Agriculture Reference
In-Depth Information
was used as C source, microorganisms produced higher amounts of organic acids
which causes more insoluble P solubilization. The influence of C on the solubili-
zation of insoluble P was determined further by Song et al. (
2008
) who used
different sugars such as glucose, sucrose, or maltose in order to assess the P
solubilization activity of
Burkholderia cepacia
(DA23). Among all sugars, P
solubilization was found to be twofold lesser in a medium containing sucrose
relative to glucose which generally resulted in the most extensive solubilization
of calcium P (Panda et al. (
2013
). Mechanistically, the P-solubilizing efficiency of
microorganisms is associated with its ability to secrete organic acids (Maliha
et al.
2004
; Khan et al.
2009
,
2010
), the nature and quantity of which, however,
varies between different sugars and microbes (Rodriguez et al.
2004
; Hu et al.
2006
;
Perrig et al.
2007
). For example, glucose, galactose, maltose, and sucrose used as
single C source were metabolized by
Bacillus
(strain T-34) and produced citric,
malic, acetic, and lactic acids in considerably higher concentrations compared to
those secreted by
Azospirillum
(WS-1) and
Enterobacter
T-41 strains (Tahir
et al.
2013
). Similar results have also been reported by others (Chen et al.
2006
;
Archana et al.
2012
) where
Azospirillum
,
Bacillus,
and
Enterobacter
produced
variable amounts of citric, oxalic, gluconic, and 2-keto-gluconic acids. Also, the
concentrations of the preferred energy source plays a pivotal role in enhancing PS
activity of microbes, and generally the PS activity increases with increasing con-
centration of sugars added to the growth medium. Increasing the concentration of
glucose, for instance, from 1 to 3 % resulted in profound increase in RP solubili-
zation by PSM because higher concentration of glucose led to increased production
of acidity, an important factor in P solubilization (Song et al.
2008
). In other reports,
a further increase in glucose concentrations from 1 to 5 % (w/v) enhanced the P
solubilization considerably, and the most obvious increment has been recorded up
to 3 % glucose which, however, decreases at 5 % glucose level (Son et al.
2006
;
Stephen and Jisha
2011
).
3.2.4 Nitrogen Source
Nitrogen (N), like many other nutrients, influences the growth and functionality of
soil-inhabiting PSM. Nitrogen is involved in various metabolisms such as it partici-
pates in synthesis of amino acids, proteins, and nucleotides. Microorganisms take
up N in ammonical, nitrite, nitrate, or amino form, depending upon the enzyme
present in their system and greatly influencing P solubilization activity (Bar-Yosef
et al.
1999
; Habte and Osorio
2012
). Recently, an in vitro experiment was carried
out to evaluate the effect of different nitrogen (N) forms (NH
4
+
and/or NO
3
) on the
dissolution of rock phosphates (RP) by the PSF
Mortierella
sp. (Habte and Osorio
2012
). It has been reported that in the presence of NH
4
Cl or NH
4
NO
3
, the solution
of pH following
Mortierella
sp. application significantly decreases from an initial
value of 7.6 to 3.4 and 3.7, respectively, while KNO
3
reduces the pH to 6.7 only.
Due to greater decrease in pH, there was significantly more P solubilized in the
