4.3 Soil microbiome
The biomass of soil microorganisms is affected by a variety of factors
such as temperature, soil moisture, plant growth and animal disturbance
(Fierer and Jackson, 2006; Zhao et al., 2006). In the study presented
here, the Shannon index was higher in high-density (HDR) than
low-density rhizosphere soil (LDR), indicating a positive effect of
high-density planting on the diversity of soil bacteria. This might have
been related to the root exudation of quinoa providing nutrients for
microbial growth and reproduction.
Proteobacteria were the overwhelmingly dominant phylum detected
in this study. They are widespread in a variety of natural and
artificial environments and represent one of the largest taxa of the
entire bacterial kingdom (Ciccarelli et al., 2006).Proteobacteria are important in the global carbon, nitrogen and
sulfur cycling (Dworkin et al., 2006) and can also serve as biological
control agents in soil-plant ecosystems (Lueders et al., 2006). Thus,Proteobacteria have an important role in agriculture.
Burkholderiales (order in phylum Proteobacteria ) were
endemic to low-density rhizosphere soils in this study, known to inhabit
mainly the roots and leaves of plants. Most of the major groups ofBurkholderiales have the nitrogen fixation, phosphate
solubilization and phytohormone production capacities that may promote
plant growth and development (Peter et al., 2002; Castanheira et al.,
2016; Zhang et al., 2000).
Both Proteobacteria and Bacteroidota were positively
correlated with soil salinity, and the levels of these two bacterial
phyla were relatively high in soils with high-density quinoa
cultivation. Further study is needed to ascertain a potential role of
these bacteria in promoting quinoa growth in saline soils.