Agriculture Reference
In-Depth Information
presence of NH
4
Cl (129.65 mg/l) than in the presence of NH
4
NO
3
(109.25 mg/l) as
reported by Habte and Osorio (
2012
). The concentration of P solubilized by
Mortierella
sp. in the presence of KNO
3
was only 0.08 mg/l. Moreover, the excess
of NH
4
+
adversely affected the growth of
Mortierella
sp. In the presence of NO
3
as the only source of N,
Mortierella
sp. not only dissolves a small amount of
inorganic phosphate (Pi) from the RP but also immobilizes most of it into its
mycelia. In contrast, in the presence of NH
4
Cl,
Mortierella
sp. has been effective
in dissolving RP, and the Pi released remained in solution, while only a little portion
was immobilized by the fungal mycelia (Habte and Osorio
2012
). In yet another
investigation, ammonium significantly decreased mineral phosphate solubilization
(mps) in a wild-type Mps
+
strain IR94-MF1 and superpositive Mps
++
of
Penicillium
rugulosum
mutants (Reyes et al.
1999
). Also, ammonium in most of the studies has
been found as a better N source than nitrate (Wenzel et al.
1994
; Asea et al.
1988
),
and
P. fluorescence,
for example, utilized (NH
4
)
2
SO
4
most efficiently and signif-
icantly decreased the pH of the medium during P solubilization. According to
Sulbaran et al. (
2009
),
P. agglomerans
MMB051, when grown in the presence of
KNO
3
, as an alternative N source, instead of (NH
4
)
2
SO
4
, changed the final pH of
the culture supernatant which was almost two units higher (pH 5.1
0.15) than that
recorded for (NH
4
)
2
SO
4
(pH 2.86
0.21). The final concentration of soluble P by
P. agglomerans
MMB051 was however lower in supernatant prepared from cells
grown in medium treated with KNO
3
(58.15 mg/l) relative to those recovered from
(NH
4
)
2
SO
4
-grown cells (95.75 mg/l). In bacteria, although different NO
3
trans-
porter systems have been identified, nitrate/proton symporter is the main transporter
for NO
3
(Rowe et al.
1994
; Kucera and Kaplan
1996
). Consequently, there may be
an increase in extracellular pH due to NO
3
uptake by bacterial cells (Crawford and
Glass
1998
) which possibly could explain the differences in the P-solubilizing
abilities of
P. agglomerans
MMB051 cells grown in the presence of NH
4
+
or
NO
3
ions (Sulbaran et al.
2009
). Similar effect of different N sources on PS
activity has been reported (Roos and Luckener
1994
; Relwani et al.
2008
).
3.2.5 Effect of CaCO
3
and Aeration
Acidic soils are generally limed to adjust the pH of the soil, while pyrite and
gypsum are used to amend alkaline/saline soils. However, addition of CaCO
3
to
the medium markedly reduces P solubilization by bacteria and fungi in liquid
media. For example,
Enterobacter intermedium
, isolated from grass rhizosphere,
even though had a strong ability to solubilize insoluble P, the concentration of
soluble P was significantly decreased to 200-250 mg/l when grown in medium
treated with 1 % CaCO
3
compared to medium without CaCO
3
(1,000 mg/l).
Furthermore, the bacteria oxidize glucose to gluconic acid and sequentially to
2-keto-gluconic acid (2-KGA) (Hwangbo et al.
2003
). Similarly, calcium added
as CaCl
2
,CaCO
3
, and Ca(OH)
2
to the medium reduces the P solubilization by
Rhizobium
and
Bradyrhizobium
from RP because CaCO
3
enhances the pH of the
