through the synergistic actions of earthworms and microbial communities, yields a
nutrient-rich and biological active organic amendment known as vermicompost
(Domínguez et al. 2010). Vermicomposting therefore fulfils the purpose of disposing
of and recycling increasing amounts of organic waste and at the same time offering
an alternative to inorganic fertilizers (Lazcano and Domínguez 2011; Gómez-Brandón and Domínguez 2014).
Beneficial effects of vermicompost on plant growth have been documented in a
wide variety of agronomic and horticultural crops (Lazcano and Domínguez 2011;
Blouin et al. 2019). In addition, extracts and teas made from vermicompost also
exhibited positive influence when used as plant growth promoters or soil conditioners (Gómez-Brandón et al. 2015), even though they do not impart the same
physical properties as vermicompost amendment. These beneficial effects have been
partially attributed to the physico-chemical properties of vermicomposts including
their buffering capacity, their high porosity and water-holding capacity and low C to
N ratio. The high content of nutrients both in their mineral and organic forms in
vermicompost has also been proposed as a plausible, albeit not exclusive, mechanism by which such improvement is achieved (Blouin et al. 2019). Indeed, Lazcano
et al. (2013) observed that the beneficial effects of vermicompost amendment on
sweet corn yields persisted even when it represented a small portion (25%) of the
total amount of nutrients supplied into the soil. This suggests that besides the amount
of organic matter and nutrient content that the vermicompost provides, it is necessary
to consider other concomitant mechanisms to get the whole picture about the
potential role of vermicompost as a plant growth promoter and/or soil conditioner.
Organic amendments contain an endogenous active microbiome that may exert a
long-term effect on the productivity and sustainability of agro-ecosystems
(Mas-Carrió et al. 2018; Domínguez et al. 2019). Focusing on this aspect is therefore
of particular interest in order to broaden our understanding about the role of
vermicompost as a plant biostimulant and unravel how its addition into soil may
enhance nutrition efficiency and/or crop quality traits, regardless of its nutrient
content. In a recent meta-analysis, Medina-Sauza et al. (2019) emphasized the
importance of how earthworm-induced changes in the soil microbiota largely impact
soil processes, particularly those occurring in the rhizosphere and related to plant
growth and health. However, it is still necessary to further evaluate the
vermicompost microbiome to shed light onto the plausible microbial-based mechanisms by which the use of vermicompost as an organic amendment may exert a
positive influence on plant growth, similar to that when earthworms are present.
The underlying biological mechanisms involved in vermicomposting largely
determine the dynamics of the process and, consequently, the properties of the
final vermicompost for its further use as a plant growth promoter and in plant disease
suppressiveness (Gómez-Brandón and Domínguez 2014). Having this in mind,
recent studies from our research group have deeply explored the compositional
changes and functional capabilities of the bacterial communities over the course of
the vermicomposting process of different plant materials including grape marc
(Kolbe et al. 2019; Gómez-Brandón et al. 2019) and the leguminous shrub Scotch
broom (Domínguez et al. 2019). Although these substrates have long been
126
M. Gómez-Brandón et al.
nutrient-rich and biological active organic amendment known as vermicompost
(Domínguez et al. 2010). Vermicomposting therefore fulfils the purpose of disposing
of and recycling increasing amounts of organic waste and at the same time offering
an alternative to inorganic fertilizers (Lazcano and Domínguez 2011; Gómez-Brandón and Domínguez 2014).
Beneficial effects of vermicompost on plant growth have been documented in a
wide variety of agronomic and horticultural crops (Lazcano and Domínguez 2011;
Blouin et al. 2019). In addition, extracts and teas made from vermicompost also
exhibited positive influence when used as plant growth promoters or soil conditioners (Gómez-Brandón et al. 2015), even though they do not impart the same
physical properties as vermicompost amendment. These beneficial effects have been
partially attributed to the physico-chemical properties of vermicomposts including
their buffering capacity, their high porosity and water-holding capacity and low C to
N ratio. The high content of nutrients both in their mineral and organic forms in
vermicompost has also been proposed as a plausible, albeit not exclusive, mechanism by which such improvement is achieved (Blouin et al. 2019). Indeed, Lazcano
et al. (2013) observed that the beneficial effects of vermicompost amendment on
sweet corn yields persisted even when it represented a small portion (25%) of the
total amount of nutrients supplied into the soil. This suggests that besides the amount
of organic matter and nutrient content that the vermicompost provides, it is necessary
to consider other concomitant mechanisms to get the whole picture about the
potential role of vermicompost as a plant growth promoter and/or soil conditioner.
Organic amendments contain an endogenous active microbiome that may exert a
long-term effect on the productivity and sustainability of agro-ecosystems
(Mas-Carrió et al. 2018; Domínguez et al. 2019). Focusing on this aspect is therefore
of particular interest in order to broaden our understanding about the role of
vermicompost as a plant biostimulant and unravel how its addition into soil may
enhance nutrition efficiency and/or crop quality traits, regardless of its nutrient
content. In a recent meta-analysis, Medina-Sauza et al. (2019) emphasized the
importance of how earthworm-induced changes in the soil microbiota largely impact
soil processes, particularly those occurring in the rhizosphere and related to plant
growth and health. However, it is still necessary to further evaluate the
vermicompost microbiome to shed light onto the plausible microbial-based mechanisms by which the use of vermicompost as an organic amendment may exert a
positive influence on plant growth, similar to that when earthworms are present.
The underlying biological mechanisms involved in vermicomposting largely
determine the dynamics of the process and, consequently, the properties of the
final vermicompost for its further use as a plant growth promoter and in plant disease
suppressiveness (Gómez-Brandón and Domínguez 2014). Having this in mind,
recent studies from our research group have deeply explored the compositional
changes and functional capabilities of the bacterial communities over the course of
the vermicomposting process of different plant materials including grape marc
(Kolbe et al. 2019; Gómez-Brandón et al. 2019) and the leguminous shrub Scotch
broom (Domínguez et al. 2019). Although these substrates have long been
126
M. Gómez-Brandón et al.