Exogenous Phosphorus Research Articles

Immobilization of Phosphorus in Sediment-Water System by Active Capping Plate Under Exogenous Phosphorus Input

Immobilization of Phosphorus in Sediment-Water System by Active Capping Plate Under Exogenous Phosphorus Input

Toward the development of an ecosystem model ensemble to support adaptive management in Lake Ontario

Notwithstanding the continuing advancement of our understanding of the broader ecosystem functioning in Lake Ontario, emerging evidence suggests that there are fundamental knowledge gaps to accurately describe the relationship between exogenous phosphorus (P) loading and in-lake total phosphorus (TP) concentrations. The whole-lake load appears to frequently exceed the Great Lakes Water Quality Agreement (GLWQA) interim target of 7000 metric tonnes·year−1, although the offshore-water P concentrations are consistently below the GLWQA interim substance concentration objective of 10 µg TP·L–1. Contrasting ecological conditions prevail in different locations of Lake Ontario, owing to the significant urban footprint along the shoreline but also the capacity of dreissenid mussels to sequester P in the littoral zone. Specifically, low ambient P levels threaten fisheries productivity in offshore waters, while nuisance benthic algae (predominantly Cladophora) and toxin-producing cyanobacteria blooms affect the water quality in the nearshore zone. The present study offers a technical analysis of the recent and ongoing modelling work that has been conducted in Lake Ontario and can be potentially used to address the multitude of ecosystem management challenges. Our aim is to provide an overview of all the major models developed by identifying their fundamental assumptions, structural attributes, and general consistency against empirical knowledge derived from the system. The existing modelling work has opted for parsimonious representations of the lower food web coupled with granular grid configurations to effectively link hydrodynamic processes and mass transport between nearshore and offshore waters. The establishment of comprehensive ecophysiological modules that will recreate the mechanisms underlying the interplay among bioavailable phosphorus, planktonic dynamics, dreissenid mussels, and Cladophora is a critical undertaking to reproduce the water quality conditions in the nearshore zone of Lake Ontario. Striving to integrate the lower food web with fisheries and ecosystem-service modelling, we also offer a technical analysis of knowledge gaps and monitoring-assessment objectives that should be addressed to ensure that ecosystem processes of management interest are adequately measured and the local modelling enterprise is focused on suitable performance indicators.

New insight into identifying sediment phosphorus sources in multi-source polluted urban river: Effect of environmental-induced microbial community succession on stability of microbial source tracking results

Identifying sediment phosphorus sources, the key to control eutrophication, is hindered in multi-source polluted urban rivers by the lack of appropriate methods and data resolution. Community-based microbial source tracking (MST) offers new insight, but the bacterial communities could be affected by environmental fluctuations during the migration with sediments, which might induce instability of MST results. Therefore, the effects of environmental-induced community succession on the stability of MST were compared in this study. Liangxi River, a highly eutrophic urban river, was selected as the study area where sediment phosphorus sources are difficult to track because of multi-source pollution and complicated hydrodynamic conditions. Spearman correlation analysis (P < 0.05) was conducted to recognize a close relationship between sediment, bacterial communities and phosphorus, verifying the feasibility of MST for identify sediment phosphorus sources. Two distinct microbial community fingerprints were constructed based on whether excluded 113 vulnerable species, which were identified by analyzing the differences of microorganisms across a concentration gradient of exogenous phosphorus input in microbial environmental response experiment. Because of the lower unknown proportion and relative standard deviations, MST results were more stable and reliable when based on the fingerprints excluding species vulnerable to phosphorus. This study presents a novel insight on how to identify sediment phosphorus sources in multi-source polluted urban river, and would help to develop preferential control strategies for eutrophication management.

Methane flux at the water-gas interface is influenced by complex interactions among phytoplankton, phosphorus inputs and methane-functional bacteria: A microcosm systems study

Phytoplankton affect carbon cycling and emissions in eutrophic reservoirs dramatically, but our knowledge about carbon emissions response to phytoplankton bloom and phosphorus enrichment is rather limited. Here we performed a microcosm experiment with five treatments to investigate how phytoplankton blooms and phosphorus addition will impact the carbon emissions and the methane-functional bacterial community. During the 43-day incubation, the CH4 and CO2 flux at the water-air interface in the five water columns fluctuated between 7.536 and 16.689 μmol and between 2788.501 and 4142.726 μmol, respectively. The flux of CH4 and CO2 during phytoplankton decay was 1.542 to 10.397 times and 4.203 to 8.622 times higher, respectively, compared to that during phytoplankton growth. Furthermore, exogenous phosphorus increases bloom biomass of phytoplankton and subsequent CH4 production, even with low nitrogen concentrations. The addition of 1 mg KH2PO4 resulted in a conservative increase of 0.0715 μmol in CH4 emission and 11.911 μmol in CO2 emission in the water column, respectively, compared to the in-situ water column. High throughput sequencing determined that hydrogenotrophic Methanoregula dominated methanogens (MPB) and Methylocystaceae dominated methanotrophs (MOB) in the sediment. Phosphorus inhibited the relative abundance of Methanoregula after incubation, resulting in a significant decrease. Real-time quantitative polymerase chain reaction indicated that the absolute abundance of MPB and MOB (i.e., the mcrA gene and the pmoA gene) in the sediments ranged from 5.1354E+06 to 6.3176E+07 copies·g−1 and 1.1656E+06 to 9.5056E+06 copies·g−1, respectively. The mcrA gene showed a preference for sediments with high organic carbon content. The effect of eutrophication on CH4 emissions is closely related to nutrient load and distinct niche of methane-functional bacteria.

The impacts of exogenous phosphorus on Cd absorption in perennial ryegrass root cell: Kinetic and mechanism study

Phosphorus (P) is critical to plants in metal-contaminated soils because it participates in various biochemical reactions during plant growth. However, the mechanisms of P in mitigating the toxicity of heavy metals to ryegrass root is still veiled. In this study, the physiological and biochemical dynamics of the ryegrass root under various cadmium (Cd) and P conditions were investigated in a hydroponic system. Cd stress decreased the length of the ryegrass root, but P application enhanced the root elongation to reduce the Cd concentration in the root. Both Cd and P dosages were positively correlated with hemicellulose 1 content, pectin content, and PME activity, while having a negative effect on cellulose content. Moreover, the addition of 80 mg L−1 P increased the contents of pectin and hemicellulose 1 by 2.5 and 5.8% even with 4 mg L−1 Cd. In addition, P supply increased pectin methylesterbase activity under Cd stress, which further changed the extra-cytoplasmic structures and cell wall composition. Thus, exogenous P promoted the immobilization of Cd onto the cell wall and protected protoplast primarily through indirectly regulating the binding capacity of the root cell wall for Cd.

Invasive and Native Plants Differentially Respond to Exogenous Phosphorus Addition in Root Growth and Nutrition Regulated by Arbuscular Mycorrhizal Fungi.

Plant invasion has severely damaged ecosystem stability and species diversity worldwide. The cooperation between arbuscular mycorrhizal fungi (AMF) and plant roots is often affected by changes in the external environment. Exogenous phosphorus (P) addition can alter the root absorption of soil resources, thus regulating the root growth and development of exotic and native plants. However, it remains unclear how exogenous P addition regulates the root growth and development of exotic and native plants mediated by AMF, affecting the exotic plant invasion. In this experiment, the invasive plant Eupatorium adenophorum and native plant Eupatorium lindleyanum were selected and cultured under intraspecific (Intra-) competition and interspecific (Inter-) competition conditions, involving inoculation with (M+) and without AMF (M-) and three different levels of P addition including no addition (P0), addition with 15 mg P kg-1 soil (P15), and addition with 25 mg P kg-1 soil (P25) for the two species. Root traits of the two species were analyzed to study the response of the two species' roots to AMF inoculation and P addition. The results showed that AMF significantly promoted the root biomass, length, surface area, volume, tips, branching points, and carbon (C), nitrogen (N), and P accumulation of the two species. Under M+ treatment, the Inter- competition decreased the root growth and nutrient accumulation of invasive E. adenophorum but increased the root growth and nutrient accumulation of native E. lindleyanum relative to the Intra- competition. Meanwhile, the exotic and native plants responded differently to P addition, exhibiting root growth and nutrient accumulation of invasive E. adenophorum increased with P addition, whereas native E. lindleyanum reduced with P addition. Further, the root growth and nutrition accumulation of native E. lindleyanum were higher than invasive E. adenophorum under Inter- competition. In conclusion, exogenous P addition promoted the invasive plant but reduced the native plant in root growth and nutrient accumulation regulated by AMF, although the native plant outcompeted the invasive plant when the two species competed. The findings provide a critical perspective that the anthropogenic P fertilizer addition might potentially contribute to the successful invasion of exotic plants.

Phosphorus release characterization of biochar loaded with inherent and exogenous phosphorus and impact on soil Pb immobilization

Phosphorus release characterization of biochar loaded with inherent and exogenous phosphorus and impact on soil Pb immobilization

The Impacts of Phosphorus-Containing Compounds on Soil Microorganisms of Rice Rhizosphere Contaminated by Lead

The cost effectiveness of using exogenous phosphorus to remediate heavy metals in soil, which would alter the structure of the soil microbial community, had been widely acknowledged. In the present study, phospholipid fatty acid (PLFA) technology was taken as the breakthrough point, and rhizosphere soil microorganisms in different growth stages (jointing stage and maturity stage) of Minghui 86 (MH) and Yangdao No.6 (YD) rice were taken as the research objects. As revealed by the results, the rhizosphere soil microorganisms of MH and YD had distinct sensitivities to exogenous phosphorus and had a certain inhibitory effect on MH and YD enhancement. The sensitivity of rice root soil microorganisms to exogenous phosphorus also varied in different growth stages of rice. Bacteria were the dominant microorganism in the soil microbial community of rice roots, and the gain of exogenous phosphorus had a certain impact on the structure of the two soil microbial communities. Through analysis of the microbial community characteristics of MH rice and YD soil after adding exogenous phosphorus, further understanding was attained with respect to the effect of exogenous phosphorus on the microbial community characteristics of rice rhizosphere soil and the impact thereof on ecological functions.

Nutrient Accumulation During Vegetative and Reproductive Growth Affected by Endogenous and Exogenous Phosphorus Applications in Maize Crop

ABSTRACT Although maize (Zea mays L.) crop has high production potential for forage and grain, however it requires efficient managerial practices for optimum yield. Adequate nutrients for optimum growth led to good vegetative and reproductive growth. Field studies were conducted to evaluate the effects of two endogenous seed phosphorus (P); i.e. SLP: seed with low endogenous phosphorus (1.5 mg kg −1 seed dry weight), and SHP: seed with high endogenous phosphorus (3.2 mg kg −1 seed dry weight). Pre-categorized seeds were tested against five rates of exogenous soil P, namely, (1) control: no P (0 kg P ha −1); (2) 50 kg P ha −1; (3) 100 kg P ha −1; (4) 150 kg P ha −1; and (5) 200 kg P ha −1. Seeds having different P contents depicted non-prominent effects on accumulation patterns with few exceptions of P (at physiological maturity (R6) and of potassium (K) (at grain filling (R4) and R6); exogenous P expressed significant effects. Nitrogen (N), P, K, zinc (Zn), and boron (B) exhibited differential accumulation behavior during maize growth. Nitrogen expressed accumulation from tasseling (VT) to R4; however, P, K, Zn, and B depicted remobilization from VT to R6. Maximum accumulation efficiency of P (50.7%), Zn (46.9%), and B (51.4%) was observed from VT to R4 growth, whereas maximum response of K (60.3%) and N (21.8%) was witnessed from R4 to R6, representing variant source-sink capacities. Boron depicted greater remobilization under low exogenous P applications. Results suggest that exogenous P application severely affects nutrient accumulation during pre- and post-grain filling growth.

Hyperphosphatemia: A Clue to Diagnosis

Serum phosphate level reference range in adults is 2.5 mg/dL to 4.5 mg/dL and in children is 3 mg/dL to 6 mg/dL. The causes of hyperphosphatemia fall into four categories. These are decreased renal excretion of phosphorus, exogenous phosphorus administration, redistribution of phosphorus, and pseudohyperphosphatemia. We report a 69-year-old gentleman presented with the history of swelling of feet and facial puffiness of 1 month duration. He had renal failure with normal sized kidneys. Serum phosphorus was high. Advanced investigations revealed plasma cell proliferative disorder (clonal bone marrow plasma cells &gt;10%) on bone marrow examination, presence of M band at the junction of beta-2 and gamma region, and elevated serum IgG and serum beta-2 microglobulin. Hyperphosphatemia in multiple myeloma may be true, or pseudohyperphosphatemia. Diligent history, examination, and investigations have yielded the possibility of pseudohyperphosphatemia owing to multiple myeloma in our patient. The interference with the phosphomolybdate ultraviolet assay for serum phosphorus estimation is one of the reasons of pseudohyperphosphatemia in multiple myeloma. The other mechanism of pseudohyperphosphatemia could be the direct binding of paraprotein to phosphorus.

Advances in researches on phosphorous inactivation materials in lake sediment

通常认为，磷是湖泊富营养化的主要限制因子，因此控制湖泊磷浓度和水平被认为是湖泊治理的关键.在外源磷输入得到有效控制之后，湖泊富营养化仍可持续几十年，这主要归咎于内源磷的释放.底泥原位化学钝化控磷技术因其操作性强、控磷效果明显，而被广泛作为湖泊内源磷的控制技术之一，而钝化材料的研发和应用是本项技术的核心.在世界范围内，研发了众多的用于底泥磷控制的钝化修复材料.本文主要梳理了国际上常用钝化材料的基本特性与研究近况，点明不同材料之间钝化效果的差异，并讨论了不同类型钝化材料的改性方法、钝化机制，分析不同环境因子对钝化材料稳定性的影响.论文最后探讨了原位化学钝化控磷技术与其他修复技术联用的污染控制效果及其可行性，并根据国际上钝化控磷技术的主要研究进展，提出钝化材料现阶段存在的不足，并对未来研究方向与应用前景进行展望.;It is generally believed that phosphorus is the main limiting factor of eutrophication, so controlling the concentration of phosphorus is considered to be the key to lake management. Lake eutrophication could continue for decades after the effective control of exogenous phosphorus input, due to the release of endogenous phosphorus from lake sediment. The technology of in-situ chemical inactivation of sediment is widely used as one of the control technologies of endogenous phosphorus in lakes because of its strong operability and obvious effect of inactivating phosphorus. The development and application of inactivation materials are the cores of this technology. Many phosphorous inactivation materials have been developed around the world. This paper reviews the research on phosphorus inactivation materials in lake sediment, including the following aspect:(1) The basic characteristics and research status of inactivation materials commonly used; (2) The differences of inactivation effect between different materials; (3) The modification methods and inactivation mechanisms of different types of inactivation materials; (4) The effects of different environmental factors on the stability of inactivation materials; (5) The effect of pollution control and feasibility of the technology of in-situ chemical inactivation combined with other remediation technologies. According to the main research progress of the technology of phosphorus inactivation, the shortcomings of inactivation materials at present are put forward, and the future research direction and application prospect are expected.

Effects of phosphorus fertilizer on kernel phytic acid and zinc bioavailability in sweet corn

<p id="C3">To clarify the effects of phosphorus fertilizer on nutritional characteristics of sweet corn kernels, the temporal (different filling stages) and spatial (upper, middle, and lower cob; kernel skin dregs, endosperm and embryo) variations of phytic acid (PA), phosphorus (P) and zinc (Zn) contents and Zn bioavailability of sweet corn kernels and their responses to exogenous phosphorus fertilizer were investigated using filed phosphorus fertilizer experiment (P fertilizer location experiment for sweet corn genotypes and P fertilizer level experiment). The results were as follows: P fertilizer mainly inhibited Zn bioavailability by suppressing Zn concentration in sweet corn kernels, and increased PA concentrations concurrently. P fertilizer input showed significant effects on the accumulation of PA, P, and Zn (mg plant^-1) after 16-24 days of silking, while inhibitory effects were detected on Zn bioavailability at different kernel filling stages. There was no significant difference in the kernel of PA (g kg^-1) and zinc bioavailability among different cob positions under medium P treatment. However, the high P level significantly improved the accumulation of PA in the middle and lower cob, while the inhibitory effect was found on the kernel of Zn concentration and Zn bioavailability at all cob positions. Among different parts of the kernel (skin dregs, endosperm, and embryo), the concentrations of PA, P, and Zn were the highest values in the embryo and their accumulation were the highest value in the endosperm, while Zn bioavailability was also the highest in the embryo. High P treatment significantly increased PA and P concentrations and decreased Zn concentration and its bioavailability at different kernel positions. Hence, optimized phosphorus fertilizer application could promote kernel Zn accumulation, while excessive P fertilizer input significantly increased PA accumulation at different filling stages, as well as in the endosperm and embryo, and eventually had a significant inhibitory effect on kernel Zn bioavailability in sweet corn at different cob and kernel positions. This study provides a theoretical reference for the biofortification of Zn in sweet corn seeds.

Cadmium Phytoextraction Potential of Ricinus communis Significantly Increased with Exogenous Application of Growth Regulators and Macronutrients

ABSTRACT Phytoremediation has emerged as promising technology for reclamation of metal-polluted sites. The present study was conducted with an aim to assess the hyperaccumulation potential of Ricinus communis for cadmium, with the application of exogenous substances, [nitrogen (N), phosphorus (P) and potassium (K)] and phytohormones [Gibberellic acid (GA3) and Indole acetic acid (IAA)]. These were applied to increase plant biomass, improve phytoextraction of Cd and its accumulation in aerial parts, with generation of endogenous proline and phenols in R. communis, grown in soil contaminated with 100 mg Cd/Kg. Plant hormones were used only as foliar spray while growth regulators were applied to soil and also used as foliar spray. T4 (Cd+NPK AS) significantly increased root length, T12 (GA3+ NPK FS) highly increased stem length and leaf length as compared to control C1 (plant only Cd). FBM was highly increased by N alone or in combination with P, K, and GA3 foliar sprayed in R. communis. Conclusively, it was found that NPK (foliar) in combination with GA3 followed by N and IAA, significantly increased biomass, Cd concentration and accumulation in all the treated plants of R. communis. Cadmium bio-concentration values for R. communis were higher than unity (1) i.e. ± 2.54. Highest significant concentration of phenolic and proline in R. communis were recorded in combination treatments of GA3 and NPK foliar spray while in other plants in NPK addition into soil treatment. Thus, R. communis has the natural potential as hyperaccumulator and further study is required for its industrial implementation in polluted soil.

Effect of phosphorus supplementation on growth, nutrient uptake, physiological responses, and cadmium absorption by tall fescue (Festuca arundinacea Schreb.) exposed to cadmium

Cadmium is a common heavy metal pollutant. In some plants, its absorption is inhibited by exogenous phosphorus. Here, the effect of P supplementation on the growth of tall fescue exposed to Cd was evaluated in a hydroponic culture experiment. Plants were exposed to five concentrations of P (0, 0.25, 0.5, 0.75, and 1.0 mmol L-1) and three concentrations of Cd (50, 100, and 150 mg L-1), and plant growth, Cd content, absorption, physiological characteristics, and nutrient accumulation were investigated. P supplementation significantly reduced the Cd content, Cd translocation factor(TF), Cd removal efficiency, plant P absorption, chlorophyll content, glutathione levels, glutathione reductase levels, and superoxide dismutase (SOD) activity in tall fescue under Cd stress (P < 0.05). Moreover, it increased the vertical growth rate and biomass of tall fescue. At a constant P concentration, the biomass and vertical growth rate significantly decreased with an increasing Cd concentration, and the shoot Cd content, SOD activity, and TF significantly increased (P < 0.05). High P supplementation (0.75 and 1.0 mmol L-1) ameliorated the damage caused by 150 mg L–1 Cd stress, and the biomass, vertical shoot and vertical root growth rates were increased by 72.06–82.06%, 250.00–316.67%, 300.00–312.00%, respectively. In the plants subjected to 50 mg L–1 Cd stress, 0.5 mmol L-1 P supplementation enhanced biomass, vertical shoot and vertical root growth rates by 29.99%, 20.41%, and 21.43%, respectively, and reduced the Cd content in shoots (45.85%) and roots (9.71%). Except for the total potassium content and catalase activity, different concentrations of Cd negatively affected all parameters tested. Such negative effects were limited by P supplementation. Optimizing the nutrient composition and concentrations could minimize the potential negative impacts of Cd on plant growth.

Effects of Exogenous Phosphorus on Rice Growth and Cadmium Accumulation and Transportation Under Cadmium Stress

In this study, we investigated the effects of exogenous phosphorus on the accumulation and transportation of cadmium in rice plants through a hydroponic experiment. In the experiment, the rice variety was Huanghuazhan, P solution concentrations were 10.0-45.0 mg ·L-1 that was made using NaH2PO4, and Cd solution concentrations were 0.1 mg ·L-1 and 0.2 mg ·L-1. The results showed that: ① the biomass in all parts of rice plants and contents of photosynthetic pigment (chlorophyll a, chlorophyll b, and carotenoid) increased gradually with an increase in exogenous P. ② Content of Cd in rice stems, leaves, husk, and brown rice increased gradually with an increase in the amounts of exogenous P. The content of Cd in brown rice increased by 2.8%-22.8% and 40.9%-61.8% when treated with Cd concentrations of 0.1 mg ·L-1 and 0.2 mg ·L-1 in hydroponic solutions, respectively. ③ Cd accumulation in rice plants was accelerated due to the application of exogenous P. Cd accumulating amounts increased from 395.1 μg ·plant-1 to 542.6 μg ·plant-1 and 639.6 μg ·plant-1 to 1082.0 μg ·plant-1 when treated with Cd concentrations of 0.1 and 0.2 mg ·L-1 in hydroponic solutions, respectively. ④ With an increase in the applied amounts of exogenous P, the P/Cd quality ratio in rice roots increased, while those in rice stems, leaves, husks, and brown rice decreased; meanwhile, the Cd transfer coefficients from root to stem (TFroot-stem) and stem to leaf (TFstem-leaf) increased. This showed that there was a certain synergistic effect between P and Cd in the rice parts. Finally, the application of exogenous P promoted the transfer of Cd from the rice root to other rice tissues, resulting in a synergistic effect on Cd accumulation and transportation in various rice tissues and increased Cd contents in brown rice.

Exogenous phosphorus treatment facilitates chelation-mediated cadmium detoxification in perennial ryegrass (Lolium perenne L.)

Cadmium (Cd) is an on-going environmental pollutant associated with hindered plant growth. In response, plants possess various strategies to alleviate Cd stress, including reactive oxygen species (ROS) scavenging and chelation-mediated Cd detoxification. The present study examined the Cd defense mechanism of perennial ryegrass (Lolium perenne L.), taking into account the effect of exogenous phosphorus (P) input. It was found that despite triggering antioxidant enzyme activity, Cd stress heightened lipid peroxidation levels. Exogenous P input partially mitigated the lipid peroxidation impact and decreased the levels of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) antioxidant enzymes, revealing reduced ROS-scavenging activity. Importantly, notable relationships were determined between the amount of Cd uptake in the root and the amount of non-protein thiols (R2 = 0.914), glutathione (R2 = 0.805) and phytochelatins (R2 = 0.904) in proportion to the amount of exogenous P applied. The levels of amino acids proline and cysteine were also enhanced by exogenous P input showing their influence in alleviating Cd stress. Overall, it is reported that Cd detoxification in ryegrass plants can be stimulated by exogenous P input, which facilitates chelation-mediated Cd detoxification processes.

Exogenous phosphorus compounds interact with nitrogen availability to regulate dynamics of soil inorganic phosphorus fractions in a meadow steppe

Abstract. Here we investigated the effects of P compounds (KH2PO4 and Ca(H2PO4)2) with different addition rates of 0, 20, 40, 60, 80, and 100 kg P ha−1 yr−1 and NH4NO3 addition (0 and 100 kg N ha−1 yr−1) on soil labile inorganic phosphorus (IP) (dicalcium phosphate, Ca2-P), moderate-cycling IP, and recalcitrant IP fractions in a calcareous grassland of northeastern China. Soil moderate-cycling IP fractions, not readily available to plants but transforming into soil-available P quickly, include variscite (Al-P), strengite (Fe-P) and octacalcium phosphate (Ca8-P); recalcitrant IP fractions include hydroxylapatite (Ca10-P) and occluded P (O-P). Soil labile and moderate-cycling IP fractions and total P significantly increased with increasing P addition rates, with higher concentrations detected for KH2PO4 than for Ca(H2PO4)2 addition. Combined N and P treatments showed lower soil labile IP and moderate-cycling IP fractions compared to ambient N conditions, due to enhanced plant productivity. Moderate-cycling IP was mainly regulated by P addition and plant P uptake to further enhance labile IP and total P concentrations with KH2PO4 and Ca(H2PO4)2 addition. Soil labile IP was also directly and negatively affected by soil pH and plant P uptake with Ca(H2PO4)2 addition. Ca(H2PO4)2 addition significantly increased the soil recalcitrant IP (Ca10-P) fraction, while KH2PO4 addition showed no impact on it. A significant positive correlation was detected between soil labile IP, moderate-cycling IP fractions and soil Olsen-P which illustrated that labile IP and moderate-cycling IP fractions were important sources for soil-available P. Our results suggest that moderate-cycling IP fractions are essential for grassland P biogeochemical cycling and the chemical form of P fertilizer should be considered during fertilization management for maintaining soil-available P.

Nitrogen and phosphorus co-doped carbon networks derived from shrimp shells as an efficient oxygen reduction catalyst for microbial fuel cells

The waste shrimp shells (SS) were used as both carbon and nitrogen sources to directly synthesize N and P co-doped carbon networks with abundant mesopores and high specific surface area by simple acid pretreatment and carbonization. Using exogenous phosphorus as dopant, the prepared catalyst (PA-SS 900) favorably possessed a high oxygen reduction reaction (ORR) activity regarding half-wave potential (0.82 V) and limiting current (4.47 mA cm−2), which approached those of commercial 20 wt% Pt/C. For practical application in microbial fuel cell (MFC), the N, P co-doped PA-SS 900 achieved a maximum power density (MPD) of 802 mW m−2 and an open circuit voltage (OCV) of 653 mV, which also were close to that (892 mW m−2 and 752 mV) based on 20% Pt/C as cathode catalyst. Remarkably, the synthetic catalyst had a better long-term stability than that of 20% Pt/C in alkaline medium. These results demonstrated that N, P co-doped PA-SS 900 was an accessible and efficient ORR catalyst in air-cathode MFC for relatively desirable energy generation and wastewater treatment. Further, the direct utilization of waste shrimp shells replacing chitin or chitosan in energy conversion is worthy of in-depth study due to the advantages of simple process, environmental friendliness and availability.

Environmental significance of phosphorus existing forms in the sediments of Yuqiao Reservoir in Tianjin

研究天津于桥水库沉积物中磷形态的空间分布特征和垂直分布特征对了解水源型水库富营养化现状及其过程具有重要的现实意义.利用抓斗式采泥器及柱状采泥器分别采集表层沉积物样品及柱状沉积物样品，采用Psenner提出的连续提取法对沉积物磷形态进行分级测定，揭示整个水库沉积物各形态磷的空间分布特征以及不同区域垂直方向上的分布规律.结果表明：于桥水库表层沉积物总磷（TP）含量为303.7~997.8 mg/kg，各形态磷含量大小顺序依次为：钙结合态磷（Ca-P） > 铁结合态磷（Fe-P） > 残渣态磷（Res-P） > 铝结合态磷（Al-P） > 有机态磷（Org-P） > 可交换态磷（Ex-P）.表层沉积物中Fe-P、Al-P、Ca-P与TP含量由东至西逐渐递减，主要受到黎河河水夹带的外源性磷输入的影响；Res-P含量由东至西逐渐递增，与活性磷的分布规律相反，表明水库下游比上游的水质更好.垂直分布上，南部区域底层与表层沉积物相差不大，说明从1960s以来磷的沉积量就比较大；西部区域沉积物中Fe-P和Org-P含量较高，随深度的增加有明显降低的趋势；中心区域的各形态磷和TP含量均较低，且随着深度增加逐渐降低，现阶段沉积物中的磷以滞留为主，释放潜力较小.;It is of great significance to study the status of eutrophication and its process in water source reservoirs by analyzing the spatial and vertical distribution characteristics of phosphorus forms in the sediment of Yuqiao Reservoir in Tianjin. The samples of surface sediments and sediment cores were collected by grab-type sampler and column-type sampler, respectively, and the phosphorus forms of sediments were analyzed by continuous extraction method proposed by Psenner, in order to reveal the spatial distribution of various forms of phosphorus in the reservoir, as well as the distribution in the vertical direction of different regions. The results showed:The contents of total phosphorus in the surface sediments of Yuqiao Reservoir were 303.7-997.8 mg/kg, and the order of the mass fraction of phosphorus forms was:Ca-P > Fe-P > Res-P > Al-P > Org-P > Ex-P. The Fe-P, Al-P, Ca-P and TP in the surface sediments gradually decreased from east to west, mainly affected by the input of exogenous phosphorus entrained by the Lihe River. The Res-P is gradually increasing from east to west, contrary to the distribution of active phosphorus, indicating that the water quality in the downstream of the reservoir is better than that in the upstream. For the vertical distribution, there is little difference between the bottom sediments and the surface sediments in the southern region, which indicates that the deposition amount of phosphorus is relatively large since the 1960s; and the Fe-P and Org-P contents in the western sediments are higher, and the trend is significantly reduced as the depth increases. The various forms of phosphorus and TP contents in the central area are almost the lowest, and gradually decrease with the depth, phosphorus in the sediments at this stage is mainly retained with small release potential.

Exogenous phosphorus enhances cadmium tolerance by affecting cell wall polysaccharides in two mangrove seedlings Avicennia marina (Forsk.) Vierh and Kandelia obovata (S., L.) Yong differing in cadmium accumulation

Phosphorous (P) is an essential element that mediates various stresses in plants. In this study, the effects of P on polysaccharides in the root cell walls of two hydroponically cultivated mangrove seedlings (A. marina and K. obovata) that differ in Cd accumulation ability were examined in the context of Cd stress. The results showed that A. marina exhibited a higher degree of tolerance to Cd than K. obovata. In both mangrove seedlings, pectin and hemicellulose 1 increased significantly with increasing P levels, the effects of which were greater in A. marina under Cd stress. In addition, cell wall pectin methylesterase (PME) activity was markedly increased in the presence of Cd and P compared with Cd alone. These effects were more pronounced in A. marina than in K. obovata. Taken together, the results of this study provide further insight into the mechanisms of P-mediated alleviation of Cd stress in mangrove seedlings.