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.