Acid Phosphatase Role in Chickpea/Maize Intercropping

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1 nnls of otny 94: , 24 doi:1.193/o/mch14, ville online t cid Phosphtse Role in hickpe/mize Intercropping S. M. LI 1, 2,L.LI 1, *, F. S. ZHNG 1 nd. TNG 3 1 Deprtment of Plnt Nutrition, hin griculturl University, eijing, 194, hin, 2 Resource nd Environmentl ollege, Northest griculturl University, Hrin, 153, hin nd 3 Deprtment of griculturl Sciences, L Troe University, undoor, Vic. 386, ustrli Received: 8 Septemer 23 Returned for revision: 9 Ferury 24 ccepted: 19 pril 24 Pulished electroniclly: 28 June 24 ckground nd ims Orgnic P comprises 3 8 % of the totl P in most griculturl soils. It hs een proven tht chickpe fcilittes P uptke from n orgnic P source y intercropped whet. In this study, cid phosphtse excreted from chickpe roots is quntified nd the contriution of cid phosphtse to the fcilittion of P uptke y intercropped mize receiving phytte is exmined. Methods For the first experiment using hydroponics, mize (Ze mys Zhongdn No. 2 ) nd chickpe (icer rietinum Son ) were grown in either the sme or seprte continers, nd P ws supplied s phytte, KH 2 PO 4 t 25 mmol P L 1, or not t ll. The second experiment involved soil culture with three types of root seprtion etween the two species: (1) plstic sheet, (2) nylon mesh, nd (3) no rrier. Mize plnts were grown in one comprtment nd chickpe in the other. Phosphorus ws supplied s phytte, (H 2 PO 4 ) 2 t 5 mg P kg 1,ornoP dded. Key results In the hydroponics study, the totl P uptke y intercropped mize supplied with phytte ws 21-fold greter thn when it ws grown s monoculture. In the soil experiment, when supplied with phytte, totl P uptke y mize with mesh rrier nd without root rrier ws 22 nd 15 times, respectively, s much s tht with solid rrier. In oth experiments, roots of oth mize nd chickpe supplied with phytte nd no P secreted more cid phosphtse thn those with KH 2 PO 4 or (H 2 PO 4 ) 2. However, verge cid phosphtse ctivity of chickpe roots supplied with phytte ws 2 3-fold s much s mize. Soil cid phosphtse ctivity in the rhizosphere of chickpe ws lso significntly higher thn mize regrdless of P sources. onclusions hickpe cn moilize orgnic P in oth hydroponic nd soil cultures, leding to n interspecific fcilittion in utiliztion of orgnic P in mize/chickpe intercropping. ª 24 nnls of otny ompny Key words: Intercropping, cid phosphtse, icer rietinum, phosphorus, chickpe, root rrier, fcilittion, monoculture, phytte, Ze mys. INTRODUTION Intercropping is ecoming more nd more importnt to increse crop productivity to meet food demnds of n incresing popultion, especilly in the northwest hin (Li et l., 1999). Intercropping, through effective use of wter, nutrients nd solr energy, cn significntly enhnce crop yields compred with monoculture cropping (Willey, 199; Morris nd Grrity, 1993). When two crops re plnted together, interspecific competition or fcilittion etween plnts my occur (Vndermeer, 1989). For exmple, mixtures of cerels nd lupins produced higher grin yields thn either crop grown lone; the yield increses were not only due to n improved nitrogen nutrition of the cerel component, ut lso to other unknown cuses (Nel, 1975). Mize yield ws incresed y intercropping with groundnut, minly ecuse of n enhnced P uptke (El Dessougi et l., 23). White lupin (Lupinus lus) exuded orgnic cids to moilize springly solule phosphte which mde more P ville for whet thn when it ws grown s monoculture (Horst nd Wschkies, 1987; Kmh et l., 1999). Pigeon pe incresed P uptke of the intercropped sorghum y exuding piscidic cid tht cheltes Fe 3+ nd susequently releses P from FePO 4 (e et l., 199). In field experiment, f en fcilitted P uptke y mize (Li et l., 23). However, ll these studies were focused on inorgnic P in the soil. In most griculturl soils, orgnic P comprises 3 8 % of the totl P (Dll, 1978). The lrgest frction of orgnic P, pprox. 5 %, is in the form of phytin nd its derivtives (Trfdr nd lssen, 1988). Orgnic P sources cn e utilized y the plnt fter they re hydrolysed y phosphtse (Gilert nd Knight, 1999). groforestry species with high cid phosphtse ctivities cn moilize nd utilize orgnic P in the soil (George et l., 22). hickpe could fcilitte P uptke y ssocited whet from n orgnic P source (Li et l., 23). The mechnism involved, however, remins uncler. The ojectives of this study were to quntify cid phosphtse excreted from chickpe roots nd to exmine whether cid phosphtse contriuted to the fcilittion of P uptke of intercropped mize tht hd een supplied with phytte. MTERILS ND METHODS Plnt mterils nd growth conditions Experiment 1. The first experiment, with four replictes, ws conducted with hydroponics culture in growth chmer t * For correspondence. E-mil lilong@cu.edu.cn nnls of otny 94/2, ª nnls of otny ompny 24; ll rights reserved Downloded from y guest on 21 Septemer 218

2 298 Li et l. cid Phosphtse Role in hickpe/mize Intercropping dy/18 2 night with 14 h photoperiod (25 mmol m 2 s 1 ). It consisted of three P nd three plnting tretments. The three P tretments were (1) without P ddition (P), (2) 25 mmol L 1 PsKH 2 PO 4, nd (3) 25 mmol L 1 P s phytte-n ( 6 H 6 O 24 P 6 N 12, SIGM P-3168). The three plnting tretments were (1) four plnts of mize (Ze mys L. Zhongdn No. 2 ) s monoculture, (2) eight plnts of chickpe (icer rietinum L. Son ) s monoculture, nd (3) two plnts of mize nd four plnts of chickpe s mixed culture. Seeds of chickpe nd mize were surfce-sterilized in 5 % H 2 O 2 for 3 min, pregerminted in the drk in Petri dish with dequte wter, nd were then plnted in qurtz snd. fter 7 8 d, plnts were trnsplnted to 2 L continers with hlf-strength nutrient solution for the first 3 d, nd therefter grown in full- strength nutrient solution with or without P supply. The nutrient solution consisted of K 2 SO , MgSO , Kl 1 1 3, (NO 3 ) , H 3 O , MnSO , uso , ZnSO , (NH 4 ) 6 MO 4 O nd EDT-Fe mol L 1. Kl (25 mm L 1 ) ws dded to the phytte nd no P tretments to equlize the mount of potssium in the KH 2 PO 4 tretment. The ph of the nutrient solution ws djusted to 6 nd the solution ws renewed every 3 d. During the whole experiment, the continers were continuously erted. Experiment 2. The experiment consisted of three P tretments nd three tretments of root seprtion etween mize nd chickpe. The three P tretments were (1) no dded P, (2) (H 2 PO 4 ) 2 H 2 O (orth-p), 5 mg P kg 1 soil (clcium slt ws used to void dding extr potssium to the soil), nd (3) phytte-n, 5 mg P kg 1 soil. Three root seprtions were (1) plstic sheet to eliminte root contct nd solute movement, (2) nylon mesh (3 mm) to prevent root contct ut permit solute exchnge, nd (3) no root seprtion (Fig. 1). Plstic pots (15 m dimeter) were cut in the middle, seprted into two comprtments nd then reconstructed. F IG. 1. Schemtic digrm illustrting seprting the root system of mize nd chickpe y solid root rrier plstic sheet (), nylon mesh () nd no root rrier (). Ech comprtment of the pot ws filled with 15 kgof ir-dried nd sieved (2 mm) soil. The soil ws low P sndy soil collected from Lu Gouqio ridge in the northest of eijing. The soil contined 42 g orgnic mtter, 3 g totl N, 17 mg NHO 3 -extrctle P nd 489 mg K per kg soil, nd hd ph (extrcted y solution of 1 mol L 1 l 2, with soil : solution of 1 : 5) of 78. sl nutrients (without P) were dded in solution to soil (mg kg 1 soil): N 2 mg s NH 4 NO 3, K 2 mg s KNO 3, Mg 5 mg s MgSO 4 7H 2 O, Fe 5 mg s FeSO 4 7H 2 O, Mn 5 mg s MnSO 4, u 5 mg s uso 4 5H 2 O nd Zn 5 mg s ZnSO 4 7H 2 O. The soil ws thoroughly mixed y shking. Six germinted seeds of chickpe nd four seeds of mize were grown in the pot (one species in ech comprtment). Plnts were thinned to five per comprtment for chickpe nd to two for mize 1 d fter sowing. The pots were wtered dily to field cpcity (16 %, w/w). Hrvesting nd soil smpling Experiment 1. fter trnsplnting for 15 d in nutrient solution, one plnt of mize nd two plnts of chickpe were smpled from ech continer every 5 d. Plnt roots were thoroughly wshed with distilled wter for ssy of cid phosphtse ctivity. Dry weights of roots nd shoots were recorded. Phosphorus concentrtion in plnt tissues ws determined using the vnodomolydte method (Westermn, 199) fter the plnt mteril ws digested in concentrted H 2 SO 4. Experiment 2. The plnts were hrvested 4 d fter sowing. Roots were seprted from soil; ny soil remining on the surfces of roots ws rushed off nd the soils plced immeditely in cold room t 4. Dry weights nd P concentrtions in shoots were mesured with the sme methods s in expt 1. Phosphtse ctivity In expt 1, the phosphtse ctivity of intct roots ws ssyed using the method of Mclchln (198). Roots were Downloded from y guest on 21 Septemer 218

3 Li et l. cid Phosphtse Role in hickpe/mize Intercropping 299 wshed in distilled wter, lotted dry nd then immersed in 1 mol L 1 cette uffer (ph 56) contining p-nitrophenyl phosphte t 3 for 1 h. lnks contining ll ingredients except the living mteril were included under the sme conditions nd smpled t the sme time s the ssy. In expt 2, the ctivity of cid phosphtse in soil ws nlysed within 7 d fter smpling y the method of Trfdr nd Jungk (1987) using cette uffer (1 mol L 1,pH56) nd p-nitrophenyl phosphte s sustrte t 3 for 1 h. One unit of cid phosphtse ctivity ws the mount of enzyme per grm root fresh weight or per g soil which produced 1 mmol of p-nitrophenyl per hour. Root length Vile roots of plnts were spred without overlps onto glss plte. The root length ws mesured y lef re scnner (I-23 re meter, ID orportion Ltd, US). Sttisticl nlysis The experiments were set up in completely rndomized design. Sttisticl significnce of differences etween tretments ws nlysed y nlysis of vrince (NOV) nd LSD (lest significnt difference) multiple comprison (SS Institute, 1985). RESULTS iomss In expt 1, the totl iomss of mize (comining intercropping nd sole) supplied with KH 2 PO 4 ws significntly greter thn tht with phytte, which ws greter thn the control (without P), indicting tht the P supply from phytte ws indequte for optiml plnt growth (Fig. 2). When the plnts were intercropped with chickpe nd supplied with phytte, the mize iomss ws incresed lmost 2- fold s compred with monoculture supplied with phytte. However, when plnts were supplied with KH 2 PO 4 or no P ws supplied, no significnt difference in iomss ws oserved etween monoculture nd intercropped mize. verge chickpe iomss of intercropped nd monoculture ws similr when P ws received s KH 2 PO 4 or phytte ut ws greter thn tht without P (Fig. 2). The cropping system did not ffect chickpe iomss regrdless of P source. In expt 2, the gretest iomss of mize ws oserved in the (H 2 PO 4 ) 2 tretment, nd ws significntly greter thn tht of plnts supplied with orgnic P (phytte) or without P ddition (Fig. 3). When plnts were intercropped with chickpe nd supplied with phytte, the iomss of mize without root seprtion nd with nylon mesh ws incresed y 49 % nd 75 %, respectively, s compred with tht with the solid rrier (Fig. 3). When P ws supplied y (H 2 PO 4 ) 2, the iomss of mize ws highest with no root rrier; this ws significntly higher thn the iomss of the mize with the solid rrier (Fig. 3). This effect ws proportionlly more striking when P ws supplied s phytte (Fig. 3). For chickpe, the iomss of plnts seprted from the mize y nylon mesh or plstic sheet ws iomss (g pot 1 ) P Phytte KH 2 PO 4 P Phytte KH 2 PO 4 Mize hickpe F IG. 2. Effect of P sources nd interspecific root interction on the iomss of mize nd chickpe grown in hydroponics (expt 1). Result of NOVs with significnt effect of min fctor (P source) nd su-fctor (intercropping): rs with different cpitl letters (, ) indicte significnt difference etween P sources (P < 5); rs with different lower cse letters (, ) indicte significnt difference etween monoculture nd intercropping (P < 5). iomss (g pot 1 ) c Solid rrier Mesh rrier No rrier P Phytte (H 2 PO 4 ) 2 P Phytte (H 2 PO 4 ) 2 Mize hickpe F IG. 3. Effect of phytte nd interspecific root interction on the iomss of mize nd chickpe grown in soil (expt 2). Result of NOVs with significnt effect of min fctor (P source) nd su-fctor (root rriers): rs with different cpitl letters (, ) indicte significnt difference etween P sources (P < 5); rs with different lower cse letters (, ) indicte significnt difference etween root rriers (P < 5). significntly higher thn tht without the rrier when P ws supplied s either (H 2 PO 4 ) 2 or phytte (Fig. 3). The comined iomss of mize nd chickpe without root rrier (33 g pot 1 ) or with nylon mesh rrier (44 g pot 1 ) supplied with phytte ws greter thn those with the solid rrier (275 g pot 1 ), indicting tht yield dvntges of mize intercropped y chickpe were due to interspecific root interctions. Phosphorus In expt 1, the P concentrtion in mize shoots ws highest in the tretment of KH 2 PO 4, followed y the phytte tretment, nd lowest in the no P control. Phosphorus Downloded from y guest on 21 Septemer 218

4 3 Li et l. cid Phosphtse Role in hickpe/mize Intercropping P concentrtion (g kg 1 d.wt) P Phytte KH 2 PO 4 P Phytte KH 2 PO 4 Mize hickpe F IG. 4. Effect of orgnic P nd intercropping mize with chickpe on P concentrtion in shoots of plnts in hydroponics (expt 1). Result of NOVs with significnt effect of min fctor (P source) nd su-fctor (root rriers): rs with different cpitl letters (, ) indicte significnt difference etween P sources (P < 5); rs with different lower cse letters (, ) indicte significnt difference etween monoculture nd intercropping (P < 5). P uptke (mg pot 1 ) P Phytte KH 2 PO 4 P Phytte KH 2 PO 4 Mize hickpe F IG. 5. Effect of orgnic P nd intercropping mize with chickpe on totl P uptke y plnts in hydroponics (expt 1). Result of NOVs with significnt effect of min fctor (P source) nd su-fctor (root rriers): rs with different cpitl letters (, ) indicte significnt difference etween P sources (P < 5); rs with different lower cse letters (, ) indicte significnt difference etween monoculture nd intercropping (P < 5). concentrtion in shoots of the intercropped mize supplied with phytte ws 12 % higher thn tht of the monoculture (Fig. 4). However, intercropping did not significntly ffect P concentrtion in mize shoots in the other two P tretments. In comprison, in chickpe no significnt difference ws oserved in the verge P concentrtion of monoculture nd intercropped plnts supplied with phytte versus KH 2 PO 4 (Fig. 4). Totl P uptke y intercropped mize supplied with phytte ws 21-fold higher thn in monoculture; however, compensting decrese in totl P uptke y chickpe did not occur (Fig. 5). There ws no significnt difference in totl P uptke y intercropped mize nd monoculture one when no P ws dded or when P ws supplied y KH 2 PO 4 (Fig. 5). In expt 2, when phytte ws supplied, P concentrtion in mize shoots ws 28 % greter with nylon mesh rrier thn tht with solid rrier (Tle 1). P concentrtions in shoots of mize supplied with (H 2 PO 4 ) 2 without root rrier nd with mesh rrier were 38 % nd 19 % higher thn tht with solid rrier, respectively. When supplied with phytte or (H 2 PO 4 ), totl P uptke y mize with no rrier or mesh rrier ws significntly higher thn with solid rrier. In contrst to mize, when chickpe plnts were supplied with phytte, P concentrtion with solid rrier nd with mesh rrier ws significntly greter thn tht without root rrier (Tle 1). hickpe with solid rrier hd the most P uptke mong the tretments of root seprtion regrdless of P sources. Totl P uptke y mize nd chickpe with mesh rrier ws greter thn tht with solid rrier indicting tht P uptke ws fcilitted y intercropping. cid phosphtse ctivity In expt 1, cid phosphtse ctivity of plnt roots supplied with orgnic P or without P ws significntly enhnced compred with those grown in inorgnic P. verge cid phosphtse ctivity of intercropped nd monoculture mize supplied with phytte or no P ddition ws 81 % nd 62% greter thn tht supplied with KH 2 PO 4 t Dy 2, respectively (Fig. 6). verge cid phosphtse ctivity secreted from intercropped nd monoculture chickpe roots supplied with phytte ws 3-fold greter thn mize t Dy 2 (Fig. 6). Similr results for mize nd chickpe were oserved t Dy 15 nd Dy 25, respectively. ompred with mize, the mgnitude of increse in cid phosphtse ctivity of chickpe ws less thn tht of mize t Dy 15 ut ws greter thn tht of mize t lter dys (dt ws not shown). In expt 2, soil cid phosphtse ctivity in the rhizosphere hd similr trend to tht of plnt roots in the hydroponic culture (expt 1) ut, the mgnitude of increse ws much lower thn tht in expt 1. verge soil cid phosphtse ctivity (comining the dt from ll root rrier tretments) in the rhizosphere of chickpe roots (15 mmol g 1 h 1 ) supplied with phytte ws twice s high s tht of mize (74 mmol g 1 h 1 ; Fig. 7). Root length verge root length of mize without P ddition ws incresed y 24 % compred with KH 2 PO 4 tretment (comined dt from monoculture nd intercropped; Fig. 8). The root length of intercropped mize ws significntly incresed compred with monoculture regrdless of P source. No significnt difference ws oserved in the root length of chickpe etween P sources. The intercropping lso does not significntly ffect the root length of chickpe. DISUSSION Mize growth increses result from the improvement of phosphorus nutrition The present study demonstrted tht intercropping of mize nd chickpe fcilitted the growth of mize when P ws Downloded from y guest on 21 Septemer 218

5 Li et l. cid Phosphtse Role in hickpe/mize Intercropping 31 T LE 1. Effect of interspecific root interction nd orgnic P on P concentrtion (g kg 1 d. wt) in shoots nd P uptke (mg pot 1 ) y mize nd chickpe in soil (expt 2) Mize hickpe Mize + hickpe P sources oncentrtion (g kg 1 d. wt.) Uptke (mg pot 1 ) oncentrtion (g kg 1 d. wt.) Uptke (mg pot 1 ) Totl P uptke (mg pot 1 ) P Solid rrier 17 * Mesh rrier No rrier LSD verge 19 y Phytte Solid rrier c Mesh rrier No rrier LSD verge (H 2 PO 4 ) 2 Solid rrier 137 c 666 c Mesh rrier No rrier c 1251 LSD verge *Men vlues of the three root rriers with the sme P source followed y different letters (,, c) re significntly different (P < 5). y Men vlues of P source tretment followed y different letters (, ) re significntly different (P < 5). cid phosphtse ctivity (µmol g 1 f.wt h 1 ) D E F supplied s phytte, n orgnic form (Figs 2 nd 3). This is consistent with the findings of Li et l. (23) tht chickpe fcilitted the growth of intercropped whet when n orgnic phosphorus source ws supplied. There ws no significnt difference in the growth nd P uptke y chickpe etween the tretments of phytte nd KH 2 PO 4 (Figs 2 5). There hve een reports of N trnsfer occurring in legume/ cerel intercropping (T et l., 1989), ut in the present study, sufficient N ws dded so tht no nodules were found on the roots of chickpe. Thus, the improved growth of mize when intercropped with chickpe ws not cused y etter N nutrition. The improved growth of intercropped mize cn e ttriuted to n improved P uptke. First, in hydroponics P concentrtion nd P uptke of the intercropped mize supplied P Phytte KH 2 PO 4 P Phytte KH 2 PO 4 Mize hickpe F IG. 6. cid phosphtse secreted y the roots of mize nd chickpe tht hd received phytte-p, KH 2 PO 4 -P or no P ddition t Dy 2 in hydroponics (expt 1). Result of NOVs with significnt effect of min fctor (P source) nd su-fctor (intercropping): rs with different mjuscule (, ) men significnt difference etween P sources (P < 5); rs with different minuscule (, ) men significnt difference etween monoculture nd intercropping (P < 5). Soil cid phosphtse ctivity (µmol g 1 soil h 1 ) Solid rrier Mesh rrier No rrier D D E P Phytte (H 2 PO 4 ) 2 P Phytte (H 2 PO 4 ) 2 Mize hickpe F IG. 7. Effect of P sources nd interspecific root interction on soil cid phosphtse ctivities in the rhizosphere of mize nd chickpe in soil (expt 2). Result of NOVs with significnt effect of min fctor (P source) nd su-fctor (root rriers): rs with different cpitl letters (, ) indicte significnt difference etween P sources (P < 5); rs with different lower cse letters (, ) indicte significnt difference etween root rriers (P < 5). with phytte were significntly higher thn in the cse of the monoculture (Fig. 4). In contrst the P concentrtion of the intercropped chickpe ws lower thn monoculture culture when phytte ws supplied (Fig. 4). Secondly, in soil culture when chickpe nd mize grew together, totl P uptke y mize ws higher with no root rrier thn with solid rrier (Tle 1). ecuse of the competition of mize roots, prt of P hydrolysed from phytte ppered to e tken up y the intercropped mize, resulting in its incresed growth compred with monoculture plnts. Similr fcilittion in P nutrition hs een found in whet/ lupin ssocitions (Horst nd Wschkies, 1987; Kmh et l., Downloded from y guest on 21 Septemer 218

6 32 Li et l. cid Phosphtse Role in hickpe/mize Intercropping Root length (cm plnt 1 ) P Phytte KH 2 PO 4 P Phytte KH 2 PO 4 Mize hickpe F IG. 8. Effect of P sources nd root interction on the root length of mize nd chickpe in hydroponics (expt 1): rs with different cpitl letters (, ) indicte significnt difference etween P sources (P < 5); rs with different lower cse letters (, ) indicte significnt difference etween monoculture nd intercropping (P < 5). 1999), sorghum/pigeon pe (e et l., 199) nd mize/ groundnut intercropping (El Dessoug et l., 23). However, such interspecific fcilittion ws not oserved when mize ws intercropped with sugr eet nd oilseed rpe (El Dessougi et l., 23). In those studies, fcilittion in P nutrition ws focused on inorgnic P. Li et l. (23) reported tht when phytte-p ws supplied, the P concentrtions in whet (29 gkg 1 in shoots nd 14 gkg 1 in roots) without root rrier etween whet nd chickpe were higher thn those in the tretments with nylon mesh or with solid rrier seprtion (19 gkg 1 in shoots nd 1gkg 1 in roots). This result lso indicted tht chickpe could fcilitte phosphorus nutrition in ssocited whet under orgnic P supply conditions. However, the mechnism of the fcilittion ws unknown. Phosphtse secreted y chickpe plys n importnt role in the improvement of mize phosphorus nutrition For phosphtes to e ville to plnts from phytte, it must e hydrolysed y phosphtse (Richrdson et l., 2). Plnt roots with high phosphtse ctivity hve gret potentil to utilize soil orgnic phosphorus (Hell, 199). Under conditions of P deficiency, cid phosphtse secreted from roots ws incresed (Nks et l., 1987; Li et l., 1997; Hys et l., 1999). In the present study, it is cler tht chickpe root ws le to secret greter mounts of cid phosphtse in hydroponic (Fig. 6) culture nd soil culture thn mize (Fig. 7), nd incresed hydrolysis of phytte. s result, chickpe could utilize phytte s effectively s KH 2 PO 4 (Fig. 2; see lso previous experiments; Li et l., 23). lthough the cid phosphtse ctivity of mize roots lso incresed significntly when orgnic P ws supplied or when no P ws dded, the enzyme secreted from mize roots ws two to three times less thn tht from chickpe (Fig. 6). The species vrition in cid phosphtse secretion nd utiliztion of orgnic P confirmed previous reports. Li et l. (1997) oserved tht rchiri decumens IT 66 hd the highest cid phosphtse ctivity in 16 plnt species either grown under P-sufficient condition or P-deficient condition. The mount of cid phosphtse secreted y legumes ws 22 % higher thn y oilseeds nd 72 % higher thn y cerels (Ydv nd Trfdr, 21). Egyptin clover (Trifolium lexndrinnm; Trfdr nd lssen, 1988) nd groforestry species (George et l., 22, ) with higher rhizosphere soil cid phosphtse ctivity could use orgnic P tht ws unville to mize. However, Furlni et l. (1987) noted phytin ws not preferred source of P for sorghum genotypes. In the present study, enhnced phosphtse ctivities were ssocited over time with chickpe ut not mize (Fig. 6). The ility of chickpe to moilize orgnic P ws greter thn tht of mize. This could e relted to root exudtion of protons nd orgnic cids. The optimum ph for phosphtse ctivity ws in the rnge of 5 6. ut cid phosphtse ctivity is still very high t ph 5 8 (Mclchln, 198). Rpe roots reduced the rhizosphere soil ph from 67 to 55 (Ghooni nd Nielsen, 1982). Evidently chickpe releses considerle mounts of orgnic nions in response to phosphorus deficiency, nd cn lower the rhizosphere soil ph from 65to 55 (Stevens, 2). In the present study, the ph in the rhizosphere of chickpe ws lso lower thn tht of mize (dt not shown), the condition conducive to hydrolysis of orgnic P y cid phosphtse. In P-deficient sndy soil, more inorgnic P ws lierted y simultneous ppliction of cid phosphtse nd orgnic cids identified in the rhizosphere solution of Hke undult thn y the seprte ppliction of orgnic cid or cid phosphtse (Neumnn nd Romheld, 2). n lterntive function of root-secreted cid phosphtse my e the rpid retrievl of P y the hydrolysis of orgnic P, which is permnently lost y diffusion or from sloughed off nd dmged root cells (Lefevre et l., 199). Further, soil ph my ffect the sorption of the enzymes nd the effect of ph on sorption of enzymes hs only recently een relized s eing importnt in mesurement of phosphtse ctivity. Root length The size of the root system is one of fctors tht determines P uptke. ecuse of its low moility in soil, P trnsport to the root surfce is minly governed y diffusion (rer, 1995). n extensive root system with fine roots is eneficil for ccessing lrge soil volume. In the intercropping system, the roots of mize nd chickpe were mixed together, so phosphte hydrolysed from phytte y chickpe could e sored y mize. The incresed root length of intercropped mize might contriute to the incresed totl P uptke in mize. In nother study, mize intercropped with groundnut produced more thn doule the root length of mono-cropped mize t no P (El Dessougi et l., 23). The reson for this is unknown. In conclusion, the increse in totl P uptke y mize when intercropped with chickpe indicted tht t limited P supply, intercropping cn contriute to more efficient utiliztion of orgnic P in soil y less P-efficient crops. This occurs ecuse of exudtion of P-moilizing compounds y the roots of P-efficient plnt species. To dte Downloded from y guest on 21 Septemer 218

7 Li et l. cid Phosphtse Role in hickpe/mize Intercropping 33 there is no direct evidence tht phosphtse ctivity produced y chickpe enhnces the minerliztion of orgnic P nd sorption y ssocited mize t the field level. Future work should compre the effects of growing norml chickpe nd mutnts defective in phosphtse ctivity on the minerliztion of soil orgnic P nd P uptke y ssocited mize. KNOWLEDGEMENTS The study ws supported y the Mjor Stte sic Reserch Development Progrm (Project numer G ), nd the Ntionl Nturl Science Foundtion of hin (Project numer 3745). LITERTURE ITED e N, rihr J, Okd K Phosphorus uptke y pigeon pe nd its role in cropping systems of the Indin sucontinent. Science 248: rer S Soil nutrient iovilility: mechnistic pproch, 2nd edn. New York: John Wiley. Dll R Orgnic phosphorus. dvnces in gronomy 29: El Dessougi H, zu Dreeele, lssen N. 23. Growth nd phosphorus uptke of mize cultivted lone, in mixed culture with other crops or fter incorportion of their residues. Journl of Plnt Nutrition nd Soil Science 166: Furlni M, lek R, Ross WM Orgnic nd inorgnic sources of phosphorus on growth nd phosphorus uptke in sorghum genotypes. Journl of Plnt Nutrition 1: Ghooni TS, Nielsen E The effect of root-induced ph chnges on the depletion of inorgnic nd orgnic phosphorus in the rhizosphere. Plnt nd Soil 143: George T S, Gregory PJ, Roinson JS, uresh RJ, Jm. 22. Utiliztion of soil orgnic P y groforestry nd crop species in the field, western Keny. Plnt nd Soil 246: George TS, Gregory PJ, Wood M, Red D, uresh RJ. 22. Phosphtse ctivity nd orgnic cid in the rhizosphere of potentil groforestry species nd mize. Soil iology & iochemistry 34: Gilert G, Knight JD cid phosphtse ctivity in phosphorusdeficient white lupin roots. Plnt, ell nd Environment 22: Hyes JE, Richrdson E, Simpson RJ Phytse nd cid phosphtse ctivitiesnd extrcts from roots of temperte psturegrss nd legume seedlings. ustrlin Journl of Plnt Physiology 26: Hell M Vrietl differences in root phosphtse ctivity s relted to the utiliztion of orgnic phosphtes. Plnt nd Soil 123: Horst G, Wschkies Phosphorus nutrition of spring whet in mixed culture with white lupin (Lupinus lus L.). Zeitschrift f ur Pflnzernährung und odenkunde 15: 1 8. Kmh M, Horst WJ, mer F, Mostf H, Mier P Moiliztion of soil nd fertilizer phosphte y cover crops. Plnt nd Soil 211: Lefevre DD, Duff MG, Fife, Julien-Inlsingh, Plxton W Response of phosphte deprivtion in rssic nigr suspension cells. Plnt Physiology 93: Li L, Tng, Rengle Z, Zhng FS. 23. hickpe fcilittes phosphorus uptke y intercropping whet from n orgnic phosphorus source. Plnt nd Soil 248: Li L, Zhng FS, Li XL, hristie P, Sun JH, Yng S, Tng. 23. Interspecific fcilittion of nutrient uptke y intercropped mize nd f en. Nutrient ycling in grocosystems 68: Li L, Yng S, Li XL, Zhng FS, hristie P Interspecific complementry nd competitive interctions etween intercropped mize nd f en. Plnt nd Soil 212: Li MG, Oski M, Ro IM, Tdno T Secretion of phytse from the roots of severl plnt species under phosphorus conditions. Plnt nd Soil 195: Mclchln K cid phosphtse ctivity of intct roots nd phosphorus nutrition in plnts. I. ssy condition nd phosphtse ctivity. ustrlin Journl of griculturl Reserch 31: Morris R, Grrity DP Resource cpture nd utiliztion in intercropping: non-nitrogen nutrients. Field rops Reserch 34: Nks JP, Gould WD, Klein D Origin nd expression of phosphtse ctivity in semi-rid grsslnd soil. Soil iology nd iochemistry 19: Nel, P Mixed cropping of lupines nd winter cerels. 4. Seeds yield nd qulity under field conditions. Journl griculturl Science 8: Neumnn G, Romheld V. 2. The relese of root exudtes s ffected y plnts physiology sttus. In: Pinton R, Vrnini Z, Nnnipieri P, eds. The rhizophere iochemistry nd orgnic sustnces t the soil plnt interfce. New York: Dekker, Richrdson E, Hdos P, Hyes JE. 2. cid phosphomonoesterse nd phytse ctivities of whet (Triticum estivum L.) roots nd utiliztion of orgnic phosphorus sustrtes y seedlings grown in sterile culture. Plnt, ell nd Environment 23: 1 9. SS Institute SS user s guide: sttistics Version 5. ry, N: SS Institute. Stevens J. 2. Differentil root exudtion of chickpe (icer rietinum L.) on different soils nd its role in phosphorus cquisition. Sc Thesis, University of Western ustrli. ustrli. T T, Fris M, Mcdowll FDH Evlution of 15 N method to mesure nitrogen trnsfer from lflf to compnion timothy. Plnt nd Soil 114: Trfdr J, lssen N Orgnic phosphorus compounds s phosphorus source for higher plnts through the ctivity of phosphtses produced y plnt roots nd microorgnisms. iology nd Fertility of Soils 5: Trfdr J, Jungk Phosphtse ctivity in the rhizosphere nd its reltion to the depletion of soil orgnic phosphorus. iology nd Fertility of Soils 31: Vndermer JH The ecology of intercropping. mridge: mridge University Press. Westermn RL Soil testing nd plnt nlysis, 3rd edn. Mdison, WI: Soil Science Society of meric. Willey RW Resource uses in intercropping systems. griculturl Wter Mngement 17: Ydv RS, Trfdr J. 21. Influence of orgnic nd inorgnic phosphorus supply on the mximum secretionof cid phosphtse y plnts. iology nd Fertility of Soils 34: Downloded from y guest on 21 Septemer 218