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Investigations into rhizosphere microflora of some plants in Libya
Zbl. Bakt. II. Abt. 134 (1979),237-242
[Botany Department, Faculty of Education, Libya University, L.A.R.]
Investigations into Rhizosphere Microflora of Some Plants
III
Libya
MOSTAFA SABRY NOUR EL DEIN SELIM and GABER ABDULLAH KHALIL With 2 Figures
Summary The present investigation deals with the effect of raising Hordeum vulgare and Arachis hypogaea at two different stages on the microbial rhizosphere population. The studies were extended to reveal the microbiological occurrence in different horizons of a soil profile corresponding in length to root regions. Bacteria were most abundant, followed by actinomycetes while fungi were less abundant and more restricted in their distribution. The three groups of microorganisms varied markedly in the rhizosphere of the two plants under investigation. The plant age had a great influence on the frequency of occurrence of the different microorganisms. One strain of bacteria, six fungi and the members of the grey series of Streptomyces were dominant. Actinomycetes and fungi diminished with the depth of soil, while the bacterial counts increased.
Zusammenfassung Die Untersuehung befaLlt sich mit dem EinfluLl von Hordeum vulgare und Arachis hypogaea wahrend zweier Wachstumsphasen auf die Mikroflora der Rhizosphare. Die Untersuchung wurde durch die Ermittlung des Vorkommens der entsprechenden Mikroorganismen in den Horizonten des Bodenprofils, die der durchwurzelten Zone entsprachen, erweitert. Bakterien kamen am hauf'igsten vor, die Aktinomyzeten folgten, und Pilze waren am wenigsten haufig, Die gruppenmalsige Zusammensetzung der Mikroflora hing von der Art der Pflanze und ihrer Wachstumsphase abo Unber den Mikroorganismen waren cine Bakterienart, sechs Pilze und Aktinomyzeten aus der Serie der "grauen Streptomyzeten" am meisten vertreten. 1m Bodenprofil nahm die Zahl der Aktionomyzeten und Pilze mit zunehmender Tiefe ab, die Zahl der Bakterien hingegen zu.
Much work has been carried out to study the distribution of microorganisms in relation to plant roots. STARKEY (1929), HARLEY (1948), CLARK (1949), GARETT (1956), LOCKHEAD (1959) reported that the roots of plants exerted rhizosphere effects that varied both quantitatively and qualitatively with the species and age of plant. PETERSON et al. (1965) pointed out that the environmental factors have a profound effect on the composition of microbial flora in the rhizosphere of wheat. JAKUBCZYK (1971) studying the effect of dead plant material decomposition on the number of heterotrophic microorganisms (bacteria, fungi and actinomycetes) found a rather strong variation in their numbers. MACURA (1960) found that the soils were heavily populated by bacteria, while fungi drop to a very low level. SCHAPOVA (1971) showed that bacteria prevailed among soil microflora from rice fields. HARRIS (1972) observed on surface films from soil crumbs many bacterial types while actinomycetes and budding yeasts were common but fungi were rarely seen.
238
M. S. N. EL D EIN SELIM and G. A. K HALIL
Materials and Methods A. Soil and root sampling and inv estigations of microorganisms Tw o plants were selec te d for this inv estigation, i.e. , Hord eum vulgare fr om family Graminea e and A rachis hypogaea from L eguminosao. The two plants wer e grown at Tarhona 35 miles east of Tripoli. R oo t s from plants at pre-flow ering and po st.fl owering stages were collected, washed carefully and the rhizosp er e so il was taken to analysis. Soi l samples wer e al so taken fr om differen t horizons of a soil profile fr ee from eultiva t ion , but from the same habitat. The profile ranges from 2 em to 42 em corr espo nd ing in d epth to root r egions. The con t ent of mi croorganism s in the sa m ples wa s exam ined by us ing the dilution plate te chnique of KJOLLER and Omrsr (1971).
B. Composition of media for growth of microorganisms Three different types of m edia were used for the growth of mi croorganisms. Th ese media had the following com p osit ion : i) Sodium caseinate-glucose m edium : Sod ium casei na te , 1.0 g; glucose, 10 g; MgS0 4 , 0.2 g; K zHP0 4 , 0.2 g; FeS0 4 , trace; distilled water, 1000 ml; agar, 15 g; pH 7,0 . ii) Asparagin - glu cose medium : Asparagin, 1.0 g iglucose, 10.0 g j KHzP0 4 , 1.0 g; agar, 20 g; pH, 7.0 ; di stilled wa ter, 1.000 m l,
iii) D ox's m edium: Sucr ose, 15.0 g; NaNO a, 2.0 g ; KH 2P04 , 1.0 g; KCl, 0.5 g; MgS0 4 , 0.5 g; F eS0 4 , 0 .0 1 g; distilled water , 1,000 m l; agar, 20.0 g ; pH 6.4.
C. Characteristics of soil tested The data for soil cha racte ristics : Total ca rbona tes , sulpha te s, nitrates, organic carb on and water- soluble sa lts were kindly hand ed over t o u s by the che m ica l laboratory, Ministry of Agricult ure, L.A .R., using the m ethod s prev iously d escribed by MONTASIR et al, (1956). The pH of t he soil sp ecime ns wa s d etermined elect r ica lly by m eans of an elec t r ic pH m eter (Cambridge) with glass elect rod e using I: 5 so il-d isti lled wa t er sus pens ion .
Results and Discussion Th e pr esent studies hav e sho wn that the rhizosphere of the two different plant covers considerably influences th e fr equ ency of microorganisms (Table 1). The rhizo sphe re of Hord eum plant seems to be least su itable for the population of mioroorganisms. On the other hand higher microflora - as expressed per gram of root oven Table 1. Microb iological population in the rhizosphere of Hord eum vulgare and A rachis hypoga ea at tw o different stages. A = pre· fl owering stage an d B = p ost -fl ower ing stage (Num ber in t housan ds per 1.0 g of oven dry wt. of roo t) Total mi cro organism s
P lant cover
Bacteri a I
Actinomycet os
Fungi
II
I
II
I
II
H ordeum tlulgare
A B
954 1,182
785 990
82.0 % 83.4%
127 180
13.3 % 15.2 %
42 12
4.5 % 1.0 %
Arachis hypogaea
A B
980 1,555
7BO 1,260
79.0 % 81.0%
140 265
14.2 % 17.0 %
60 30
6. 1 % 1.9 %
I: II
= =
Thousands per gram of oven d ry weight of root. % of total mi croorganism s.
Investigations into Rhizosphere Microflora of Some Plants 1600
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dry weight - is recorded from Arachis rhizosphere. The observed differences between the two plants may be attributed to the variation in the root excretion of nutrient and chemical substances promoting the growth of soil microorganisms (ROVIRA 1959, ROUATT et al. 1963, PETERSON et al. 1965, and PRIANO 1971). In general, the rhizosphere of the two plants under investigation is heavily populated by microorganisms when compared with the soil free from cultivation (Fig. 1). This appears to be due to the role of the organic matter in the soil which attains a higher content in the cultivated soil than in the uncultivated soil (Table 2). A fact which indicates some sort of correlation between organic matter and the frequency of microorganisms in the soil (SRIVASTAVA and MISHRA 1971). Bacteria, however, are very highly represented in the rhizosphere region fluctuating between 79.5 % and 83.7 % of the total microflora (Table 1). Actinomycetes predominate amounting up to 17.0 % of microbial population found in the rhizosphere of Arachis plant. Fungi, on the other hand, drop to a very low level making 1.0 % to 6.1 % of the total microorganisms. The frequency of the different microorganisms varied according to the age of the plant (Table 1). Bacteria and aotinomycetes, in general, were less frequent at the early age of growth of the plants under investigation i.e. at the pre-flowering stage. On the contrary, fungi were more frequently met with on the isolation plates at the same stage of plant growth. It is worth mentioning that the main genera of fungi predominating soil appear to assume maximum levels during post-flowering stage (Table 3). The wide distribution of bacteria and actinomycetes in proportion of the fungi are rather interesting. One possible interpretation can be postulated on the basis 16 Zbl. Bakt. II. Abt., Bd. 134
240
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of the abilit y of bacteria and actinomycetes to form antibiotics and to their broad carbon utilization (LINDENFELSER and PRIDHAM 1962). In addition, the fact that the soil pH being 7.0-8.0 (Tabl e 2) which coincide with the optimum reactions for bacteria and actinomycet cs may explain the ability of t hese organisms to exist in a complex competitive environment . Such a pH is quite unfavourable for the growth of fun gi. Another explanation for the high proportion of actinomycetes is that enri chment of soil with bacteria leads to an extensive actinomycetes development. Th eir excessive growth is du e largely to the introducti on of a fresh supply of availabl e nutrients in the form of bacterial cells. Most aut hors believe the rhizospheric zone is more appropriate for ba cteria than for fungi and actinomycetes because easily available organic subs tances ar e exuded by plant roots. This is t rue for t he humid and semihumid climatic condit ions. Th e same compounds were found in the root exudate s of different plant s in arid zone, too. But the la ck of water in soil might cause these subst ances to be less available to bacte ri a. Th at is probably why the xerophytic microflora, like actinomycet es and fun gi, develops mor e intensively t han could be expecte d considering the chemical structure of r oot exudates of exper iment al plants.
Investigations into Rhizosphere Microflora of Some Plants
241
Table 2. Characteristics of the soil samples Soil samples tested
Soil type
Colour of soil
pH of soil samples
Organic carbon
Non-cult.ivated
Sandy loam
Yellow brown
7.2 8.0
1.52
7.8
Cultivated
Sandy loam
Light brown
7.4 8.1
3.20
12.0
Total C0 3 %
CaC0 3
S04
%
%
N0 3
Total watersol. salt
3.8
2.4
+
0.140
4.60
0.6
++
0.474
Table 3. More common fungi isolated from the root region of Hordeum vulgare and Arachis hypogaea at pre-flowering stage (A) or at post-flowering stage (B) and from the soil profile (S) according to their degree of abundance Fungus
Plant
Soil
Hordeum
Aspergillus sp. Alternaria sp. Ounninghamella sp. Fusarium sp. Mucor sp. Penicillium sp.
Arachis
(A)
(B)
(A)
(B)
+++ + ++ + ++ ++
++++ + +++ ++ +++ ++
++ + + ++ ++ ++
++++ ++ +++ ++ +++ ++
++ +
+
++
Table 4. Microbiological population in the different horizons of a soil profile at Tarhona (Number in thousands per 1.0 g of oven dry sand) Depth of a horizon (em)
Total Bacteria microorganisms II I
Actinomycetes
Fungi
I
II
I
II
2 13 25 35 42
820 780 697 47.3 105.3
170 120 100 6 0.3
20.7% 15.4% 14.3 % 12.7% 0.28%
20 30 17 0.3
2.5% 3.8% 2.4% 0.6%
I
=
Thousands per gram, II
630 630 580 41 105
=
76.8% 80% 83% 87% 99.6%
% of total microorganisms.
One strain of bacteria belonging to the aerobic spore forming bacilli (genus Bacillus) occurred permanently. Using the method of classification of KNIGHT and PROOM (1950), and SMITH et al. (1952), we found that the bacterium belongs morphologically to group I (spore cylindrical, central; spore wall thin; sporangium is not swollen). The diameter of the vegetative rod is less than 0.9 u, so the bacterium belongs to Subtilis group. The actinomycetes isolated (as determined by PRIDHAM et al. 1958) belong mostly to the grey series while the other series occur in negligible numbers (SELIM 1971). The types of fungal spp. in the rhizosphere of the two plants exhibited much similarity (Table 3). Aspergillus species showed the highest frequency of occurrence of all the isolated fungal groups. These results are in complete agreement with those obtained by WAKSMAN (1917), JENSEN (1931), SABET (1935) and TOLBA and ALI (1972). The genera Mucor and Cunninghamella come next in the order of frequency 16·
242
M. S. N. EL DEIN SELlM and G. A. KHALIL, Investigations into Rhizosphere Microflora
of fungal genera. Next come Penicillium, Fusarium and Alternaria species which were less frequently met with on isolation plates than the above mentioned species. The study of the microbiological occurrence in different horizons of a soil profile corresponding in length to root regions, indicates definite vertical zonation where definite associations of microorganisms occur (Table 4). It is not contrary to the expectation that the numbers of microorganisms are most abundant near the surface where an aerobic condition is likely to prevail. As the depth of the profile increases bacteria slightly dominate, while actinomycetes and fungi do not occur any more. These results accord with that of W AKSMAN an d CURTIS (1956) and DUTTA (1967). The marked preponderance of bacteria with depth of soil is surely due to their ecological requirement of their mode of life. References CLARK, F. E.: Soil microorganisms and plant roots. Adv. Agron. I (1949), 241. DUTTA, B. S.: Sci. Cult. 33 (1967), 288. GARRET, S. D.: Biology of Root-Infecting Fungi. Cambridge University Press, London 1956. HARLEY, J. L.: Mycorrhiza and soil ecology. Biol. Rev. Cambridge Phil. Soc. 23 (1948), 127. HARRIS, P. J.: Soil BioI. Biochem. 4 (1972),105. JACKS, H.: Fruit World Mark. Graw. 13 (1972),193. JAKUBCZYK, H.: Roczn. Nauk Roln. 19 (1971), 121. JENSEN, H. L.: The fungus flora of the soils. Soil Sci. 31 (1931), 123. KJOLLER, A., and ODUM, S.: Arctic 24 (1971), 230. KNIGHT, B. C. J. G., and PROOM, D.: J. Gen. Microbiol. 4 (1950), 11. LINDENFELSER, L. A., and PRIDHAM, 1. G.: Ind. Microbiol. 3 (1962),245. MACURA, J., VAGNEROVA, K., and CATSKA, V.: Rhizosphere microflora of wheat. Fol. microbiol. 5 (1960), 298. MONTASIR, A. H., MosTAFA, M. A., and ELWAN, S. H.: Development of soil microflora under Zygophylleum album L. and Zygophylleum cocchieum L. Ain Shams Univ. Sci. Bull. No.1, 1956. PETERSON, E. A., ROUATT, J. W., and KATZNELSON, H.: Canad. J. Microbiol. 11 (1965), 483. PRIANO, L. J.: Rev. Ecol. BioI. Sol 8 (1971), 491. PRIDHAM, J. T., HESSELTINE, C. W., and BENEDICT, R. G.: A guide for the classification of Streptomycetes according to selected group placement of strains in morphological sections. Appl. Microbiol. 6 (1958), 52. ROUATT, J. W., PETERSON, F. A., KATZNELSON, H. T., and HENDERSON, V. F.: Microorganisms in the root zone in relation to temperature. Canad, J. Microbiol. 9 (1963), 227. ROVIRA, A. D.: Root excretion in relation to the rhizosphere effect. IV. Influence upon the microorganisms in the soil. Historical and introductory. Plant and Soil 11 (1959), 53. SABET, Y. S.: A preliminary study of the Egyptian soil fungi. Bull. Fac. Sci., Egypt Univ, 5 (1935), 1. SELIM, M. S. N.: Search for antagonistic Actinomycetae in Libyan soils. Canad. J. Microbiol. 17 (1971), 131. SHAROVA, L. N.: Mikrobiologiya 40 (1971),102. SMITH, N. R., GORDON, R. E., and CLARK, F. E.: Agriculture Monograph No. 16, USA Dept. Agric., 1952. SRIVASTAVA, V. B., and MISHRA, R. R.: Microbiol. Esp. 24 (1971),193. STARKEY, R. L.: Some influences of the development of higher plants. Soil Sci. 27 (1929), 319. TOLBA, M. K., and ALI, M. I.: Studies on rhizosphere microflora of cotton plants in Egypt. J. Bot. 15 (1972). WAKSMAN, S. A.: Is there any fungous flora in the soil? Soil Sci. 3 (1917),565. Authors' addresses: Dr. MOSTAFA SABRY NOUR EL DEIN SELIM, Faculty of Education, Ain Shams University, Roxy, Cairo, Egypt; GABER ABDULLAH KHALIL, Faculty of Education, Libya University, L.A.R.
[Botany Department, Faculty of Education, Libya University, L.A.R.]
Investigations into Rhizosphere Microflora of Some Plants
III
Libya
MOSTAFA SABRY NOUR EL DEIN SELIM and GABER ABDULLAH KHALIL With 2 Figures
Summary The present investigation deals with the effect of raising Hordeum vulgare and Arachis hypogaea at two different stages on the microbial rhizosphere population. The studies were extended to reveal the microbiological occurrence in different horizons of a soil profile corresponding in length to root regions. Bacteria were most abundant, followed by actinomycetes while fungi were less abundant and more restricted in their distribution. The three groups of microorganisms varied markedly in the rhizosphere of the two plants under investigation. The plant age had a great influence on the frequency of occurrence of the different microorganisms. One strain of bacteria, six fungi and the members of the grey series of Streptomyces were dominant. Actinomycetes and fungi diminished with the depth of soil, while the bacterial counts increased.
Zusammenfassung Die Untersuehung befaLlt sich mit dem EinfluLl von Hordeum vulgare und Arachis hypogaea wahrend zweier Wachstumsphasen auf die Mikroflora der Rhizosphare. Die Untersuchung wurde durch die Ermittlung des Vorkommens der entsprechenden Mikroorganismen in den Horizonten des Bodenprofils, die der durchwurzelten Zone entsprachen, erweitert. Bakterien kamen am hauf'igsten vor, die Aktinomyzeten folgten, und Pilze waren am wenigsten haufig, Die gruppenmalsige Zusammensetzung der Mikroflora hing von der Art der Pflanze und ihrer Wachstumsphase abo Unber den Mikroorganismen waren cine Bakterienart, sechs Pilze und Aktinomyzeten aus der Serie der "grauen Streptomyzeten" am meisten vertreten. 1m Bodenprofil nahm die Zahl der Aktionomyzeten und Pilze mit zunehmender Tiefe ab, die Zahl der Bakterien hingegen zu.
Much work has been carried out to study the distribution of microorganisms in relation to plant roots. STARKEY (1929), HARLEY (1948), CLARK (1949), GARETT (1956), LOCKHEAD (1959) reported that the roots of plants exerted rhizosphere effects that varied both quantitatively and qualitatively with the species and age of plant. PETERSON et al. (1965) pointed out that the environmental factors have a profound effect on the composition of microbial flora in the rhizosphere of wheat. JAKUBCZYK (1971) studying the effect of dead plant material decomposition on the number of heterotrophic microorganisms (bacteria, fungi and actinomycetes) found a rather strong variation in their numbers. MACURA (1960) found that the soils were heavily populated by bacteria, while fungi drop to a very low level. SCHAPOVA (1971) showed that bacteria prevailed among soil microflora from rice fields. HARRIS (1972) observed on surface films from soil crumbs many bacterial types while actinomycetes and budding yeasts were common but fungi were rarely seen.
238
M. S. N. EL D EIN SELIM and G. A. K HALIL
Materials and Methods A. Soil and root sampling and inv estigations of microorganisms Tw o plants were selec te d for this inv estigation, i.e. , Hord eum vulgare fr om family Graminea e and A rachis hypogaea from L eguminosao. The two plants wer e grown at Tarhona 35 miles east of Tripoli. R oo t s from plants at pre-flow ering and po st.fl owering stages were collected, washed carefully and the rhizosp er e so il was taken to analysis. Soi l samples wer e al so taken fr om differen t horizons of a soil profile fr ee from eultiva t ion , but from the same habitat. The profile ranges from 2 em to 42 em corr espo nd ing in d epth to root r egions. The con t ent of mi croorganism s in the sa m ples wa s exam ined by us ing the dilution plate te chnique of KJOLLER and Omrsr (1971).
B. Composition of media for growth of microorganisms Three different types of m edia were used for the growth of mi croorganisms. Th ese media had the following com p osit ion : i) Sodium caseinate-glucose m edium : Sod ium casei na te , 1.0 g; glucose, 10 g; MgS0 4 , 0.2 g; K zHP0 4 , 0.2 g; FeS0 4 , trace; distilled water, 1000 ml; agar, 15 g; pH 7,0 . ii) Asparagin - glu cose medium : Asparagin, 1.0 g iglucose, 10.0 g j KHzP0 4 , 1.0 g; agar, 20 g; pH, 7.0 ; di stilled wa ter, 1.000 m l,
iii) D ox's m edium: Sucr ose, 15.0 g; NaNO a, 2.0 g ; KH 2P04 , 1.0 g; KCl, 0.5 g; MgS0 4 , 0.5 g; F eS0 4 , 0 .0 1 g; distilled water , 1,000 m l; agar, 20.0 g ; pH 6.4.
C. Characteristics of soil tested The data for soil cha racte ristics : Total ca rbona tes , sulpha te s, nitrates, organic carb on and water- soluble sa lts were kindly hand ed over t o u s by the che m ica l laboratory, Ministry of Agricult ure, L.A .R., using the m ethod s prev iously d escribed by MONTASIR et al, (1956). The pH of t he soil sp ecime ns wa s d etermined elect r ica lly by m eans of an elec t r ic pH m eter (Cambridge) with glass elect rod e using I: 5 so il-d isti lled wa t er sus pens ion .
Results and Discussion Th e pr esent studies hav e sho wn that the rhizosphere of the two different plant covers considerably influences th e fr equ ency of microorganisms (Table 1). The rhizo sphe re of Hord eum plant seems to be least su itable for the population of mioroorganisms. On the other hand higher microflora - as expressed per gram of root oven Table 1. Microb iological population in the rhizosphere of Hord eum vulgare and A rachis hypoga ea at tw o different stages. A = pre· fl owering stage an d B = p ost -fl ower ing stage (Num ber in t housan ds per 1.0 g of oven dry wt. of roo t) Total mi cro organism s
P lant cover
Bacteri a I
Actinomycet os
Fungi
II
I
II
I
II
H ordeum tlulgare
A B
954 1,182
785 990
82.0 % 83.4%
127 180
13.3 % 15.2 %
42 12
4.5 % 1.0 %
Arachis hypogaea
A B
980 1,555
7BO 1,260
79.0 % 81.0%
140 265
14.2 % 17.0 %
60 30
6. 1 % 1.9 %
I: II
= =
Thousands per gram of oven d ry weight of root. % of total mi croorganism s.
Investigations into Rhizosphere Microflora of Some Plants 1600
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HORDEU M
ARAC H I 5
DEPT H
OF
A
HORI ZO N
(em)
Fig. 1
dry weight - is recorded from Arachis rhizosphere. The observed differences between the two plants may be attributed to the variation in the root excretion of nutrient and chemical substances promoting the growth of soil microorganisms (ROVIRA 1959, ROUATT et al. 1963, PETERSON et al. 1965, and PRIANO 1971). In general, the rhizosphere of the two plants under investigation is heavily populated by microorganisms when compared with the soil free from cultivation (Fig. 1). This appears to be due to the role of the organic matter in the soil which attains a higher content in the cultivated soil than in the uncultivated soil (Table 2). A fact which indicates some sort of correlation between organic matter and the frequency of microorganisms in the soil (SRIVASTAVA and MISHRA 1971). Bacteria, however, are very highly represented in the rhizosphere region fluctuating between 79.5 % and 83.7 % of the total microflora (Table 1). Actinomycetes predominate amounting up to 17.0 % of microbial population found in the rhizosphere of Arachis plant. Fungi, on the other hand, drop to a very low level making 1.0 % to 6.1 % of the total microorganisms. The frequency of the different microorganisms varied according to the age of the plant (Table 1). Bacteria and aotinomycetes, in general, were less frequent at the early age of growth of the plants under investigation i.e. at the pre-flowering stage. On the contrary, fungi were more frequently met with on the isolation plates at the same stage of plant growth. It is worth mentioning that the main genera of fungi predominating soil appear to assume maximum levels during post-flowering stage (Table 3). The wide distribution of bacteria and actinomycetes in proportion of the fungi are rather interesting. One possible interpretation can be postulated on the basis 16 Zbl. Bakt. II. Abt., Bd. 134
240
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S.
N.
EL DEIN S ELI M
and G. A.
KHALIL
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)
F ig. 2
of the abilit y of bacteria and actinomycetes to form antibiotics and to their broad carbon utilization (LINDENFELSER and PRIDHAM 1962). In addition, the fact that the soil pH being 7.0-8.0 (Tabl e 2) which coincide with the optimum reactions for bacteria and actinomycet cs may explain the ability of t hese organisms to exist in a complex competitive environment . Such a pH is quite unfavourable for the growth of fun gi. Another explanation for the high proportion of actinomycetes is that enri chment of soil with bacteria leads to an extensive actinomycetes development. Th eir excessive growth is du e largely to the introducti on of a fresh supply of availabl e nutrients in the form of bacterial cells. Most aut hors believe the rhizospheric zone is more appropriate for ba cteria than for fungi and actinomycetes because easily available organic subs tances ar e exuded by plant roots. This is t rue for t he humid and semihumid climatic condit ions. Th e same compounds were found in the root exudate s of different plant s in arid zone, too. But the la ck of water in soil might cause these subst ances to be less available to bacte ri a. Th at is probably why the xerophytic microflora, like actinomycet es and fun gi, develops mor e intensively t han could be expecte d considering the chemical structure of r oot exudates of exper iment al plants.
Investigations into Rhizosphere Microflora of Some Plants
241
Table 2. Characteristics of the soil samples Soil samples tested
Soil type
Colour of soil
pH of soil samples
Organic carbon
Non-cult.ivated
Sandy loam
Yellow brown
7.2 8.0
1.52
7.8
Cultivated
Sandy loam
Light brown
7.4 8.1
3.20
12.0
Total C0 3 %
CaC0 3
S04
%
%
N0 3
Total watersol. salt
3.8
2.4
+
0.140
4.60
0.6
++
0.474
Table 3. More common fungi isolated from the root region of Hordeum vulgare and Arachis hypogaea at pre-flowering stage (A) or at post-flowering stage (B) and from the soil profile (S) according to their degree of abundance Fungus
Plant
Soil
Hordeum
Aspergillus sp. Alternaria sp. Ounninghamella sp. Fusarium sp. Mucor sp. Penicillium sp.
Arachis
(A)
(B)
(A)
(B)
+++ + ++ + ++ ++
++++ + +++ ++ +++ ++
++ + + ++ ++ ++
++++ ++ +++ ++ +++ ++
++ +
+
++
Table 4. Microbiological population in the different horizons of a soil profile at Tarhona (Number in thousands per 1.0 g of oven dry sand) Depth of a horizon (em)
Total Bacteria microorganisms II I
Actinomycetes
Fungi
I
II
I
II
2 13 25 35 42
820 780 697 47.3 105.3
170 120 100 6 0.3
20.7% 15.4% 14.3 % 12.7% 0.28%
20 30 17 0.3
2.5% 3.8% 2.4% 0.6%
I
=
Thousands per gram, II
630 630 580 41 105
=
76.8% 80% 83% 87% 99.6%
% of total microorganisms.
One strain of bacteria belonging to the aerobic spore forming bacilli (genus Bacillus) occurred permanently. Using the method of classification of KNIGHT and PROOM (1950), and SMITH et al. (1952), we found that the bacterium belongs morphologically to group I (spore cylindrical, central; spore wall thin; sporangium is not swollen). The diameter of the vegetative rod is less than 0.9 u, so the bacterium belongs to Subtilis group. The actinomycetes isolated (as determined by PRIDHAM et al. 1958) belong mostly to the grey series while the other series occur in negligible numbers (SELIM 1971). The types of fungal spp. in the rhizosphere of the two plants exhibited much similarity (Table 3). Aspergillus species showed the highest frequency of occurrence of all the isolated fungal groups. These results are in complete agreement with those obtained by WAKSMAN (1917), JENSEN (1931), SABET (1935) and TOLBA and ALI (1972). The genera Mucor and Cunninghamella come next in the order of frequency 16·
242
M. S. N. EL DEIN SELlM and G. A. KHALIL, Investigations into Rhizosphere Microflora
of fungal genera. Next come Penicillium, Fusarium and Alternaria species which were less frequently met with on isolation plates than the above mentioned species. The study of the microbiological occurrence in different horizons of a soil profile corresponding in length to root regions, indicates definite vertical zonation where definite associations of microorganisms occur (Table 4). It is not contrary to the expectation that the numbers of microorganisms are most abundant near the surface where an aerobic condition is likely to prevail. As the depth of the profile increases bacteria slightly dominate, while actinomycetes and fungi do not occur any more. These results accord with that of W AKSMAN an d CURTIS (1956) and DUTTA (1967). The marked preponderance of bacteria with depth of soil is surely due to their ecological requirement of their mode of life. References CLARK, F. E.: Soil microorganisms and plant roots. Adv. Agron. I (1949), 241. DUTTA, B. S.: Sci. Cult. 33 (1967), 288. GARRET, S. D.: Biology of Root-Infecting Fungi. Cambridge University Press, London 1956. HARLEY, J. L.: Mycorrhiza and soil ecology. Biol. Rev. Cambridge Phil. Soc. 23 (1948), 127. HARRIS, P. J.: Soil BioI. Biochem. 4 (1972),105. JACKS, H.: Fruit World Mark. Graw. 13 (1972),193. JAKUBCZYK, H.: Roczn. Nauk Roln. 19 (1971), 121. JENSEN, H. L.: The fungus flora of the soils. Soil Sci. 31 (1931), 123. KJOLLER, A., and ODUM, S.: Arctic 24 (1971), 230. KNIGHT, B. C. J. G., and PROOM, D.: J. Gen. Microbiol. 4 (1950), 11. LINDENFELSER, L. A., and PRIDHAM, 1. G.: Ind. Microbiol. 3 (1962),245. MACURA, J., VAGNEROVA, K., and CATSKA, V.: Rhizosphere microflora of wheat. Fol. microbiol. 5 (1960), 298. MONTASIR, A. H., MosTAFA, M. A., and ELWAN, S. H.: Development of soil microflora under Zygophylleum album L. and Zygophylleum cocchieum L. Ain Shams Univ. Sci. Bull. No.1, 1956. PETERSON, E. A., ROUATT, J. W., and KATZNELSON, H.: Canad. J. Microbiol. 11 (1965), 483. PRIANO, L. J.: Rev. Ecol. BioI. Sol 8 (1971), 491. PRIDHAM, J. T., HESSELTINE, C. W., and BENEDICT, R. G.: A guide for the classification of Streptomycetes according to selected group placement of strains in morphological sections. Appl. Microbiol. 6 (1958), 52. ROUATT, J. W., PETERSON, F. A., KATZNELSON, H. T., and HENDERSON, V. F.: Microorganisms in the root zone in relation to temperature. Canad, J. Microbiol. 9 (1963), 227. ROVIRA, A. D.: Root excretion in relation to the rhizosphere effect. IV. Influence upon the microorganisms in the soil. Historical and introductory. Plant and Soil 11 (1959), 53. SABET, Y. S.: A preliminary study of the Egyptian soil fungi. Bull. Fac. Sci., Egypt Univ, 5 (1935), 1. SELIM, M. S. N.: Search for antagonistic Actinomycetae in Libyan soils. Canad. J. Microbiol. 17 (1971), 131. SHAROVA, L. N.: Mikrobiologiya 40 (1971),102. SMITH, N. R., GORDON, R. E., and CLARK, F. E.: Agriculture Monograph No. 16, USA Dept. Agric., 1952. SRIVASTAVA, V. B., and MISHRA, R. R.: Microbiol. Esp. 24 (1971),193. STARKEY, R. L.: Some influences of the development of higher plants. Soil Sci. 27 (1929), 319. TOLBA, M. K., and ALI, M. I.: Studies on rhizosphere microflora of cotton plants in Egypt. J. Bot. 15 (1972). WAKSMAN, S. A.: Is there any fungous flora in the soil? Soil Sci. 3 (1917),565. Authors' addresses: Dr. MOSTAFA SABRY NOUR EL DEIN SELIM, Faculty of Education, Ain Shams University, Roxy, Cairo, Egypt; GABER ABDULLAH KHALIL, Faculty of Education, Libya University, L.A.R.