9 Phosphate Solubilization by Endophytes from the Tropical Plants
209
and biotechnology (Golinska et al. 2015). Still a large number of plants have yet to
be investigated.
9.2 Phosphorus Solubilization by Microorganisms
Phosphorus (P) is one of the major growth-limiting macronutrients required for
proper plant growth, particularly in tropical areas (Santana et al. 2016). Based on the
availability of P to plants, the different forms of P can be categorized as soluble P
and insoluble P. The soluble form is easily available for uptake by plants. In contrast,
an insoluble form is very stable in soil and persists in an unavailable form (Ahemad
et al. 2009). Inspite of its abundance in soil and therefore cannot support the plant
growth due to its unavailability. Moreover, almost 75% of phosphorus applied as
fertilizer forms complexes with soil and becomes unavailable for the plants (Ezawa
et al. 2002). More details about the identification of the major processes of the soil P
cycle that affect soil solution P concentrations as dissolution–precipitation, sorption
desorption, and mineralization–immobilization (biologically mediated conversions
of P between inorganic and organic forms) are presented in a review by Sims and
Pierzynski (2005) and other publications.
Microorganisms play an important role in all three major components of the
soil P cycle such as (1) release of complexing or mineral dissolving compounds,
e.g., organic acid anions, siderophores, protons, hydroxyl ions, CO 2 , (2) liberation
of extracellular enzymes (biochemical P mineralization), and (3) the release of P
during substrate degradation (biological P mineralization) (Sharma et al 2013).
Some bacterial species have mineralization and solubilization potential for organic
and inorganic phosphorus, respectively (Hilda and Fraga 2000; Khiari and Parent
2005). Phosphorus solubilizing activity is determined by the ability of microbes to
release metabolites such as organic acids, which through their hydroxyl and carboxyl
groups chelate the cation bound to phosphate, the latter being converted to soluble
forms (Sagoe et al. 1998).
9.3 Endophytic Microorganisms: A Way to Reduce
the Application of Agrochemicals in Agrobiology
Systems
Agriculture is anti-ecological by nature, and the large-scale use of chemical fertilizers, insecticides, fungicides, herbicides, and antibiotics has led to profound biological changes. The increasing use of fertilizers and highly productive systems has
also created environmental problems such as the deterioration of soil quality, surface
water, and groundwater, as well as air pollution, reduced biodiversity, and suppressed
ecosystem function (Vance 2001). Additionally, chemical pesticides and fertilizers
209
and biotechnology (Golinska et al. 2015). Still a large number of plants have yet to
be investigated.
9.2 Phosphorus Solubilization by Microorganisms
Phosphorus (P) is one of the major growth-limiting macronutrients required for
proper plant growth, particularly in tropical areas (Santana et al. 2016). Based on the
availability of P to plants, the different forms of P can be categorized as soluble P
and insoluble P. The soluble form is easily available for uptake by plants. In contrast,
an insoluble form is very stable in soil and persists in an unavailable form (Ahemad
et al. 2009). Inspite of its abundance in soil and therefore cannot support the plant
growth due to its unavailability. Moreover, almost 75% of phosphorus applied as
fertilizer forms complexes with soil and becomes unavailable for the plants (Ezawa
et al. 2002). More details about the identification of the major processes of the soil P
cycle that affect soil solution P concentrations as dissolution–precipitation, sorption
desorption, and mineralization–immobilization (biologically mediated conversions
of P between inorganic and organic forms) are presented in a review by Sims and
Pierzynski (2005) and other publications.
Microorganisms play an important role in all three major components of the
soil P cycle such as (1) release of complexing or mineral dissolving compounds,
e.g., organic acid anions, siderophores, protons, hydroxyl ions, CO 2 , (2) liberation
of extracellular enzymes (biochemical P mineralization), and (3) the release of P
during substrate degradation (biological P mineralization) (Sharma et al 2013).
Some bacterial species have mineralization and solubilization potential for organic
and inorganic phosphorus, respectively (Hilda and Fraga 2000; Khiari and Parent
2005). Phosphorus solubilizing activity is determined by the ability of microbes to
release metabolites such as organic acids, which through their hydroxyl and carboxyl
groups chelate the cation bound to phosphate, the latter being converted to soluble
forms (Sagoe et al. 1998).
9.3 Endophytic Microorganisms: A Way to Reduce
the Application of Agrochemicals in Agrobiology
Systems
Agriculture is anti-ecological by nature, and the large-scale use of chemical fertilizers, insecticides, fungicides, herbicides, and antibiotics has led to profound biological changes. The increasing use of fertilizers and highly productive systems has
also created environmental problems such as the deterioration of soil quality, surface
water, and groundwater, as well as air pollution, reduced biodiversity, and suppressed
ecosystem function (Vance 2001). Additionally, chemical pesticides and fertilizers