Phosphorus alleviates aluminum-induced inhibition of growth and photosynthesis in Citrus

Physiologia Plantarum137:298–311.2009Copyright?Physiologia Plantarum2009,ISSN0031-9317 Phosphorus alleviates aluminum-induced inhibition of

growth and photosynthesis in Citrus grandis seedlings

Huan-Xin Jiang a,b,Ning Tang a,c,Jin-Gui Zheng d,Yan Li e and Li-Song Chen a,c,f,?

a Institute of Horticultural Plant Physiology,Biochemistry and Molecular Biology,Fujian Agriculture and Forestry University,Fuzhou350002,

PR China

b College of Life Science,Fujian Agriculture and Forestry University,Fuzhou350002,PR China

c College of Horticulture,Fujian Agriculture an

d Forestry University,Fuzhou350002,PR China

d Biotechnology Center,Fujian Agricultur

e and Forestry University,Fuzhou350002,PR China

e College o

f Resources and Environment,Fujian Agriculture and Forestry University,Fuzhou350002,PR China

f Fujian Key Laboratory for Plant Molecular and Cell Biology,Fujian Agriculture and Forestry University,Fuzhou350002,PR China

Correspondence

*Corresponding author,

e-mail:lisongchen2002@https://www.sodocs.net/doc/6c2546210.html,

Received21May2009;revised30July 2009

doi:10.1111/j.1399-3054.2009.01288.x Limited data are available on the effects of phosphorus(P)and aluminum

(Al)interactions on Citrus spp.growth and photosynthesis.Sour pummelo (Citrus grandis)seedlings were irrigated for18weeks with nutrient solution containing50,100,250and500μM KH2PO4×0and1.2m M AlCl3·6H2O.Thereafter,P and Al in roots,stems and leaves,and leaf chlorophyll

(Chl),CO2assimilation,ribulose-1,5-bisphosphate carboxylase/oxygenase

(Rubisco)and Chl a?uorescence(OJIP)transients were measured.Under Al stress,P increased root Al,but decreased stem and leaf Al.Shoot growth is more sensitive to Al than root growth,CO2assimilation and OJIP transients. Al decreased CO2assimilation,Rubisco activity and Chl content,whereas it increased or did not affect intercellular CO2concentration.Al affected CO2assimilation more than Rubisco and Chl under250and500μM P.Al decreased root,stem and leaf P,leaf maximum quantum yield of primary photochemistry(F v/F m)and total performance index(PI tot,abs),but increased leaf minimum?uorescence(F o),relative variable?uorescence at K-and I-steps.P could alleviate Al-induced increase or decrease for all these parameters.We conclude that P alleviated Al-induced inhibition of growth and impairment of the whole photosynthetic electron transport chain from photosystem II(PSII)donor side up to the reduction of end acceptors of photosystem I(PSI),thus preventing photosynthesis inhibition through increasing Al immobilization in roots and P level in roots and shoots. Al-induced impairment of the whole photosynthetic electron transport chain may be associated with growth inhibition.

Abbreviations–ABS/RC,absorption?ux per RC;Al,aluminum;BSA,bovine serum albumin;Chl,chlorophyll;DW,dry weight; EDTA,ethylenediaminetetraacetic acid;ET o/ABS(φEo),quantum yield of electron transport;ET o/RC,electron transport?ux per RC;ET o/TR o(ψEo),probability that a trapped exciton moves an electron into the electron transport chain beyond

Q?A ;F m,maximum?uorescence;F o,minimum?uorescence;MDA,malondialdehyde;F v/F m(TR o/ABS orφPo),maximum

quantum yield of primary photochemistry;OEC,oxygen evolving complex;OJIP,Chl a?uorescence;P,phosphorus;PI tot,abs, total performance index;PSI,photosystem I;PSII,photosystem II;RC,reaction center;PVPP,polyvinylpolypyrrolidone; RE o/ABS(φRo),quantum yield for the reduction of end acceptors of PSI per photon absorbed;RE o/ET o(δRo),ef?ciency with which an electron can move from the reduced intersystem electron acceptors to the PSI end electron acceptors;RE o/RC, reduction of end acceptors at PSI acceptor side per RC;Rubisco,ribulose-1,5-bisphosphate carboxylase/oxygenase;RuBP, ribulose-1,5-bisphosphate;TR o/RC,trapped energy?ux per RC.

298Physiol.Plant.137,2009

Introduction

Aluminum(Al)toxicity and phosphorus(P)de?ciency are major limiting factors for plant growth in acid soils,and plants growing in acid soils often suffer from both P de?-ciency and Al toxicity(Kochian et al.2004).Al decreased P content in roots,stems and leaves of‘Nemaguard’peach(Prunus persica)(Graham2001),and in roots and shoots of beech(Fagus sylvatica)(P?a hlsson1990). McLaughlin and James(1989)suggested that Al-induced P de?ciency symptoms in plants were due to a combina-tion of decreased root elongation and interruption of cell metabolism,as well as immobilization of P by Al on,or within,the root surface.P de?ciency was considered to be the key cause of growth decrease in Al-stressed plants (Quartin et al.2001).As reported by Gaume et al.(2001), the toxic effect of Al on plant growth was alleviated with increasing P concentration in roots.Pierre and Stuart (1933)showed that P could alleviate Al toxicity due to direct precipitation of Al–P in the zone of P incorpora-tion.Al did not inhibit rice(Oryza sativa)shoot growth in plants pre-cultured with P,but Al retarded shoot growth in plants pre-cultured without P.P pre-culture slightly increased Al deposition(presumably due to the forma-tion of Al–P in the roots),thus leading to decreased Al content in the shoots and markedly increased P level in the shoots of rice(Nakagawa et al.2003).Salinas and Sanchez(1977)reported that adequate P could enhance Al-tolerance in maize(Zea mays).Recently,Sun et al. (2008)demonstrated that P enhanced Al-tolerance in Al-tolerant Lespedeza bicolor,possibly through improving P accumulation and translocation to shoots and increasing Al exclusion from root tips after P application.

Al decreases CO2assimilation in many plant species including Citrus spp.(Chen et al.2005a,2005b,Jiang et al.2008),tomato(Lycopersicon esculentum)(Simon et al.1994),and maize(Lidon et al.1999).Previous investigators proposed that Al caused a decline in CO2assimilation as a result of the increased closure of photosystem II(PSII)reaction centers(RCs)and the decreased electron transport rate of PSII(Chen et al. 2005a,Moustakas et al.1995).Recent work showed that the impaired photosynthetic electron transport capacity accompanied by lack of reducing equivalents was the main factors contributing to decreased CO2assimilation in Al-treated plants(Jiang et al.2008).P de?ciency also affects photosynthesis in many plant species, including tea(Camellia sinensis)(Lin et al.2009), satsuma mandarin(Citrus unshiu)(Guo et al.2002, 2003)and tomato(De Groot2003).Guo et al.(2002) reported that P-de?cient satsuma mandarin exhibited a 6%decrease in maximum PSII ef?ciency of dark-adapted leaves(F v/F m)and a49.5%decrease in electron transport rate.Like Al,P de?ciency also decreased photosynthetic electron transport capacity by impairing the whole electron transport chain from PSII donor side up to the photosystem I(PSI),thus decreasing the rate of CO2 assimilation(Lin et al.2009).Therefore,P application may prevent Al-induced impairment of the whole photosynthetic electron transport chain,thus preventing the inhibition of photosynthesis by decreasing Al level and increasing P level in leaves.To our knowledge,little information is available on the ameliorative effects of P on Al-induced inhibition of photosynthesis.

Citrus belongs to evergreen subtropical fruit trees and is cultivated in humid and subhumid of tropical, subtropical and temperate regions of the world mainly on acid soils.Although the effects of Al toxicity or low P on growth and CO2assimilation of citrus have been studied by few researchers(Chen et al.2005a,2005b, Guo et al.2002,2003,Jiang et al.2008),Al toxicity and low P are almost always investigated separately as independent factors.In this paper,we investigated the effects of P and Al interactions on growth,the contents of P and Al in roots,stems and leaves, and leaf CO2assimilation,ribulose-1,5-bisphosphate carboxylase/oxygenase(Rubisco,EC 4.1.1.39)and chlorophyll(Chl)a?uorescence(OJIP)transients in the seedlings of sour pummelo(Citrus grandis),an Al-sensitive rootstock used in pummelo cultivation. The objective of this study was to test the hypothesis that P alleviates Al-induced inhibition of growth and impairment of the whole photosynthetic electron transport chain from PSII donor side up to the PSI,thus preventing the inhibition of photosynthesis by increasing Al immobilization in roots and P level in roots and shoots (leaves),and decreasing Al level in shoots(leaves). Materials and methods

Plant culture and treatments

This study was conducted from February to Novem-ber2007at Fujian Agriculture and Forestry Univer-sity(FAFU).Seeds of sour pummelo(Citrus grandis (L.)Osbeck)were germinated in sand in plastic trays. Five weeks after germination,uniform seedlings with single stem were selected and transported to6L pots containing sand.Seedlings,three to a pot,were grown in a greenhouse under natural photoperiod at FAFU. Each pot was supplied with500ml of nutrient solu-tion containing the following macronutrients(in m M): KNO3,1;Ca(NO3)2,1;KH2PO4,0.5;and MgSO4, 0.5;and micronutrients(inμM):H3BO3,10;MnCl2, 2;ZnSO4,2;CuSO4,0.5;(NH4)6Mo7O24,0.065;and Fe-ethylenediaminetetraacetic acid(EDTA),20,every

Physiol.Plant.137,2009299

two days.Six weeks after transplanting,the treatments

were applied for18weeks:until the end of the exper-

iment,each pot was supplied daily until dripping with

nutrient solution.There were eight treatments in total,

including four P levels(50,100,250and500μM KH2PO4)×two Al levels[0(?Al)and1.2m M AlCl3·6H2O(+Al)].Al was supplied together with nutrient

solutions and no Al–P precipitates were formed in the

nutrient solutions.K concentration was maintained at a

constant by the addition of K2SO4.The pH of the nutrient

solutions was adjusted to4.1–4.2using HCl or NaOH.

At the end of the experiment,the fully expanded(about

7-weeks-old)mature leaves from different replicates and

treatments were chosen for all the measurements.For

the determination of Rubisco,Chl,protein,Al and P,

leaf discs(0.61cm2in size)were collected at noon in

full sun,frozen in liquid N2.For the determination of

root protein,Al and P,approximately10-mm-long root

apices were excised from the same seedlings used for

sampling leaves and frozen in liquid N2.Both leaf and

root samples were stored at?80?C until assayed. Measurements of root and shoot dry weight(DW) At the end of the experiment,12trees per treatment from different pots were harvested.The trees were divided into roots and shoots.The plant materials were then dried at 80?C for48h and the DW measured.

Assays of Chl and total soluble protein,total P and total Al

Leaf Chl was extracted and measured according to

Lichtenthaler(1987).Brie?y,two frozen leaf discs were

extracted with8ml of80%(v/v)acetone for24h in the

dark.The extracts were determined using Libra S22

ultraviolet-visible spectrophotometer(Biochrom Ltd.,

Cambridge,UK).

Root and leaf total soluble protein was extracted

with50m M Na2HP4–KH2PO4(pH7.0)and5% (w/v)insoluble polyvinylpolypyrrolidone(PVPP),and determined according to Bradford(1976)using bovine serum albumin(BSA)as standard.

Roots,stems and leaves were wet digested in a

HNO3/HCl/HClO4mixture.P and Al in the solution were

determined using the ammonium molybdate/ascorbic

acid spectrophotometric assay(Ames1966)and col-

orimetrically by the aluminon method(Hsu1963),

respectively.

Leaf gas exchange measurements Measurements were made by a CI-301PS portable photosynthesis system(CID,WA)at ambient CO2concentration with a photosynthetic photon?ux of1300μmol m?2s?1between9:30and11:00on a clear day (Chen et al.2005a,Lin et al.2009).During measuring, leaf temperature and relative humidity were28±0.2?C and76±0.5%,respectively.

Leaf Rubisco activity measurements

Rubisco was extracted according to Chen et al.(2005a). Two frozen leaf discs from the same leaf were ground with a pre-cooled mortar and pestle in1ml extraction buffer containing50m M Hepes–KOH(pH7.5),10m M MgCl2,2m M EDTA,10m M dithiothreitol,1%(v/v) Triton X-100,5%(w/v)insoluble PVPP,1%(w/v)BSA and10%(v/v)glycerol.The extract was centrifuged at 13000g for40s in2?C,and the supernatant was used immediately for assay of Rubisco activity.

Rubisco activity was determined according to Lin et al.(2009).For initial activity,50μl of sample extract was added to a cuvette containing900μl of an assay solution,immediately followed by adding50μl of10 m M ribulose-1,5-biphosphate(RuBP),then mixing well. The change of absorbance at340nm was monitored for40s.For total activity,50μl of10m M RuBP was added15min later,after50μl of sample extract was combined with900μl of an assay solution to fully activate all the Rubisco.The assay solution for both initial and total activity measurements,whose?nal volume was1ml,contained100m M Hepes–KOH(pH 8.0),25m M KHCO3,20m M MgCl2,3.5m M ATP, 5m M phosphocretaine,5units NAD-glyceraldehyde-3-phosphate dehydrogenase(EC1.2.1.12),5units3-phosphoglyceric phospokinase(EC2.7.2.3),17.5units creatine phosphokinase(EC2.7.3.2),0.25m M NADH, 0.5m M RuBP and50μl sample extract.Rubisco activation state was calculated as the ratio of initial activity to total activity.

Measurements of leaf OJIP transients

OJIP transient was measured by a Handy Plant Ef?ciency Analyzer(Handy PEA,Hansatech Instruments Limited, Norfolk,UK)according to Strasser et al.(1995).All the measurements were done with3h dark-adapted plants at room temperature.

OJIP was analyzed according to the JIP test(Appenroth et al.2001,Smit et al.2009,Strasser et al.2000,2004, Tsimilli-Michael and Strasser2008).The following data from the original measurements were used:the?uo-rescence intensity at20μs(considered as minimum ?uorescence F o);the maximal?uorescence intensity, equal to maximum?uorescence(F m)since the excita-tion intensity was high enough to ensure the closure

300Physiol.Plant.137,2009

of all RCs of PSII;the?uorescence intensity at300μs (F300μs),2ms(J-step,F J)and30ms(I-step,F I).The JIP test represents a translation of the original data to biophysical parameters and the performance index.The following parameters that all refer to time0(start of?uo-rescence induction)are:(a)the speci?c energy?uxes per RC for absorption(ABS/RC),trapping(TR o/RC),electron transport(ET o/RC)and reduction of end acceptors at PSI acceptor side(RE o/RC);(b)the?ux ratios or yields,i.e. the maximum quantum yield of primary photochemistry (φPo=TR o/ABS=F v/F m),the probability that a trapped exciton moves an electron into the electron transport chain beyond Q A?(ψEo=ET o/TR o),the quantum yield of electron transport(φEo=ET o/ABS),the quantum yield for the reduction of end acceptors of PSI per photon absorbed(φRo=RE o/ABS)and the ef?ciency with which an electron can move from the reduced intersystem electron acceptors to the PSI end electron acceptors (δRo=RE o/ET o);(c)the total performance index(PI tot,abs), measuring the performance up to the PSI end elec-tron acceptors(PI tot,abs=(RC/ABS)×(φPo/(1?φPo))×(ψEo/(1?ψEo))×(δRo/(1?δRo));(d)the IP phase(IP phase=(F t–F o)/(F I–F o)–1=(F t–F I)/(F I–F o),where F t is the?uorescence intensity at time t after onset of actinic illumination).It has been suggested that the amplitude of IP phase is considered as a measure of the amount of reduced end acceptors at PSI acceptor side and that the IP phase represents the last and slowest rate-limiting step of the photosynthetic electron transport chain(Schansker et al.2005).For full de?nitions and calculations of all above-mentioned parameters except for IP phase,see Table S1.

Extended analysis of OJIP transients was done by cal-culation of the relative variable?uorescence(Jiang et al. 2008,Smit et al.2009,Strauss et al.2007):(A)between F o and F m(V t=(F t–F o)/(F m–F o))and(B)between F o and F300μs(W K=(F t–F o)/(F300μs–F o))and the differ-ences between the treated and the control samples.Clear bands are visible in these transients,where treatments rise above the control transient which is the reference line.Positive L, K, J and I-bands appear around 130,300μs,2and30ms,respectively,and are asso-ciated with the ungrouping of PSII units(Strasser1978), the uncoupling of the oxygen evolving complex(OEC, Hakala et al.2005,Strasser1997),the accumulation of Q?A(Strasser et al.2004)and the increased proportion of Q B-non-reducing PSII RCs(Cao and Govindjee1990, Chylla and Whitmarsh1989),respectively.

Experimental design and statistical analysis

There were30pot seedlings per treatment in a com-pletely randomized design.Experiments were performed with4–12replicates(one plant from different pots per replicate).Differences among treatments were separated by the least signi?cant difference test at P<0.05level. Results

Seedling growth

Root DW did not signi?cantly change in response to P supply except for a slight decrease at the lowest P supply without Al stress,whereas increased with increasing P supply under Al stress(Fig.1A).P did not signi?cantly affect shoot DW without Al stress,whereas it increased with increasing P supply under Al stress(Fig.1B).

Root/shoot ratio did not signi?cantly change in response to P without Al stress,whereas decreased with increasing P supply under Al stress.Root/shoot ratio was higher in+Al seedlings than in?Al ones under50or 100μM P,but was similar between Al treatments under 250or500μM P(Fig.1C).

P and Al contents in roots,stems and leaves

Root Al content increased as P supply increased from50 to250μM under Al stress,then remained unchanged at the highest P supply,whereas it did not signi?cantly change in response to P without Al stress(Fig.2A). Stem Al content did not signi?cantly change in response to P without Al stress,whereas decreased as P supply increased from50to100μM under Al stress,then did not signi?cantly change with further increasing P supply.Al content was higher in+Al stems than in?Al ones under 50,100or250μM P,but no signi?cant differences were found between Al treatments under500μM P(Fig.2B). No signi?cant differences were found in leaf Al content among Al and P combinations except for a large increase under50μM P+1.2m M Al and100μM P+1.2m M Al (Fig.2C).

Al signi?cantly decreased P content of roots,stems and leaves.Root,stem and leaf P content increased with increasing P supply with or without Al stress except that stem P content remained unchanged as P supply increased from250to500μM without Al stress (Fig.2D–F).

Leaf Chl,root and leaf total soluble protein

Chl content did not signi?cantly change in response to P without Al stress,while increased as P supply increased from50to250μM under Al stress,then remained unchanged at the highest P supply.Chl content was lower in+Al leaves than in?Al ones under50or100μM P,but no signi?cant differences were found between

Physiol.Plant.137,2009301

P supply to seedlings (μM)

50

100

250

500

R o o t /s h o o t

0.00

0.250.50

0.75S h o o t D W (g p l a n t –1)

8

16

24

R o o t D W (g p l a n t –1)

5

10

15

Fig.1.Effects of P and Al interactions on root DW (A),shoot DW (B)and root/shoot ratio (C)of sour pummelo seedlings.Each point represents the mean of 12replicates with standard error.Each variable was analyzed by 2(Al levels)×4(P levels)ANOVA.(A)P values for Al,P and the interactions between the two were 0.0000,0.0000and 0.2092,respectively;(B)and (C)P values for Al,P and the interactions between the two were all <0.0001.Different letters indicate signi?cant differences at P <0.05.

Al treatments under 250or 500μM P (Fig.3A).No signi?cant differences were found in leaf Chl a /b ratio among Al and P combinations except for a decrease under 50μM P +1.2m M Al and 100μM P +1.2m M Al (Fig.3B).

Leaf total soluble protein content did not signi?cantly change in response to P except for a slight increase at the highest P supply without Al stress,while decreased with decreasing P supply under Al stress (Fig.3C).Root

total soluble protein content did not signi?cantly differ among Al and P combinations (Fig.3D).Leaf gas exchange and Rubisco

In the absence of Al stress,P did not signi?cantly affect leaf CO 2assimilation except for a slight decrease under 50μM P,whereas CO 2assimilation in +Al leaves increased as P supply increased from 50to 250μM ,then kept unchanged at the highest P supply.Al decreased CO 2assimilation (Fig.4A).Leaf stomatal conductance did not signi?cantly differ among Al and P combinations except for a decrease under 1.2m M Al +50μM P (Fig.4B).Leaf intercellular CO 2concentration did not signi?cantly change in response to P without Al stress,but increased as P supply decreased from 500to 100μM under Al stress,then kept unchanged at the lowest P supply.Al increased intercellular CO 2concentration under 50or 100μM P,but did not affect it under 250or 500μM P (Fig.4C).

Both initial and total Rubisco activity did not signi?cantly change in response to P without Al stress,but increased as P supply increased from 50to 250μM under Al stress,then kept unchanged at the highest P supply (Fig.4D and E).Initial Rubisco activity was lower in +Al leaves than in ?Al ones under 50,100or 250μM P,but did not differ between Al treatments under 500μM P (Fig.4D).Similarly,total Rubisco activity was lower in +Al leaves than in ?Al ones under 50or 100μM P,but was similar between the two under 250or 500μM P (Fig.4E).Leaf Rubisco activation state did not signi?cantly differ among Al and P combinations (Fig.4F).

Leaf OJIP transients and related parameters OJIP transients showed little change in response to P in the absence of Al (Fig.5A).Al increased the hetero-geneity of samples,which decreased with increasing P supply (see Fig.S1).OJIP transients from +Al leaves showed a large rise at the O-step and a large depression at the P-step under 50μM P or similar P-step under 100μM P (Fig.5A).Al decreased the maximum amplitude of IP phase,which decreased with decreasing P supply (Fig.5B).

Detailed analysis of the normalized ?uorescence transients showed that Al increased the relative variable ?uorescence at the K-,J-,I-and L-steps,which decreased with increasing P supply (Fig.6A–D).

In the absence of Al stress,15?uorescence parameters did not signi?cantly change in response to P except for a slight increase for ET o /ABS,ET o /TR o and ET o /RC in 500μM P-treated leaves (Fig.7and Table 1).No

302

Physiol.Plant.137,2009

50

100

250

500L e a f A l c o n t e n t (m g g -1 D W )

0.00

0.070.140.210.28S t e m A l c o n t e n t (m g g -1 D W )

-0.020.000.020.040.060.080.100.120.140.160.18R o o t A l c o n t e n t (m g g -1 D W )

0.00.51.01.52.0

P supply to seedlings (μM)

50100250

500

L e a f P c o n t e n t (m g g -1 D W )0.0

0.5

1.0

1.5S t e m P c o n t e n t (m g g -1 D W )

0.00.4

0.8

R o o t P c o n t e n t (m g g -1 D W )0.0

0.5

1.0

1.5

2.02.5

Fig.2.Effects of P and Al interactions on the contents of P and Al in sour pummelo roots,stems and leaves.Each point represents the mean of 4–6replicates with standard error.Each variable was analyzed by 2(Al levels)×4(P levels)ANOVA.P values for Al,P and the interactions between the two were <0.0001,0.0049and 0.4744(A);<0.0001,0.0033and 0.0001(B);<0.0001,<0.0001and <0.0001(C);<0.0001,<0.0001and 0.3022(D);<0.0001,<0.0001and 0.0065(E);and <0.0001,<0.0001and 0.3385(F),respectively.Different letters indicate signi?cant differences at P <0.05.

P supply to seedlings (μM)

50100

250

500

A c t i v a t i o n s t a t e (%)

30

60T o t a l R u b i s c o a c t i v i t y

(μm o l m -2 s -1)0

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I n i t i a l R u b i s c o a c t i v i t y (μm o l m -2 s -1)

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1827

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250500I n t e r c e l l u l a r C O 2 c o n c e n t r a t i o n (μm o l m o l -1)

100200300S t o m a t a l c o n d u c t a n c e (m m o l m -2 s -1)0255075C O 2 a s s i m i l a t i o n (μm o l m -2 s -1)036

912

Fig.4.Effects of P and Al interactions on CO 2assimilation (A),stomatal conductance (B),intercellular CO 2concentration (C),initial Rubisco activity (D),total Rubisco activity (E),and activation state (F)in sour pummelo leaves.Each point represents the mean of 5–7replicates with standard error.Each variable was analyzed by 2(Al levels)×4(P levels)ANOVA.P values for Al,P and the interactions between the two were <0.0001,<0.0001and 0.0001(A);0.0014,0.0629and 0.0770(B);<0.0001,0.0113and 0.0222(C);<0.0001,0.0025and 0.0158(D);<0.0001,0.0051and 0.0020(E);0.5646,0.2018and 0.9599(F),respectively.Different letters indicate signi?cant differences at P <0.05.

Time (ms)

0.0

0.1

0.2

0.3W K

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0.050.15

0.250.350.450.550.650.750.850.951.050.00.1

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-1

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4V t

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0.750.850.951.05-2

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01

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3

ΔV t

-0.050.050.15

0.25

0.35

0.45

Fig.6.Effects of P and Al interactions on OJIP transients expressed as the kinetics of relative variable ?uorescence:(A)between F o and F m :V t =(F t –F o )/(F m –F o )and (B)the differences of the eight samples to the reference sample treated with 500μM P +0m M Al ( V t ),(C)between F o and F 300μs :W K =(F t –F o )/(F 300μs –F o )and (D)the differences of the 8samples to the reference sample ( W K )of dark-adapted sour pummelo leaves.Each point represents the mean of 8–10replicates.

signi?cant differences were found in F I and F m among Al and P combinations except for a decrease in 50μM P +1.2m M Al-treated leaves and an increase in 250μM P +1.2m M Al-treated ones (Table 1).F o ,F 300μs ,F J (Table 1),ABS/RC and TR o /RC (Fig.7D and E)decreased as P supply increased from 50to 250μM

under Al stress,then remained unchanged at the highest P supply;All the ?ve parameters were higher in +Al leaves than in ?Al ones under 50or 100μM P,but did not signi?cantly differ between the two under 250or 500μM P except that F 300μs and F J were higher in +Al leaves than in ?Al ones under 250μM P (Table 1).

Physiol.Plant.137,2009

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P supply to seedlings (μM)

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0.0

0.71.42.12.8

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P I t o t ,a b s -0.2

0.00.20.40.60.81.01.21.4δR o (R E o /E T o )

0.000.09

0.180.270.36

ψE o (E T o /T R o )

0.00

0.11

0.220.330.44

R E o /R C

0.00

0.07

0.140.210.28A B S /R C

012345

6E T o /R C

0.00.2

0.40.60.81.0?R o (R E o /A B S )

0.000.040.080.12?E o (E T o /A B S )

0.0

0.10.2

0.30.4?P o (F v /F m o r T R o /A B S )

0.0

0.20.40.60.81.0

Fig.7.Effects of P and Al interactions on φPo (A),φEo (B),φRo (C),ABS/RC (D),TR o /RC (E),ET o /RC (F),RE o /RC (G),ψEo (H),δRo (I)and PI tot,abs (J)of dark-adapted sour pummelo leaves.Each point represents the mean of 8–10replicates with standard error.Each variable was analyzed by 2(Al levels)×4(P levels)ANOVA.(A)–(F)and (H)P values for Al,P and the interactions between the two were all <0.0001;P values for Al,P and the interactions between the two were <0.0001,<0.0001and 0.0001(G);<0.0001,0.5806and 0.6788(I);and <0.0001,<0.0001and 0.0407(L),respectively.Different letters indicate signi?cant differences at P <0.05.

F v /F m (TR o /ABS),ET o /ABS,RE o /ABS,ET o /RC,RE o /RC,ET o /TR o and PI tot,abs (Fig.7A–C,F–H and J)increased as P supply increased from 50to 250μM under Al stress,then remained unchanged at the highest P supply.All the seven parameters were lower in +Al leaves than in ?Al ones under 50or 100μM P,and were not

higher in +Al leaves than in ?Al ones under 250or 500μM P.However,RE o /ET o did not signi?cantly change in response to P with or without Al stress.RE o /ET o were lower in +Al leaves than in ?Al ones under 50,100or 250μM P,but did not signi?cantly differ between Al treatments under 500μM P (Fig.7I).

306

Physiol.Plant.137,2009

Table 1.Effects of P and Al interactions on data extracted from the recorded ?uorescence transient OJIP.Each value is the mean of 8–10replicates with standard error.Each variable was analyzed by 2(Al levels)×4(P levels)ANOVA.P values for Al,P and the interactions between the two were all <0.0001(F o ,F 300μs and F m );P values for Al,P and the interactions between the two were <0.0001,0.0003and 0.6103(F J );and 0.0394,0.4773and 0.0693(F I ),respectively.Different letters for the same parameters indicate signi?cant differences at P <0.05.

F o

F 300μs F J F I F m P supply (μM )?Al +Al ?Al +Al ?Al +Al ?Al +Al ?Al +Al 50435c 936a 1013cd 1709a 1706bc 2034a 2294abc 2186c 2626ab 2252c 100431c 668b 1001cd 1432b 1707bc 2016a 2271bc 2396ab 2608ab 2568ab 250412c 467c 926d 1097c 1593c 1798b 2209bc 2472a 2549ab 2755a 500

419c

447c

925d

1054cd

1565c

1716bc

2199bc

2338abc

2541ab

2620ab

M a x i m u m a m p l i t u d e o f I P p h a s e

0.000.030.060.090.120.15I n i t i a l R u b i s c o a c t i v i t y (μm o l m -2 s -1)

612182430

CO 2 assimilation (μmol m -2 s -1

)

246

P I t o t ,a b s

0.0

0.20.40.6

Shoot DW (g plant -1

)

5

101520

25

Fig.8.Initial Rubisco activity (A,D),maximum amplitude of IP phase (B,E)and PI tot,abs (C,F)in relation to leaves CO 2assimilation and shoot DW in sour pummelo seedlings.Each point is the mean ±standard error for the independent variables (n =5or 12)and the dependent variables (n =5?10).Maximum amplitude of IP phase =(F m ?F o )/(F I ?F o )?1.

Leaf initial Rubisco activity,maximum amplitude of IP phase and PI tot,abs in relation to CO 2assimilation and shoot DW

Leaf CO 2assimilation increased with increasing leaf initial Rubisco activity (Fig.8A),maximum amplitude of IP phase (Fig.8B)and PI tot,abs (Fig.8C),respectively.Leaf initial Rubisco activity (Fig.8D),maximum amplitude of IP phase (Fig.8E)and PI tot,abs (Fig.8F)increased with increasing shoot DW,respectively.

Discussion

P alleviated Al-induced inhibition of root and shoot growth (Fig.1A and B),as found for rice (Nakagawa et al.2003),Lespedeza bicolor (Sun et al.2008),maize (Salinas and Sanchez 1977)and sorghum (Tan and Keltjens 1990a,1990b).P-induced amelioration of growth inhibition may be related to the following two factors,including:(a )the formation of Al–P at the root surface and/or in the root tissues and less Al

Physiol.Plant.137,2009

307

accumulation in stems and leaves(Fig.2A–C);and (b)increased P level in the roots,stems and leaves (Fig.2D–F).Our?nding that root Al content increased from50to250μM,then remained unchanged at the highest P supply under Al stress(Fig.2A–C)indicates that increased insoluble Al–P,which are non-toxic to plants,at the root surface and/or in the root tissues is likely responsible for the lower stem and leaf Al level at high P supplies(Fig.2B and C).This agrees with previous view that insoluble non-toxic Al–P precipitates may accumulate at the root surface and/or in the root tissues (Taylor1991).Our?nding that Al increased root/shoot ratio under50or100μM P(Fig.1D)agrees with early reports for citrus(Chen et al.2005a,Jiang et al.2008) and‘Nemaguard’peach(Graham2001).However,Al did not affect the ratio under250or500μM P(Fig.1D), meaning that high P can alleviate Al-induced increase in root/shoot ratio.

Our results showed that the CO2assimilation in+Al leaves increased with increasing P supply ranging from 50to250μM,then kept unchanged at the highest P supply(Fig.4A),indicating that P can alleviate Al-induced inhibition of photosynthesis.The present work (Fig.4A–C),like that of early workers(Chen et al.2005a, Jiang et al.2008)indicates that Al-induced inhibition of CO2assimilation is primarily caused by non-stomatal factors.The decrease in CO2assimilation in+Al leaves could not be explained alone by the decrease in Chl, at least under250and500μM P,because Chl content was not signi?cantly lower in+Al leaves than in?Al leaves(Fig.3A).This inference is also supported by our previous observations that Al treatment decreased CO2 assimilation in‘Cleopatra’tangerine(Citrus reshni)and sour pummelo leaves by40and60%,respectively,but only decreased Chl content by8and34%,respectively (Chen et al.2005a,Jiang et al.2008).Similarly,the decrease in CO2assimilation in+Al leaves could not be explained alone by the decrease in initial and total Rubisco activity,at least under500μM P,because no signi?cant differences were found in initial and total Rubisco activity between+Al leaves and–Al ones (Fig.4D and E).The?nding that Al decreased total Rubisco activity except for a similar activity between Al treatments under250and500μM P(Fig.4E)contrasts with our previous reports that the decrease in CO2 assimilation in+Al leaves of‘Cleopatra’tangerine (Chen et al.2005a)and sour pummelo(Jiang et al. 2008)was unaccompanied by decreased total Rubisco activity.In previous experiments,the nutrient solution for‘Cleopatra’tangerine,an Al-tolerant citrus rootstock (Chen et al.2005a)and sour pummelo(Jiang et al.2008) contained250μM P+50μM B and100μM P+46μM B, respectively.In addition,we found that B could alleviate Al-induced decrease of total Rubisco activity(data not

shown).Thus,the lower Rubisco activity(Fig.4D and E)

may be associated with the lower B concentration in the

nutrient solution.

We found that Al-induced positive L became

less pronounced with increasing P supply(Fig.6D),

indicating that P increase the energetic grouping or

co-operativity between PSII units in+Al leaves(Strasser

1978).The physiological effect of a higher grouping is

that it contributes to a higher stability of the sample

toward stress(Tsimilli-Michael and Strasser2008).This

is also supported by our data that P decreased the

heterogeneity of+Al samples(Fig.S1).

The decrease in F v/F m(TR o/ABS)in50μM P+1.2 m M Al-treated leaves resulted from both a decrease in F m and an increase in F o(Table1,Fig.5A),as found for

Al-treated(Jiang et al.2008)and B-de?cient(Han et al.

2009)sour pummelo leaves.In contrast,the decline

of F v/F m in100μM P+1.2m M Al-treated leaves was caused by an increase in F o(Table1,Fig.5A),as reported for B-excess sour pummelo leaves(Han et al.2009).Our

results that F v/F m in+Al leaves increased with increasing P supply ranging from50to250μM,then remained unchanged at the highest P supply(Fig.7A)means that

P can prevent Al-induced decrease in maximum PSII

ef?ciency of dark-adapted sour pummelo leaves.

The appearance of positive K in OJIP transients from +Al leaves(Fig.6B)means that the OEC is damaged (Hakala et al.2005,Srivastava et al.1997)and the

energetic connectivity between photosynthetic units is

changed(Srivastava et al.1997).This is also supported

by the data that+Al leaves had increased deactivation of

OEC(Fraction of OEC=[1?(V K/V J)]treated sample/[1?(V K/V J)]control,an estimation of the fraction of OEC

in comparison with the control,where V K is the

relative variable?uorescence at300μs and V J is the relative variable?uorescence at J-step,Appenroth

et al.2001)(data not shown)and less energy exchange

between independent PSII units,as indicated by positive

L(Fig.6D).The fraction of electrons from the RCs at the acceptor side is not only related to the

capacity of electron donation to the RCs,but also

related to the electron transport capacity from RCs to

electron acceptors.Based on the increased relative

variable?uorescence at J-and I-steps(V J and V I: V J=(F J?F o)/(F m?F o)and V I=(F I?F o)/(F m?F o)) (Fig.6A)and the decreased maximum amplitude of IP

phase in+Al leaves(Fig.5B),we conclude that the

acceptor side of PSII was damaged more severely than

the donor side under Al stress.This inference is also

supported by the observation that+Al leaves had a

lower F v(F v=F m–F o)and a higher F o(Table1and Fig.5A),which is the characteristic of photoinhibitory

308Physiol.Plant.137,2009

damage at PSII acceptor side(Setlik et al.1990).Al decreased the yields(φPo,φEo,φRo,ψEo;Fig.7A–C and H),the?uxes(ET o/RC and RE o/RC;Fig.7F and G)and the amount of reduced end electron acceptors at the PSI acceptor side,as indicated by the decreased maximum amplitude of IP phase(Fig.5B),and damaged all of the photochemical and non-photochemical redox reactions, as indicated by the decreases in PI tot,abs(Fig.7J).Our results showed that shoot growth was more sensitive to Al toxicity than root growth,CO2assimilation, OJIP transient and most related parameters(Table1, Figs.1A,B,4A,5A and7).These results demonstrated that Al impaired the whole photosynthetic electron transport chain from PSII donor side up to the reduction of end acceptors of PSI,which may be associated with growth inhibition.With increasing P supply,Al-induced positive L, K, J and I became less pronounced(Fig.6B and D)and Al-induced decrease in yields(Fig.7A–C and H),?uxes(Fig.7F and G), maximum amplitude of IP phase(Fig.5B)and PI tot,abs (Fig.7J)was lessened,indicating that P can alleviate Al-induced impairment of the whole photosynthetic electron transport chain.Regressive analysis showed that CO2assimilation decreased with decreasing maximum amplitude of IP phase(Fig.8B)and PI tot,abs(Fig.8C), respectively,and IP phase(Fig.8E)and PI tot,abs(Fig.8F) decreased with decreasing shoot DW.Therefore,we conclude that P lessened Al-induced inhibition of CO2 assimilation through alleviating Al-induced impairment of the whole photosynthetic electron transport chain. Because+Al leaves only utilized a small fraction of the absorbed light energy in photosynthetic electron transport,more excess excitation energy existed in+Al leaves.The excess absorbed light also in turn can lead to the production of1O2and reduced active oxygen species,causing damage to photosynthetic apparatus and cell structure(Chen and Cheng2003,Chen et al. 2005b).However,we found that1.6m M Al treatment decreased CO2assimilation of sour pummelo leaves,but did not increase leaf malondialdehyde(MDA)level(data not shown).Similar results were obtained with2m M Al-treated‘Cleopatra’tangerine leaves(Chen et al.2005b). Therefore,Al-induced decrease in CO2assimilation could not be attributed to photo-oxidative damage.The lack of a correlation between CO2assimilation and MDA in sour pummelo and‘Cleopatra’tangerine leaves did not necessarily imply that all the citrus genotypes should have the same physiological behavior against Al stress, because citrus is not a homogenous type of plants and there are very different species and cultivars.In fact,lipid peroxidation in response to Al stress has been reported in some plant species,including pea(Pisum sativum) (Yamamoto et al.2001),Brassica napu(Basu et al.2001),soybean(Glycine max)(Cakmak and Horst1991),rice (Meriga et al.2004),rice bean(Vigna umbellata)and French bean(Phaseolus vulgaris)(Subrahmanyam1998). To conclude,our?ndings support the hypothesis that P alleviates Al-induced inhibition of growth and impairment of the whole photosynthetic electron transport chain from PSII donor side up to the reduction of end acceptors of PSI through increasing Al immobilization in roots and P level in roots and shoots, thus preventing the decrease of CO2assimilation. Acknowledgements–This study was?nancially supported by the National Natural Science Foundation of China(No. 30771487)and the Natural Science Foundation of Fujian Province of China(No.B0710011).

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Additional Supporting Information may be found in the online version of this article:

Table S1.Summary of parameters,formulae and their description using data extracted from chlorophyll a?uorescence(OJIP)transient.

Figure S1.Effects of P and Al interactions on high irradiance actinic-light-induced OJIP transients of dark-adapted sour pummelo leaves plotted on a logarithmic time scale(0.01to1s).Gray circles are single measurement and black circles are mean transients of all measured samples.

Please note:Wiley-Blackwell are not responsible for the content or functionality of any supporting materials supplied by the authors.Any queries(other than missing material)should be directed to the corresponding author for the article.

Edited by A.Krieger-Liszkay

Physiol.Plant.137,2009311

ASTM B733-04 Standard Specification for Autocatalytic (Electroless) Nickel-Phosphorus Coatings on Me

Designation:B733–04 Standard Speci?cation for Autocatalytic(Electroless)Nickel-Phosphorus Coatings on Metal1 This standard is issued under the?xed designation B733;the number immediately following the designation indicates the year of original adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.A superscript epsilon(e)indicates an editorial change since the last revision or reapproval. This standard has been approved for use by agencies of the Department of Defense. 1.Scope 1.1This speci?cation covers requirements for autocatalytic (electroless)nickel-phosphorus coatings applied from aqueous solutions to metallic products for engineering(functional)uses. 1.2The coatings are alloys of nickel and phosphorus pro-duced by autocatalytic chemical reduction with hypophosphite. Because the deposited nickel alloy is a catalyst for the reaction, the process is self-sustaining.The chemical and physical properties of the deposit vary primarily with its phosphorus content and subsequent heat treatment.The chemical makeup of the plating solution and the use of the solution can affect the porosity and corrosion resistance of the deposit.For more details,see ASTM STP265(1)2and Refs(2)(3)(4)and(5). 1.3The coatings are generally deposited from acidic solu-tions operating at elevated temperatures. 1.4The process produces coatings of uniform thickness on irregularly shaped parts,provided the plating solution circu-lates freely over their surfaces. 1.5The coatings have multifunctional properties,such as hardness,heat hardenability,abrasion,wear and corrosion resistance,magnetics,electrical conductivity provide diffusion barrier,and solderability.They are also used for the salvage of worn or mismachined parts. 1.6The low phosphorus(2to4%P)coatings are microc-rystalline and possess high as-plated hardness(620to750HK 100).These coatings are used in applications requiring abra-sion and wear resistance. 1.7Lower phosphorus deposits in the range between1and 3%phosphorus are also microcrystalline.These coatings are used in electronic applications providing solderability,bond-ability,increased electrical conductivity,and resistance to strong alkali solutions. 1.8The medium phosphorous coatings(5to9%P)are most widely used to meet the general purpose requirements of wear and corrosion resistance. 1.9The high phosphorous(more than10%P)coatings have superior salt-spray and acid resistance in a wide range of applications.They are used on beryllium and titanium parts for low stress properties.Coatings with phosphorus contents greater than11.2%P are not considered to be ferromagnetic. 1.10The values stated in SI units are to be regarded as standard. 1.11The following precautionary statement pertains only to the test method portion,Section9,of this speci?cation.This standard does not purport to address all of the safety concerns, if any,associated with its use.It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limita-tions prior to use. 2.Referenced Documents 2.1ASTM Standards:3 B368Test Method for Copper-Accelerated Acetic Acid-Salt Spray(Fog)Testing(CASS Testing) B374Terminology Relating to Electroplating B380Test Method of Corrosion Testing of Decorative Electrodeposited Coatings by the Corrodkote Procedure B487Test Method for Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of a Cross Section B499Test Method for Measurement of Coating Thick-nesses by the Magnetic Method:Nonmagnetic Coatings on Magnetic Basis Metals B504Test Method for Measurement of Thickness of Me-tallic Coatings by the Coulometric Method B537Practice for Rating of Electroplated Panels Subjected to Atmospheric Exposure 1This speci?cation is under the jurisdiction of ASTM Committee B08on Metallic and Inorganic Coatings and is the direct responsibility of Subcommittee B08.08.01on Engineering Coatings. Current edition approved Aug.1,2004.Published August2004.Originally approved https://www.sodocs.net/doc/6c2546210.html,st previous edition approved in1997as B733–97. 2The boldface numbers given in parentheses refer to a list of references at the end of the text. 3For referenced ASTM standards,visit the ASTM website,https://www.sodocs.net/doc/6c2546210.html,,or contact ASTM Customer Service at service@https://www.sodocs.net/doc/6c2546210.html,.For Annual Book of ASTM Standards volume information,refer to the standard’s Document Summary page on the ASTM website. 1 Copyright?ASTM International,100Barr Harbor Drive,PO Box C700,West Conshohocken,PA19428-2959,United States. Copyright by ASTM Int'l (all rights reserved); Reproduction authorized per License Agreement with PATRICK SPITZ (PARKER HANNIFIN); Mon Jan 23 04:59:17 EST 2006

五氧化二磷

中文名五氧化二磷 英文名Phosphorus pentoxide 别名磷酸酐 无水磷酸 磷酐 P2O5 氧化磷(V) 英文别名Phosphoric anhydride Phosphorus(V) oxide phosphorus pentoxidedessicant Phosphorous Pentoxide Phosphorus pentoxide 99+ % for analysis diphosphorus pentaoxide PhosphorusV oxideACSwhitepowder Phosphorusoxidewhitepowder Phosphoric Pentoxide P2O5 tricyclo[3.3.1.1~3,7~]tetraphosphoxane 1,3,5,7-tetraoxide 1,3-dioxodiphosphoxane-1,3-diium-1,3-diolate Phosphorus(Ⅴ)oxide Phosphorous Pentoxide (P2O5) CAS 1314-56-3

EINECS 215-236-1 化学式P2O5 分子量141.945 inchi InChI=1/O5P2/c1-6(2)5-7(3)4 熔点340-360℃ 物化性质性状白色单斜晶体或粉末。 熔点580~585℃ 相对密度2.39 溶解性溶于水生成磷酸并放出大量热，溶于硫酸。不溶于丙酮和氨。产品用途用作干燥剂、脱水剂、糖的精制剂，并用于制取磷酸、磷化合物及气溶胶等用作半导体硅的掺杂源、脱水干燥剂、有机合成缩合剂及表面活性剂，也用于高纯磷酸的制备 危险品标志 C - 腐蚀性物品 风险术语R35 - 引起严重灼伤。 安全术语S22 - 切勿吸入粉尘。 S26 - 不慎与眼睛接触后，请立即用大量清水冲洗并征求医生意见。S45 - 若发生事故或感不适，立即就医(可能的话，出示其标签)。 上游原料黄磷 下游产品四氯三氧化二磷O,O-二乙基硫代磷酰氯2-氯-5-氯甲基吡啶三氯乙腈复合肥治螟磷乳油(40%) 氨鲁米特盐酸阿米替林抗静电剂抗静电剂P 抗静电剂PK 单烷基醚磷酸酯多聚磷酸铵水处理剂POE 涤纶油剂

表面流人工湿地中磷的季节性迁移转化规律

表面流人工湿地中磷的季节性迁移转化规律 摘要：研究了上海市梦清园芦苇人工湿地中磷的季节性迁移转化规律，结果表明，该人工湿地中，基质吸附和沉降是湿地磷的主要去除方式，其对磷的去除量一直保持在总磷去除量的５０％以上，春季可达９２．０８％，秋季最低也达５７．８１％。但由于基质的吸附作用偏弱，磷的沉降占主导地位。植物对磷的吸收量即去除量随季节变化比较明显，在夏、秋、冬三季，其可以占到总磷去除量的２０％以上。此外，外界的磷源输入占总磷去除量的１６％，因此，在开放性水处理系统中外界引起的磷污染问题也应引起重视。 关键词：表面流人工湿地；磷；基质吸附 Ａｂｓｔｒａｃｔ：ＳｅａｓｏｎａｌｍｉｇｒａｔｉｏｎａｎｄｄｉｓｔｒｉｂｕｔｉｏｎｏｆｐｈｏｓｐｈｏｒｕｓｗａｓｓｔｕｄｉｅｄｉｎｓｕｒｆａｃｅｆｌｏｗｃｏｎｓｔｒｕｃｔｅｄＭｅｎｇｑｉｎｇｙｕａｎａｒｔｉｆｉｃｉａｌｒｅｅｄｗｅｔｌａｎｄ．Tｈｅｒｅｓｕｌｔｉｎｄｉｃａｔｅｄｔｈａｔｓｕｂｓｔｒａｔｅｓａｄｓｏｒｐｔｉｏｎａｎｄｓｅｄｉｍｅｎｔａｔｉｏｎｗｅｒｅｔｈｅｍａｉｎｐａｔｈｓｏｆｐｈｏｓｐｈｏｒｕｓｒｅｍｏｖａｌ，ｗｈｉｃｈｃｏｎｔｒｉｂｕｔｅｄｔｏｍｏｒｅｔｈａｎｈａｌｆｏｆｔｈｅｔｏｔａｌｐｈｏｓｐｈｏｒｕｓｒｅｍｏｖａｌｃｏｎｔｅｎｔ；ｉｎｓｐｒｉｎｇ，ｔｈｅｙａｃｃｏｕｎｔｅｄｆｏｒａｓｈｉｇｈａｓ９２．０８％；ｗｈｉｌｅｉｎａｕｔｕｍｎｗｈｅｎｔｈｅｐｈｏｓｐｈｏｒｕｓｒｅｍｏｖａｌｃｏｎｔｅｎｔｗａｓｔｈｅｌｏｗｅｓｔ，ｔｈｅｙａｃｃｏｕｎｔｅｄｆｏｒ５７．８１％．Ａｎｄｓｅｄｉｍｅｎｔａｔｉｏｎｗａｓｄｏｍｉｎａｎｔｉｎｔｈｅｓｅｔｗｏｐｈｏｓｐｈｏｒｕｓｒｅｍｏｖａｌｐａｔｈｓ．Ｔｈｅａｂｓｏｒｐｔｉｏｎｏｆｐｌａｎｔｓｄｉｆｆｅｒｅｄｆｒｏｍｓｅａｓｏｎｔｏｓｅａｓｏｎ；ｉｎｓｕｍｍｅｒ，ａｕｔｕｍｎａｎｄｗｉｎｔｅｒ，ｉｔｃｏｕｌｄｃｏｎｔｒｉｂｕｔｅｔｏｍｏｒｅｔｈａｎ２０％ｏｆｔｈｅｔｏｔａｌｐｈｏｓｐｈｏｒｕｓｒｅｍｏｖａｌｃｏｎｔｅｎｔ．Ｍｅａｎｗｈｉｌｅ，ａｔｍｏｓｐｈｅｒｉｃｐｈｏｓｐｈｏｒｕｓｄｅｐｏｓｉｔｉｏｎａｌｓｏａｃｃｏｕｎｔｅｄｆｏｒ１６％ｏｆｔｈｅｔｏｔａｌｐｈｏｓｐｈｏｒｕｓｒｅｍｏｖａｌｃｏｎｔｅｎｔ，ｗｈｉｃｈｍｕｓｔｂｅｐａｉｄａｔｔｅｎｔｉｏｎｔｏｉｎｔｈｅｏｐｅｎｉｎｇｗａｔｅｒｔｒｅａｔｍｅｎｔｓｙｓｔｅｍｄｅｓｉｇｎ． Ｋｅｙｗｏｒｄｓ：ｓｕｒｆａｃｅｆｌｏｗｃｏｎｓｔｒｕｃｔｅｄｗｅｔｌａｎｄ；ｐｈｏｓｐｈｏｒｕｓ；ａｄｓｏｒｐｔｉｏｎｏｆｓｅｄｉｍｅｎｔｓ 人工湿是一种新型生态污水处理技术，在湿地除磷功能的研究中，一般认为，人工湿地中磷的去除主要以基质的吸附固定为主，植物的吸收作用也会从湿地系

Rethinking early Earth phosphorus geochemistry

磷是一种重要的生物元素，生命起源（导致包含在生物分子中）的途径很难被确定。大多数生命起源的磷酸化反应都以正磷酸盐作为磷源。这里认为在早期地球上磷的地球化学由低氧化态的磷化合物控制，如亚磷酸盐HPO32-其比正磷酸盐易溶，活性强。这种低氧化态磷源于宇宙大爆炸时期掉落的外太空物质或在其影响下产生，它们长期存在于弱还原环境中。换一种说法就是：在早期地球上磷的地球化学提供了与生命起源相关的磷化合物，但这种形成路径未探明。建议了一种形成缩合磷酸盐的简易反应路径，并且与当今生命体生化利用低氧化态的磷是一致的。建议研究：可以测定太古代的岩石中的低氧化态的磷化合物。 陨星生命起源磷酸盐生命起源前的氧化还原化学 磷是许多生态系统的限制元素。磷在生物化学普遍存在，因为磷酸化的生物大分子在复制和遗传信息、新陈代谢、结构（磷脂）都起着重要作用。磷的多个重要的性质使磷酸在生物系统中很有利，包括热力学不稳定性协同动力学稳定性、电荷和配体、在典型氧化还原环境下恒定的氧化态。这些性质对形成大的包含信息的聚合体是非常重要的，因此与早期生命的起源与发展密切相关。 1、磷的地球化学和天体化学 图一中表现了在生命体中磷的主要的形式。能被生命利用的无机磷：正磷酸盐orthophosphate焦磷酸盐pyrophosphate和其他缩合磷酸盐，亚磷酸盐phosphite次磷酸盐hypophosphite和磷化氢phosphine这些无机形式的磷要么被作为有机体的磷源来合成生物大分子或者可能是磷代谢的代谢副产物（PH3）。另外，正磷酸盐作为细胞的缓冲剂，能保持细胞内pH大约为7。有机磷包括c-o-p、c-p，都是由酶作用无机磷形成。 在地壳表面的氧化还原环境中磷是一种亲岩元素，因此正磷酸是当今地壳表面主要的无机磷。通过正磷酸矿物溶解，正磷酸盐的浓度是可缓冲的。像磷灰石Ca5(PO4)3(OH,F,Cl)来自当今的地壳，白磷钙矿Ca9MgH(PO4)7和钙磷石CaHPO4·2H2O,来自在生命介入前的磷灰石沉积。因为磷酸盐矿物是难溶的并且磷的地球化学循环缓慢，因此正磷酸的浓度是长期生命发展过程中的主要限制性营养物。 从地球表面氧化还原环境的P相的热力学推测出正磷酸盐占主导地位（Fig.2A）。在地球表面，正磷酸盐矿物是磷的主要携带者，因为在陆地的氧化还原环境没有低氧化态磷化合物是稳定的。通过地质过程可能形成低浓度的其他P相，但是这些相不存在热力学平衡并缓

单位换算

How Many? A Dictionary of Units of Measurement ? Russ Rowlett and the University of North Carolina at Chapel Hill Table of Contents About the Dictionary Using the Dictionary SI Units for Clinical Data The following table provides factors for converting conventional units to SI units for selected clinical data. Source: JAMA Author Instructions. Conversion: q to convert from the conventional unit to the SI unit, multiply by the conversion factor; q to convert from the SI unit to the conventional unit, divide by the conversion factor. Component Conventional Unit Conversion Factor SI Unit Acetaminophenμg/mL 6.62μmol/L Acetoacetic acid mg/dL0.098mmol/L Acetone mg/dL0.172mmol/L Acid phosphatase units/L 1.0U/L Alanine mg/dL112.2μmol/L Alanine aminotransferase (ALT)units/L 1.0U/L Albumin g/dL10g/L Alcohol dehydrogenase units/L 1.0U/L Aldolase units/L 1.0U/L Aldosterone ng/dL0.0277nmol/L Alkaline phosphatase units/L 1.0U/L Aluminum ng/mL0.0371μmol/L Aminobutyric acid mg/dL97μmol/L Amitriptyline ng/mL 3.61nmol/L Ammonia (as NH3)μg/dL0.587μmol/L Amylase units/L 1.0U/L Androstenedione ng/dL0.0349nmol/L Angiotensin I pg/mL0.772pmol/L

A bacterium that can grow by using arsenic instead of phosphorus

A bacterium that can grow by using arsenic instead of phosphorus 一株可能利用砷替代磷作為生長所需元素的細菌 ABSTRACT: Life is mostly composed of the elements carbon, hydrogen, nitrogen, oxygen, sulfur and phosphorus. Although these six elements make up nucleic acids, proteins and lipids and thus the bulk of living matter, it is theoretically possible that some other elements in the periodic table could serve the same functions. Here we describe a bacterium, strain GFAJ-1 of the Halomonadaceae, isolated from Mono Lake, CA, which substitutes arsenic for phosphorus to sustain its growth. Our data show evidence for arsenate in macromolecules that normally contain phosphate, most notably nucleic acids and proteins. Exchange of one of the major bio-elements may have profound evolutionary and geochemical significance. 生命主要由碳，氫，氮，氧，硫和磷等元素所組成,然而這六種元素可組成核酸,蛋白質和脂質,因此這些大量的生命組成物質,理論上在元素週期表上可能會有其他元素有相同的功能.在此我們描述一株Halomonadaceae屬的細菌strain GFAJ-1，分離自加州的Mono湖.一種利用砷替代磷作為生長所需元素的細菌.研究數據顯示在正常含有磷酸鹽的大分子中含有砷酸鹽,尤其是核酸和蛋白質.替換主要的生物元素可能會深深影響演化和地球化學的重要性. Biological dependence on the six major nutrient elements carbon, hydrogen, nitrogen, oxygen, sulfur, and phosphorus is complemented by a selected array of other elements, usually metal(loid)s present in trace quantities that serve critical cellular functions, such as enzyme cofactors(1). There are many cases of these trace elements substituting for one another. A few examples include the substitution of tungsten for molybdenum and cadmium for zinc in some enzyme families (2, 3) and copper for iron as an oxygen-carrier in some arthropods and mollusks(4). In these examples and others, the trace elements that interchange share chemical similarities that facilitate the swap. However, there are no prior reports of substitutions for any of the six major

Electroless nickel–phosphorus plating on graphite powder

Materials Science and Engineering A 471 (2007) 165–168 Short communication Electroless nickel–phosphorus plating on graphite powder M.Palaniappa?,G.Veera Babu,K.Balasubramanian Non-Ferrous Materials Technology Development Center,Kanchanbagh Post,Hyderabad500058,India Received26October2006;received in revised form27February2007;accepted1March2007 Abstract Electroless deposition technique was used to coat Ni–P on graphite particles with high deposition rate and bath stability by activating the graphite powder in a furnace at380?C for1h.The effect of plating time,size of the powder and weight of the powder were studied.It was found that by a simple and controlled plating method a uniform and continuous layer of nickel could be deposited on the surface of graphite particles.Scanning electron microscopy images and EDS spectra before and after electroless nickel plating con?rm that nickel is deposited on the surface of graphite particles.The rate of increase in weight percent nickel over graphite decreases with time and reaches a plateau.Further increase in weight is attained by plating the same powders in a fresh bath to obtain desired Ni–P alloy mass. ? 2007 Elsevier B.V. All rights reserved. Keywords:Electroless;Activation;Graphite 1.Introduction Nickel–graphite particulate composite gas-turbine insert materials use the combination of good corrosion resistance and high temperature resistance of nickel and solid lubrica-tion of graphite.Addition of graphite improves the anti-friction property of the inserts,resulting in lower wear and tear of turbine blades.Powder metallurgical processing route for man-ufacture of such materials is extensively used.Metal coating on graphite powders can avoid strong interfacial reactions, minimizing the reactions between the matrix and reinforce-ment particles.Coating of graphite powders will result in better compaction and higher sinter densities,and consider-able reduction of losses in carbon particles during sintering process. The electrochemical reduction of nickel during electroless plating is a fairly simple reaction.It is well known that the elec-troless nickel coating(EN)is the autocatalytic deposition of Ni–P alloy from an aqueous solution on to a substrate without the application of external current[1–5].EN coatings provide characteristics that expand the physical properties beyond those of pure nickel coating systems.These coatings are widely used in the mechanical,chemical and electronic industries because of ?Corresponding author.Tel.:+914024341332/2545;fax:+914024342567. E-mail addresses:mpalaniappa@https://www.sodocs.net/doc/6c2546210.html,,mpalaniappa@nftdc.res.in (M.Palaniappa).their unique corrosion and wear resistance[6],hardness,lubric-ity,uniformity of deposit regardless of geometries,solderability and bondability and nonmagnetic properties[7].The structure, composition,plating rate and properties of electroless Ni–P coat-ings are determined by several factors of which pH,temperature, nickel ion concentration and hypophosphite concentration are signi?cant.Randin and Hinterman[8]determined that the phos-phorous content of the deposit increases as the pH of the bath decreases.Plating bath temperature increases the plating rate[9] although a very high temperature can lead to decomposition of the plating bath. Electroless deposition process has undergone numerous mod-i?cations to meet the challenging needs of a variety of industrial applications since Brenner and Riddell invented the process in 1946.The advantage of high stability of plating bath,controlla-bility and reproducibility of the process has been adopted as an effective tool for surface modi?cation technology[10].The orig-inal Ni–P plating on metals has been adapted to deposit on the surface of ceramic particles.Studies related to plating of metal on to ceramic substrates such as SiC[11,12],Al2O3[13],carbon nano-tubes[14]and graphite[15]which do not have catalytic surface have employed the use of sensitization step(SnCl2)fol-lowed by activation(PdCl2),prior to plating[16].Nickel plating on ceramic particles is dif?cult because it does not have catalyt-ically active surface[14].As far as deposition of metal on the surface of graphite particles by electroless plating is concerned very few literature is available. 0921-5093/$–see front matter? 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2007.03.004

Preparation of microencapsulated red phosphorus through melamine cyanurate self-assembly

Preparation of microencapsulated red phosphorus through melamine cyanurate self-assembly and its performance in flame retardant polyamide 6 INTRODUCTION With the development of halogen-free flame retardants worldwide in recent years, red phosphorus (RP) has been widely applied in many flame retarded polymers. As an important phosphorus flame retardant, it shows some distinct advantages such as low cost, little smoke, and low toxicity. The flame retardancy mechanisms of RP have been described as follows: the oxidation of RP first occurs with increasing temperature, then the produced oxide reacts with the water from decomposed polymer to produce metaphosphoric acid, phosphoric acid, and polyphosphoric acid, which can cover the surface of the burning materials by a liquid film, and further promote the dehydration of polymers to form a stable char layer. Such a condensed phase process was emphasized as a predominant mechanism. Second, a certain amount of PO [dot] free radicals are produced during combustion, and they can effectively capture H [dot] and HO [dot] active free radicals, which induce the chain degradation of the polymer, thus decreasing the rate of fuel formation and thus retarding the gas phase of the fire [1-3]. Among all phosphorus-based flame retardants, the phosphorus content of RP is the highest. At the same loading level, RP can generate more acids and PO [dot] free radicals, therefore it shows better flame retardancy when compared with other phosphorus-based products. Nevertheless, RP has some disadvantages as a flame retardant. Because of chemical instability, it is sensitive to friction and heat and its dust is easily flammable and explosive, causing some safety problems. Besides' its tendency to slowly react with moist air (with phosphine evolution), its reddish-brown color also restrict its extensive commercial applications. Accordingly, some special surface treatments are needed to modify the properties of RP used as a flame retardant. The current modification methods involve inorganic and polymeric microencapsulation [4, 5]. The former is usually realized through the reactions between soluble salt of magnesium, aluminium, zinc, and soluble hydroxide to produce insoluble hydroxide precipitated on the RP powder surface to form an encapsulation film. Also for film formation, in-situ polymerization of various thermosetting resins including melamine, urea, phenolic, and epoxy resins is usually adopted to encapsulate RP. Both these methods have been commercialized; however, there still exist some problems. Inorganic encapsulated RP shows an easily damaged encapsulation layer, low ignition point, and poor compatibility with polymers. Comparatively, polymeric encapsulated RP shows better properties, but still has tendency to react with moisture and the preparation process is relatively complicated, furthermore, some noxious monomer such as formaldehyde is usually needed and this results in some noticeable ecological and physical problems.