas the majority of the total PO4 pool, on average ∼64%, is occluded in the crystalline Fe and Al (hydr)oxide fraction. Only this smaller reversibly adsorbed fraction is thus available for participating in sorption reactions that determine the solid-solution partitioning of PO4. Overall, this research provides new insights into the reactivity of the metal (hydr)oxide fraction in weathered tropical soils and highlights the relevance of these pedogenic materials in determining the speciation and availability of PO4.