Response of kidney bean to arbuscular mycorrhizal inoculation and ...

Acta Agriculturae Scandinavica Section B-Soil and Plant, 2006; 56: 101 109

ORIGINAL ARTICLE

Response of kidney bean to arbuscular mycorrhizal inoculation and mycorrhizal dependency in P and Zn deficient soils

I. ORTAS & C. AKPINAR Department of Soil Science, Faculty of Agriculture, The University of Cukurova, Adana, Turkey

Abstract Since most of the Central Anatolian soils are P and Zn deficient, mycorrhizae may help plants to obtain sufficient nutrients from the soil without the need to apply additional chemical fertilizers. As far as is known, some plants are strongly mycorrhizal dependent for P nutrition, but less is known about the mycorrhizal dependence with Zn nutrition. Hypotheses were tested under P and Zn deficient soils to find out whether kidney bean plants are mycorrhizal dependent or not. Kidney bean (Phaseolus vulgaris L.) plants were grown for 8 weeks in two widely distributed calcareous clay soils with low nutrient content from Central Anatolian Sultano¨nu¨ and Konya soils (sterilized by autoclaving). The experiment was conducted with three levels of phosphorus (0, 25, 125 mg P kg 1 soil), and two rates of Zn (0 and 5 mg Zn kg1soil) Two selected arbuscular mycorrhizal (AM) species (Glomus mosseae and G. etunicatum) were inoculated. In the Sultano¨nu¨ soil, mycorrhizal inoculation increased plant growth and P and Zn uptake. The positive effect of mycorrhizal inoculation on plant P content and uptake was found to be higher when higher levels of phosphorus were applied. The soil from Konya with a high concentration of boron inhibited normal growth of kidney bean plants. Mycorrhizal root colonization was different with mycorrhizal inoculation. Root colonization was not affected by P and Zn application, but it has been shown that the plant is strongly dependent on P nutrition, especially at low P application levels. However, although mycorrhizal inoculation increased plant concentration of Zn, plants were less dependent on Zn nutrition.

Keywords: Mycorrhizae, phosphorus, zinc, mycorrhizal dependency, bean plant.

Introduction Arbuscular mycorrhizae (AM) are an integral part of most plants in nature (Gianinazzi et al., 1982) and occur in nearly 90% of species of the plant community (Smith & Read, 1997). One of the most dramatic effects of mycorrhizal infection on the host plant is an increase in phosphorus (P) (Koide, 1991) and zinc (Zn) (Lambert et al., 1979; Kothari et al., 1991a; Ortas et al., 2001; Ortas, 2003) uptake mainly due to the capacity of the mycorrhizal fungi to absorb their ions from the soil and transfer them to the host roots (Asimi et al., 1980; George et al., 1995). In addition, mycorrhizal infection results in an increase in the uptake of other macro- and micronutrients (Marschner & Dell, 1994). Based on plant ability to grow with or without mycorrhizae at different levels of nutrients, plants can be separated into two major groups: nonmycotrophic and mycotrophic. Mycotrophic plants

are also classified according to their degree of dependence on the mycorrhizae from obligatory to facultative. Plants obtain benefits from mycorrhizae by enhancing nutrient and water uptake and also other benefits, such as resistance to stress factors. It has been hypothesized that mycorrhizal dependency is largely controlled by the root architecture system (Baylis, 1975) and nutrient requirements (Ortas et al., 2001). Plants with coarsely branched roots and with few or no root hairs are expected to be more dependent on mycorrhizae than plants with finely branched root systems (Smith & Read, 1997). Gerdemann (1975) and Shibata and Yano (2003) defined mycorrhizal dependency as the degree to which a plant species is dependent on the mycorrhizal condition to produce its maximum growth at a given level of soil fertility. This definition is most pronounced for P requirement, but not for other nutrients such as Zn (Ortas et al., 2001). Plenchette et al. (1983) however

Correspondence: I Ortas, Department of Soil Sciences, Faculty of Agriculture, Curkurova University, Adana, TR-01330, Turkey. E-mail: asportas@ mail.cu.edu.tr

(Received 4 January 2005; accepted 8 March 2005) ISSN 0906-4710 print/ISSN 1651-1913 online # 2006 Taylor & Francis DOI: 10.1080/09064710510029196

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I. Ortas & C. Akpinar

suggested a definition of mycorrhizae dependency by expressing the dry mass of a mycorrhizal plant as the dry mass of a non-mycorrhizal plant at a given level of soil fertility. An earlier definition of mycorrhizae dependency by Menge et al. (1978) is expanded and modified to give a percentage increase of yield relative to that of non-mycorrhizal plants. In this definition the range is between zero and 100%, rather than an unlimited percentage increase. The result is likely to vary depending on the nutrient status of the soil, so it is suggested that the relative mycorrhizal dependency should be associated with the level of available phosphorus. The degree of plant dependence is of great practical and ecological interest. Sylvia (1986) tested mycorrhizal dependency by using two AM fungi Glomus intraradices and G. etunicatum with three different levels of available phosphorus. Azcon and Barea (1997) suggested mycorrhizal dependency for a representative plant species in Mediterranean shrubs (Lavandula spica L.) as a key factor in its use for re-vegetation strategies in desertificationthreatened areas. Tawaraya (2003) also reported that cultivated plant species show a lower mycorrhizal dependency than wild plant species. Li and Christie (2001) indicated that MD of the genotype with relatively high P efficiency was lower than that of the genotypes with lower P efficiencies and also the linear correlation analysis revealed that mycorrhizal dependency was primarily controlled by P uptake efficiency. It is known that some plants are strongly mycorrhizal dependent for P nutrition, but less is known about the mycorrhizal dependency with Zn nutrition. In the present study we attempted to study the role of mycorrhizal inoculation on growth of kidney beans in two calcareous soils having both Zn and P deficiency. Hypotheses were to be tested in P and Zn deficient soils in order to elucidate whether kidney bean plants are mycorrhizal dependent or not in terms of P and Zn uptake. Materials and methods Two widely distributed Zn- and P-deficient calcareous Konya and Sultano¨nu¨ soils from Central Anatolia were used in the experiment during the year 2002. Concentrations of NaHCO3 extractable P and DTPA-extractable Zn were very low, and below the critical deficiency level (i.e., 32 kg P2O5 ha1 and 0.15 mg Zn kg 1 soil) (Table I). Kidney bean was grown in two soils, low in phosphorus (P) and zinc (Zn) content and fertilized with three levels of P (P0 /0, P1/25, P2 /125 mg P kg 1 soil) and two levels of Zn (Zn0/0 and Zn1/5 mg Zn kg 1soil) in 2 kg soil. The soil was

Table I. Selected physical, chemical and biological properties of soils. Properties Clay Loam Sand CaCO3 Organic matter Salt (soluble) B 1) pH CEC P2O5 2) Zn 3) Fe 3) Mn 3) Cu 3) Indigenous mycorrhizae

Unit

Sultano¨nu¨ Konya

%

mg B kg-1 soil (H2O) Cmolc kg-1 kg/ha (mg-1 kg)

Spores number/ 10 g dry soil

50.6 30.6 18.8 15 0.7 0.08 1.2 8.04 38 40.37 0.19 2.64 2.13 0.95 57

44.6 40.4 15.0 32 1.2 0.06 23.7 8.01 26 30.28 0.15 2.03 4.68 0.42 39

1) CaCO2/Mannitol; 2) 0.5 N NaHCO3 extractable; 3) DTPA extractable.

treated with 200 mg N kg 1 soil [100 mg kg 1 soil N- (NH4)2SO4, 100 mg kg 1 soil N-KNO3] and 5 mg/kg soil Fe (Fe-EDDHA), and placed in 3-litre pots. Plants were inoculated with the AM fungi G. mosseae ((Nicolson & Gerdemann) Rothamsted Isolate, UK) and G. etunicatum ((Becker & Gerdemann) Nutri-Link Isolate, USA). A level of 1000-spore per pot was placed 3 cm below the seeds. The non-inoculated pots received the same amount of mycorrhizal spore-free inoculum. Soils were sterilized by autoclaving, and the kidney bean plants were grown for 8 weeks in pots under greenhouse conditions. Kidney bean seeds were disinfected for 2 min in a 5.25% sodium hypochlorite solution and then rinsed several times with deionized water and then with tap water. Three kidney bean seeds were sown per pot and thinned to one seedling after a week. The experiment was arranged in a randomized complete block design with three replications. The pots were randomly rearranged twice per week. Distilled water was added daily by weighting to maintain 75% water holding capacity for normal plant growth. The plants were grown in a greenhouse at 25 288C and at a relative humidity of 60 to 80%, with 16-h day and 8-h dark photoperiods. Mycorrhizal dependency (MD) was calculated by using the following formula (Plenchette et al., 1983): MD (Dry WTmycorrhizalDry WTnon-mycorrhizal )= Dry Wtmycorrhizal )100 Plants were harvested at maturation stage. In the milk stage 10 leaves from each plot were taken as suggested by Jones (1998) for analysis of nutrient

Mycorrhizal inoculation of kidney bean

103

Figure 1. The effect of mycorrhizal inoculation, P and Zn rate on bean shoot growth.

contents. After drying at 758C, the plant leaves were ground using a Tema mill. Ground plant material was ashed at about 5508C, and the residue was extracted with 3.3% HCl. After the digestion of the plant material, the concentration of phosphorus was determined according to Murphy and Riley (1962) by using a flame photometer. At harvest roots were separated from the soil by washing with running tap water, then with distilled water. Roots were dried on a tissue paper. Prior to drying, small subsamples were taken from roots and preserved in a mixture of ethanol, glacial acetic acid and formalin for determination of root length and mycorrhizal infection. A small proportion of preserved roots was stained as described by Koske and Gemma (1989), and examined for the degree of mycorrhizal infection according to Giovannetti and Mosse (1980). All statistical analyses were performed with use of Statistical Analysis System (SAS, 1987). Tukey test was used for means separation within the treatments

Results and discussion Mycorrhizal inoculation of G. etunicatum and G. mosseae significantly increased plant growth in the Sultano¨nu¨ soil but not in the Konya soil. Mycorrhizal species differed in their effects on plant growth; in the Sultano¨nu¨ soil, G. mosseae was much more effective than G. etunicatum, however mycorrhizae caused no growth increase in the Konya soil (Figure 1). Since kidney beans are so sensitive to salt stress effect in the Konya soil, the plant did not grow normally. The Sultano¨nu¨ and Konya soils had different responses to the P and Zn applications. In the Sulatano¨nu¨ soil, without P addition, application of both the mycorrhizae fungi species increased plant growth. Zn application also increased plant growth, but in the Konya soil the effect was less marked. Without mycorrhizal inoculation, shoot and root dry matter production were affected by P and Zn deficiency, and increases in supply of adequate amounts of P and Zn significantly enhanced plant growth, especially for the Sultano¨nu¨ soil (Figure 1). When the soil was inoculated with mycorrhizal

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Table II. Significance of p -values (probability) from analysis of variance for different plant parameters. Sources Soil Mycorrhizae Soil/Mycorrhizae Zinc Soil/Zinc Mycorrhizae/Zinc Soil/Mycorrhizae xZinc Phosphorus Soil/Phosphorus Mycorrhizae/Phosphorus Soil/Mycor. /Phosphorus Phosphorus/Zinc Soil/Phosphorus /Zinc Mycor. /Phosphorus/Zinc Soil/Mycor/Phos./Zinc

SD

Shoot DW

Root DW

Infection %

Root Length

P%

mg P/plant

Zn

1 2 2 1 1 2 2 2 2 4 4 2 2 4 4

0.0001 0.0030 0.0395 0.0017 0.0011 0.3585 0.1999 0.0014 0.0553 0.3131 0.3173 0.2899 0.2895 0.7928 0.8562

0.0001 0.0288 0.4842 0.0862 0.0611 0.0737 0.2925 0.0418 0.0115 0.6176 0.4606 0.7586 0.1557 0.7939 0.2895

0.0001 0.0001 0.0008 0.0955 0.3036 0.8368 0.5323 0.4014 0.3914 0.9400 0.8098 0.2182 0.3581 0.3516 0.7271

0.0001 0.0001 0.0105 0.0001 0.6400 0.1219 0.0013 0.0014 0.0402 0.1195 0.8057 0.2591 0.5373 0.1277 0.0342

0.0004 0.0241 0.5568 0.0827 0.5034 0.0911 0.9601 0.0008 0.1282 0.9957 0.9955 0.8135 0.7481 0.6835 0.8084

0.0001 0.0037 0.0525 0.0026 0.0055 0.0349 0.0652 0.0014 0.0800 0.8879 0.9295 0.2989 0.3020 0.7646 0.7568

0.0001 0.0001 0.0605 0.0001 0.0434 0.0980 0.0986 0.0001 0.2256 0.7032 0.9224 0.7379 0.9860 0.0883 0.2628

species, P and Zn fertilization only slightly increased plant growth. There was little difference in plant growth between the levels of P fertilization. In contrast, Zn addition significantly increased plant growth irrespective of P addition. Compared to P supply, the effect of Zn on plant growth was much greater, especially at higher P rates in the Sultano¨nu¨ soil. However, in the Konya soil, because of high boron (B) concentration (Table I), mycorrhizal inoculation and nutrient supply did not make a significant contribution (Figure 1). In this case mycorrhizal inoculation had a slightly higher effect than nutrient supply. Statistically, mycorrhizal inoculation, zinc and phosphorus treatments were

highly significant (p B/0.0017 and p B/0.0014). Soil and Zn interaction was also found to be significant (p B/0.0011) (Table II). Although the same amounts of mycorrhizae spores were used in the experiment, mycorrhizae species were different in terms of their effects on plant parameters. Since mycorrhizae spores are different in terms of efficiency, they may have different effects. Soil ecological characteristics can also sometimes lead to differences (Abbott & Robson, 1984; Ortas, 2003). In the Sultano¨nu¨ soil, increasing P addition increased plant root weight, but had less effect in the Konya soil (Table III). Zinc application

Table III. Effect of inoculation and different levels of P and Zn treatments and mycorrhizae species on root dry weight (DW), root length and mycorrihizal root infection. Mycorrhizae

Treatment

Root DW (g/pot)

Root Length (m)

Mycorrhizal Infection (%)

Root DW (g/pot)

Sultano¨nu¨

Control

Control

G.etunicatum

G.etunicatum

G.mosseae

G.mosseae

P0Zn0 P1Zn0 P2Zn0 P0Zn1 P1Zn1 P2Zn1 P0Zn0 P1Zn0 P2Zn0 P0Zn1 P1Zn1 P2Zn1 P0Zn0 P1Zn0 P2Zn0 P0Zn1 P1Zn1 P2Zn1

0.839/0.15 0.929/0.30 0.759/0.35 0.939/0.03 1.149/0.15 1.189/0.15 0.989/0.12 1.009/0.10 1.049/0.11 1.059/0.31 1.179/0.15 1.169/0.20 0.879/0.18 0.849/0.11 0.949/0.10 0.929/0.17 0.989/0.04 0.989/0.06

Mean (three replicates) is SE (Standard error).

90.99/13.7 104.09/6.1 106.89/20.5 89.09/10.9 118.79/41.5 107.59/14.4 88.59/3.2 115.69/39.6 105.29/5.6 94.49/15.1 135.29/30.0 124.69/15.8 84.79/5.4 95.89/12.4 98.89/10.7 87.19/19.4 160.89/56.6 152.39/40.7

Root Length (m)

Mycorrhizal Infection (%)

Konya 12.209/4.30 10.209/1.95 11.309/9.02 7.509/3.32 4.009/2.03 10.009/10.28 24.009/3.17 89.289/5.31 91.549/3.82 92.449/0.76 89.589/4.90 92.119/3.79 87.679/9.20 92.329/1.77 89.879/2.10 90.329/8.89 85.369/7.90 88.649/2.34

0.369/0.20 0.419/0.05 0.399/0.01 0.419/0.05 0.459/0.13 0.659/0.15 0.499/0.17 0.659/0.05 0.649/0.15 0.579/0.06 0.619/0.03 0.619/0.15 0.529/0.21 0.539/0.20 0.559/0.09 0.539/0.12 0.549/0.11 0.319/0.02

37.09/18.1 42.39/16.7 45.09/7.8 40.09/2.9 46.59/30.5 51.79/16.0 78.19/26.9 44.49/8.8 63.09/28.0 79.29/11.4 89.09/17.0 90.09/20.5 72.69/53.0 81.69/9.8 86.09/21.8 84.49/19.9 88.59/43.7 87.09/37.0

5.209/4.19 1.009/3.97 2.009/6.79 2.009/4.22 3.009/12.58 1.009/7.75 51.009/7.02 52.009/22.26 47.009/35.33 48.009/8.31 47.009/14.45 51.009/11.18 54.009/13.40 54.009/12.09 39.009/10.57 41.009/4.81 29.009/21.73 38.009/8.28

Mycorrhizal inoculation of kidney bean also increased root development. Mycorrhizae species, especially G. etunicatum, increased root growth in the Sultano¨nu¨ soil, but not in the Konya soil. Increasing P addition in the Sultano¨nu¨ soil increased root length. In the control plant, P0Zn0 treatment produced 91 m root length, while P2Zn0 treatment produced 107 m length (Table III). Mycorrhizal and Zn application also slightly increased root length. Non-inoculated P2Zn1 treatment produced 107 m length, but G. etunicatum produced 125 m and G. mosseae produced 152 m length. In the Konya soil mycorrhizal inoculation produced more root length than non-mycorrhizal control plants did, but in the Konya soil with the same fertilizer treatment there was less effect on root length. Mycorrhizal inoculation significantly increased plant percentage of root colonization in both soils. In the Sultano¨nu¨ soil, with control plants, mycorrhizal percentage ranged from 4 to 12%, but mycorrhizal inoculated plants changed from 24 to 92% (Table III). In the Konya soil, with control plants, root infection ranged from 1 to 5%, while in mycorrhizal inoculated plants it ranged from 29 to 54%. Compared to the Sultano¨nu¨ soil, plants grown in the Konya soil had less root infection, but increasing P addition also contributed to the root infection. With regard to the plant-fungus interactions, it is expected that the extent of mycorrhizal colonization of the root system and related plant responses will vary in different plant-fungus combinations (Smith & Read, 1997). The study of host response to inoculation with a single fungus isolate can provide useful information. This is particularly true where the inoculating fungus exhibits a broad host range, as was the case with the G. mosseae and G. etunicatum isolates used in this study. We found mycorrhizae species to be different in root infection and dependency ratio in a low-fertility soil with increased P and Zn in the soil solution. This may be the effect of soil ecological parameters on root infection. Very high and very low phosphorus levels could reduce mycorrhizal colonization (Amijee et al., 1989; Koide & Li, 1990; Koide, 1991). The level of phosphorus in the plant has been also shown to influence the establishment of mycorrhizae with high levels inhibiting colonization by mycorrhizae (Menge et al., 1978; Graham et al., 1981; Miranda et al., 1989; Asimi et al., 1980; Ortas et al., 2002a). However, no information related to mycorrhizal dependency with excess Zn application on root infection was obtained. Colpaert et al. (1992) reported on effects of Zn toxicity on ectomycorrhizae.

105

There is some conflicting information in the literature about the critical level of P requirement for optimum mycorrhizal infection. The benefits of mycorrhizae were greatest when soil phosphorus levels were at or below 40 mg kg1 (Ortas et al., 1996). Research by Abbott and Robson (1979) concluded that levels of soil phosphorus higher than those required for plant growth eliminated the development of the arbuscules of mycorrhizae. When the soil level of bicarbonate-soluble phosphorus exceeded 133 140 mg kg 1 the rate of infection was found to decrease (Abbott & Robson, 1977, 1979; Amijee et al., 1989; Ortas et al., 2002a). Schubert and Hayman (1986) found mycorrhizae were no longer effective when 100 mg or more P was added per kg of soil. In the present experiment, since the Konya soil has high boron concentration, this may have a negative effect on root colonization. Increasing the P application increased the P percentage of plants. In control plants with P0Zn0 treatment the P content was 0.12%, while in the P2Zn0 treatment it was 0.20% (Table IV). In the Konya soil with P0Zn0 treatment the P content was 0.16%, while in the P2Zn0 treatment the P content increased to 0.24% (Table IV). Mycorrhizal inoculation also significantly increased the P content of the plant. In the Sultano¨nu¨ soil G. mosseae inoculated plants had higher P content than G. etunicatum inoculated plants. Inoculation significantly increased the P uptake (p B/0.004; Table II). As all AM fungi may have a similar strategy for host growth enhancement in low-fertility soils, by increasing nutrient acquisition, the results and their interpretation obtained with a single isolate could change, although not to a great extent, when a different effective isolate is used to colonize the plants. However, with an adequate P supply for plant growth, AM colonization may be determined by specific plant factors related to mycorrhizal dependence. High P is known to depress mycorrhizae formation, consequently the plant may obtain less P, but in the present study such an effect was not uniform among mycorrhizae species for both soils. Mycorrhizae formation, response to added P, host nutrient requirement, and mycorrhizae responsiveness are all interrelated. Janos (1996) stated that host independence of AM is a consequence of low nutrient requirement or the ability of roots alone to take up all required mineral nutrients. In the present experiment mycorrhizal inoculation, regardless of P addition, significantly increased P uptake even in the Konya soil. Mycorrhizal inoculation also increased the plant Zn uptake, but in the Konya soil, since the plant did not grow normally, Zn content was very high compared to the Sultano¨nu¨ soil. In the Konya soil

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Table IV. The effect of P, Zn and mycorrhizal inoculation on kidney bean plant root and shoot P concentration. Mycorrhizae

Treatment

Shoot

Root

Shoot

Root

%P Sultano¨nu¨

Control

Control

G.etunicatum

G.etunicatum

G.mosseae

G.mosseae


0.129/0.02 0.139/0.01 0.149/0.01 0.189/0.03 0.209/0.05 0.209/0.02 0.179/0.04 0.199/0.02 0.199/0.01 0.199/0.11 0.239/0.08 0.239/0.12 0.179/0.12 0.219/0.09 0.229/0.13 0.199/0.09 0.219/0.04 0.219/0.07

Konya 0.209/0.06 0.159/0.03 0.169/0.06 0.179/0.01 0.189/0.15 0.299/0.07 0.209/0.07 0.169/0.08 0.269/0.01 0.219/0.04 0.219/0.05 0.239/0.03 0.229/0.04 0.269/0.13 0.239/0.03 0.189/0.01 0.199/0.02 0.249/0.02

0.169/0.03 0.179/0.07 0.249/0.02 0.179/0.05 0.269/0.03 0.309/0.03 0.179/0.03 0.249/0.05 0.259/0.10 0.219/0.02 0.229/0.05 0.299/0.04 0.209/0.07 0.329/0.04 0.319/0.05 0.229/0.18 0.229/0.02 0.319/0.04

0.099/0.03 0.159/0.01 0.189/0.06 0.149/0.03 0.159/0.01 0.159/0.02 0.179/0.02 0.139/0.06 0.209/0.01 0.209/0.03 0.119/0.04 0.189/0.01 0.169/0.17 0.229/0.06 0.159/0.02 0.199/0.04 0.179/0.02 0.179/0.09


the plant shoot Zn concentration was variable between mycorrhizal and non-mycorrhizal plants (Table V). There were no regular responses to P and Zn application, but mycorrhizal inoculated plants had less Zn content than non-mycorrhizal inoculated plants. It is argued that mycorrhizae are keeping the plant alive against high Zn toxicity. As is

known, over 100 mg kg 1 Zn is a toxic level (Jones, 1998). Mycorrhizal species were different in their effect on nutrient uptake; G. mosseae was only a little more effective than G. etunicatum . According to Jones (1998), in non-inoculated plants, P and Zn concentration were usually under the critical concentration,

Table V. The effect of P, Zn and mycorrhizal inoculation on kidney bean plant roots and shoots Zn concentration. Mycorrhizae Species

Treatment

Shoot Zn

Root Zn

Shoot Zn

Root Zn

mg kg 1 KM Sultano¨nu¨ Control

Control

G.etunicatum

G.etunicatum

G.mosseae

G.mosseae



9.49/0.8 11.39/0.8 12.79/2.1 13.09/2.0 13.49/1.2 13.19/0.8 13.39/0.6 13.29/2.1 13.49/2.7 14.59/2.7 15.39/0.7 19.79/1.6 16.19/1.6 16.69/1.7 17.89/2.0 16.99/5.4 16.89/2.4 18.59/3.7

Konya 15.69/1.3 15.89/2.0 16.39/1.2 14.39/2.0 18.09/3.4 19.09/2.9 12.39/0.9 14.89/2.6 15.29/0.7 15.79/2.5 19.79/6.9 23.69/6.0 12.29/0.9 16.19/0.1 19.89/4.5 21.59/2.2 20.19/1.7 22.49/1.9

135.29/35.8 144.49/29.2 156.29/3.8 142.39/11.5 145.29/27.1 137.19/13.7 103.79/18.5 103.29/11.1 133.09/15.3 134.09/27.8 119.79/7.5 112.19/7.3 108.09/6.4 119.09/4.3 132.19/25.0 131.09/20.1 139.79/15.4 120.29/17.1

26.79/14.4 25.49/15.7 15.29/1.8 16.59/4.2 40.89/18.6 20.29/7.2 58.89/41.5 23.99/11.6 33.29/17.1 46.69/1.9 16.59/4.3 17.69/3.4 31.49/5.6 22.79/8.2 15.19/4.3 53.99/7.7 33.79/4.6 23.79/2.6

Mycorrhizal inoculation of kidney bean

107

Table VI. Effect of P and Zn interaction on mycorrhizal dependency for kidney bean plants. Mycorrhizae species

G. etunicatum

G. mosseae

P and Zn Supply mg kg 1 soil

P0 P1 P2 P0 P1 P2 P0 P1 P2 P0 P1 P2

but with inoculated plants the nutrient concentration was above the critical level. It has been shown that the total Zn content in shoots was higher in mycorrhizal than non-mycorrhizal plants grown in soils with low P (Kothari et al., 1991a,b; Heggo & Barakah, 1994; Liu et al., 2000; Ortas, 2003). Similar results were also reported for wheat grown in calcareous soil (Goh et al., 1997). The results obtained indicate that kidney bean is a mycorrhizal-dependent plant at low P and Zn supply. Mycorrhizal inoculation in soils with P and Zn deficiency is a critical factor for MD in crop production as well as in P and Zn uptake (Ortas et al., 2002a, b; Ortas, 2003). Phosphorus treatments generally reduced mycorrhizal dependency, but Zn application did not lead to any difference (Table VI). Beneficial effects were higher with G. etunicatum inoculation than with G. mosseae inoculation. In the present experiment, although mycorrhizal inoculation increased plant Zn uptake, the plant was found to be much more mycorrhizal dependent on P nutrition. To date, all the experiments conducted have shown similar results (Ortas et al., 2001Ortas et al., 2002; Ortas, 2003). Responsiveness relates directly to host-growth rate and internal P demand (Miranda et al., 1989; Koide, 1991), while mycorrhizal dependency is more related to the nutrient absorption ability of a noncolonized plant than to its nutrient requirement. Plant dependency of mycorrhizae arises when uptake by roots alone of mineral nutrients at a given level of supply is insufficient (Janos, 1996). Adjoud et al. (1996) reported that most mycorrhiza-dependent plant species tended to be those having the highest leaf phosphorus concentration in the absence of a fungal symbiont, and the mycorrhiza-dependent plant species seem to have greater phosphorus requirements and consequently rely more on the symbiotic association. Bryla and Koide (1998)

Mycorrhizal dependency (%) Sultano¨nu¨

Konya

49 21 17 45 16 16 43 16 28 33 20 17

37 24 17 17 25 16 14 4 24 20 28 26

Zn0

Zn1

Zn0

Zn1

measured mycorrhizal response of two tomato genotypes and mycorrhizal dependency was related to their ability to acquire and utilize phosphorus. Habte and Manjunath (1991) suggested that critical P concentrations in soil solutions are useful for classifying host species into AM-dependency categories. Plenchette and Morel (1996) reported that the mycorrhizal dependency of soybeans was highly correlated with the P concentration in the soil solution. It seems that mycorrhizal dependence is an inherent characteristic for which plant nutrient requirements and uptake efficiency are important parameters, especially for P requirement. Considering the importance of mycorrhizae dependence for plant survival (Janos, 1980), it is of the utmost interest to categorize species according to this characteristic. Conclusions Irrespective of P and Zn treatments, mycorrhizal inoculation increased shoot and root dry weight in the Sultano¨nu¨ soil. Increasing P and Zn supply positively affected plant growth. In particular, Zn supply significantly increased dry weight. Plant growth was depressed by boron due to the high B concentration in the Konya soil. G. mosseae and G. etunicatum resulted in higher percentages of mycorrhizal infection than non-mycorrhizal plants. G. mosseae and G. etunicatum inoculation also significantly increased plant P and Zn contents in the Sultano¨nu¨ soil. Although plant growth was strongly affected by the P and Zn supply, and mycorrhizal inoculation increased P and Zn uptake, this was more strongly dependent on the P supply than Zn supply. Results obtained support the hypothesis that kidney bean is mycorrhizal dependent, nevertheless with increasing P and Zn, the

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dependency is reduced. Lower mycorrhizal dependency was more pronounced for P requirement than Zn requirement.

Acknowledgement This study was funded by grants from State Planning Organization (DPT) and TUBITAK.

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