Peanut/maize intercropping induced changes in rhizosphere and nutrient concentrations in shoots

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1 Plant Physiology and Biochemistry 45 (2007) 350e356 Research article Peanut/maize intercropping induced changes in rhizosphere and nutrient concentrations in shoots A. Inal a, A. Gunes a, F. Zhang b, I. Cakmak c, * a Ankara University, Faculty of Agriculture, Department of Soil Science and Plant Nutrition, Ankara, Turkey b College of Resources and Environmental Science, China Agricultural University Beijing , PR China c Sabanci University, Faculty of Engineering and Natural Sciences, Istanbul, Turkey Available online 14 March Abstract A greenhouse study was conducted to investigate the rhizosphere effects on iron (Fe), phosphorus (P), nitrogen (N), potassium (K), calcium (Ca), zinc (Zn), and manganese (Mn) nutrition in peanut plants (Arachis hypogaea L.) by intercropping them with maize (Zea mays L.). In addition, we studied the release of phytosiderophores and the ferric reductase activity of roots, ph and acid phosphatases in the rhizosphere and bulk soil, and the secretion of acid phosphatases in roots. Our results revealed that shoot yields of peanut and maize plants were decreased by intercropping the plants, as compared to monocultured plants. Growing peanut plants in a mixture with maize, enhanced the shoot concentrations of Fe and Zn nearly 2.5-fold in peanut, while the Mn concentrations of peanut were little affected by intercropping. In the case of maize, the shoot concentrations of Fe, Zn and Mn were not significantly affected by intercropping with peanut. Intercropping also improved the shoot K concentration of peanut and maize, while it negatively affected the Ca concentration. In the intercropping of peanut/maize, the acid phosphatase activity of the rhizosphere and bulk soil and root secreted acid phosphatases were significantly higher than that of monocultured peanut and maize. In accordance, the shoot P concentrations of peanut and maize plants were much higher when they were intercropped with peanut or maize, respectively. The rhizosphere and bulk soil ph values were not clearly affected by different cropping systems. When compared to their monoculture treatments, the secretion of phytosiderophore from roots and the root ferric reducing capacity of the roots were either not affected or increased by 2-fold by the intercropping, respectively. The results indicate the importance of intercropping systems as a promising management practice to alleviate Fe deficiency stress. Intercropping also contributes to better nutrition of plants with Zn, P and K, most probably by affecting biological and chemical process in the rhizosphere. Ó 2007 Elsevier Masson SAS. All rights reserved. Keywords: Maize; Intercropping; Peanut; Phosphatases; Rhizosphere; Phytosiderophore; Ferric reductase 1. Introduction The intercropping system greatly contributes to crop production by its effective utilization of resources, as compared to the monoculture cropping system [7,17,18,43]. Currently, this system is attracting increasing interesting in low-input crop production systems and is being extensively investigated [20,43,45]. Inter-specific root interactions affect nutrient Abbreviations: APase, acid phosphatase; BS-APase, bulk soil acid phosphatase; BS-pH, bulk soil ph; FR, ferric reductase; RS-APase, rhizosphere soil acid phosphatase; RS-pH, rhizosphere soil ph; S-APase, root secreted acid phosphatase. * Corresponding author. Tel.: þ ; fax: þ address: cakmak@sabanciuniv.edu (I. Cakmak). mobilization in the rhizosphere and contribute efficiently to nutrient acquisition by intercropping [41]. It has been well documented that an important N-transfer takes place in intercropping systems of legumes with cereals [12,14,25,34]. Sharma and Gupta [32] showed that N- and P-nutrition of pearl millet was greatly improved by intercropping with legumes. Interspecific facilitation of P-uptake by intercropped species has also been reported for inorganic P-sources. For example, white lupin improved P-uptake when it was intercropped with wheat [8,11]. Pigeonpea improved P-uptake of sorghum [2], and chickpea contributed to P-uptake by maize and wheat [19,22]. Possibly, these effects on P-utilization are related to the release or activation of enzymes (e.g. like acid phosphates) and root exudation of carboxylates, which improve solubility and uptake /$ - see front matter Ó 2007 Elsevier Masson SAS. All rights reserved. doi: /j.plaphy

2 A. Inal et al. / Plant Physiology and Biochemistry 45 (2007) 350e of P in rhizosphere [26,30]. Plant roots release enzymes like phosphatases and phytase [10,21,42], and carboxylates [26,40] under P deficiency, allowing mobilization and utilization of P in soil under P deficiency stress [9]. Significant increases in the acid phosphatase secretion from roots under P-deficient conditions have been shown in lupin [37,41], maize [42] and maize and chickpea [22] plants. Intercropping is also effective in improving mobilization and uptake of micronutrients. For example, Fe nutrition of peanut plants was significantly improved when intercropped with maize, possibly due to rhizosphere interactions between peanut and maize [44,45,46]. Peanut develops Strategy I mechanisms in response to Fe deficiency, such as increases in ferric reductase activity of roots and acidification of the rhizosphere by releasing protons from the roots [31,45,46]. Graminaceous plant species respond to Fe and Zn deficiency by exuding phytosiderophores in order to increase the available Fe and Zn to the plant roots [24]. But, research reports related to intercropping systems are limited on the availability of Fe. In fruit orchards on calcareous soil, leaf chlorosis disappears when grasses are grown along the rows of trees [38]. This effect of grasses has been ascribed to increased Fe availability in the rhizosphere caused by the release of phytosiderophores from roots of grasses. Very recently, Cesco et al. [4] showed that when cocultivated with grass, Fe deficiency susceptible citrus rootstocks could utilize Fe that is solubilized from Fe-hydroxide by phytosiderophores released from roots of grasses. Intercropping also affects the utilization of other minerals in the rhizosphere, such as Ca and Mg. In a wheat and chickpea intercropping system Li et al. [20] showed that besides micronutrients uptake of Ca and Mg is also increased in plants depending on the source of P used in the experiment. This improvement in nutrient use was ascribed to rhizosphere acidification. To our knowledge, in many of the intercropping studies, most attention has been given to the yield parameters and N, P and Fe nutrition of the plants. In the present study, we tried to obtain more information on the shoot concentrations of different macro and micro nutrients (e.g. N, P, K, Ca, Fe, Zn, and Mn) and explain the possible physiological mechanisms involved in the utilization of P and Fe in the rhizosphere, with regard to the complementary and competitive interactions between peanut and maize plants. The physiological mechanisms tested were the release of phytosiderophores from roots, ferric reductase activity of roots and changes in ph and acid phosphatase activity in both rhizospheres and bulk soil. 2. Materials and methods 2.1. Plant growth A factorial experiment with three replicates was conducted in a glasshouse by growing peanut (Arachis hypogaea L. cv. NC-7) as a monocrop and intercropping it with maize (Zea mays L. cv. Hamidiye) in 4-liter plastic pots for 35 days. The number of maize and peanut plants was three in monoculture separately. The ratio of peanut:maize was 3:3 in the intercropping treatment. The soil in the experiment was collected from the plough layer (0e20 cm) of experimental fields of the Agricultural Faculty, Ankara ( N; E). Some of the characteristics of the soil measured by using standard methods were as follows: field capacity 24%; texture clay loam; CaCO g kg 1 ; ph (1:2.5 water) 7.61; EC 0.38 ds m 1 ; organic matter 4.60 mg kg 1 ; total N 0.92 g mg kg 1. The concentrations of NH 4 O Ac-extractable K, Ca and Mg were as follows: 666, 4170 and 530 mg kg 1, respectively. The NaHCO 3 -available P was mg kg 1 ; DTPA-extractable Zn, Fe and Mn were 0.72, 5.67 and 17 (mg kg 1 ) respectively; and NaOAc-extractable B was 1.69 mg kg 1. To create a low nutrient environment and facilitate the isolation of roots, 1500 g of air-dried soil was mixed with an equal volume of coarse (2.00e4.00 mm) pumice stone. The plants were grown under natural light conditions (approximate day conditions during the span of the experiment; 28e32 C air temperature, 400e450 mmol m 2 s 1 light intensity and 45e50% relative humidity). A basal dose of N (NH 4 NO 3 ) was applied to all the pots at the 150 mg kg 1 level and mixed thoroughly with soil. During the experiment, soil was kept at approximately 60% of the field water holding capacity Determination of relative chlorophyll The levels of relative chlorophyll just before harvest were recorded from the young leaves of all the plants in each pot by a chlorophyll meter (CM 100, Spectrum Technologies Inc, USA) Harvest and plant mineral analysis Plants were harvested and weighed for fresh weight determinations. They were then washed with tap water and deionized water. The dry weights of shoots were measured after drying at 65 C for 72 h. For the measurements of mineral nutrients, plant samples were ashed in a muffle furnace at 500 C for 6 h, dissolved in 5 ml of 2 M HNO 3, and finally diluted to 25 ml with reverse osmosis water. Extracts were filtered and stored in plastic vials until analyzed. Nitrogen was determined by the Kjeldahl procedure. Potassium was measured by flamephotometer (Jenway PFP7, ELE Instrument Co. Ltd.). Phosphorus was determined spectrophotometrically (Schimadzu UV-VIS 1201), and Ca, Fe, Zn and Mn were determined by AAS (Analytic Jena Vario 6). Measurements were made on three independent replications. As described by Veneklaas et al. [40] at the time of harvest, the plastic bags that containing the soil plus root system were cut open and placed on the bench. Root systems were held by the stem base and gently lifted out of the soil (bulk soil) and clumps of soil that were trapped between the roots were taken out. The soil that remained adhering to the roots was defined as rhizosphere soil. The roots from all the pots after the washing processes (see below) were divided almost equally into three parts for the measurement of root secreted acid phosphatases, ferric reducing capacity and phytosiderophore release.

3 352 A. Inal et al. / Plant Physiology and Biochemistry 45 (2007) 350e356 The duration of the root washing was 5 min per sample. After the collection of root exudates, the roots were dried at 65 C for 72 h and weighed to determine the total root dry weight Determination of acid phosphatase in rhizosphere (RS-APase) and bulk soil (BS-APase) Acid phosphatase activity in rhizosphere and bulk soil was determined by the method of Tabatabai [36] using acetate buffer (0.1 M, ph 5.6) and p-nitrophenyl phosphate ( p-npp) as a substrate at 30 C for 1 h. One unit of APase activity was expressed as the amount of enzyme from per gram of soil which produced 1 mmol of p-nitrophenyl per hour Determination of root secreted acid phosphatase (S-APase) The roots of plants were immersed in saturated CaSO 4 solution, then rinsed three times with deionized water and placed in 300 ml of aerated deionized water for 24 h to collect the root exudates. The activity of S-APase was assayed after 24 h of root exudation, using p-nitrophenyl phosphate ( p-npp) as a substrate [35]. An aliquot of solution adjusted to a total volume of 5 ml with distilled water was added to 0.5 ml of 1 M sodium acetate buffer (ph 5) and 1 ml of M p-npp in reagent tubes. Tubes were maintained at 37 C for 1 h and the reaction was terminated by the addition of 20 ml of 0.5 M NaOH. The absorbance at 410 nm was measured to determine the amount of released p-nitrophenol ( p-np). Root secreted acid phosphatase (S-APase) activity was expressed as mmol of p-npp hydrolyzed h g 1,DWat 37 C Measurement of rhizosphere (RS-pH) and bulk soil ph (BS-pH) Rhizosphere and bulk soil ph was measured by a ph meter (WTW, Inolab) in a 1:2.5 water extract after shaking for 12 h Determination of root phytosiderophore release (PS) The roots of maize from monocropping and intercropping with maize were immersed in saturated CaSO 4 solution, then rinsed three times with deionized water and placed in 300 ml of aerated deionized water for 4 h to collect the root exudates. Phytosiderophore (PS) was indirectly determined by calculating the amount of Fe(III) mobilized from Fe hydroxide with a modified method of Takagi [39]. An aliquot of 0.5 ml of 1 mm FeCl 3 was added to 9 ml of the root exudates. The mixture was shaken for 1 h to produce Fe(III)- PS compounds, followed by another 15 min of shaking after the addition of 1 ml of buffer solution of 0.5 M sodium acetate adjusted to ph 7.0 by acetic acid, to precipitate the remaining Fe(III). The solution was then filtered. The filtrate was acidified by adding 0.2 ml of 1.5 M H 2 SO 4 and incubated for 20 min at 55 C with 0.5 ml of 1.15 M hydroxylammonium chloride as the reductant to convert Fe(III)-PS to Fe(II)-PS. The reduced Fe-PS complex was then exposed to ferrozine to form a red color. The absorption measurement at 562 nm was recorded (Shimadzu UV-VIS 1201) and the phytosiderophore release rates were calculated as Fe equivalents Measurement of root ferric reducing capacity (ferric reductase activity, FR) The roots from peanut were immersed in saturated CaSO 4 solution for 30 min, immediately washed with deionized water, and then transferred to a 250 ml aluminum foil covered Erlenmeyer flask containing 200 ml 0.01 M MES buffer (ph 6) and 0.2 mm ferrozine (disodium salt of 3-(2-pyridyl- 5,6-bis(4-phenylsulfonic acid)-1,2,4-triazine). Iron was supplied as 0.5 mm Fe(III)EDTA. Iron reduction was measured after 1 h by measuring the absorbance of the pink colored solution at 520 nm (Shimadzu UV-VIS 1201), Root fresh weight was recorded and reduction rates were calculated on a root FW basis [15,16] Statistical analysis The experiment was designed in a completely randomized design with three replicates. Statistical significance of difference was determined by analysis of variance (ANOVA) and the LSD test at P 0.05 for multiple comparisons. 3. Results 3.1. Shoot growth and chlorophyll content Shoot dry weights of intercropped peanut and maize plants decreased significantly when compared to those in the corresponding monoculture cropping. However, peanut intercropped with maize exhibited healthy growth and did not show iron deficiency symptoms, and the young leaves from monocultured peanut plants were chlorotic. Supporting this, as a measure of healthy or vigorous growth, relative chlorophyll readings of peanut and maize increased significantly in the intercropping system (Table 1) Iron, zinc and manganese concentrations Iron concentrations of the intercropped plants increased. However, only the increase in peanut grown with maize from 40.4 to mg kg 1 was found to be statistically significant (Table 1). The zinc concentration of intercropped peanut with maize increased significantly from 10.4 to 26.2 mg kg 1. Non-significant decreases were observed in the Zn concentrations of intercropped maize. The manganese concentration of peanut grown with maize increased significantly, from 29.0 to 33.4 mg kg 1, while the Mn concentrations of maize remained unchanged in response to intercropping.

4 A. Inal et al. / Plant Physiology and Biochemistry 45 (2007) 350e Table 1 Shoot dry weight, chlorophyll and the shoot concentrations of iron (Fe), zinc (Zn) and manganese (Mn) of peanut and maize grown as monocrops and intercrops Cropping treatments Dry weight Chlorophyll Fe (mg kg 1 DW) Zn (mg kg 1 DW) Mn (mg kg 1 DW) (g plant 1) (mg kg 1 DW) Monocropping peanut Intercropping peanut F values 193** 45.38** 110** 14.0* 9.38* Monocropping maize Intercropping maize F values 72** 33.80** 1.73 ns 6.05 ns 2.52 ns The values are means of three replicates. *P< 0.05, **P < 0.01, ns, non-significant Nitrogen, phosphorus, potassium and calcium concentrations The nitrogen concentration of peanut and maize in response to intercropping was not significantly changed. Phosphorus concentrations of intercropped peanut and maize increased from 1.56 to 1.84 g kg 1 and 0.99 to 1.70 g kg 1, respectively. Intercropping significantly enhanced K concentrations of the plants when compared to the monocropping system. However, Ca concentrations of intercropped peanut and maize were significantly decreased (Table 2) Root dry weight Root dry weight of peanut was lower than that of maize (Table 3). As expected, the combined root biomass in intercropping (3.47 g pot 1, respectively) was significantly higher when compared to sole cropping of peanut and maize (1.30 and 2.51 g pot 1, respectively) Acid phosphatase activity in rhizosphere (RS-APase) and bulk soil (BS-APase) Soil acid phosphatase activity, measured using p-npp as a substrate both in the rhizosphere and bulk soil, is shown in Table 3. Acid phosphatase activity of the rhizosphere soil (RS-APase) was comparatively higher than that of bulk soil (BS-APase). RS-APase was highest in peanut/maize cropping (0.38 mmol g 1 h 1 ), compared to 0.30 mmol g 1 h 1 in Table 2 Nitrogen (N), phosphorus (P), potassium (K) and calcium (Ca) concentrations of peanut and maize grown as monocrops and intercrops Cropping treatments Monocropping peanut Intercropping peanut N P K Ca F values 0.45 ns 10.3* 70.2** 20.7** Monocropping maize Intercropping maize F values 0.57 ns 10.8* 9.64* 8.53* The values are means of three replicates. *P< 0.05, **P < 0.01, ns, nonsignificant. peanut and 0.07 mmol g 1 h 1 maize grown soil. BS-APase activity also significantly varied depending on plant species and cropping system. Activity of BS-APase was significantly higher in peanut grown soil when compared to maize grown soil. In the intercropped peanut and maize plants, BS-APase activity was also significantly higher when compared to their sole cropping (Table 3) Root secreted acid phosphatase (S-APase) activity As can be seen in Table 3, the secretion of root acid phosphatase (S-APase) was significantly higher in peanut/maize roots (25.5 mmol g 1 h 1 ) when compared to sole peanut (17.8 mmol g 1 h 1 ) and maize roots (14.8 mmol g 1 h 1 ) ph of rhizosphere (RS-pH) and bulk soil(bs-ph) The ph of rhizosphere soil was slightly lower than the ph of bulk soil. However, only the differences in BS-pH depending on cropping system were found significant (Table 4) Root phytosiderophore (PS) release and ferric reductase capacity (FR) The release of PS from maize roots was 0.40 mmol Fe g 1 FW h 1 but it was decreased to 0.35 mmol Fe g 1 FW h 1 when peanut and maize were intercropped (Table 4). As seen from Table 4, root FR activity (Fe(III) reducing capacity) was found to be significantly higher in intercropped peanut and maize roots (0.56 mmol Fe g 1 FW h 1 ) than that of monocropped peanut (0.29 mmol Fe g 1 FW h 1 ). Table 3 Effect of peanut and maize intercropping on the root dry weight, rhizosphere soil acid phosphatase (RS-APase) and bulk soil acid phosphatase (BS-APase), and the root secreted acid phosphatase (S-APase) activities Cropping treatments Root dry weight (g pot 1 ) RS-APase (mmol g 1 h 1 ) BS-APase (mmol g 1 h 1 ) S-APase (mmol g 1 h 1 ) Peanut Maize Peanut/maize F values 8.54* 18.0** 26.62** 30.6** LSD The values are means of three replicates. *P < 0.05, **P < 0.01.

5 354 A. Inal et al. / Plant Physiology and Biochemistry 45 (2007) 350e356 Table 4 Effect of peanut and maize intercropping on the rhizosphere ph (RS-pH), bulk soil ph (BS-pH), phytosiderophore (PS) released from maize root and root ferric reductase capacity in peanut (FR) Cropping treatments 4. Discussion RS-pH BS-pH PS FR (mmol Fe g 1 FW h 1 ) (mmol Fe g 1 FW h 1) Peanut nd 0.29 Maize nd Peanut/maize F values 0.17 ns 6.21* 7.29* 48.46** LSD e 0.08 The values are means of three replicates. *P < 0.05, **P < 0.01, ns, nonsignificant Effects of peanut intercropping with maize on the growth of plants and nutrient uptake As discussed by Nielsen and Jensen [27], facilitative root interactions are important in nutrient poor soils and low input agro-ecosystems due to critical interspecific competition for plant growth factors. As compared to monoculture cropping systems, intercropping may affect crop yields as a result of effective use of water, mineral nutrients and solar energy [20,29,44]. Our results clearly show that rhizosphere was modified by the roots of intercropped peanut and maize plants. This modification improved P and Fe availability, in particular, but also other nutrients, including K, Zn and Mn. This study demonstrates that interspecific root interactions and rhizosphere effects between intercropped peanut and maize were associated with the FR activity from peanut roots and the release of PS of maize roots, contributing to increased chemical availability of Fe and Zn. In addition, improvement in S-APase and soil acid phosphatase activity (RS-APase and BS-APase) might be responsible for the increased P nutrition to plants in an intercropping system. The shoot yield of intercropped peanut was lower than that of monoculture peanut (Table 1). This may have resulted mainly from competition or root development shortage by associated maize in small pots. In fact, total root dry weight was 3.47 g pot 1 in the intercropping of peanut and maize, while the calculated total root dry weight of peanut and maize was 3.81 g pot 1. The shoot yield of intercropped maize was also lower when compared to sole cropping. However, intercropped peanut with maize did not exhibit typical Fe deficiency symptoms. This observation was clearly supported by relative chlorophyll readings. In the intercropping system, P concentration of the plant species was increased when compared to their sole cropping (Table 2). This may be attributable mainly to decreased RSpH and to a greater extent to increased phosphatase activities in soil and root in the intercropping system and consequently to increased RS-P concentration. We also observed significant increases in RS-APase activities, when compared to BS- APase. In intercropping systems, the RS-APase and S-APase activities were higher especially in peanut than in maize. The increase in phosphatase activity under interspecific nutritional competition, and thus the high requirement for phosphorus, was responsible for the increases in P concentrations in the rhizosphere of intercropping. As also reported by Rengel [30] and Liu et al. [23], plants acquire P under P deficiency by modifying their root physiology and morphology. Such modifications may involve increased release of APase and decreases in the ph of the rhizosphere. The induction of intracellular and extracellular acid phosphatases in response to P deficiency is a well known response in higher plants [28]. Our rhizosphere ph, RS-APase and S-APase activity data were consistent with previous reports [9,23,24]. The data presented here suggest that plant roots and also leaves produce substantial amounts of phosphatase when there is competition for P between peanut and maize. The increase in phosphatase possibly resulted from enhanced demand for P. Table 2 shows relatively low levels of P in plant tissues. It is well known that phosphatases are inducible in plants suffering from P deficiency [5]. Nitrogen concentrations in the plant species did not vary significantly in response to intercropping (Table 2). This may be due to a sufficient amount of applied N (150 mg kg 1 ) at the beginning of the experiment. The K concentrations of the plant species was significantly increased, and Ca was decreased, when the plants were grown together (Table 2). The reason for such differential effects on K and Ca concentrations of plants caused by intercropping remains unknown. It is possible that enhanced K uptake by intercropping resulted in a reducing effect on Ca uptake due to the cationic antagonism between K and Ca The role of the rhizosphere of maize in the improvement of peanut iron nutrition Rhizosphere ph, after 60 days of growth, was slightly acidified regardless of plant species or cropping system due to the root exudates of the plants to the rhizosphere (Table 4). It was noticed that P starvation induces H þ release of roots [23] and plants enhance exudation of organic acids under P deficiency [24]. The possible second reason for rhizosphere acidification is Fe deficiency. Iron deficiency has generally been shown to cause increases in organic acid concentrations in root exudates of plant species. Increases in inorganic acid concentrations in roots of Fe-deficient plants are fairly ubiquitous, and occur both in Strategy I (e.g. peanut) and Strategy II (e.g. maize) plant species [1,15]. The soil used in this experiment was high in ph and lime. These experimental soil conditions are inducing factors of iron deficiency in plants. Plant species develop physiological responses to increase iron uptake under Fe deficiency. These responses, for dicots and non-graminaceous monocots (Strategy I plants, e.g. peanut), include the release of hydrogen and reductants from roots and increasing Fe(III) reduction at the root surface [1,3,31]. A good relationship was found between Fe(III) reduction capacity and the resistance to iron-deficiency in the field for some herbaceous dicot plants, such as soybean [13], dry bean genotypes [6], and peanut [44]. However, under Fe deficient conditions, graminaceous plants (Strategy II plants, e.g. maize) enhance the

6 A. Inal et al. / Plant Physiology and Biochemistry 45 (2007) 350e release of phytosiderophores, which are effective in mobilizing Fe(III) from calcareous soils [30,33]. In the present study, ferric reductase activity of peanut intercropped with maize was found to be higher than that of monocropped peanut (Table 4). However, the release of phytosiderephore from maize in monocropping was found to be higher than that of maize in intercropping. The iron concentration of the intercropped peanut was significantly enhanced by maize (Table 1). The improvement of Fe nutrition of peanut can result from an increase in ferric reductase activity. In intercropping cropping systems, improvement of iron nutrition of legume plants by graminaceous plants was also reported previously for peanut by maize [45,45,46]. The release of phytosiderophore by Strategy II plants also improves Zn nutrition [24,30]. In the current study, Zn nutrition of peanut was improved by the associated maize. Enhanced production of phytosiderophore by maize and acidification of the rhizosphere might be responsible for the increases in Zn concentration of peanut. In this work, the possible mechanisms of the root interactions and the nutritional interrelationship between intercropped peanut and maize plants were explained by the parameters of the rhizosphere ph, root ferric reductase activity of peanut plants, release of phytosiderephore of maize, and root secreted and soil APase activity. We concluded that peanut facilitated P nutrition on its own and in association with maize, while maize improved Fe and Zn nutrition of peanut in the intercropping system of maize and peanut. Since this study was conducted in pots under glasshouse conditions and where root growth was largely confined, field validation of the results based on the physiological measurements is necessary before a definite recommendation can be made. References [1] J. Abadia, A.F.L. Millan, A. Rombola, A. 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