Objectives The soil physicochemical properties and microbial community differences significantly affect the release of volatile organic compounds (VOCs) in the rhizosphere of maize. In-depth study is expected to make a positive contribution to fully exploiting the rhizosphere biological potential and rhizosphere manipulation.
Methods Soils were collected from the tillage layers of Dezhou, Laishui, Baoding, Nanchang, Mengjin and Shangqiu, and used for a pot experiment. The VOCs emitted from maize rhizosphere were identified using solid-phase microextraction (SPME) fiber and Gas Chromatography–Mass Spectroscopy-Real-Time Quantitative (qPCR), and High-Throughput Sequencing technology were used to determine the bacterial and fungal communities.
Results About 44 VOCs were detected, belonging to alkanes, alkenes, esters, amines, organic acids and aromatics. Many of these compounds were closely related to the growth and metabolism of plants or microorganisms. Two amine compounds, N-Benzyl-N-ethyl-p-isopropyl benzamide and D-2-Bromolysergic acid diethylamide, were detected in all treatments and they accounted for 54.2% of the total. The second and third abundant VOCs were alkanes and alkenes, which accounted for 31.1% and 7.6% of the total. The VOCs in number and richness released in soil from Nanchang were significantly higher than those in soils from the other places, and most of them were alkanes and olefins. Six unique organic acids and esters were detected from Baoding. Among the six soils, the abundances of bacteria in Shangqiu and Baoding were significantly higher than those in others, and the abundance of fungi in Nanchang was significantly higher than those of others, but the abundance, richness and diversity of bacteria in Nanchang were significantly lower than those in other soils. The main bacteria in the six soils were Thaumarchaeota, Actinobacteria, Proteobacteria, Chloroflexi, Acidobacteria, Firmicutes, Phytophthora and Unclassified, they accounted for 92.1% of the total bacterial community. The main fungi were Ascomycota, Basidiomycota and Chytridiomycota, they accounted for 98.3% of the total fungal community. Chloroflexi only accounted for an absolute advantage in the soil from Nanchang, and the relative abundances of Thaumarchaeota and Proteobacteria in Nanchang soil were significantly less than those of other soils. Ascomycota was an absolutely dominant fungi in all six soils. The number and richness of VOCs released from rhizosphere of maize were significantly negatively correlated with pH, nitrate nitrogen, bacterial diversity and fungal diversity (P < 0.05), and significantly positively correlated with ammonium nitrogen and the number of fungi (P < 0.01). The VOCs were significantly and negatively correlated with the relative abundances of Thaumarchaeota, Proteobacteria and Acidobacteria (P < 0.05), and positively correlated with the Chloroflexi (P < 0.01), while the correlation with the main fungal phylum was not significant.
Conclusions There are significant differences in microbial community structure and composition among the rhizosphere soils with different physical and chemical properties. pH is an important factor affecting the growth of microorganisms. The number of fungi in acid soil is significantly higher than that in neutral soil, but the number of bacteria, microbial community richness and diversity are significantly lower than that of neutral soil. The production and release of VOCs are affected by many factors such as soil, microbes and plants. The higher the soil organic matter content, the better gas permeability and the larger number of microorganisms, the more abundant VOCs are released.
DownLoad: