T. asperellum Q1 agents may be equipped with multiple
mechanisms for plant growth promotion under salt stress
because it possesses a variety of plant growth-promoting
properties, such as phosphate solubilization. The soluble
P content in the medium depends on the solubilization of
insoluble phosphate and the consumption of the solubilized
phosphate by the strain for its growth. In solubilizing
processes of TCP and DCP, which are common forms of
insoluble phosphate and the consumption of the solubilized phosphate by
the strain for its growth.in solubilizing processes
of TCP and DCP, which are common forms of phosphatenin soils, it was found that a significant decrease
in pH accompanied with the release of phosphorous from
DCP and TCP in culture supernatants. Moreover, three organic acids (oxalic acid, formic acid and lactic acid) were
detected in culture broth by the high performance liquid
chromatography (HPLC) (data not shown). Although the
peak of the reduction in pH was not coincided with the peak
of solubilization of phosphorus source (maybe it was caused
by different growth rates of T. asperellum Q1 with various
forms of phosphates), it still could be concluded that the
solubilization of TCP and DCP was intimately linked to some
organic acids produced by T. asperellum Q1. Extensive researches
have demonstrated that organic acids produced by
bacteria and parts of fungal species such as Penicillium spp.
are vital to solubilization of insoluble inorganic phosphates
(Rashid et al. 2004). Moreover, the same three organic
acids were also detected in culture broth inoculated with
another T. asperellum
have just been published recently (Zhao and Wang 2014).
Phytate is the major organic phosphorus compounds
in soil which is not readily available to plants as a source
of phosphorus. To make this form of P available for plant
nutrition, it must be hydrolyzed to inorganic P. Mineralization
of most organic phosphorous compounds is carried