Three species of
Microorganisms are known to play a fundamental role in biogeochemical cycling of P in natural and agricultural ecosystems. Gerretsen [
The widespread use of phosphate-solubilizing microbial inoculants remains limited due to inconsistent results under field conditions. This is mainly due to the functional efficiency of microorganisms, which is largely governed by environmental conditions. The forest and cropped soils in the Indian Himalayan Region (IHR) are generally acidic [
The fungal cultures were originally isolated from soil samples collected from various forest locations in higher altitudes (1800–3610 m above sea level) of the IHR, and maintained on agar slants at 4°C in the culture collection developed in the microbiology laboratory of the GB Pant Institute of Himalayan Environment and Development, Almora. The fungal cultures have also been deposited and accessioned at the Indian Type Culture Collection (ITCC), Indian Agricultural Research Institute, New Delhi (Accession numbers ITCC2546-
The initial pH of the media, before autoclaving, was 7.50. The autoclaved medium was then inoculated with 5 mm disc cultures of the respective fungi and incubated at 21°C for 42 days. The culture filtrate was withdrawn from selected flasks on every 7th day of incubation by vacuum filtration through Whatman numbers 42 filter paper. The filtrate was then analyzed for P2O5 production following the chlorostannous reduced molybdophosphoric acid blue method [
Plant-growth-promoting abilities of the three fungal species were performed following a pot-based assay under greenhouse conditions (temp.: 25 ± 0.5°C; humidity: 75–85%). Maize (
For taking measurements on growth parameters (shoot and root length and dry weight of shoot, root, and seed), plants were harvested at peak flowering time (approx. 3 months after sowing,
The data were analyzed with the computer programme Excel (Microsoft Corp.) for graphical representation, and the mean values and variance among the means (fixed effects or model I one-way ANOVA), SPSS/PC [
Solubilization of aluminium phosphate and biomass production by
Maximum aluminium phosphate solubilization (18%, Figure
Maximum (6%) solubilization of iron phosphate, decline in pH, and production of biomass (522 mg) were recorded on day 28 (Figure
Solubilization of iron phosphate and biomass production by
Effect of carbon ((a), (c), and (e)) and nitrogen ((b), (d), and (f)) sources on the aluminum phosphate solubilization efficiency and biomass production of
Effect of carbon ((a), (c), and (e)) and nitrogen ((b), (d), and (f)) sources on the iron phosphate solubilization efficiency and biomass production of
Maximum solubilization of iron phosphate (8%), reduction in pH (4.03), and production of biomass were recorded on day 21 (Figure
Maximum iron phosphate solubilization (4%), the minimum pH (4.73) and the maximum production in biomass were recorded on day 42 (Figure
Positive response of inoculation with three species of
Effect of phosphate-solubilizing
Treatment | Shoot length (cm) | Root length (cm) | Biomass production and yield (g dry weight) | Harvest index | ||
---|---|---|---|---|---|---|
Shoot | Root | Seed | ||||
Maize | ||||||
Control |
|
|
|
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0.32 |
|
|
|
|
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|
0.39 |
ANOVA |
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NA |
|
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|
|
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|
0.69 |
ANOVA |
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|
|
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NA |
|
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|
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0.68 |
ANOVA |
|
|
|
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|
NA |
Wheat | ||||||
Control |
|
|
|
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|
68.08 |
|
|
|
|
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|
124.14 |
ANOVA |
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|
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NA |
|
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|
102.78 |
ANOVA |
|
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NA |
|
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|
|
|
|
82.92 |
ANOVA |
|
|
|
|
|
NA |
ANOVA: analysis of variance; NA: not detected; *significant increment as compared to control.
In wheat-based experiments, inoculation with
The phosphate solubilization efficiency by microorganisms depends on the form of insoluble phosphate. The three fungal cultures used in the present study exhibited differential responses towards solubilization of aluminium and iron phosphate. The Al and Fe phosphate solubilization efficiency observed, in the present study, are lower than previously reported tricalcium phosphate solubilization efficiency [
The effect of nutritional aspects, such as carbon and nitrogen sources, on microbial phosphate solubilization efficiency has been studied by various workers [
Maximum solubilization of aluminium phosphate, in some of the instances, was recorded with less production of biomass. In case of
At suboptimal growth conditions, where phosphate solubilization was found to be maximum, a highly significant negative correlation was observed between a reduction in pH and the production of biomass. This was an indication of the direct relationship between cell proliferation and phosphate solubilization with reference to pH and growth conditions. Metabolic alteration, due to extracellular pH and involvement of different signaling pathways, has been reported [
Use of P-solubilizing fungi in plant nutrition is well reported [
The fixation of P depends on the soil acidity. In acidic soils, free oxides and hydroxides of Al and Fe fix P, while in alkaline soils P is fixed with Ca and Mg. Aluminium and iron phosphate-solubilizing microorganisms play a major role in P mobilization in low temperature environments of Himalayan soils, which are mostly acidic. Effectiveness of the
Documentation of microbial diversity, including mycorrhizae, in various ecological niches of the Indian Himalayan Region (IHR) with particular reference to biotechnological applications, such as development of microbial inoculants for colder regions, has received attention in recent times [
Director, G. B. Pant Institute of Himalayan Environment and Development, Almora, is thanked for encouragement and extending the facilities. Department of Science and Technology and Ministry of Environment and Forests, Government of India, New Delhi, are acknowledged for their financial support.