Agriculture Reference
In-Depth Information
6.1
Introduction
Phosphorus, identified as an essential element for all life forms (Smil
2000
), is the
second most important plant macronutrient after N (Donahue et al.
1990
). Phos-
phorus accounts for the biomass buildup, the energy transfer, signal transduction,
macromolecular biosynthesis, photosynthesis, and respiration chain reactions
(Vance et al.
2003
; Fern´ndez et al.
2007
). Sadly, this highly vital element is one
of the least accessible (only 0.1 % of the total soil P reserve) nutrients to the plants
(Zou et al.
1992
; Takahashi and Anwar
2007
). Owing to the suboptimal levels of P,
it is often considered a limiting factor to primary production across a diverse range
of ecosystem (Elser et al.
2007
) and may cause a 5-15 % loss in plant yields
(Hinsinger
2001
). The low availability of P in soil is primarily due to its highly
reactive nature as it readily forms insoluble complexes with the soil ions. Thus, to
fulfill the growing P demands for food production and to maintain a balanced
fertility in soils and, hence, to achieve a low-input, sustainable eco-friendly agri-
culture targets, a better management of the soil P reserve is urgently needed. Many
strategies have been introduced by the scientists across different regions where the
role of phosphate-solubilizing microorganisms involving bacteria (Zaidi
et al.
2009
; Ahmad et al.
2013
), fungi (Khan et al.
2010
), and actinomycetes
(Gangwar et al.
2012
) in increasing plant yields and soil quality via P supply has
been recognized. Among these, actinomycetes as P solubilizers (de Vasconcellos
et al.
2010
; Hamdali et al.
2012
) have been less explored despite showing a better
genetic and greater biodiversity potential (Pathom-Aree et al.
2006
; Thangapandian
et al.
2007
). Also, they represent heterogeneous and abundant microbial
populations and hugely affect cycling of nutrient in soil ecosystems (Elliot and
Lynch
1995
; Figueiredo et al.
2010
). Recently, the role of actinomycetes in
sustainable agriculture (Johansson et al.
2004
; Strap
2011
) via P supply to plants
has been identified. Some other actinomycetes, for example, endophytic actinomy-
cete (Ara´ jo et al.
2000
; Kunoh
2002
; Lee et al.
2008
; Qin et al.
2008
), which fix
atmospheric N into NH
3
and export the fixed N to the host plants, have also shown
PS activity (Gangwar et al.
2012
). In a study, almost 44 % of the endophytic
actinomycetes isolated from rice had PS activity, among which
S. lavendulae
R22 solubilized the maximum (26.5 mg/100 ml) amount of P, while
Micromonospora
R19 isolate could solubilize the minimum amount of
P. Realizing the plant-growth-promoting potentials of actinomycetes which involve
one or simultaneous mechanisms, here, the recent advances in P solubilization by
actinomycetes and its impact on crop production are highlighted.
