Screening of Polyphosphate Accumulating Organisms and Their Phosphorus Removal Performance

[Objectives]To study the phosphorus removal performance of phosphate accumulating organisms(PAOs).[Methods]Activated sludge from domestic sewage treatment plant was used as the strain source,and phosphate accumulating organisms were screened by plate streaking method and dilution coating plate method.Six kinds of excellent phosphate accumulating organisms were obtained by metachromatic granule staining experiment,total phosphorus experiment and simulated sewage phosphorus removal experiment to assist the observation of bac-terial morphology and experiment of phosphorus removal capacity.In addition,the influencing factors of phosphorus removal capacity(nitrogen source,trace metal ions)were analyzed.[Results]In the case of simulated sewage,the phosphorus removal rate of strain b was the highest,reaching 66.25%,while the phosphorus removal rate of strain e and f was about 10%lower than that of the phosphorus uptake experiment.[Conclusions]This study is expected to provide a theoretical reference for the gradual optimization of the screening method of phosphorus re-moval bacteria in domestic sewage treatment.

Effects of Nitrogen,Phosphorus and Potassium Application on Growth and Dry Matter Accumulation in Mulberry

In this paper, the effect of different fertilizer treatments on the main indexes of growth and development and dry matter accumulation of perennial mulberry, which is cut and pruned in summer, were studied with ‘3414’ field experiment design. The results showed that N, P, and K at proper amounts could promote mulberry growth and development, improve its dry matter content, increase its dry matter accumulation. The effects of N, P, K on leaf yield per plant were respectively expressed as follows： N2 N3 N1 N0 , P2 P1 P3 P0 , K2 K1 K3 K0 . It can be concluded that the recommended fertilizer amounts of dry matter accumulations in mulberry leaf were 694.36 kg/hm2 of N, 198.15 kg/hm2 of P, and 274.26 kg/hm2 of K and the dry matter achieved the maximum at 8 045.04 kg/hm2 . The recommended fertilizer amounts of accumulated dry matter in branch were 1 000.05 kg/hm2 of N, 242.04 kg/hm2 of P, and 218.01 kg/hm 2 of K, and the dry matter achieved the maximum at 5 969.05 kg/hm2 . The recommended fertilizer amount in young shoots were 883.76 kg/hm2 of N, 204.48 kg/hm2 of P and 426.59 kg/hm2 of K and dry matter achieved the maximum at 1 410.24 kg/hm2 . This paper could provide reference for the construction of highly-qualified mulberry field in Sichuan hilly area.

Effects of tree size and organ age on variations in carbon,nitrogen,and phosphorus stoichiometry in Pinus koraiensis

Carbon(C),nitrogen(N),and phosphorus(P)are of fundamental importance for growth and nutrient dynamics within plant organs and deserve more attention at regional to global scales.However,our knowledge of how these nutrients vary with tree size,organ age,or root order at the individual level remains limited.We determined C,N,and P contents and their stoichiometric ratios(i.e.,nutrient traits)in needles,branches,and fine roots at different organ ages(0-3-year-old needles and branches)and root orders(1st-4th order roots)from 64 Pinus koraiensis of varying size(Diameter at breast height ranged from 0.3 to 100 cm)in northeast China.Soil factors were also measured.The results show that nutrient traits were regulated by tree size,organ age,or root order rather than soil factors.At a whole-plant level,nutrient traits decreased in needles and fine roots but increased in branches with tree size.At the organ level,age or root order had a negative effect on C,N,and P and a positive effect on stoichiometric ratios.Our results demonstrate that nutrient variations are closely related to organ-specific functions and ecophysiological processes at an individual level.It is suggested that the nutrient acquisition strategy by younger trees and organ fractions with higher nutrient content is for survival.Conversely,nutrient storage strategy in older trees and organ fractions are mainly for steady growth.Our results clarified the nutrient utilization strategies during tree and organ ontogeny and suggest that tree size and organ age or root order should be simultaneously considered to understand the complexities of nutrient variations.

Phosphorus accumulation by bacteria isolated from a continuous-flow two-sludge system

In this article, polyphosphate-accumulating organisms （PAOs） from a lab-scale continuous-flow two-sludge system was isolated and identified, the different phosphorus accumulation characteristics of the isolates under anoxic and aerobic conditions were investigated. Two kinds of PAOs were both found in the anoxic zones of the two-sludge system, one of them utilized only oxygen as electron aeceptor, and the other one utilized either nitrate or oxygen as electron aeceptor. Of the total eight isolates, five isolates were capable of utilizing both nitrate and oxygen as electron acceptors to uptake phosphorus to some extent. And three of the five isolates showed good phosphorus accumulative capacities both under anoxic or aerobic conditions, two identified as Alcaligenes and one identified as Pseudomonas. Streptococcus was observed weak anoxic phosphorus accumulation because of its weak denitrification capacity, but it showed good phosphorus accumulation capacity under aerobic conditions. One isolates identified as Enterobacteriaceae was proved to be a special species of PAOs, which could only uptake small amounts of phosphorus under anoxic conditions, although its denitrification capacity and aerobic phosphorus accumulation capacity were excellent.

Long-term phosphorus accumulation and agronomic and environmtal critical phosphorus levels in Haplic Luvisol soil, northern China

Sufficient soil phosphorus （P） content is essential for achieving optimal crop yields, but accumulation of P in the soil due to excessive P applications can cause a risk of P loss and contribute to eutrophication of surface waters. Determination of a critical soil P value is fundamental for making appropriate P fertilization recommendations to ensure safety of both environment and crop production. In this study, agronomic and environmental critical P levels were determined by using linear-linear and linear-plateau models, and two segment linear model, for a maize （Zea mays L.）-winter wheat （Triticum aestivum L.） rotation system based on a 22-yr field experiment on a Haplic Luvisol soil in northern China. This study included six treatments： control （unfertilized）, no P （NoP）, application of mineral P fertilizer （MinP）, MinP plus return of maize straw （MinP＋StrP）, MinP plus low rate of farmyard swine manure （MinP＋L.Man） and MinP plus high rate of manure （MinP＋ H.Man）. Based on the two models, the mean agronomic critical levels of soil Olsen-P for optimal maize and wheat yields were 12.3 and 12.8 mg kg-1, respectively. The environmental critical P value as an indicator for P leaching was 30.6 mg Olsen-P kg-1, which was 2.4 times higher than the agronomic critical P value （on average 12.5 mg P kg-1）. It was calculated that soil OIsen-P content would reach the environmental critical P value in 41 years in the MinP treatment, but in only 5-6 years in the two manure treatments. Application of manure could significantly raise soil Olsen-P content and cause an obvious risk of P leaching. In conclusion, the threshold range of soil Olsen-P is from 12.5 to 30.6 mg P kg-1 to optimize crop yields and meanwhile maintain relatively low risk of P leaching in Haplic Luvisol soil, northern China.

Characterization of the Growth,Chlorophyll Content and Lipid Accumulation in a Marine Microalgae Dunaliella tertiolecta under Different Nitrogen to Phosphorus Ratios

Microalgal lipids are regarded as main future feedstock of biofuels for its higher efficiency of accumulation and sus- tainable production. In order to investigate the effect of various nitrogen to phosphorus ratios on cells growth, chlorophyll content and accumulation of lipids in Dunaliella tertiolecta, experiments were carried out in modified microalgal medium with inorganic nitrogen （nitrate-nitrogen） or organic nitrogen （urea-nitrogen） as the sole nitrogen source at initial N：P ratios ranging from 1：1 to 32：1. The favorable N：P of 16：1 in the nitrate-N or urea-N medium yielded the maximum cell density and specific growth rate. Decrease in chlorophyll content were observed at the N：P of 4：1 in both nitrate-N and urea-N cultures. It was also observed that the maximum lipids concentration was obtained at the N：P of 4：1 in both nitrate and urea nutrient medium. The lipid productivity and lipid content of cultures in the urea-N medium at the N：P of 4： lwere markedly higher than those from cultures with other N：P ratios （p〈 0.05）. The results of this work illustrate the possibility that higher ratios of nitrogen to phosphorus have enhancing effect on cells growth of D. tertiolecta. Conversely, higher lipid accumulation is associated with a decrease in chlorophyll content under lower ratios of nitro- gen to phosphorus. The results confirm the hypothesis of this study that a larger metabolic flux has been channeled to lipid accumu- lation in D. tertiolecta cells when the ratios of nitrogen to phosphorus drop below a critical level.

Subcellular Accumulation of Cadmium in Corn and WheatPlants at Different Levels of Phosphorus

Corn and wheat plants were grown in a nutrient culture solution at four levels of phosphorus (0, 0.12,0.60 and 3.0 mmol L-1) and two levels of cadmium (0 and 4.0 pmol L--1) in greenhouse for a 18-day period.The concentrations of phosphorus and cadmium in cell wall, cytoplasm and vacuoles of roots and leaveswere examined by cell fractionation techniques. With increasing phosphorus in medium, the contents of Pin cell wall, cytoplasm and vacuoles of corn and wheat roots and leaves increased. The highest content of Pwas observed in cell wall, next in vacuoles, and the lowest in cytoplasm. The wheat subcellular fractions inboth roots and leaves had higher concentrations of phosphorus than those of corn. Increasing phosphorus inmedium significantly inhibited the intracellular Cd accumulation in both species. However, at P concentrationup to 3.0 mmol L--1, the Cd content in cell wall was increased. Increasing phosphorus resulted in reductionof the subcellular Cd content in corn and wheat leaves. Compared with corn, the wheat roots had a higherCd content in the cell wall and vacuoles and a lower in cytoplasm, while in leaf subcellular fractions thewheat cell had a higher Cd content in its vacuoles and a lower one in its cytoplasm. The results indicate thatphosphorus may be involved in sequestration of Cd ionic activity in both cell wall and vacuoles by forminginsoluble Cd phosphate.

Effects of Long-term Fertilization on Phosphorus Accumulation and Migration in Purple Soil

Based on a long-term location test lasting for 20 years, the accumulation and migration of phosphorus in purple soil was studied. The results showed that P2Os input in paddy-upland rotation was 120.0 kg/（ hm2 · a） （a conventional level of phosphorus application）, and P had a surplus of 53.9 kg/（hm2 · a）. Phosphorus accumulating in soil increased available phosphorus （Olsen-P） content, and the positive correlation between P changing balance and Olsen-P change in wheat-rice rotation was extremely significant. The mixed application of organic fertilizer and chemical P fertilizer can speed up accumulation of available phosphorus in soil. Olsen-P content in all treatments with P fertilizer was higher in 0 -60 cm soil than that of treatments without P fertilizer, and Phosphorus applied in surface soil moved to soil at a depth of 60 cm, increasing risk of P leakage and loss. The migration of phosphorus in soil is affected by P input, type of organic fertilizer and planting method. The quantities of phosphorus moving down increased with the increase of P input, and the application of pig manure can lead to migration of phosphorus in soil more easily compared with straw. The migration of phosphorus from soil to water mainly occurred in the first ten days after rice was transplanted, and paddy field drainage should not be conducted in the first 30 days after rice was transplanted.

Effects of Substitution of Organic Manure for Chemical Fertilizer on Phosphorus Accumulation and Grain Yield in Maize

In order to explore the response of maize phosphorus absorption to the appropriate proportion of organic fertilizer substitution for reduced chemical fertilizer,a field experiment with eight treatments was conducted in 2018.The eight treatments in the trial were:(1)CK;(2)M0+F;(3)M1+F1;(4)M1+F2;(5)M2+F1;(6)M2+F2;(7)M3+F1 and(8)M3+F2.In these treatments,M0,M1,M2 and M3 were organic fertilization of 0,15(low),30(medium)and 45(high)m3•hm-2,respectively.F1 and F2 indicated 20%and 40%reduction of conventional chemical fertilization.The soil nutrient content,phosphorus accumulation,dry weight,yield and yield components of maize were analyzed.The results showed that the phosphorus accumulation of maize stalks and leaves were 3.30%-43.17%and 10.98%-84.95%higher in M3+F1 treatment(20%reduction of chemical fertilizer with organic fertilizer of 45 m3•hm-2)than those in the conventional treatment(M0+F)during the maize reproductive period.At R2 stage,stalk and shoot P accumulation of M3+F1 treatment were 24.67%-43.18%and 20.34%-25.19%higher than other treatments,respectively.At V12 stage,leaf P accumulation of M3+F1 increased by 84.95%compared with other treatments.The maize yield of M3+F1 was significantly higher than that of other treatments,even though the partial productivity of the total phosphorus fertilizer of M3+F2 was the highest in the treatments.It could be found that the substitution of organic fertilizer for chemical fertilizer improved crop yield,phosphorus fertilizer efficiency and accumulation.M3+F1 treatment had the most positive effects on improving maize phosphorus accumulation and yield.

Accumulation Laws of Nitrogen and Phosphorus in Wetland Plants

To study the accumulation regularity of nitrogen and phosphorus in typical constructive plants in coastal wetland,samples of Suaeda glauca(Bunge) Bunge,Phragmites austrahs and Tamarix chinensis Lour,were taken from the Yellow River Delta National Coast Wetland Nature Reserve,nitrogen and phosphorus content in plants was measured and analyzed.The results showed that ① nitrogen and phosphorus content in different wetland plants is correlated;② different species in the same place and the same species in different spaces show different accumulation regularity of nitrogen and phosphorus;③ nitrogen and phosphorus content in plants is closely related to nitrogen and phosphorus content in the habitat;④ nitrogen content in T.chinensis Lour,is the highest,the mean is 11.63 g/kg,and phosphorus content in S glauca(Bunge) Bunge is the highest,the mean is 1.38 g/kg;⑤ nitrogen content in the 3 species:T.chinensis Lour.> S.glauca(Bunge) Bunge > P.australis;⑥ nitrogen content in aboveground parts of all plants is significantly higher than that in underground parts,and phosphorus content in aboveground parts of all plants except S.glauca(Bunge) Bunge is significantly higher than that in underground parts;⑦ nitrogen content in the 3 species in the study area is significantly higher than phosphorus content in these species.

Effi ciency of phosphorus accumulation by plankton,periphyton developed on submerged artifi cial substrata and metaphyton:in-situ observation in two shallow ponds

Phosphorus overenrichment of shallow ponds prevailing in wetlands leads to their eutrophication causing the collapse of those vulnerable habitats.The potential of phosphorus accumulation by periphyton developed on artificial substrata has been investigated in two shallow ponds(Bara?ka and?iroki Rit)in northwest Serbia and compared to the same ability of plankton and metaphyton.The periphyton substrate carrier has been submerged from May to October.Both continuously(CS)and monthly developed(MS)periphyton were sampled.Autotrophic component of all investigated communities has been qualitatively assessed.Maximum accumulation of only 14.7 mg TP/m^(2) was recorded in three-month exposed periphyton CS.MS exposed from July to August reached maximal 12.7 mg TP/m^(2).Plankton community that was characterized by more diverse and abundantly developed algal component was more effective in phosphorus accumulation(0.7 mg/g dry weight)in comparison with dominantly inorganic and diatom-dominated periphyton in Bara?ka.Unstable conditions caused by recent revitalization(dredging organic matter and mud from pond basin—redigging)as well as rapid desiccation of?iroki Rit disabled making an unambiguous conclusion about the efficiency of phosphorus accumulation among different communities,but suggested slight potential of phosphorus harvesting by metaphyton in this pond.Due to the shorter exposure time that brings the reduced risk of unpredictable changes in the ecosystem,as well as the considerable amount of accumulated phosphorus,large-scale application of one-month exposed periphyton developed on artificial substrates would be more advisable for phosphorus harvesting in nutrient affected shallow ponds.

TCP1表达对HL60和HL60/A 细胞增殖及细胞内药物蓄积的调控作用及其机制

目的:研究TCP1表达对HL60及HL60/A细胞增殖及细胞内药物蓄积的影响及其机制。方法:利用慢病毒转染技术构建敲低、过表达TCP1的HL60/A细胞和HL60细胞及其对照组细胞,Western blot评估敲低、过表达效率。采用CCK-8法检测细胞增殖能力;激光共聚焦显微镜及流式细胞术检测细胞内的药物蓄积;流式细胞术及Western blot检测膜转运蛋白(MRP1、P-gP)及p-AKT的表达水平。结果:在HL60/A细胞中敲低TCP1的表达能够抑制细胞增殖,增加细胞内药物蓄积,降低转运蛋白MRP1及P-gP的表达,在HL60细胞中过表达TCP1能够促进细胞的增殖,减少细胞内药物蓄积,提高转运蛋白MRPI及P-gP的表达。同时利用PI3K抑制剂LY294002抑制PI3K/AKT信号能够拮抗TCP1过表达所致的细胞增殖活性增强、细胞内药物蓄积减少及MRP1、P-gP表达的升高。结论:TCP1能够促进细胞增殖,并通过激活PI3K/AKT信号促进转运蛋白MRP1、P-gP的表达,降低细胞内的药物蓄积。

Effect of Phopshate Fertilizer and Manure on Crop Yield, Soil P Accumulation, and the Environmental Risk Assessment

Phosphorus （P） applied from fertilizer and manure is important in increasing crop yield and soil fertility; however, excessive uses of phosphate fertilizer and manure may also increase P loss from agricultural soils, posing environmental impact. A long term experiment was conducted on a calcareous soil （meadow cinnamon） in Hebei Province, China, from 2003 to 2006 to investigate the effects of phosphate fertilizer and manure on the yield of Chinese cabbage, soil P accumulation, P sorption saturation, soluble P in runoff water, and P leaching. P fertilizer （P2O5） application at a rate of 360 kg ha^-1 or manure of 150 t ha^-1 significantly increased Chinese cabbage yield as compared to the unfertilized control. However, no significant yield response was found with excessive phosphate or manure application. Soil Olsen-P, soluble P, bioavailable P, the degree of phosphorus sorption saturation in top soil layer （0-20 cm）, and soluble P in runoff water increased significantly with the increase of phosphate fertilizer and manure application rates, whereas the maximum phosphorus sorption capacity （Qm） decreased with the phosphate fertilizer and manure application rates. Soil Olsen-P and soluble P also increased significantly in the sub soil layer （20-40 cm） with the high P fertilizer and manure rates. It indicates that excessive P application over crop demand can lead to a high environmental risk owing to the enrichment of soil Olsen-P, soluble P, bioavailable P, and the degree of phosphorus sorption saturation in agricultural soils.

Effect of external and internal phosphate status on arsenic toxicity and accumulation in rice seedlings

Phosphorus （P） deficiency is thought to exacerbate the arsenic （As） phytotoxicity in paddy rice. The experiments were conducted to investigate the effects of external phosphate supply on As accumulation in rice and its toxicity under phosphate deficiency conditions. Rice seedlings pretreated with a phosphorus deficient nutrient solution （-P） for 14 d accumulated more As than those pretreated with a normal phosphorus supply nutrient solution （＋P）. Rice protreated with -P showed As toxicity symptoms after being exposed to 50 μmol/L arsenate for 4 h, while ＋P rice did not show any toxicity symptoms. Arsenic toxicity symptoms can be alleviated by increasing external P concentrations. The arsenate uptake rate and accumulation corresponded with the As toxicity in rice plants. Arsenic concentrations in rice roots decreased with increasing external phosphate concentrations. The lowest As accumulation and the highest P accumulation were found when the external P concentration reached 100μmol/L. In short, P deficiency increased the sensitivity of rice to arsenate and increasing of external phosphate supply could alleviate As toxicity.

Profile Characteristics and Potential EnvironmentalEffect of Accumulated Phosphorusin Soils ofVegetable Fields in Beliing

Profile characteristics of accumulated P in 10 representativesoils of vegetable fields in suburban districts of Beijing wereinvestigated. Bioavailability of the accumulated P and its potentialeffect n the environment were studied in a greenhouse pot experimentand a soil column experiment. The results showed that theconcentration of Olsen-P in the 0～20 cm soil samples of thevegetable fields ranged from 2.1 to 358.0 mg kg^-1, which was 2 to 10times higher than that of the crop field sin the suburbs of Beijing.Most of the excessive phosphorus was accumulated in the topsoils.

Effects of Amino Acids Replacing Nitrate on Growth,Nitrate Accumulation,and Macroelement Concentrations in Pak-choi (Brassica chinensis L.)

A hydroponic experiment was carried out to determine the influence of replacing 20% of nitrate-N in nutrient solutions with 20 individual amino acids on growth, nitrate accumulation, and concentrations of nitrogen （N）, phosphorus （P）, and potassium （K） in pak-choi （Brassica chinensis L.） shoots. When 20% of nitrate-N was replaced with arginine （Arg） compared to the full nitrate treatment, pak-choi shoot fresh and dry weights increased significantly （P ≤ 0.05）, but when 20% of nitrate-N was replaced with alanine （Ala）, valine （Val）, leucine （Leu）, isoleucine （Ile）, proline （Pro）, phenylalanine （Phe）, methionine （Met）, aspartic acid （Asp）, glutamic acid （Glu）, lysine （Lys）, glycine （Gly）, serine （Ser）, threonine （Thr）, cysteine （Cys）, and tyrosine （Tyr）, shoot fresh and dry weights decreased significantly （P ≤ 0.05）. After replacing 20% of nitrate-N with asparagine （Asn） and glutamine （Gin）, shoot fresh and dry weights were unaffected. Compared to the full nitrate treatment, amino acid replacement treatments, except for Cys, Gly, histidine （His）, and Arg, significantly reduced （P ≤0.05） nitrate concentrations in plant shoots. Except for Cys, Leu, Pro, and Met, total N concentrations in plant tissues of the other amino acid treatments significantly increased （P ≤ 0.05）. Amino acids also affected total P and K concentrations, but the effects differed depending on individual amino acids. To improve pak-choi shoot quality, Gln and Asn, due to their insignificant effects on pak-choi growth, their significant reduction in nitrate concentrations, and their increase in macroelement content in plants, may be used to partially replace nitrate-N.

PbPH5,an H^(+)P-ATPase on the tonoplast,is related to malic acid accumulation in pear fruit

Organic acid content is one of the most important factors influencing fruit flavors.The predominant organic acid in most pear cultivars is malic acid,but the mechanism controlling its accumulation remains unclear.In this study,by comparing gene expression levels and organic acid contents,we found that the expression of PbPH5,which encodes a P_(3A)-ATPase,is highly correlated with malic acid accumulation in four different pear species,with correlation coefficients of 0.932**,0.656*,0.900**,and 0.518*(*,P<0.05;**,P<0.01)for Pyrus bretschneideri Rehd.,P.communis Linn.,P.pyrifolia Nakai.,and P.ussuriensis Maxim.,respectively.Moreover,the overexpression of PbPH5 in pear significantly increased the malic acid content.In contrast,silencing PbPH5 via RNA interference significantly decreased both its transcript level and the pear fruit malic acid content.A subcellular localization analysis indicated that PbPH5 is located in the tonoplast.Additionally,a phylogenetic analysis indicated that PbPH5 is a PH5 homolog gene that is clustered with the Petunia hybrida,Malus domestica,and Citrus reticulata genes.Considered together,these findings suggest that PbPH5 is a functionally conserved gene.Furthermore,the accumulation of malic acid in pear fruit is at least partly related to changes in the PbPH5 transcription levels.

Effects of low nutrition on photosynthetic capacity and accumulation of total N and P in three climber plant species

To study the effects of low nutrition on pho tosynthetic capacity and accumulation of total nitrogen(N) and phosphorus(P) in three climber plant species Pharbitis nil(Linn.) Choisy, Lonicera japonica Thunb. and Parthenocissus tricuspidata(Sieb.et Zucc.) Planch, al climber plants were exposed to low nutrition at 6 levels(Hoagland solution as control, 1/2, 1/4, 1/8, 1/16 and 1/32 strength Hoagland solution) for 30 days. Photosynthetic capacity was determined by measuring leaf chlorophyl fluorescence, chlorophyll content, carbonic anhydrases activity and growth. Accumulation of total N and P was studied by measuring N and P content in plant tissues. Low nutrition decreased the photosynthetic capacity of P. nil while L. japonica maintained high photosynthetic capacity under low nutrition. Photosynthetic apparatus of P. tricu spidata suffered no damage when exposed to low nutrition L. japonica and P. tricuspidata had better adaptability to low nutrition than P. nil. With a faster growth rate, P. ni consumed more nutrition(N and P), and its growth was mainly affected by P deficiency under low nutrition Although L. japonica suffered damage from N and P deficiency simultaneously, but the nutrient deficiency was not serious except for 1/32-strength Hoagland solution P. tricuspidata grew slowly, so its requirement of N and Pwere the least, even if it was mainly affected by the P deficiency, it could still grow well under low nutrition.With the consideration of fertilizing N and P fertilizers in karst areas which were with lower N and P contents, plant species, N/P ratio threshold and low nutrition level should be taken into account synchronously. This study could provide a general consideration for the planning and developing low nutrition resistant plants and fertilizing the three climber plant species in the low nutrition environment.

Topsoil phosphorus signature in five forest types along an urban-suburban-rural gradient in Nanchang, southern China

Conversions from rural to urban land uses have the potential to greatly modify soil phosphorus （P） levels. Soils in shrubs, Masson pine forest, conifer and broadleaf mixed forest, evergreen broadleaved forest and bamboo forest in the mid-subtropical region along an urban-rural gradient in Nanchang City, southern China, were analyzed for total P and P fractions using the modified Hedley P sequential fractionation method. Results show that the topsoil total P and total exactable P concentrations were significantly higher in the urban area （0.71 g·kg^-1 and 378.50 mg·kg^-1, respectively） than in the suburban （0.30 g·kg^-1 and 150.74 mg·kg^-1, respectively） and rural areas （0.31 g·kg^-1 and 147.38 mg·kg^-1, respectively） （p〈0.05）. Among the five P fractions of resin-P, NaHCO3-P NaOH-P, Sonication-P and HCI-P, the relative abundance of HCl-P in urban forest soils （36%） was the highest and also significantly higher than in suburban （8%） and rural soils （6%）, while NaOH-P was the dominant form in suburban （41%） and rural soils （50%）. Phosphorus accumulation in the urban soils could affect the cycle of P in urban forest systems, particularly the HCl-P fraction that might rapidly enrich aquatic systems in urban areas.

Effects of long-term phosphorus fertilization and straw incorporation on phosphorus fractions in subtropical paddy soil

Study on soil phosphorus（P） fraction is an important aspect in probing the mechanisms of soil P accumulation in farmland and mitigating its losing risk to the environment. We used a sequential extraction method to evaluate the impacts of long-term fertilization and straw incorporation on inorganic, organic, and residual P（Pi, Po, and Pre） fractions in the plow layer（0–20 cm） of acidic paddy soil in southern China. The experiment comprised of six treatments：（i） no fertilizer control（CK）;（ii） straw incorporation and green manure（SG）;（iii） nitrogen and P fertilizer（NP）;（iv） NP＋SG;（v） NP＋K fertilizer（NPK）; and（vi） NPK＋SG. The results showed that, compared to the initial total soil P content（TSP, 600 mg kg^–1 in 1990）, long-term（20 years） combined continuous P fertilizer and SG significantly increased P accumulation（by 13–20%） while single fertilization（39.3 kg P ha^–1 yr^–1） could maintain soil P status at the most. The average soil P fractions comprised of extractable Pi, Po, and Pre by 51.7, 33.4, and 14.9% in total soil P, respectively. With comparison of no fertilizer addition（CK）, long-term single fertilization significantly（P〈0.05） increased the accumulation of Na HCO3^–, Na OH^–, and HCl^– extractable Pi fractions accounting for two- to three-fold, while SG increased the accumulation of Na HCO3^– and Na OH^– extractable Piand Po accounting for 12–60%. Though the mobilization of Pre fractions was not significant（P〉0.05）, our data indicate that SG may partially substitute for fertilizer P input and minimizing soil P accumulation and subsequent environmental risk in the subtropical paddy soil.