Agriculture Reference
In-Depth Information
Table 9.3
Organic acid recoveries after 40 days of application in aerobic rice soil
Recovery (%) in PSB
non-inoculated treatments
Recovery (%) in PSB
inoculated treatments
Dose of organic acids applied (mM)
Oxalic acid
Malic acid
Oxalic acid Malic acid
0
0
0
0
0
10
6.0
2.2
14.4
4.5
20
3.8
2.4
7.7
3.8
30
3.7
1.6
5.7
2.7
Modified from Panhwar et al. (
2013
)
PSB
phosphate-solubilizing bacteria,
mM
millimole
compounds degradability mostly depends on the physicochemical and biochemical
properties of their molecules, e.g., nucleic acids, phospholipids, and sugar phos-
phates are easy to break down, but phytic acid, polyphosphates, and phosphonates
decay more slowly (McGrath et al
.
1998
). Alkaline and acid phosphatases use
organic phosphate as a substrate to change it into inorganic form (Beech
et al.
2001
). The major mechanism for mineralization of soil organic P is the
production of acid phosphatases. Phosphate can be released from organic com-
pounds in soil by three different enzymes. Acid phosphatases and phytases perform
major role for the P solubilization due to the presence of their substrates in soil.
9.3.2.6 Enzymatic Dissolution of Phosphates
Organic P compounds in soil are mineralized by phosphatases, phytases,
phosphonatases, and C-P lyases. The microbial-released phosphatases are an exten-
sively distributed exoenzyme and play vital roles in mineralization and dissolution
of organic P compounds in the rhizosphere (Rodriguez et al.
2006
). Phosphate-
solubilizing bacterial strains have the ability to produce phytohormones and phos-
phatase enzymes and make it available to plants (Ponmurugan and Gopi
2006
;
Relwani et al.
2008
; Aseri et al.
2009
). While plants do not take up P in the
insoluble form, it can become soluble by acid and alkaline phosphatase. Phospha-
tase is an enzyme which eliminates P from its substrate by hydrolyzing phosphoric
acid monoesters into a P ion and a molecule with a free hydroxyl group. The root
phosphatase activities can be helpful to the plants for their greater consumption of
soil organic P (Asmar et al.
1995
). Different PSB, namely,
Sinorhizobium
sp. AS017 and
Sinorhizobium
sp. AS016, have shown maximum activity of acid
phosphatase. A corn experiment by Pantujit and Pongsilp (
2010
) concluded that
PSE008 had maximum alkaline phosphatase activity. Besides this, PSB increased
plant dry weight and P content as compared to control in corn crop. The majority of
the microorganisms in soil contain phytase (myoinositol hexaphosphate
phosphohydrolase) that can hydrolyze sodium phytate, resulting in inorganic P
(Greaves et al.
1963
). There are many bacterial strains such as
Escherichia coli
,
B. subtilis
,
B. amyloliquefaciens
, and
Klebsiella
spp.; yeasts like,
Schwanniomyces
castellii
,
S. occidentalis
,
Hansenula polymorpha
, and
Rhodotorula gracilis
; and
