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Phytotechnology with Biomass Production
Microorganisms play key roles in soil ecosystem functions and supply
important services, especially organic matter mineralization, nutrient
cycling, and contribution to formation of humic substances (Blagodatskaya
& Kuzyakov, 2013). Microorganisms associate with all parts of plant and
form various interactions (Arora, 2013), and the term holobiont is used
to stress the ubiquity of plant–microbe interactions (Hassani et al., 2018).
The plant–microbe cooperation can be classified by various criteria, and the
crucial benchmark is the profit which plant gains from such interactions
which usually are neutral or positive (with mutualistic or symbiotic microorganisms); however, sometimes they could be negative (with parasitic or
pathogenic microorganisms).
The symbiotic microorganisms can be classified as endosymbionts (living
inside plant) or exosymbionts (living on the surface of plant). Symbiosis is a
both-side positive relationship; nevertheless it is always described as “give
cheap and take expensive”, i.e., partners invest their surpluses and cover
insufficiencies from the partner. Plants, as photoautotrophic organisms,
mainly supply organic substances produced during photosynthesis. Indeed,
microbial partners, often heterotrophic, consume them, provide to plants
mineral nutrients (like fixed nitrogen or available phosphate), and protect
against parasites or regulatory substances (Arora, 2013).
The effectiveness of phytoremediation depends on soil contamination level
and historical background of soil exploitation. It also depends on the presence
and accessibility of contaminants in the rhizosphere, their bioavailability to
plant’s root system, and the ability of plant–microbe association to intercept,
absorb, accumulate, and/or degrade the contaminants (Vangronsveld
et al., 2009). The plant–microbe associations are used to increase contaminant bioavailability and mobility in different environmental matrices
(soil, water, wetlands, etc.) (Alkorta et al., 2004; Chu & Chan, 2003; Epelde
et al., 2008; Mukherjee & Zimmerman, 2013). Contaminants inhibit plant
growth and development and thereby reduce the phytoremediation effectiveness (Thion et al., 2013). In order to overcome this reduction, the plant–
microbe partnership is used (Mitter et al., 2016). For example, the use of the
C65 strain allowed Populus euphratica to more efficiently extract zinc from
the contaminated environment, facilitating growth inhibition caused by
heavy metals (Zhu et al., 2015).
7.1 Role of Plant–Microbe Association in Phytoremediation
The numerous studies are focused on using microorganisms (rhizo- and
endophytic bacteria) for increasing the efficiency of phytoremediation technology and stimulating the plant development (Mitter et al., 2016). The main
part of the research has been done in greenhouse conditions, while in situ